Comptia Security+

Comptia Security+
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Syngress knows what passing the exam means to
you and to your career. And we know that you
are often financing your own training and
certification; therefore, you need a system that is
comprehensive, affordable, and effective.
Boasting one-of-a-kind integration of text, DVD-quality
instructor-led training, and Web-based exam simulation, the
Syngress Study Guide & DVD Training System guarantees 100% coverage of exam
The Syngress Study Guide & DVD Training System includes:
Study Guide with 100% coverage of exam objectives By reading
this study guide and following the corresponding objective list, you
can be sure that you have studied 100% of the exam objectives.
Instructor-led DVD This DVD provides almost two hours of virtual
classroom instruction.
Web-based practice exams Just visit us at
certification to access a complete exam simulation.
Thank you for giving us the opportunity to serve your certification needs. And
be sure to let us know if there’s anything else we can do to help you get the
maximum value from your investment. We’re listening.
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SSCP Systems Security Certified Practitioner
Study Guide & DVD Training System
The need for qualified information security specialists is at an all-time
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ISBN: 1-931836-80-9
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software for the edge you need to pass the exam on your first try.
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Will Schmied
Robert J. Shimonski
Dr. Thomas W. Shinder
Tony Piltzecker
Technical Editor
Technical Editor
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MCSE Implementing and Administering Security in a
Windows 2000 Network Study Guide & DVD Training System
Copyright © 2003 by Syngress Publishing, Inc. All rights reserved. Printed in the United States of
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Printed in the United States of America
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ISBN: 1-931836-84-1
Technical Editor:Thomas W. Shinder M.D
Cover Designer: Michael Kavish
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Page Layout and Art by: Shannon Tozier
Technical Reviewer: Robert J. Shimonski
Copy Editor: Darlene Bordwell and Judy Edy
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Distributed by Publishers Group West in the United States and Jaguar Book Group in Canada.
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We would like to acknowledge the following people for their kindness and support in
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Page vi
Will Schmied (BSET, MCSE, CWNA, MCSA, Security+, Network+, A+)
is a featured writer on Windows 2000 and Windows XP technologies for He has also authored several works for various Microsoft
certification exams.Will provides consulting and training on Microsoft products to small and medium sized organizations in the Hampton Roads,VA
area. He holds a bachelor’s degree in Mechanical Engineering Technology
from Old Dominion University and is a member of the American Society of
Mechanical Engineers and the National Society of Professional Engineers.
Will currently resides in Newport News,VA with his wife, Allison, and their
children, Christopher, Austin, Andrea, and Hannah.
Dave Bixler is the Technology Services Manager and Information Security
Officer for Siemens Business Systems Inc., one of the world’s leading IT service providers, where he heads a consulting group responsible for internal IT
consulting, and is also responsible for information security company-wide.
Dave has been working in the computer industry for longer than he cares to
remember, working on everything from paper tape readers to Windows .NET
servers. He currently focuses on Internet technologies, specifically thin client
servers, transparent proxy servers, and information security. Dave’s industry
certifications include Microsoft’s MCP and MCSE, and Novell’s MCNE.
Martin Grasdal (MCSE+I, MCSE/W2K, MCT, CISSP, CTT, A+), Director
of Web Sites and CTO at, has worked in the computer
industry for over nine years. He has been an MCT since 1995 and an MCSE
since 1996. His training and networking experience covers a broad range of
products, including NetWare, Lotus Notes,Windows NT and 2000,
Exchange Server, IIS, Proxy Server, and ISA Server. Martin also works
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Page vii
actively as a consultant. His recent consulting experience includes contract
work for Microsoft as a Technical Contributor to the MCP Program on projects related to server technologies. Martin has served as Technical Editor for
several Syngress books, including Configuring ISA Server 2000: Building
Firewalls for Windows 2000 (ISBN: 1-928994-29-6), and Configuring and
Troubleshooting Windows XP Professional (ISBN: 1-928994-80-6). Martin lives
in Edmonton, Alberta, Canada with his wife, Cathy, and their two sons.
Technical Reviewer & Contributor
Robert J. Shimonski (Sniffer SCP, Cisco CCDP, CCNP, Nortel NNCSS,
Server+, Network+, i-Net+, A+, e-Biz+,TICSA, SPS) is the Lead Network
Engineer and Security Analyst for Thomson Industries, a leading manufacturer and provider of linear motion products and engineering. One of
Robert’s responsibilities is to use multiple network analysis tools to monitor,
baseline, and troubleshoot an enterprise network comprised of many protocols and media technologies.
Robert currently hosts an online forum for and is
referred to as the “Network Management Answer Man,” where he offers
daily solutions to seekers of network analysis and management advice.
Robert’s other specialties include network infrastructure design with the
Cisco and Nortel product line for enterprise networks. Robert also provides
network and security analysis using Sniffer Pro, Etherpeek, the CiscoSecure
Platform (including PIX Firewalls), and Norton’s AntiVirus Enterprise
Robert has contributed to many articles, study guides and certification
preparation software,Web sites, and organizations worldwide, including MCP
Magazine,,, and Robert’s background includes positions as a Network Architect at Avis Rent A Car and
Cendant Information Technology. Robert holds a bachelor’s degree from
SUNY, NY and is a part time Licensed Technical Instructor for Computer
Career Center in Garden City, NY teaching Windows-based and
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Page viii
Networking Technologies. Robert is also a contributing author for
Configuring and Troubleshooting Windows XP Professional (Syngress Publishing,
ISBN: 1-928994-80-6) BizTalk Server 2000 Developer’s Guide for .NET
(Syngress, ISBN: 1-928994-40-7), and Sniffer Pro Network Optimization &
Troubleshooting Handbook (Syngress, ISBN: 1-931836-57-4).
Technical Editors
Thomas W. Shinder M.D. (MVP, MCSE) is a computing industry veteran who has worked as a trainer, writer, and a consultant for Fortune 500
companies including FINA Oil, Lucent Technologies, and Sealand Container
Corporation.Tom was a Series Editor of the Syngress/Osborne Series of
Windows 2000 Certification Study Guides and is author of the best selling
book Configuring ISA Server 2000: Building Firewalls with Windows 2000
(Syngress Publishing, ISBN: 1-928994-29-6).Tom is the editor of the Win2k News newsletter and is a regular contributor to
TechProGuild. He is also content editor, contributor, and moderator for the
World’s leading site on ISA Server 2000, Microsoft recognized Tom’s leadership in the ISA Server community and awarded him their
Most Valued Professional (MVP) award in December of 2001.
Tony Piltzecker (CISSP, MCSE, CCNA, Check Point CCSA, Citrix CCA,
Security+) is author of the CCSA Exam Cram and co-author of the
Security+ Study Guide and DVD Training System (Syngress Publishing, ISBN:
1-931836-72-8). He is a Network Architect with Planning Systems Inc., providing network design and support for federal and state agencies.Tony’s specialties include network security design, implementation, and testing.Tony’s
background includes positions as a senior networking consultant with
Integrated Information Systems and a senior engineer with Private
Networks, Inc. He holds a bachelor’s degree in Business Administration and
is a member of ISSA.Tony resides in Leominster, MA with his wife, Melanie,
and his daughter, Kaitlyn.
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Page ix
About the Study Guide &
DVD Training System
In this book, you’ll find lots of interesting sidebars designed to highlight the most important concepts being presented in the main text.These include the following:
Exam Warnings focus on specific elements on which the reader needs to
focus in order to pass the exam.
Test Day Tips are short tips that will help you in organizing and remembering
information for the exam.
Notes from the Underground contain background information that goes
beyond what you need to know from the exam, providing a deep foundation
for understanding the security concepts discussed in the text.
Damage and Defense relate real-world experiences to security exploits while
outlining defensive strategies.
Head of the Class discussions are based on the author’s interactions with students in live classrooms and the topics covered here are the ones students have
the most problems with.
Each chapter also includes hands-on exercises. It is important that you work through
these exercises in order to be confident you know how to apply the concepts you have
just read about.
You will find a number of helpful elements at the end of each chapter. For example,
each chapter contains a Summary of Exam Objectives that ties the topics discussed in that
chapter to the published objectives. Each chapter also contains an Exam Objectives Fast
Track, which boils all exam objectives down to manageable summaries that are perfect
for last minute review. The Exam Objectives Frequently Asked Questions answers those questions that most often arise from readers and students regarding the topics covered in the
chapter. Finally, in the Self Test section, you will find a set of practice questions written in
a multiple-choice form similar to those you will encounter on the exam.You can use the
Self Test Quick Answer Key that follows the Self Test questions to quickly determine what
information you need to review again.The Self Test Appendix at the end of the book provides detailed explanations of both the correct and incorrect answers.
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Additional Resources
There are two other important exam preparation tools included with this Study Guide.
One is the DVD included in the back of this book.The other is the practice exam available from our website.
Instructor-led training DVD provides you with almost two hours of
virtual classroom instruction. Sit back and watch as an author and trainer
reviews all the key exam concepts from the perspective of someone taking the
exam for the first time. Here, you’ll cut through all of the noise to prepare you
for exactly what to expect when you take the exam for the first time.You will
want to watch this DVD just before you head out to the testing center!
Web based practice exams. Just visit us at
to access a complete Exam Simulation.These exams are written to test you on
all of the published certification objectives.The exam simulator runs in both
“live” and “practice” mode. Use “live” mode first to get an accurate gauge of
your knowledge and skills, and then use practice mode to launch an extensive
review of the questions that gave you trouble.
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Table of Contents and
Security+ Exam Objectives
All of CompTIA’s published objectives for the Security+
exam are covered in this book. To help you easily
find the sections that directly support particular
objectives, we’ve referenced the domain and
objective number next to the corresponding text
in the following Table of Contents. In some chapters, we’ve made the judgment that it is probably
easier for the student to cover objectives in a
slightly different sequence than the order of the
published CompTIA objectives. By reading this study guide
and following the corresponding exam objective list, you
can be sure that you have studied 100% of CompTIA’s
Security+ exam objectives.
™ Domain 1.0 General Security Concepts …………………………1
Chapter 1 Access Control, Authentication, and Auditing ……3
Introduction to AAA ………………………………………………4
What is AAA? …………………………………………………5
Access Control ………………………………………………6
Authentication ………………………………………………6
Auditing ……………………………………………………7
Access Control………………………………………………………7
MAC/DAC/RBAC ……………………………………………8
DAC …………………………………………………………9
Authentication ……………………………………………………12
Kerberos ………………………………………………………17
CHAP …………………………………………………………20
Certificates ……………………………………………………21
Tokens …………………………………………………………23
Multi-Factor …………………………………………………24
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Mutual Authentication…………………………………………25
Biometrics ……………………………………………………26
Auditing ……………………………………………………………27
Auditing Systems ………………………………………………27
Logging ………………………………………………………32
System Scanning ………………………………………………32
Disabling Non-Essential Services, Protocols, Systems
and Processes ……………………………………………………34
Non-Essential Services…………………………………………34
Non-Essential Protocols ………………………………………35
Disabling Non-Essential Systems ………………………………36
Disabling Non-Essential Processes ……………………………36
Disabling Non-Essential Programs ……………………………36
Summary of Exam Objectives ……………………………………40
Exam Objectives Fast Track ………………………………………41
Exam Objectives Frequently Asked Questions ……………………43
Self Test ……………………………………………………………44
Self Test Quick Answer Key ………………………………………52
Chapter 2 Attacks …………………………………………………53
Attacks ……………………………………………………………54
Active Attacks ……………………………………………………55
DoS/DDoS ……………………………………………………56
Resource Consumption Attacks ……………………………57
DDoS Attacks ………………………………………………58
Software Exploitation and Buffer Overflows …………………63
SYN Attacks …………………………………………………64
Spoofing ………………………………………………………65
Man in the Middle Attacks ……………………………………69
Replay Attacks …………………………………………………70
TCP/IP Hijacking ……………………………………………71
Wardialing ……………………………………………………71
Dumpster Diving ………………………………………………72
Social Engineering ……………………………………………72
Passive Attacks ……………………………………………………73
Vulnerability Scanning …………………………………………74
Sniffing and Eavesdropping ……………………………………75
1.4.11 Password Attacks …………………………………………………76
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Brute Force Attacks ……………………………………………76
Dictionary-Based Attacks………………………………………77
Malicous Code Attacks ……………………………………………77
Malware ………………………………………………………77
Viruses ……………………………………………………78
Trojan Horses ………………………………………………80
Logic Bombs ………………………………………………83
Worms ……………………………………………………83
Back Door ……………………………………………………84
Summary of Exam Objectives ……………………………………86
Exam Objectives Fast Track ………………………………………87
Exam Objectives Frequently Asked Questions ……………………89
Self Test ……………………………………………………………90
Self Test Quick Answer Key ………………………………………94
™ Domain 2.0 Communication Security …………………………95
Chapter 3 Remote Access and E-mail …………………………97
Introduction ………………………………………………………98
The Need for Communication Security …………………………98
Communications-Based Security………………………………99
Remote Access Security …………………………………………100
802.1x ………………………………………………………100
EAP ………………………………………………………102
Vulnerabilities ……………………………………………103
VPN …………………………………………………………105
Site-to-Site VPN …………………………………………105
Remote Access VPN………………………………………107
RADIUS ……………………………………………………108
Authentication Process ……………………………………109
Vulnerabilities ……………………………………………109
TACACS/+ …………………………………………………110
TACACS …………………………………………………110
XTACACS ………………………………………………110
TACACS+ ………………………………………………111
Vulnerabilities ……………………………………………112
PPTP/L2TP …………………………………………………113
PPTP ……………………………………………………113
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SSH …………………………………………………………118
How SSH Works …………………………………………118
IPSec …………………………………………………………118
IPSec Authentication ……………………………………121
ISAKMP …………………………………………………121
Eavesdropping ……………………………………………122
Data Modification…………………………………………122
Identity Spoofing …………………………………………123
User Vulnerabilities and Errors ……………………………123
Administrator Vulnerabilities and Errors …………………123
E-mail Security …………………………………………………124
MIME ………………………………………………………127
S/MIME ……………………………………………………127
PGP …………………………………………………………128
How PGP Works …………………………………………129
PGP Interface Integration…………………………………129
SMTP Relay………………………………………………136
E-mail and Viruses ………………………………………139
Spam ………………………………………………………141
Hoaxes ……………………………………………………142
Summary of Exam Objectives ……………………………………144
Exam Objectives Fast Track ………………………………………147
Exam Objectives Frequently Asked Questions …………………149
Self Test …………………………………………………………151
Self Test Quick Answer Key………………………………………158
Chapter 4 Wireless ………………………………………………159
Introduction ………………………………………………………160
Wireless Concepts ………………………………………………160
Understanding Wireless Networks……………………………160
Overview of Wireless Communication in a
Wireless Network …………………………………………161
Radio Frequency Communications ………………………161
Spread Spectrum Technology ……………………………163
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Wireless Network Architecture……………………………165
CSMA/CD and CSMA/CA ……………………………166
Wireless Local Area Networks ………………………………168
WAP …………………………………………………………169
WTLS ………………………………………………………170
IEEE 802.11 …………………………………………………170
IEEE 802.11b ……………………………………………171
Ad-Hoc and Infrastructure Network Configuration …………173
WEP …………………………………………………………174
Creating Privacy with WEP ………………………………176
Authentication ……………………………………………178
Common Exploits of Wireless Networks ……………………184
Passive Attacks on Wireless Networks ……………………184
Active Attacks on Wireless Networks ……………………190
MITM Attacks on Wireless Networks ……………………191
Wireless Vulnerabilities ………………………………………191
WAP Vulnerabilities …………………………………………192
WEP Vulnerabilities …………………………………………193
Security of 64-Bit versus 128-Bit Keys …………………197
Acquiring a WEP Key ……………………………………198
Addressing Common Risks and Threats ……………………202
Finding a Target …………………………………………202
Finding Weaknesses in a Target ……………………………206
Exploiting Those Weaknesses ……………………………207
Sniffing ………………………………………………………208
Protecting Against Sniffing and Eavesdropping……………211
Spoofing (Interception) and Unauthorized Access …………211
Protecting Against Spoofing and Unauthorized Attacks …213
Network Hijacking and Modification ………………………213
Protection against Network Hijacking and Modification…215
Denial of Service and Flooding Attacks………………………215
Protecting Against DoS and Flooding Attacks ……………218
IEEE 802.1x Vulnerabilities …………………………………218
Site Surveys …………………………………………………219
Additional Security Measures for Wireless Networks ………219
Using a Separate Subnet for Wireless Networks …………220
Using VPNs for Wireless Access to Wired Network ………220
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Temporal Key Integrity Protocol …………………………223
Message Integrity Code (MIC) …………………………223
IEEE 802.11i Standard ……………………………………224
Summary …………………………………………………………228
Exam Objectives Fast Track ………………………………………231
Exam Objectives Frequently Asked Questions …………………234
Self Test …………………………………………………………237
Self Test Quick Answer Key………………………………………242
Chapter 5 Web Security …………………………………………243
Introduction ………………………………………………………244
Web Security ……………………………………………………244
Web Server Lockdown ………………………………………245
Managing Access Control …………………………………246
Handling Directory and Data Structures …………………247
Eliminating Scripting Vulnerabilities ………………………247
Logging Activity …………………………………………248
Performing Backups ………………………………………249
Maintaining Integrity ……………………………………249
Finding Rogue Web Servers ………………………………250
Stopping Browser Exploits……………………………………254
Exploitable Browser Characteristics ………………………254
Web Spoofing ……………………………………………255
Web Server Exploits …………………………………………257
1.3.1/1.3.2 SSL and HTTP/S ……………………………………………258
SSL and TLS ………………………………………………258
S-HTTP …………………………………………………259
Instant Messaging ……………………………………………261
Vulnerabilites ……………………………………………261
IP Addressing Conventions ……………………………261
File Transfer ……………………………………………261
Privacy …………………………………………………261
Web-based Vulnerabilities ……………………………………262
Understanding Java-, JavaScript-, and
ActiveX-based Problems…………………………………262
Preventing Problems with Java, JavaScript, and ActiveX …265
Programming Secure Scripts………………………………270
Code Signing: Solution or More Problems?………………272
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Page xxi
Understanding Code Signing ……………………………272
The Strengths of Code Signing …………………………273
Problems with the Code Signing Process…………………273
JavaScript ……………………………………………………275
ActiveX ………………………………………………………276
Dangers Associated with Using ActiveX …………………278
Avoiding Common ActiveX Vulnerabilities ………………280
Lessening the Impact of ActiveX Vulnerabilities …………282
Buffer Overflows ……………………………………………286
Making Browsers and E-Mail Clients More Secure …………288
Restricting Programming Languages ……………………288
Keep Security Patches Current……………………………289
Cookie Awareness …………………………………………289
Securing Web Browser Software ……………………………290
Securing Microsoft Internet Explorer ……………………290
CGI …………………………………………………………294
What is a CGI Script and What Does It Do? ……………295
Typical Uses of CGI Scripts ………………………………297
Break-ins Resulting from Weak CGI Scripts…………………301
CGI Wrappers ……………………………………………303
whisker …………………………………………………303
FTP Security ……………………………………………………307
S/FTP ………………………………………………………307
Blind FTP/Anonymous………………………………………307
1.5.3/1.5.4 FTP Sharing and Vulnerabilities………………………………308
Packet Sniffing FTP Transmissions……………………………308
Directory Services and LDAP Security …………………………312
LDAP …………………………………………………………312
Summary of Exam Objectives ……………………………………315
Exam Objectives Fast Track ………………………………………315
Exam Objectives Frequently Asked Questions …………………318
Self Test …………………………………………………………320
Self Test Quick Answer Key………………………………………326
™ Domain 3.0 Infrastructure Security ……………………………327
Chapter 6 Devices and Media …………………………………329
Introduction ………………………………………………………330
Device-based Security ……………………………………………330
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Page xxii
Firewalls ………………………………………………………331
Packet Filtering Firewalls …………………………………332
Application Layer Gateways ………………………………337
Stateful Inspection Firewalls ………………………………339
Routers ………………………………………………………342
Switches ………………………………………………………345
Wireless ………………………………………………………348
Modems ………………………………………………………349
RAS …………………………………………………………352
Telecom/PBX ………………………………………………354
Virtual Private Network ……………………………………355
Network Monitoring/Diagnostic ……………………………362
Workstations …………………………………………………363
Servers ………………………………………………………367
Mobile Devices ………………………………………………368
Media-based Security ……………………………………………369
Coax Cable …………………………………………………370
Thin Coax ………………………………………………370
Thick Coax ………………………………………………371
Vulnerabilities of Coax Cabling …………………………372
UTP/STP Cable ……………………………………………372
Fiber Optic Cable ……………………………………………375
Removable Media ……………………………………………376
Magnetic Tape ……………………………………………377
Hard Drives ………………………………………………378
Diskettes …………………………………………………379
Flashcards …………………………………………………380
Smart Cards ………………………………………………381
Summary of Exam Objectives ……………………………………382
Exam Objectives Fast Track ………………………………………385
Exam Objectives Frequently Asked Questions …………………386
Self Test …………………………………………………………387
Self Test Quick Answer Key………………………………………393
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Page xxiii
Chapter 7 Topologies and IDS …………………………………395
Introduction ………………………………………………………396
Security Topologies ………………………………………………397
Security Zones ………………………………………………398
Introducing the Demilitarized Zone ……………………402
Intranet ……………………………………………………409
VLANs ………………………………………………………414
Network Address Translation …………………………………416
Tunneling ……………………………………………………420
Intrusion Detection ……………………………………………422
1.4.1/1.4.2 Network- and Host-Based IDSs ……………………………424
Signature-Based IDSs and Detection Evasion ………………429
Popular Commercial IDS Systems……………………………431
Honeypots and Honeynets …………………………………433
Judging False Positives and Negatives ………………………436
Incident Response ……………………………………………437
Summary of Exam Objectives ……………………………………438
Exam Objectives Fast Track ………………………………………439
Exam Objectives Frequently Asked Questions …………………441
Self Test …………………………………………………………443
Self Test Quick Answer Key………………………………………448
Chapter 8 System Hardening……………………………………449
Introduction ………………………………………………………450
1.5.1 Concepts and Processes of OS and NOS Hardening ……………451
File System……………………………………………………453
Updates ………………………………………………………454
Service Packs………………………………………………456
Patches ……………………………………………………456
1.5.2 Network Hardening………………………………………………458
Updates (Firmware) …………………………………………459
Configuration ………………………………………………459
Enabling and Disabling Services and Protocols …………459
Access Control Lists ………………………………………467
1.5.5 Application Hardening……………………………………………468
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Updates ………………………………………………………469
Service Packs………………………………………………470
Patches ……………………………………………………470
Web Servers …………………………………………………470
E-mail Servers ………………………………………………472
FTP Servers …………………………………………………473
DNS Servers …………………………………………………473
NNTP Servers ………………………………………………474
File and Print Servers ………………………………………475
DHCP Servers ………………………………………………477
Data Repositories ……………………………………………478
Directory Services…………………………………………479
Databases …………………………………………………480
Summary of Exam Objectives ……………………………………482
Exam Objectives Fast Track ………………………………………482
Exam Objectives Frequently Asked Questions …………………483
Self Test …………………………………………………………485
Self Test Quick Answer Key………………………………………493
™ Domain 4.0 Basics of Cryptography …………………………495
Chapter 9 Basics of Cryptography ……………………………497
Introduction ………………………………………………………498
Algorithms ………………………………………………………499
What Is Encryption? …………………………………………499
Symmetric Encryption Algorithms …………………………500
DES and Triple DES………………………………………501
Advanced Encryption Standard (Rijndael) ………………503
International Data Encryption Algorithm ………………504
Asymmetric Encryption Algorithms …………………………505
Diffie-Hellman ……………………………………………507
El Gamal …………………………………………………508
RSA ………………………………………………………509
Hashing Algorithms …………………………………………510
Concepts of Using Cryptography ………………………………512
Confidentiality ………………………………………………513
Integrity ………………………………………………………514
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Digital Signatures …………………………………………515
MITM Attacks ……………………………………………516
Authentication ………………………………………………518
Non-Repudiation ……………………………………………519
Digital Signatures …………………………………………519
Access Control ………………………………………………519
Summary of Exam Objectives ……………………………………520
Exam Objectives Fast Track ………………………………………521
Exam Objectives Frequently Asked Questions …………………522
Self Test …………………………………………………………525
Self Test Quick Answer Key………………………………………530
Chapter 10 Public Key Infrastructure …………………………531
Introduction ………………………………………………………532
PKI ………………………………………………………………532
Certificates ……………………………………………………535
X.509 ……………………………………………………536
Certificate Policies ………………………………………538
Certificate Practice Statements ……………………………539
Certificate Revocation List ………………………………540
Online Certificate Status Protocol ………………………541
Trust Models …………………………………………………541
Single CA Model …………………………………………543
Hierarchical Model ………………………………………543
Web-of-Trust Model ……………………………………546
Standards and Protocols ………………………………………546
Key Management Lifecycle ………………………………………549
Centralized versus Decentralized Keys ………………………549
Storage ………………………………………………………550
Hardware Key Storage versus Software Key Storage ……550
Private Key Protection ……………………………………552
Escrow ………………………………………………………552
Expiration ……………………………………………………554
Status Checking …………………………………………555
Suspension ……………………………………………………556
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Status Checking …………………………………………557
Recovery ……………………………………………………557
Key Recovery Information ………………………………558
M of N Control …………………………………………558
Destruction …………………………………………………560
Key Usage ……………………………………………………561
Multiple Key Pairs (Single, Dual) …………………………561
Summary of Exam Objectives ……………………………………562
Exam Objectives Fast Track ………………………………………563
Exam Objectives Frequently Asked Questions …………………564
Self Test …………………………………………………………565
Self Test Quick Answer Key………………………………………572
™ Domain 5.0 Operational and Organization Security ………573
Chapter 11 Incident Response …………………………………575
Introduction ………………………………………………………576
Physical Security …………………………………………………576
Access Control ………………………………………………578
Physical Barriers …………………………………………582
Social Engineering……………………………………………585
Environment …………………………………………………587
Wireless Cells ……………………………………………589
Location …………………………………………………590
Shielding …………………………………………………591
Fire Suppression …………………………………………593
Forensics …………………………………………………………594
Awareness …………………………………………………595
Conceptual Knowledge …………………………………597
Understanding ……………………………………………597
What Your Role Is ………………………………………598
Chain of Custody ……………………………………………602
Preservation of Evidence ……………………………………603
Collection of Evidence ………………………………………607
Risk Identification ………………………………………………610
Asset Identification……………………………………………611
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Risk Assessment ………………………………………………614
Threat Identification …………………………………………617
Summary of Exam Objectives ……………………………………620
Exam Objectives Fast Track ………………………………………620
Exam Objectives Frequently Asked Questions …………………622
Self Test …………………………………………………………624
Self Test Quick Answer Key………………………………………630
Chapter 12 Policies and Disaster Recovery …………………631
Introduction ………………………………………………………632
Policies and Procedures …………………………………………633
Security Policies………………………………………………635
Restricted Access Policies …………………………………635
Workstation Security Policies ……………………………636
Physical Security Policies …………………………………636
Acceptable Use Policies ………………………………………637
Due Care ……………………………………………………640
Privacy ………………………………………………………642
Separation of Duties …………………………………………644
Need to Know ………………………………………………645
Password Management ………………………………………646
Strong Passwords …………………………………………647
Password Changes and Restrictions ………………………648
Using Passwords as Part of a Multifaceted
Security System …………………………………………648
Administrator Accounts …………………………………649
SLA …………………………………………………………649
Disposal/Destruction …………………………………………650
HR Policy ……………………………………………………652
Code of Ethics ……………………………………………654
Incident Response Policy ……………………………………654
Privilege Management ……………………………………………659
User/Group/Role Management ……………………………659
Single Sign-on ………………………………………………662
Centralized versus Decentralized ……………………………663
Auditing ………………………………………………………665
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Privilege …………………………………………………666
Usage ……………………………………………………666
Escalation …………………………………………………667
MAC/DAC/RBAC …………………………………………667
Education and Documentation …………………………………669
User Awareness ………………………………………………671
Education ……………………………………………………673
Online Resources ……………………………………………674
Documentation ………………………………………………675
Standards and Guidelines ……………………………………676
Systems Architecture …………………………………………677
Change Documentation ……………………………………679
Logs and Inventories …………………………………………680
Classification …………………………………………………681
Notification ………………………………………………682
Retention/Storage ……………………………………………683
Destruction …………………………………………………684
Disaster Recovery ………………………………………………684
Backups ………………………………………………………685
Rotation Schemes…………………………………………686
Offsite Storage ……………………………………………689
Secure Recovery ……………………………………………690
Alternate Sites ……………………………………………692
Disaster Recovery Plan ………………………………………693
Business Continuity ………………………………………………695
Utilities ………………………………………………………697
High Availability/Fault Tolerance ……………………………698
Summary of Exam Objectives ……………………………………701
Exam Objectives Fast Track ………………………………………702
Exam Objectives Frequently Asked Questions …………………705
Self Test …………………………………………………………707
Self Test Quick Answer Key………………………………………713
Appendix A: Self Test Questions, Answers,
and Explanations …………………………………………………715
Index …………………………………………………………………803
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This book’s primary goal is to help you prepare to take and pass CompTIA’s
Security+ exam. Our secondary purpose in writing this book is to provide exam
candidates like you with knowledge and skills that go beyond the minimum requirements for passing the exam, and help to prepare you to work in the real world of
computer and network security.
What is CompTIA Security+?
Computer and network security is the hottest subspecialty in the IT field today, and
a number of product vendors and vendor-neutral organizations offer certification
exams to allow IT professionals to test their knowledge and skills in basic security
practices and standards.The Computing Technology Industry Association (CompTIA)
has positioned itself for the last two decades as a leading trade association devoting to
promoting standards and providing IT education. One of CompTIA’s primary roles
has been development of vendor-neutral certification exams to evaluate the skill sets
of current and aspiring IT professionals.
CompTIA’s certifications are well regarded within the IT community, particularly
as validation of basic credentials that can be used by employers in screening candidates for entry-level positions. Microsoft, Cisco, Novell, and other vendors allow the
use of CompTIA certifications in some of their own certification programs as electives or substitution for one of their exams. For example, the CompTIA A+ and
Network+ certifications can be applied toward Microsoft’s MCSA certification.
One advantage of the CompTIA exams that make them especially popular is the
fact that unlike most vendor-specific exams, they are considered to be lifetime certifications that do not expire; once you’ve obtained a CompTIA certification, you
never have to renew it.
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At the time of this writing, CompTIA offers certifications in 12 specialty areas of
technology, including the very popular A+ (PC hardware technician), Network+
(basic computer networking), and Server+ (mid- to upper-level server technicians). A
full listing of CompTIA certification programs can be found on their Web site at Security+ certification is one of CompTIA’s
newest programs, developed in response to an ever-increasing need for trained security professionals.
Path to Security+
The Security+ certification is a new addition to CompTIA’s repertoire. Only one
exam is required to obtain the certification; however, it is a relatively comprehensive
exam that covers a wide range of security concepts, including:
Domain 1.0: General Security Concepts
Domain 2.0: Communications Security
Domain 3.0: Infrastructure Security
Domain 4.0: Basics of Cryptography
Domain 5.0: Operational and Organizational Security
Exam questions were written by subject matter experts working in the IT
industry, and went through beta testing in late summer/early fall of 2002.The exam
went live in December 2002.
Prerequisites and Preparation
In comparison to other security certifications, such as the CISSP and SANS GIAC,
the Security+ is an entry-level certification, and there are no prerequisites (prior
exams or certifications) required to take the exam. However, CompTIA specifies that
the target audience for the exam consists of professionals with two years of networking experience.We recommend that test-takers have a good grasp of basic computer networking concepts, as mastering many of the topics—especially in the
domains of communications and infrastructure security—requires a basic understanding of network topology, protocols, and services.
Passing the A+ and Network+ exams prior to pursuing the Security+ certification, although not required, provides an excellent foundation for a better understanding when studying security topics and is recommended by CompTIA. Because
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this is a vendor-neutral exam, it also helps to have some exposure to the computer
operating systems most commonly used in a business environment:Windows and
Hands-on experience in working with the security devices and software covered
in the exam (for example, firewalls, certificate services, virtual private networks
[VPNs], wireless access, and so forth) is invaluable, although it is possible to pass the
exam without direct hands-on experience.The Exercises in each chapter are designed
to walk readers through the practical steps involved in implementing the security
measures discussed in the text.
Exam Overview
The structure of this book is designed to closely follow the exam objectives. It is
organized to make it easy to review exam topics according to the objective domain
in which they fall. Under each learning domain listed above, we go into detail to
provide a good overview of the concepts contained in each subsection of the
CompTIA objectives.Throughout this study guide, you will find numbered icons in
the margin indicating which CompTIA Security+ exam objective is being covered.
You will find a complete guide to every objective in the Table of Contents to this
book. Following is a brief overview of the specific topics covered:
Domain 1.0: General Security Concepts
Introduction This section introduces the “AAA” triad of security concepts: access control, authentication, and auditing. Readers are also introduced to the terminology used in the computer security field, and learn
about the primary purposes of computer/network security: providing confidentiality of data, preserving integrity of data, and ensuring availability of
data to authorized users.
Access Control This section focuses on ways that network security specialists can control access to network resources, and discusses three important
types of access control: Mandatory Access Control (MAC), Discretionary
Access Control (DAC), and Role Based Access Control (RBAC).
Authentication This section covers the many available methods for
authenticating users and computers on a network (that is, validating the
identity of a user or computer before establishing a communication session).
Industry standard protocols are covered, including Kerberos (used by both
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UNIX and newer Windows operating systems for authenticating users
requesting access to resources), and the Challenge Handshake Authentication
Protocol (CHAP) used for authenticating remote access users. Use of digital
certificates, tokens, and user/password authentication are discussed. Multifactor authentication (use of more than one authentication method for
added security), mutual authentication (two-way authentication between
client and server), and biometric authentication (use of physiological characteristics to validate identity) are all thoroughly covered.
Non-essential Services and Protocols This section discusses those services and protocols that are often installed by default on network computers,
which can be disabled for added security when not specifically needed.
Attacks This section introduces readers to some of the more commonly
used exploits used by hackers to attack or intrude upon systems, including
Denial of Service (DoS), backdoor attacks, spoofing, man-in-the-middle
(MITM) attacks, replay,TCP/IP hijacking, weak key and mathematical
exploits, password cracking methods, and software exploits.The reader will
learn not only the technical details of how these attacks work, but will also
become aware of how to prevent, detect, and respond to such attacks.
Malicious Code This section deals with computer viruses,Trojan horse
programs, logic bombs, worms, and other destructive “malware” that can be
introduced—either deliberately or accidentally—into a system, usually via
the network.
Social Engineering This section examines the phenomenon of using
social skills (playacting, charisma, persuasive ability) to obtain information
(such as passwords and account names) needed to gain unauthorized access
to a system or network. Readers will learn how these “human exploits”
work and how to guard against them.
Auditing This section covers the ways that security professionals can use
logs and system scanning tools to gather information that will help detect
attempted intrusions and attacks, and to detect security holes that can be
plugged before outsiders have a chance to find and exploit them.
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Domain 2.0: Communication Security
Remote Access This section deals with securing connections that come
via phone lines, dedicated leased lines, wireless technology, and across the
Internet.The reader will learn about the 802.1x standards that govern
implementation of wireless networking and the use of VPNs to create a
secure “tunnel” from one site to another through the Internet. Popular
remote authentication methods, such as Remote Authentication Dial-In
User Service (RADIUS) and Terminal Access Controller Access System
(TACACS+) will be discussed, and readers will learn about tunneling protocols such as Point-to-Point Tunneling Protocol (PPTP) and Layer 2
Tunneling Protocol (L2TP), as well as Secure Shell (SSH). Readers will also
learn about Internet Protocol Security (IPSec), which can be used either as
a tunneling protocol or for encryption of data as it moves across the network (and which will be a standard part of the next generation of IP, IPv6).
Vulnerabilities related to all these technologies will be covered, as well.
E-mail This section will discuss how e-mail can be secured, including both
client-side and server-side technologies. Use of Secure Multipurpose
Internet Mail Extensions (MIME) and Pretty Good Privacy (PGP) will be
discussed, as will spam (unwanted e-mail advertising) and e-mail hoaxes.
Web-based Services This section discusses World Wide Web-based vulnerabilities and how Web transactions can be secured using Secure Sockets
Layer/Transport Layer Security (SSL/TLS) and Secure Hypertext Transfer
Protocol (S-HTTP).The reader will get a good background in how the Web
works, including naming conventions and name resolution. Modern Web
technologies that present security or privacy vulnerabilities will also be covered, including JavaScript, ActiveX, buffer overflows, cookies, signed applets,
CGI script, and others.
Directory Services This section will introduce the reader to the concept
of directory services and will discuss the X.500 and Lightweight Directory
Access Protocol (LDAP) standards upon which many vendors’ directory services (including Novell’s NDS and Microsoft’s Active Directory) are built.
File Transfer This section discusses the File Transfer Protocol (FTP),
how files are shared and the vulnerabilities that are exposed through file
sharing, the dangers of blind/anonymous FTP, and how protections can be
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implemented using Secure FTP (S/FTP).This section also addresses packet
sniffing, the capture and examination of individual communications packets
using protocol analyzer tools.
Wireless This section goes into detail about various protocols used in wireless communication and security, including the Wireless Transport Layer
Security (WTLS) protocol and the Wired Equivalent Privacy (WEP) protocol.
We also discuss the Wireless Application Protocol (WAP) that is used for communications by wireless mobile devices such as mobile phones, and the 802.1x
standards for port-based authentication.
Domain 3.0: Infrastructure Security
Devices This section provides an overview of the plethora of hardware
devices that are involved in implementing network security, including firewalls, routers, switches, wireless access points, modems, Remote Access
Services (RAS) servers, telecom/PBX equipment, hardware-based Virtual
Private Networks (VPNs), Intrusion Detection Systems (IDSs), network
monitoring and diagnostic equipment, workstations, servers, and mobile
communication devices.The role each plays in network security will be
Media This section reviews the types of physical media over which network communications can take place, including coaxial cable, unshielded
and shielded twisted pair (UTP/STP), and fiber optic cabling.We also take a
look at removable media on which computer data can be stored, including
tape, recordable CD/DVD, hard disks, floppy diskettes, flash media (Compact
Flash, SD cards, MMC, SmartMedia, and memory sticks), and smart cards
(credit card sized devices containing a tiny “computer on a chip”), which are
capable of both storing and processing information.
Security Topologies This section explores the ways in which topological
structure can impact security issues on a network, and examines the concept
of security zones and how the network can be divided into areas (including
the DMZ, intranet, and extranet) for application of differing security levels.
We also take a look at how virtual LANs (VLANs) can be used in a security
context, and the advantages of Network Address Translation (NAT) and tunneling in creating an overall security plan.
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Intrusion Detection This section deals with IDS devices, both networkbased and host-based. Readers will learn the differences between active and
passive detection and where each fits into the security plan.We also discuss
the role of honeypots and honeynets in distracting, detecting, and identifying
attackers, and provide information on incident response in relation to network intrusions and attacks.
Security Baselines This section takes a three-pronged approach to overall
system hardening.We discuss how to harden (secure) computer/network
operating systems, including the file system.The importance of applying hot
fixes, service packs, patches, and other security updates is emphasized. Next
we discuss hardening of the network, with a focus on the importance of
configuration/settings and use of access control lists (ACLs). Finally, we discuss application hardening, with specifics on how to secure Web servers, email servers, FTP servers, DNS servers, Network News Transport Protocol
(NNTP) servers, file and print servers, Dynamic Host Configuration
Protocol (DHCP) servers, and data repositories (including directory services
and databases).
Domain 4.0: Basics of Cyrptography
Basics of Cryptography This section introduces the concepts upon which
encryption technologies are based, including symmetric and asymmetric algorithms and hashing algorithms. Readers will learn how encryption can provide confidentiality, integrity, authentication, and non-repudiation.The use of
digital signatures is discussed.We show readers how cryptographic algorithms
and digital certificates are used to create a Public Key Infrastructure (PKI) for
validating identity through a trusted third party (certification server). Key
management, certificate issuance, expiration and revocation, and other elements of a PKI are discussed.
Domain 5.0: Operational and Organizational Security
Operational/Organizational Security This section deals with the
important topic of physical security and the environmental factors that affect
security.We also cover disaster recovery plans, encompassing backup policies,
off-site storage, secure recovery, and business continuity. Security policies and
procedures are covered in detail, with a focus on acceptable use policies, due
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care, privacy issues, separation of duties, need to know, password management, service level agreements (SLAs), disposal/destruction policies, human
resources policies, and incident response policies. Privilege management,
computer forensics awareness (including chain of custody and collection/
preservation of evidence), risk identification, education and training of users,
executives and HR personnel, and documentation standards and guidelines
are also important components of this learning domain.
Exam Day Experience
Taking the exam is a relatively straightforward process. Both Vue and Prometric
testing centers administer the Security+ exam (the exam code is SY0-101).You
can register for, reschedule, or cancel an exam through the Vue Web site at or the Prometric Web site at’ll
find listings of testing center locations on these sites. Accommodations are made for
those with disabilities; contact the individual testing center for more information.
Exam price varies depending on the country in which you take the exam. In
addition, discounted prices are available for individuals whose companies are members of CompTIA.
Exam Format
Exams are timed; candidates are given 120 minutes to finish the Security+ exam. At
the end of the exam, you will find out your score and whether you passed or failed.
Questions are generally multiple-choice format, of both knowledge-based and skillbased question types. Knowledge-based questions are simple factual questions (for
example, “Which of the following is the encryption protocol used with L2TP to
secure VPN tunnels?”). Skill-based questions provide scenario situations and ask the
exam-taker to determine a best course of action, based on the information given
about the scenario.
You will not be allowed to take any notes or other written materials with you
into the exam room.You will be provided with a pencil and paper, however, for
making notes during the exam or doing calculations.
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Test-Taking Tips
Different people work best using different methods. However, there are some
common methods of preparation and approach to the exam that are helpful to many
test-takers. In this section, we provide some tips that other exam candidates have
found useful in preparing for and actually taking the exam.
Exam preparation begins before exam day. Ensure that you know the concepts and terms well and feel confident about each of the exam objectives.
Many test-takers find it helpful to make flash cards or review notes to study
on the way to the testing center. A sheet listing acronyms and abbreviations
can be helpful, as the number of acronyms (and the similarity of different
acronyms) when studying IT topics can be overwhelming.The process of
writing the material down, rather than just reading it, will help to reinforce
your knowledge.
Many test-takers find it especially helpful to take practice exams that are
available on the Internet and within books such as this one.Taking the practice exams not only gets you used to the computerized exam-taking experience, but also can be used as a learning tool.The best practice tests include
detailed explanations of why the correct answer is correct and why the
incorrect answers are wrong.
When preparing and studying, you should try to identify the main points of
each objective section. Set aside enough time to focus on the material and
lodge it into your memory. On the day of the exam, you should be at the
point where you don’t have to learn any new facts or concepts, but need
simply to review the information already learned.
The Exam Warnings in this book highlight concepts that are likely to be
tested.You may find it useful to go through and copy these into a notebook
as you read the book (remembering that writing something down reinforces
your ability to remember it) and then review them just prior to taking the
The value of hands-on experience cannot be stressed enough. Although the
Security+ exam questions tend to be generic (non-vendor specific), they are
based on test-writers’ experiences in the field, using various product lines.
Thus, there might be questions that deal with the products of particular
hardware vendors, such as Cisco Systems, or particular operating systems,
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such as Windows or UNIX.Working with these products on a regular basis,
whether in your job environment or in a test network that you’ve set up at
home, will make you much more comfortable with these questions.
Know your own learning style and use study methods that take advantage of
it. If you’re primarily a visual learner, reading, making diagrams, or watching
video files on CD may be your best study methods. If you’re primarily auditory, listening to classroom lectures, playing audiotapes in the car as you
drive, and repeating key concepts to yourself aloud may be more effective. If
you’re a kinesthetic learner, you’ll need to actually do the exercises, implement the security measures on your own systems, and otherwise perform
hands-on tasks to best absorb the information. Most of us can learn from all
of these methods, but have a primary style that works best for us.
Use as many little mnemonic tricks as possible to help you remember facts
and concepts. For example, to remember which of the two IPSec protocols
(AH and ESP) encrypts data for confidentiality, you can associate the “E” in
encryption with the “E” in ESP.
Although it may seem obvious, many exam-takers ignore the physical
aspects of exam preparation.You are likely to score better if you’ve had sufficient sleep the night before the exam, and if you are not hungry, thirsty,
hot/cold, or otherwise distracted by physical discomfort. Eat prior to going
to the testing center (but don’t indulge in a huge meal that will leave you
uncomfortable), stay away from alcohol for 24 hours prior to the test, and
dress appropriately for the temperature in the testing center (if you don’t
know how hot or cold the testing environment tends to be, you may want
to wear light clothes with a sweater or jacket that can be taken off).
Before you go to the testing center to take the exam, be sure to allow time
to arrive on time, take care of any physical needs, and step back to take a
deep breath and relax.Try to arrive slightly early, but not so far in advance
that you spend a lot of time worrying and getting nervous about the testing
process.You may want to do a quick last-minute review of notes, but don’t
try to “cram” everything the morning of the exam. Many test-takers find it
helpful to take a short walk or do a few calisthenics shortly before the exam,
as this gets oxygen flowing to the brain.
Before beginning to answer questions, use the pencil and paper provided to
you to write down terms, concepts, and other items that you think you may
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have difficulty remembering as the exam goes on. For example, you might
note the differences between MAC, DAC, and RBAC.Then you can refer
back to these notes as you progress through the test.You won’t have to
worry about forgetting the concepts and terms you have trouble with later
in the exam.
Sometimes the information in a question will remind you of another concept or term that you might need in a later question. Use your pencil and
paper to make note of this in case it comes up later on the exam.
It is often easier to discern the answer to scenario questions if you can visualize the situation. Use your pencil and paper to draw a diagram of the network that is described to help you see the relationships between devices, IP
addressing schemes, and so forth.This is especially helpful in questions
dealing with how to set up DMZs and firewalls.
When appropriate, review the answers you weren’t sure of. However, you
should only change your answer if you’re sure that your original answer was
incorrect. Experience has shown that more often than not, when test-takers
start second-guessing their answers, they end up changing correct answers to
the incorrect. Don’t “read into” the question (that is, don’t fill in or assume
information that isn’t there); this is a frequent cause of incorrect responses.
—Debra Littlejohn Shinder
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4:10 PM
Page 1
Domain 1.0
General Security
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Page 2
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Page 3
Chapter 1
Access Control,
Authentication, and
Domain 1.0 Objectives in this Chapter:
Introduction to AAA
Access Control
Disabling Non-Essential Services, Protocols,
Systems, and Processes
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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Page 4
Domain 1.0 • General Security Concepts
Security+ is a security fundamentals and concepts exam. No security concepts
exam would be complete without questions on Access Control, Authentication,
and Auditing (AAA). In this chapter, you will study CompTIA’s test objectives
for Section 1, “General Security Concepts.”You will be introduced to AAA and
its finer details, as well as the concepts and terminology that will be explored and
developed in later chapters.We will end this chapter with a discussion on
removing non-essential services to secure any platform you may be working on.
As you progress through this chapter and the rest of the book, pay particular attention to new or different acronyms or names that are presented for various processes and procedures. Different security groups
and professionals may use descriptions that are foreign to you or that
you learned differently. We will use and detail the acronyms and short
names of these procedures or concepts, with an emphasis on the terminology presented in the Security+ exam. In this chapter, if the concept is
proprietary to a particular vendor, we will indicate this and provide further reference, if needed, to explain the concept or terminology.
Introduction to AAA
AAA is a primary concept in understanding computer and network security and
access security.These concepts are used daily to protect property, data, and systems from intentional or unintentional damage.These three concepts are used to
support the Confidentiality, Integrity, and Availability (CIA) security concept, as
well as for access to networks and equipment using Remote Authentication DialIn User Service [non-proprietary] (RADIUS) and Terminal Access Controller
Access Control System [owned by Cisco] (TACACS/TACACS+).
A more detailed description of AAA is discussed in RFC 3127, which can be
found at
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Head of the Class…
Access Control, Authentication, and Auditing • Chapter 1
Letters, Letters, and More Letters
As mentioned at the beginning of this chapter, it is important to understand the acronyms used in the Security+ exam. For purposes of the
Security+ exam, two specific abbreviations need to be explained to avoid
confusion. For general security study and the Security+ exam, AAA is
defined as “Access Control, Authentication, and Auditing.” Do not confuse this with Cisco’s implementation and description of AAA, which is
“Authentication, Auditing, and Accounting.” While similar in function and
usage, the Security+ exam uses the first definition.
The second abbreviation requiring clarification is CIA. For purposes
of the Security+ exam, CIA is defined as “Confidentiality, Integrity, and
Availability.” Other literature and resources may refer to CIA as
“Confidentiality, Integrity, and Authentication.”
What is AAA?
Head of the Class…
AAA is a group of processes used to protect data, equipment, and confidentiality
of property and information. As mentioned earlier, one of the goals of AAA is to
provide CIA. CIA can be briefly described as follows:
Confidentiality The contents or data are not revealed
Integrity The contents or data are intact and have not been modified
Availability The contents or data are accessible if allowed
Let’s Talk About Access and Authentication
Access control involves the use of hardware, policies, or software to either
allow or deny entry to the item being protected. For example, a closed
and locked door is a form of access control. If the door is locked, access
is denied. If is the door is unlocked and open, implicit access is allowed.
If the door is locked and we have been given a key, explicit access is
allowed. Therefore, access control is merely setting the stage for whether
or not the door is open, and how it may be entered.
The second part of AAA is authentication. This involves verifying that
the person coming through the door is valid. For example, when entering a
workplace, an individual may have to present an identification card to verify
who they are. Those without identification are termed unauthenticated and
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Domain 1.0 • General Security Concepts
refused entrance. This assists access control by verifying that the individual
entering is a valid person.
Why is this difference important? Because it leads to authorization,
or permission, and expands the level of control. Access control sets the
conditions of access. Authentication verifies identity. Authorization sets
the conditions of travel or use of resources within the control area. In the
workplace example, the three parts interact: access control defines when
and where to enter, authentication verifies identity, and authorization
allows individuals to work in or on a particular item. Together, they allow
users to control the use of their resources.
AAA consists of three separate areas that work together.These areas provide a
level of basic security in controlling access to resources and equipment in networks.This control allows users to provide services that assist in the CIA process
for further protection of systems and assets. Let’s start with basic descriptions of
the three areas, and then break each down to explore their uses and the security
they provide. Finally, we will work with examples of each AAA component.
Access Control
Access control can be defined as a policy, software component, or hardware component that is used to grant or deny access to a resource.This can be an advanced
component such as a smart card, a biometric device, or network access hardware
such as routers, remote access points such as remote access service (RAS) and virtual private networks (VPNs), or the use of wireless access points (WAPs). It can
also be a file or shared resource permissions assigned through the use of a network operating system (NOS) such as Microsoft Windows NT 4.0,Windows
2000 Active Directory, or Novell NetWare family with Novell Directory Services
(NDS). Finally, it can be a rule set that defines the operation of a software component limiting entrance to a system or network.We will explore a number of
alternatives and possibilities for controlling access.
Authentication can be defined as the process used to verify that a machine or user
attempting access to the networks or resources is, in fact, the entity being presented.We will examine a process that proves user identity to a remote resource
host.We will also review a method of tracking and ensuring non-repudiation of
authentication (see Chapter 9). For this chapter, non-repudiation is the method
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Access Control, Authentication, and Auditing • Chapter 1
used (time stamps, particular protocols, or authentication methods) to ensure that
the presenter of the authentication request cannot later deny they were the originator of the request. In the following sections, authentication methods include
presentation of credentials (such as a username and password, smart card, or personal identification number [PIN]) to a NOS (logging on to a machine or network), remote access authentication, and a discussion of certificate services and
digital certificates.The authentication process uses the information presented to
the NOS (such as username and password) to allow the NOS to verify the identity based on those credentials.
Auditing is the process of tracking events, errors, access, and authentication
attempts on a system. Much like an accountant’s procedure for keeping track of
the flow of funds, you need to be able to follow a trail of access, access attempts,
machine problems or errors, and other events that are important to the systems
being monitored and controlled. In the case of security auditing, you will learn
about the policies and procedures that allow administrators to track access
(authorized or unauthorized) to the network, local machine, or resources.
Auditing is not enabled by default in many NOS’, and administrator’s must often
specify the events or objects to be tracked.This becomes one of the basic lines of
defense in the security and monitoring of network systems.Tracking is used
along with regular reading and analysis of the log files generated by the auditing
process to better understand if the access controls are working.
Access Control
As we further develop the concepts of AAA, we need to explore the subcomponents of the three parts. In the case of access control, we must further explore
methods and groupings that apply to the area.We will look at new terminology
and then explore, through examples, what the subcomponents control and how
they are used to secure networks and equipment.
The following access control concepts sections are discussed and tested
in more than one area of the Security+ exam. Make sure you read the
descriptions and learn the acronyms involved in these access control
methods, so that you are fully prepared to explore the concepts and
answer the questions.
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In discussing access control, mandatory access control (MAC), discretionary access
control (DAC), and role-based access control (RBAC) are individual areas that
take on a new meaning.
MAC, in this context, is not a network interface card (NIC) hardware
address, but rather a concept called mandatory access control.
DAC is short for discretionary access control, which those who have taken
Microsoft classes will have heard referred to as the use of discretionary
access control lists (DACLs).
RBAC (role-based access control) should not be confused with rule-based
access control.
All three methods have varying uses when trying to define or limit access to
resources, devices, or networks.The following sections explore and illustrate each
of the three access control methods.
In the following sections, the term Windows NT-based is used to define
all Windows operating systems that are based on the NT kernel. This
includes Windows NT (all versions), Windows 2000, Windows XP
Professional, and Windows .NET Server. The term Windows 9.x-based is
used to describe Windows operating systems including Windows 95,
Windows 98, and Windows ME. Windows XP Home contains some
functionality from both platforms, and will be mentioned specifically if
MAC is generally built into and implemented within the operating system being
used, although it may also be designed into applications. MAC components are
present in UNIX, Linux, Microsoft’s Windows NT-based operating systems,
Open BSD, and others. Mandatory controls are usually hard-coded, and set on
each object or resource individually. MAC can be applied to any object within
an operating system, and allows a high level of granularity and function in the
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granting or denying of access to the objects. MAC can be applied to each object,
and can control access by processes, applications, and users to the object. It cannot
be modified by the owner or creator of the object.
The following example illustrates the level of control possible:When using
MAC, if a file has a certain level of sensitivity (or context) set, the system will not
allow certain users, programs, or administrators to perform operations on that file.
Think of setting the file’s sensitivity higher than that of an e-mail program.You
can read, write, and copy the file as desired, but with an access level of root, superuser, or administrator, you cannot e-mail the file to another system because the
e-mail program lacks clearance to manipulate the file’s level of access control.This
level of control is useful in, for instance, the prevention of “Trojan horse” attacks,
since you can set the access levels appropriately to each system process, thus
severely limiting the ability of the Trojan horse to operate.The Trojan horse
would have to have intimate knowledge of each of the levels of access defined on
the system to compromise it or make the Trojan horse viable within it.
To review briefly, MAC is:
Non-discretionary The control settings are hard coded and not modifiable by the user or owner
Multilevel Control of access privileges is definable at multiple access
Label-based May be used to control access to objects in a database
Universally Applied Applied to all objects
DAC is the setting of access permissions on an object that a user or application has
created or has control of.This includes setting permissions on files, folders, and
shared resources.The “owner” of the object in most OS environments applies discretionary access controls.This ownership may be transferred, as in the Windows
NT-based environment, or controlled by root or other superuser accounts in other
systems. DAC settings cannot be applied to locally created or stored resources on a
Windows 9.x-based machine, although Windows 9.x users can work with DAC
settings on personal files created and stored on a machine that supports DAC, such
as the Windows NT-based systems and NetWare. It is important to understand that
DAC is assigned or controlled by the owner, rather than being coded into the
system. DAC does not allow the fine control available with MAC, but requires less
coding and administration of individual files and resources.
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To summarize, DAC is:
Discretionary Not hard-coded, and not automatically applied by the
OS/NOS or application
Controllable Controlled by the owner of the object (file, folder, or
other types)
Transferable The owner may give control away
RBAC can be described in different ways.The most familiar process is a comparison or illustration utilizing the “groups” concept. In Windows NT/Windows
2000, UNIX/Linux, and NetWare systems; the concept of groups is used to simplify the administration of access control permissions and settings.When creating
the appropriate groupings, you have the ability to centralize the function of setting the access levels for various resources within the system.We have been
taught that this is the way to simplify the general administration of resources
within networks and local machines. However, although the concept of RBAC is
the same, it is not the exact same structure.With the use of groups, a general level
of access based on a user or machine object grouping is created for the convenience of the administrator. However, when the group model is used, it does not
allow for the true level of access that should be defined, and the entire membership of the group gets the same access.This can lead to unnecessary access being
granted to some members of the group. RBACs allow for a more granular and
defined access level, without the generality that exists within the group environment. A role definition is developed and defined for each job in an organization,
and access controls are based on that role.This allows for centralization of the
access control function, with individuals or processes being classified into a role
that is then allowed access to the network and to defined resources.This type of
access control requires more development and cost, but is superior to MAC in
that it is flexible and able to be redefined more easily. RBAC can also be used to
grant or deny access to a particular router or to File Transfer Protocol (FTP) or
In summary, RBAC is:
Job based
Highly configurable
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Access Control, Authentication, and Auditing • Chapter 1
More flexible than MAC
More precise than groups
Be careful! RBAC has two different definitions in the Security+ exam. The
first is defined as Role-Based Access Control. A second definition of RBAC
that applies to control of (and access to) network devices, is defined as
Rule-Based Access Control. This consists of creating access control lists
for those devices, and configuring the rules for access to them.
Almost all current NOSs allow administrators to define or set DAC settings. UNIX and Linux accomplish this either by way of a graphical user
interface (GUI) or at a terminal window as the superuser creating
changes to the settings using the chmod command. Windows NT-based
operating systems set DAC values using Windows Explorer.
For this exercise, you will view the DAC settings in Windows 2000 or
Windows XP Professional. Please note that if you try this in Windows XP
Home edition, the DAC settings will not be available. To start, open
Windows Explorer. Navigate to the %systemroot%\system32 folder (where
%systemroot% is the folder Windows 2000 or XP Professional is installed
in). Highlight this folder’s name and select Properties. Select the Security
tab; you should see a window as shown in Figure 1.1.
Notice that the administrator account is granted full control permission for this folder. Check the access settings for other users and groups
that are defined on your machine. You should notice that the system has
full control, but that various other access settings are in place for different types of access permissions. Within the Windows NT-based OS,
this is the area that allows you to control and modify the DAC settings
for your resources.
Similar DAC settings are in place for all files and folders stored on NT
File System (NTFS) partitions, as well as all objects that exist within Active
Directory and all Registry keys.
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Figure 1.1 Viewing the Discretionary Access Control Settings on a Folder
A similar function is available in most other OSs. As mentioned,
UNIX and Linux use the chmod process to control access through DAC.
NetWare also has a file access system in place that is administered by the
administrator (who has “Supervisor” rights).
Authentication, when looked at in its most basic form, is simply the process used
to prove the identity of someone or something that wants access.This can involve
highly complex and secure methods, which may involve higher costs and more
time, or can be very simple. For example, if someone you personally know comes
to your door, you visually recognize them, and if you want them to enter, you
open the door. In this case, you have performed the authentication process
through your visual recognition of the individual. All authentication processes
follow this same basic premise; that we need to prove who we are or who the
individual, service, or process is before we allow them to use our resources.
Authentication allows a sender and receiver of information to validate each
other as the appropriate entities with which they want to work. If entities
wishing to communicate cannot properly authenticate each other, there can be
no trust in the activities or information provided by either party. Only through a
trusted and secure method of authentication can administrators provide for a
trusted and secure communication or activity.
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Access Control, Authentication, and Auditing • Chapter 1
Notes from the Underground…
The simplest form of authentication is the transmission of a shared password
between entities wishing to authenticate each other.This can be as simple as a
secret handshake or a key. As with all simple forms of protection, once knowledge
of the secret key or handshake is disclosed to non-trusted parties, there can no
longer be trust in who is using the secrets.
Many methods can be used by an unauthorized person to acquire a secret
key, from tricking someone into disclosing it, to high-tech monitoring of communications between parties to intercept the key as it is passed between parties.
However the code is acquired, once it is in a non-trusted party’s hands, it can be
used to falsely authenticate and identify someone as a valid party, forging false
communications or utilizing the user’s access to gain permissions to the available
Original digital authentication systems shared a secret key across the network
with the entity with which they wanted to authenticate. Applications such as
Telnet and FTP are examples of programs that simply transmit the username and
password, in Cleartext to the party they are authenticating. Another area of concern is Post Office Protocol 3 (POP3) e-mail, which, in its default state, sends the
complete username and password information in cleartext, with no protection.
Cleartext Authentication
Cleartext (non-encrypted) authentication is still widely used by many
people who receive their e-mail through POP3. By default, POP3 client
applications send the username and password unprotected in cleartext
from the e-mail client to the server. There are several ways of protecting
e-mail account passwords, including connection encryption.
Encrypting connections between e-mail clients and servers is the only
way of truly protecting your e-mail authentication password. This prevents anyone from capturing your password or any e-mail you transfer to
your client. Secure Sockets Layer (SSL) is the general method used to
encrypt the connection stream from the e-mail client to the server.
If you protect a password using Message Digest 5 (MD5) or a similar
crypto cipher, it is possible for anyone who intercepts your “protected”
password to identify it through a brute force attack. A brute force attack
is when someone generates every possible combination of characters and
runs each version through the same algorithm used to encrypt the original password until a match is made and a password is cracked.
Authentication POP (APOP) is used to provide password-only encryption for e-mail authentication. It employs a challenge/response method
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Domain 1.0 • General Security Concepts
(defined in RFC1725) that uses a shared time stamp provided by the
authenticating server. The time stamp is hashed with the username and
the shared secret key through the MD5 algorithm.
There are still some problems with this process. The first is that all
values are known in advance except the shared secret key. Because of this,
there is nothing provided to protect against a brute force attack on the
shared key. Another problem is that this security method attempts to protect a password, but does nothing to prevent anyone from viewing e-mail
as it is downloaded to an e-mail client.
An example of a brute force attack that can produce a brute force dictionary from specific character sets can be found at
tools/files. This tool can be used to generate a specific password dictionary,
which can then be used with brute force attacking tools to try to obtain
passwords. Other brute force crackers, including POP, Telnet, FTP, and HTTP,
can be found at Further discussion
of why and how these tools are used can be found in Chapter 2.
The problem with this method of authentication is that anyone that monitors
a network can possibly capture a secret key and use it to gain access to the services or to attempt to gain higher privileged access with your stolen authentication information.
What methods can be used to provide a stronger defense? As discussed previously, sharing a handshake or secret key does not provide long-lasting and secure
communication or the secure exchange of authentication information.This has
led to more secure methods of protection of authentication mechanisms.The following sections examine a number of methods that provide a better and more
reliable authentication process.
One of the operations performed in security monitoring and analysis is
packet sniffing—the analysis of network traffic and packets being transmitted to and from the equipment. This involves using appropriate software to intercept, track, and analyze the packets being sent over the
network. In this exercise, you are going to do some packet sniffing
and detection work. The steps you use will give you the opportunity to
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Access Control, Authentication, and Auditing • Chapter 1
experience first-hand what has been discussed so far about authentication. Analysis of the traffic on your network provides you with the
opportunity to detect unwanted and unauthorized services, equipment,
and invaders in your network.
Many products exist that allow you to analyze the traffic on your network. A number of these are proprietary. For example, Microsoft provides Network Monitor on Windows NT-based server products for use by
administrators and server operators to examine network traffic to and
from individual machines.
A higher-powered version is available in other Microsoft products,
including System Management Server (SMS) v.1.2 and v.2.0.
Products are also available from vendors such as Fluke Networks,
Network Associates Sniffer Pro product line, and Agilent’s Advisor product.
Best of all, there are free products. To try this exercise, use any of the
above products or one of the following:
This exercise is described using the free tool, ettercap. Let’s get
started by verifying the presence of cleartext passwords that are sent on
networks daily.
Perform the following steps to set up for the exercise.
1. Download and install your tool of choice. Note that ettercap and
Ethereal are available for most platforms.
2. Find and note the following information: your POP3 server’s fully
qualified domain name (FQDN) or Internet Protocol (IP) address, a
valid username for that server, and a valid password for that server.
3. Launch the application you are using (these notes are for
4. Choose to monitor the appropriate network interface if you have
more than one interface configured. In Windows, pick the actual
adaptor, not the NDISWAN virtual connection.
5. In ettercap, after you have launched the application and are at
the initial screen detailing the detected local area network (LAN)
IP addresses, press the S key. This should give you a display that
looks similar to the following:
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Domain 1.0 • General Security Concepts
6. Your display should now begin to detect and record the network
activities on your LAN.
To capture the traffic to your e-mail server, you can do either
of the following:
1. Launch your e-mail application and retrieve your e-mail from
the POP3 server.
2. Using Telnet, open port 110 on your e-mail server’s address,
and enter USER <username> and PASS <password> to login
to the e-mail server. Enter quit to exit and return to ettercap.
7. After you have retrieved your e-mail, find a line in the ettercap
display that shows a connection that occurred to the e-mail
server. Use your arrow keys to move up and down the list, and
highlight one of the entries. It will look something like this:
8. Press the Return [Enter] key for the following (or similar) display:
Notice that ettercap has captured the username and password either
that you entered or that your e-mail program sent to the e-mail server.
These credentials have been sent and received in cleartext, and thus are
readable by anyone actively monitoring the network either in LAN or at
the connection at the e-mail server. As indicated, unless you have taken
steps to secure this traffic, these passwords are not protected during this
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Kerberos (currently Kerberos v5), is used as the preferred network authentication
protocol in many medium and large environments to authenticate users and services requesting access to resources. Kerberos is a network protocol designed to
centralize the authentication information for the user or service requesting the
resource.This allows authentication of the entity requesting access (user, machine,
service, or process) by the host of the resource being accessed through the use of
secure and encrypted keys and tickets (authentication tokens) from the authenticating Key Distribution Center (KDC). It allows for cross-platform authentication, and will be available in upcoming implementations of various NOSs.
Kerberos is very useful in the distributed computing environments currently
used, because it centralizes the processing of credentials for authentication.
Kerberos utilizes time stamping of its tickets, to help ensure they are not compromised by other entities, and an overall structure of control that is called a realm.
Some platforms use the defined terminology, while others such as Windows 2000
use their domain structure to implement the Kerberos concepts.
Kerberos is described in RFC 1510, available on the Web at www.cis.ohio-state
.edu/cgi-bin/rfc/rfc1510.html. Developed and owned by the Massachusetts
Institute of Technology (MIT), information about the most current and previous
releases of Kerberos is available on the Web at
Let’s look at how the Kerberos process works, and how it helps secure
authentication activities in a network. First, let’s look at Figure 1.2, which shows
the default components of a Kerberos v5 realm.
As can be seen in Figure 1.2, there is an authentication server requirement
(the KDC). In a Kerberos realm, whether in a UNIX-based or Windows-based
OS, the authentication process is the same. For this purpose, imagine that a client
needs to access a resource on the resource server. Look at Figure 1.3 as we proceed to follow the path for the authentication, first for logon, then at Figure 1.4
for the resource access path.
As seen in Figure 1.3, two events are occurring as credentials are presented
(password, smart card, biometrics) to the KDC for authentication. First, the
authentication credential is presented to the KDC. Secondly, the KDC issues a
Ticket Granting Ticket (TGT) that is associated with the access token while you
are actively logged in and authenticated.This TGT expires when you (or the service) disconnect or log off the network.This TGT is cached locally for use
during the active session.
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Domain 1.0 • General Security Concepts
Figure 1.2 Kerberos Required Components
(User, Service, or Machine)
Resource Server
or Storage
Key Distribution
Center (KDC)
Figure 1.3 Authentication Path for Logon Access in a Kerberos Realm
3: TGT is cached
locally while user or
service is logged on
1: During logon,
credential validated
by KDC
Key Distribution
Center (KDC)
(User, Service, or Machine)
2: KDC, after
issues a TGT
Figure 1.4 shows the process for resource access in a Kerberos realm. It starts
by presenting the previously granted TGT to the authenticating KDC.The
authenticating KDC returns a session ticket to the entity wishing access to the
resource.This session ticket is then presented to the remote resource server.The
remote resource server, after accepting the session ticket, allows the session to be
established to the resource.
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Access Control, Authentication, and Auditing • Chapter 1
Figure 1.4 Resource Access in Kerberos Realms
Key Distribution
Center (KDC)
1: TGT Presented
2: Session Ticket
returned to requesting
client or service
3: Session Ticket
presented to target
server or resource
4: Session
allowed for session
(User, Service, or Machine)
Resource Server
or Storage
Kerberos uses a time stamp and we need to understand where and when the
time stamp is used. Previously mentioned was the concept of non-repudiation (see
Chapter 9), which is one reason for the use of the time stamps. In the case of
Kerberos, the time stamp is also used to limit the possibility of replay or spoofing of
credentials (see Chapter 2). Replay is the capture of information, modification of
the captured information, and retransmission of the modified information to the
entity waiting to receive the communication. If unchecked, this allows for impersonation of credentials when seeking access. Spoofing is the substitution of
addressing or authentication information to try to attain access to a resource
based on information acceptable to the receiving host, but not truly owned by
the sender.The initial time stamp refers to any communication between the
entity requesting authentication and the KDC. Normally, this initial time period
will not be allowed to exceed five minutes. If clocks are not synchronized
between the systems, the credentials (tickets) will not be granted if the time differential exceeds the established limits. Session tickets from the KDC to a
resource must be presented within this time period or they will be discarded.The
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Domain 1.0 • General Security Concepts
session established between the resource server and the requesting entity is also
time-stamped, but generally lasts as long as the entities logon credential is valid.
This can be affected by system policies like logon hour restrictions, which are
defined in the original access token.TGT tickets are not part of the default fiveminute period. Rather, they are cached locally on the machine, and are valid for
the duration of the logged-on session.
One of the methods that can be used protect information when using remote
access to a resource is the Challenge Handshake Authentication Protocol (CHAP)
CHAP is a remote access authentication protocol used in conjunction with
Point-to-Point Protocol (PPP) to provide security and authentication to users of
remote resources.You will recall that PPP replaced the older Serial Line Internet
Protocol (SLIP). PPP not only allows for more security than SLIP, but also does
not require static addressing to be defined for communication. PPP allows users
to use dynamic addressing and multiple protocols during communication with a
remote host. CHAP is described in RFC 1994, available at
cgi-bin/rfc/rfc1994.html.The RFC describes a process of authentication that works
in the following manner:
CHAP is used to periodically verify the identity of the peer using a threeway handshake.This is done upon initial link establishment, and may be repeated
anytime after the link has been established.
After the link establishment phase is complete, the authenticator sends a
“challenge” message to the peer.
The peer responds with a value calculated using a “one-way hash”
The authenticator checks the response against its own calculation of the
expected hash value. If the values match, the authentication is acknowledged; otherwise the connection should be terminated.
At random intervals, the authenticator sends a new challenge to the
peer, and repeats steps one through three.
CHAP operates in conjunction with PPP to provide protection of the credentials presented for authentication and to verify connection to a valid resource.
It does not operate with encrypted password databases, and therefore is not as
strong a protection as other levels of authentication.The shared secrets may be
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stored on both ends as a cleartext item, making the secret vulnerable to compromise or detection. CHAP may also be configured to store a password using oneway reversible encryption, which uses the one-way hash noted earlier.This
provides protection to the password, because the hash must match the client
wishing to authenticate with the server that has stored the password with the
hash value. CHAP is better than Password Authentication Protocol (PAP), however, since PAP sends passwords across the network in cleartext.
Certificates are systems that create, distribute, store, and validate digitally created
signature and identity verification information about machines, individuals, and
services. Certificates are used more frequently since the development and expansion of Internet-based transactions has grown. Certificates are now used for Webbased authentication for access to remote systems, and for encryption of
information on local machines.They are also be used for directory services access
in various operating systems, smart cards, digital signatures for e-mail, and
encrypting e-mail. Additionally, they may be used for authentication when implementing a secure network protocol such as IPSec to protect data transmission
within systems. All of these become parts of the Public Key Infrastructure (PKI),
which is described as the plan or methods for exchange of authentication information and protection of that information (see Chapter 10).
Certificates are created by a trusted third party called a certification authority
(CA), which may also be called a certificate authority.This CA may be a commercially available service point, such as Verisign or Thawte. A CA can also be created
within an enterprise to manage and create certificates that are used only within
an organization or with trusted partners. A certificate from a reputable provider
indicates that the server being accessed is legitimate. CAs may also grant certificates for software signing.This process indicates to the individual downloading
the software that it has been manufactured or written by the specified individual
or company.The path for the certificate should be verifiable and unbroken.This
indicates a high probability that the software has not been tampered with since it
was originally made available for download. Additionally, certificates may be used
in processes such as data encryption or in network protocols requiring their use,
such as IPSec, when the sending and receiving machines must be verifiable.
The certificates can be installed via the Web browser on client machines to
identify and authenticate users. In some OSs such as Windows 2000, certificates can
be mapped to user accounts in Active Directory, and then associated with the access
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tokens generated by the operating system when the user logs on, making the local
installation of the certificate optional on the workstation being used.Web servers
must have a Web server certificate installed in order to participate in SSL.
Remember that certificates must be issued from a verifiable and identifiable CA. This can be a commercial entity, such as Verisign or Thawte, or
a standalone or enterprise CA within your organization. The path to the
CA must be unbroken, or the certificate may be viewed as invalid. A
compromised or physically unsecured CA will require recreation of your
entire PKI infrastructure.
Username and password combinations have been used for authenticating users for
many years. Most OSs have had some form of local authentication that could be
used if the OS was designed to be used by multiple users.Windows, NetWare,
UNIX, and Linux have all had local authentication paths since their creation.
Although this is the most common authentication method, it is not without its
problems. From a security standpoint, it is important to understand that the first
line of defense of a system is the creation and maintenance of a password policy
that is enforced and workable.You need to both implement and enforce the
policy to ensure that this rudimentary protection is in place in your network.
Most OSs have methods of utilizing username/password policies.
Password policies that require a user-created password less than 6 characters
long are regarded as low (or no) security level. Password policies that require
between 8 and 13 characters are regarded as a medium security level. Policies
requiring 14 or more characters are regarded as a high security level. Additionally,
passwords must contain:
Upper and lower case alphabetic characters
Special characters
No dictionary words
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No portion of the username in the password
No personal identifiers should be used including birthdays, social security number, pet’s name, and so on
To achieve the medium security level, implement the use of 8 characters,
including upper/lower case, numbers, and special characters. For high security,
implement the medium security settings, and enforce the previous settings plus
no dictionary words and no use of the username in the password. Be aware that
the higher the number of characters or letters in a password, the more chance
exists that the user will record the password and leave it where it can be found.
You will work at about the 8-character range, and require periodic changes of
the password.
Strong password policies are covered in greater detail in Chapter 12.
Token technology is another method that can be used in networks and facilities to
authenticate users.These tokens are not the access tokens that are granted during a
logon session by the NOS. Rather, they are physical devices used for randomization
of a code that can be used to assure the identity of the individual or service which
has control of them.Tokens provide an extremely high level of authentication
because of the multiple parts they employ to verify the identity of the user.Token
technology is currently regarded as more secure than most forms of biometrics,
because impersonation and falsification of the token values is extremely difficult.
Token authentication can be provided by way of either hardware- or software-based tokens. Let’s take a look at the multiple pieces that make up the process for authentication using token technology.
To start with, you must have a process to create and track random token
access values.To do this, you normally utilize at least two components.They are:
1. A hardware device that is coded to generate token values at specific
2. A software- or server-based component that tracks and verifies that these
codes are valid.
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To use this process, the token code is entered into the server/software monitoring system during setup of the system.This begins a process of tracking the
token values, which must be coordinated. A user wishing to be authenticated
visits the machine or resource they wish to access, and enters a PIN number in
place of the usual user logon password.They are then asked for the randomly
generated number currently present on their token.When entered, this value is
checked against the server/software system’s calculation of the token value. If they
are the same, the authentication is complete and the user can access the machine
or resource. Some vendors have also implemented a software component that can
be installed on portable devices, such as handhelds and laptops, that emulates the
token device and is installed locally.The authentication process is the same; however; the user enters the token value into the appropriate field in the software,
which is compared to the required value. If correct, the user may log on and
access the resource.Vendors such as RSA Security offer products and solutions
such as SecurID to utilize these functions. Others implemented processes that
involved the use of One Time Password Technology, which often uses a pre-generated list of secured password combinations that may be used for authentication,
with a one-time use of each.This provides for a level of randomization, but in its
basic implementation is not as random as other token methods.
Multi-factor authentication is the process in which we expand on the traditional
requirements that exist in a single factor authentication like a password.To
accomplish this, multi-factor authentication will use another item for authentication in addition to or in place of the traditional password.
Following are four possible types of factors that can be used for multi-factor
A password or a PIN can be defined as a something you know factor.
A token or Smart Card can be defined as a something you have factor.
A thumbprint, retina, hand, or other biometrically identifiable item can
be defined as a something you are factor.
Voice or handwriting analysis can be used as a something you do factor.
For example, most password-based single authentication methods use a password. In multi-factor authentication methods, you might substitute the “something you know” factor with a “something you have” factor or a “something you
are” factor.
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A smart card or token device can be a “something you have” factor. Multifactor authentication can be extended, if desired, to include such things as handwriting recognition or voice recognition.The benefit of multi-factor authentication
is that it requires more steps for the process to occur, thus adding another checkpoint to the process, and therefore stronger security. For instance, when withdrawing money from the bank with a debit card (“something you have”) you also
have to have the PIN number (“something you know”).This can be a disadvantage
if the number of steps required to achieve authentication becomes onerous to the
users and they no longer use the process or they attempt to bypass the necessary
steps for authentication.
To summarize, multi-factor authentication is more secure than other methods
because it adds steps that increase the layers of security. However, this must be
balanced against the degree to which it inconveniences the user, since this may
lead to improper use of the process.
Mutual Authentication
Mutual authentication is a process where both the requestor and the target entity
must fully identify themselves before communication or access is allowed.This
can be accomplished in a number of ways.You can share a secretor you can use a
Diffie-Hellman key exchange (see Chapter 9) that provides a more secure
method of exchange that protects the secret being used for the verification and
authentication process. Another method that can be used for mutual authentication is Certificates.To verify the identities, the CA must be known to both parties, and the public keys for both must be available from a trusted KDC.
One area that uses the mutual authentication process is access of a user to a
network via remote access or authentication via a RADIUS server.This case
requires the presence of a valid certificate to verify that the machine is the entity
that is allowed access to the network. For instance, early implementations of
Windows-based RAS servers had the ability to request or verify a particular
telephone number to try to verify the machine location.With the development
of call forwarding technologies, however, it became apparent that this was no
longer satisfactory. Mutual authentication allows you to set secure parameters and
be more confident that communication is not being intercepted by a Man in the
Middle (MITM) attacker (see Chapter 2 and Chapter 9) or being redirected in
any way.
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Biometric devices can provide a higher level of authentication than, for example,
a username/password combination. However, although they can be used for
mutual authentication plans and tend to be relatively secure, they are not impervious to attack. For instance, in the case of fingerprint usage for biometric identification, the device must be able to interpret the actual presence of the print.
Early devices that employed optical scans of fingerprints were fooled by fogging
of the device lenses, which provided a raised impression of the previous user’s
print as it highlighted the oils left by a human finger. Some devices are also subject to silicon impressions or fingerprinting powders that raise the image. Current
devices may require a temperature or pulse sense as well as the fingerprint to
verify the presence of the user, or another sensor that is used in conjunction with
the print scanner, such as a scale. Biometrics used in conjunction with smart cards
or other authentication methods lead to the highest level of security.
When preparing for the Security+ exam, it is sometimes helpful to have
a sheet of abbreviations and acronyms with definitions handy for review.
When taking an exam that includes information for vendors you are not
familiar with, the acronyms can be overwhelming. Flash cards may prove
to be helpful for overcoming this obstacle.
Auditing provides methods for tracking and logging activities on networks and
systems, and links these activities to specific-user accounts or sources of activity.
In the case of simple mistakes or software failures, audit trails can be extremely
useful in restoring data integrity.They are also a requirement for trusted systems
to ensure that the activity of authorized individuals can be traced to their specific
actions, and that those actions comply with defined policy.They also allow for a
method of collecting evidence to support any investigation into improper or
illegal activities.
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Access Control, Authentication, and Auditing • Chapter 1
Auditing Systems
Auditing of systems must occur with a thorough understanding of the benefits of
the process. As you create your auditing procedures, you are trying to develop a
path and trail system in the logging of the monitored events that allows you to
track usage and access, either authorized or unauthorized.To do this, you must
consider the separation of duties that improves security and allows for better definition of your audit policies and rules.
To assist in catching mistakes and reducing the likelihood of fraudulent activities, the activities of a process should be split among several people.This process is
much like the RBAC concepts discussed earlier.This segmentation of duties
allows the next person in line to possibly correct problems simply because they
are being viewed with fresh eyes.
From a security point of view, segmentation of duties requires the collusion
of at least two people to perform any unauthorized activities.The following
guidelines assist in assuring that the duties are split so as to offer no way other
than collusion to perform invalid activities.
No access to sensitive combinations of capabilities. A classic
example of this is control of inventory data and physical inventory. By
separating the physical inventory control from the inventory data control, you remove the unnecessary temptation for an employee to steal
from inventory and then alter the data so that the theft is left hidden.
Prohibit conversion and concealment. Another violation that can be
prevented by segregation is ensuring that there is supervision for people
who have access to assets. An example of an activity that could be prevented if properly segmented follows a lone operator of a night shift.This
operator, without supervision, could copy (or “convert”) customer lists and
then sell them to interested parties.There have been instances reported of
operators actually using the employer’s computer to run a service bureau.
The same person cannot both originate and approve
transactions. When someone is able to enter and authorize their own
expenses, it introduces the possibility that they might fraudulently enter
invalid expenses for their own gain.
These principles, whether manual or electronic, form the basis for why audit
logs are retained.They also identify why people other than those performing the
activities reported in the log should be the ones who analyze the data in the
log file.
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In keeping with the idea of segmentation, as you deploy your audit trails, be
sure to have your log files sent to a secure, trusted location that is separate and
non-accessible from the devices you are monitoring.This will help ensure that if
any inappropriate activity occurs, the person who performs it cannot falsify the
log file to state the actions did not take place.
During the discussion of using auditing as a method to track access
attempts within systems, it was mentioned that you must define an
audit policy that reflects the needs of your organization and the need to
track access in your system. This process is used to configure the types of
activity or access you wish to monitor. For the exercise on auditing, you
will be using either Windows 2000 (any version) or Windows XP
Professional. (Please note that Windows XP Home does not support
auditing of object access, so it cannot be used for this exercise.)
When configuring auditing in Windows 2000 or Windows XP, it must
be configured at the local machine level, unless the machine is a member
machine participating in an Active Directory domain, in which case the
Auditing policy may be configured at the domain level through the use of
Group policy.
This also applies to auditing on domain controllers if they are configured at the local security settings level. The settings applied to domain
controllers at the local security level are not automatically applied to all
domain controllers unless they are configured in the Default Domain
controller policy in Active Directory.
To start the audit process, you must access the local security policy
Microsoft Management Console (MMC) in Administrative Tools. This is
reached through Start | Programs | Administrative Tools | Local
Security Policy. When you have opened the tool, navigate to Local
Policies | Audit Policy; you should see a screen as shown in Figure 1.5.
Next, double-click the Audit Logon Events item, which will open the
Properties screen shown in Figure 1.6. Select both check boxes to enable
auditing of both successful and failed logon events. When auditing logon
events you are logging events requiring credentials on the local machine.
Note that the first auditing choice is “Audit account logon events.” In this
selection, auditing is tracked only for those asking for authentication
via accounts that are stored on this machine, such as with a domain
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controller. The setting being used tracks all requests with an exchange of
authentication information on the local machine where it is configured.
Figure 1.5 The Audit Policy Screen
Figure 1.6 Selecting the Appropriate Item for Auditing
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As shown in Figure 1.7, the security setting condition has changed to
reflect your choices. Your screen should also reflect that you are now
auditing “Success and Failure for Logon Events.”
Figure 1.7 Auditing Conditions Enabled and Defined
Following successful initialization of auditing, you must test the settings to make sure the system is performing the auditing tasks that have
been set up. For this exercise, log off your machine, then attempt to
logon using credentials that you know do not exist or using an incorrect
password. Then, log back on correctly and return to the exercise. Proceed
to Event Viewer in the Administrative Tools folder by traversing Start |
Programs | Administrative Tools | Event Viewer. Double-click on the
Security; you should see a screen similar to the one shown in Figure 1.8.
Note that we have audited and recorded both success and failure events,
noted by the key and lock icons. Highlight a Failure Audit event, as
shown, and then double-click on the item.
After double-clicking on a Failure Audit item, you will see a screen
similar to the one depicted in Figure 1.9. Note that in this particular
case, an unknown user (Sam) tried to logon and was unsuccessful. The
auditing process is working, and detected the attempted breach.
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Figure 1.8 The Security Event Window in Event Viewer
Figure 1.9 A Logon/Logoff Failure Event Description
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Now that you have successfully implemented auditing, do not forget
that auditing is useless if you never review the logs and records it generates. Auditing is also capable of tracking access by processes, applications,
and users to other objects within a particular environment. You should
define a strong audit policy that checks access and authentication to critical files, and randomly checks other resources to detect trends and attacks
and limit their damage.
Most modern database applications support some level of transaction log detailing
the activities that occurred within the database.This log can then be used to
rebuild the database or to create a duplicate database at another location.
Providing this detailed level of database logging consumes a great deal of drive
space.This intense logging is not needed for most applications.You will generally
only have basic informative messages utilized in system resource logging.
The logging features provided on most networks and systems involve logging
known or partially known resource event activities.While these logs are sometimes used for analyzing system problems, they are also useful for processing the
log files and checking for both valid and invalid system activities
Damage & Defense…
Read Those Logs!
One of the major problems with auditing is the simple fact that many network administrators do not have time to read and analyze the log files on
a regular basis. Auditing provides us with the ability not only to provide
a chronological path of access or attack, but also to spot trends of unauthorized activity so that they can be blocked before they do any damage.
Unfortunately, many organizations do not devote the time to examine
audit logs until after an attack. Good maintenance and procedures
regarding the analysis of the log files will benefit your security efforts. Be
System Scanning
System scanning, when viewed from the context of a security system specialist or
security administrator, is the use of appropriate technologies to detect and repair
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potential areas of vulnerability within the system.This involves tools that are used
to evaluate potential or real problems that could lead to a security breach. Among
these, you may see or use tools that:
Check the strength of and compliance with password policies
Measure the ability to access networks from an outside or foreign network
Provide analysis of known security vulnerabilities in NOS or hardware
Test a system’s responses to various scenarios that could lead to denial of
service (DoS) or other problems such as a system crash.
System scanning is useful in a number of different areas. In addition to scanning for security weaknesses, it is useful in monitoring tools that have been used
in the past to monitor network and device performance, as well as in specialized
scanning methods used to detect and repair potential weaknesses.While the primary emphasis is to provide security, you also have an obligation under the concepts of AAA and the CIA triad discussed earlier to provide system availability
and dependability. Use of the appropriate network and machine monitoring tools
can help to detect and eliminate congestion and traffic problems on the network,
high processor loads or other deviances in systems, and bad or failing components.This, in turn, allows you to be alerted to potential problems that may
accompany other types of activity.
In the current environment, there are a number of security scanning
options available. Among them are two that are included in the Security+
exam, System Administrator Tool for Analyzing Networks (SATAN) and Nessus
( Both SATAN and Nessus are UNIX-based tools that allow
penetration testing, probing, and analysis. SATAN was first introduced in 1995,
and scans for and reports on vulnerabilities that may be present in UNIX systems. As originally introduced, SATAN reported on vulnerabilities that had been
previously known, to verify their fix condition. It also had the ability, through a
Web interface, to detect and report vulnerabilities present in UNIX systems.
Nessus is a tool set that utilizes a server component and a client component, with
expanded capabilities and greater functionality than SATAN. For example, Nessus
has the ability to probe and launch DoS attacks against specific hosts and is very
useful in detecting the vulnerabilities of a remote system. It is important to note,
however, that this type of scanning will likely be looked at as an attack and
should not be used against systems that you are not responsible for.
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Along with the ability to evaluate and mount attacks against systems, you
must also use tools that are appropriate to the NOS that you are using, clients
you are operating, and the devices you use to communicate on the networks. As
you scan, you are searching for known problems that exist in each of these areas,
and detailing the potential for harm to your systems. Use these tools to proactively check and repair these vulnerabilities and to provide a stable and problemfree environment.
There are many benefits to being proactive in the system and network scanning area. It is much better to spot trends and track them in relation to potential
attacks or DoS attacks than to be taken unaware.Vigilance, good planning, and
use of the tools can eliminate many of the security issues that occur. Remember
that a high percentage of attacks or problems in systems come from inside networks. Scan and be informed.
In the Security+ exam, removal and control of non-essential services,
protocols, systems, and programs is tested generally, but is also covered
again later in the Security+ exam objectives when discussing system, OS,
NOS, and application hardening. Pay attention to the descriptions presented here, and to the concepts and procedures presented in Chapter 8
when discussing hardening of these components.
Disabling Non-Essential Services,
1.3 Protocols, Systems and Processes
This section of the Security+ exam covers a number of different areas that should
be examined and controlled in your network and system environments.We hear
often that we should disable unnecessary or unneeded services.While here, we
will look not only at services, but at protocols, systems, and processes that rob systems of resources and allow potential attacks to occur that could damage your
Non-Essential Services
Let’s begin with a discussion about the concept of non-essential services. Nonessential services are the ones you do not use, or have not used in some time. For
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many, the journey from desktops to desktop support to servers to entire systems
support involved new issues to work on. And as we progressed, we wanted to see
what things could be done with the new hardware and its capabilities. In addition, we were also often working on a system that we were not comfortable with,
had not studied, and had little information about. Along with having a superior
press for using the latest and greatest information, we hurried and implemented
new technologies without knowing the pitfalls and shortcomings.
Non-essential services may include network services, such as Domain Name
System (DNS) or Dynamic Host Control Protocol (DHCP),Telnet,Web, or FTP
services.They may include authentication services for the enterprise, if located on
a non-enterprise device.They may also include anything that was installed by
default that is not part of your needed services.
Systems without shared resources need not run file and print services. In a
Linux environment, if the machine is not running as a e-mail server, then remove
sendmail. If the system is not sharing files with a Windows-based network, then
remove Samba. Likewise, if you are not using NIS for authentication, you should
disable the service or remove it.
Non-Essential Protocols
Non-essential protocols can provide the opportunity for an attacker to reach
or compromise your system.These include network protocols such as
Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)
(NWLink in Windows NT, 2000, and XP) and NETBIOS Extended User
Interface (NetBEUI). It also includes the removal of unnecessary protocols such
as Internet Control Messaging Protocol (ICMP), Internet Group Management
Protocol (IGMP), and specific vendor supplied protocols such as Cisco’s Cisco
Discovery Protocol (CDP), which is used for communication between Cisco
devices, but may open a level of vulnerability in your system. It should also
include the evaluation of protocols used for communication between network
devices that are proprietary or used by system device manufacturers, such as the
protocols used by Cisco to indicate private interior gateways to their interoperating devices.
Evaluation of the protocols suggested for removal may show that they are
needed in some parts of the system, but not others. Many OS platforms allow the
flexibility of binding protocols to certain adaptors and leaving them unbound on
others, thus reducing the potential vulnerability level.
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Disabling Non-Essential Systems
While working with the development and growth of networks and environments, we often retain older systems and leave them active within the overall
system.This can be a serious breach, as we may not pay attention to these older
systems and keep them up to date with the latest security patches and tools. It is
important to realize that older systems, particularly those whose use is extremely
low, should have a planned decommissioning policy in place. Systems not necessary for your particular operation should be disabled, removed, and sterilized with
good information removal practices before being recycled, donated, or destroyed.
Disabling Non-Essential Processes
Processes running on your systems should be evaluated regarding their necessity
to operations. Many processes are installed by default, but are rarely or never used
by the OS. In addition to disabling or removing these processes, you should regularly evaluate the running processes on the machine to make sure they are necessary. As with disabling unnecessary protocols and services and systems, you must
be aware of the need for the processes and their potential for abuse that could
lead to system downtime, crashes, or breach. UNIX, Linux,Windows server and
workstation systems, and NetWare systems all have mechanisms for monitoring
and tracking processes, which will give you a good idea of their level of priority
and whether they are needed in the environments you are running.
Disabling Non-Essential Programs
Like the other areas we have discussed, it is appropriate to visit the process of
disabling or removing unnecessary programs. Applications that run in the background are often undetected in normal machine checks, and can be compromised or otherwise affect your systems negatively. An evaluation of installed
programs is always appropriate. Aside from the benefit of more resources being
available, it also eliminates the potential that a breach will occur.
As discussed in this section, it is important to eliminate unused services,
protocols, processes, and applications to eliminate potential security vulnerabilities. It is also important to eliminate these extra functions and
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capabilities to maximize the performance of the systems. Items not in
use require no resources, so there is an added benefit to disabling
unused portions of the systems. In this exercise, we will disable the
Telnet service to eliminate the potential for attack.
Be cautious when accessing or modifying controls that may disable or
remove system services or processes. Incorrect settings or use of the controls may disable your machine and require a complete reinstallation.
Do not perform these tasks on a production machine without the
permission of your administrator or employer. The consequences can
be severe.
To begin, access the Services MMC window. This may be reached by
clicking Start | Programs | Administrative Tools | Services in either
Windows 2000 or Windows XP Professional. When the window is open,
scroll down and highlight the Telnet Server item. As shown in Figure
1.10, you should see that the service is set for manual start, but is not
currently started.
Figure 1.10 The Services Panel MMC Window
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To change the properties or startup type of a service, double-click the
service name. You will view a window as shown in Figure 1.11. For this
exercise, choose the Telnet service name, and double-click it to reach the
window shown in the figure. If you expand the startup type drop down,
you will see that you can choose from automatic, manual, or disabled.
Figure 1.11 The Telnet Service Properties Page
As shown in Figure 1.12, select the Disabled settingand click Apply.
You will see that the state of the startup type has changed from
Manual to Disabled, as shown in Figure 1.13.
When you have successfully disabled the service, open a command
prompt window (type cmd at the Run line on the Start menu) and type
the following command: net start telnet server. If you have successfully
disabled the service, you should receive a message informing you that
the service is disabled.
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Figure 1.12 Selecting to Disable the Telnet Service
Figure 1.13 Telnet Service Disabled
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Summary of Exam Objectives
In this chapter, you worked on concepts tested in the Security+ exam relating to
general security concepts.These objectives include having a working knowledge
of the concepts of AAA.These concepts are widely used to support the concept
of CIA by providing the methodology to protect resources and track the access
given to them.
We found that as we looked at the separate components of AAA, there were a
number of ways to accomplish the goal of controlling the security of our networks and systems by using the appropriate methodologies.We discovered that
we have three distinct methods of providing access control. MACs are rules that
are defined and hard-coded into operating systems and applications to allow or
deny access to services or applications. In the case of DAC, the user or service
that owns an object, such as a file has control of who or what else has the ability
to access the file or object, and at what level. Finally, we explored the capabilities
of RBAC.This method, while requiring much more initial design and administrative resources to set up, allowed us to refine and sharpen the level of access
based on job function, rather than the more general group concept used in the
past.This method allows much more flexibility in definition of the access level.
We looked at the concept of authentication and found that there are a
number of different methods that can be used to authenticate.We looked at the
danger of cleartext username and password transmission on our networks, and a
number of methods that provide for a stronger verification of the entity
requesting the use of our systems or resources. In the realm of authentication, we
also looked at the concept of realms and the way they are used by Kerberos to
provide authentication services. Certificates, and the CA hierarchy that goes with
them, can be used to verify the authenticity of machines, users, software, and
communications.We also viewed the concept of using third-party authentication
tools such as multi-factor authentication, which can be provided by the use of a
PIN and identification card,Token technologies, and the use of biometrics and
biometric devices.
Further exploration of the AAA components led us to discuss and work with
the concept of auditing. It is important to define the appropriate policy that controls, monitors and evaluates the activity that is occurring in and on our systems.
This includes monitoring the conditions of access and the authorization processes
to ensure the appropriate levels of control are maintained throughout the system.
We learned that it is important to maintain appropriate records, to control access
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to those records, and to analyze them appropriately to help determine the condition of the system.
Additionally, we reviewed the concepts of disabling or removing unnecessary
services, protocols, and applications from our environment to help minimize
the effects that could occur from weaknesses.This process includes the evaluation
and detection of inappropriate applications, services, and components within systems that can lead to system compromise and also showed us that removal of
these unnecessary components can assist in freeing up resources for use within
the system.
Exam Objectives Fast Track
Introduction to AAA
; AAA is made up of three distinct but interdependent parts: access
control, authentication, and auditing.
; Access control consists of the rules for controlling the methods and
conditions of access to your system.
; Authentication defines the methods for setting the rules for establishing
the methods of authentication of the service or user requesting access to
the system or resources.
; Auditing contains the suggestions and procedures for monitoring access
and authentication processes in your systems, and secures the log files
and records of these efforts.
Access Control
; MAC is a level of access that is defined and hard-coded in the OS or
application, and not easily changed.
; DAC are defined by the owner of an object (such as files), and are
modifiable and transferable as desired.
; RBACs are defined by job function and are definable with much more
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; Kerberos is a multi-platform authentication method that requires tickets
(tokens) and a KDC. It exists as a realm in most platforms, and is utilized
in the domain environment in Windows 2000 Active Directory
; CHAP can utilize a shared secret, and uses a one-way hash to protect
the secret.
; Certificates require a CA, which is used to create the digital certificates
used for digital signatures, mutual identification, and verification.
; Username/password is the most basic security usage, and is available in
most platforms.
; Tokens are hardware and software devices for random generation of
passcodes to further secure the authentication process.
; Multi-factor authentication is the use of more than one type of
authentication concurrently to strengthen the authentication process,
such as requiring a card and PIN together.
; Mutual authentication consists of using various methods to verify both
parties to the transaction to the other.
; Biometrics is used with devices that have the ability to authenticate
something you already have, such as a fingerprint or retinal image.
; An auditing policy must be established and evaluated to determine what
resources or accesses need to be tracked.
; Usually retained in log files, which may be used to track paths and
violations. Good logging may be used for prosecution, if necessary.
; Important that someone is responsible for viewing and analyzing
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Access Control, Authentication, and Auditing • Chapter 1
Removing Non-Essential Services
; Remove unused and unneeded components from servers, network
components, and workstations, including functions such as DNS and
; Remove unnecessary protocols from network communication systems
and devices that operate in your system. Evaluate the need for each
protocol, and unbind or remove as appropriate in your environment.
; Remove unnecessary or unused programs from workstations and servers
to limit potential problems that may be introduced through their
Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: What is the difference between access controls and authentication? They seem
to be the same.
A: Access controls set the condition for opening the resource.This could be the
time of day, where the connection originates, or any number of conditions.
Authentication verifies that the entity requesting the access is verifiable and
who the entity is claiming to be.
Q: My users are using Win9.x workstations. I can’t find where to set DAC settings on these machines.
A: Win9.x machines do not have the ability to have DAC settings configured for
access to items on the local machine.Win9.x users logged into a domain may
set DAC settings on files they own stored on remote NTFS-formatted drives.
Q: The idea of RBACs seems very complicated.Wouldn’t it be easier just to use
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Domain 1.0 • General Security Concepts
A: Easier, yes. More secure, NO! RBACs allow much finer control over which
users get access.This is backwards from the conventional teaching that had us
use the groups to ease administrative effort.
Q: You discussed the necessity to disable or remove services. I work with
Windows 2000 servers, and would like some guidelines to follow.
A: A good place to start learning the process of hardening is the Syngress
Publishing book, Hack Proofing Windows 2000 Server (1-931836-49-3).
Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
What is AAA?
1. While trying to understand the components of AAA, we think about the
concept of a locked door.Which of the following would define the concept
of the locked door?
A. Auditing
B. Authentication
C. Authorization
D. Access control
2. Jane has been talking about AAA, and insists that one of the roles of AAA is
to provide CIA.What is CIA?
A. Control, intelligence, action
B. Central intelligence agency
C. Confidentiality, integrity, availability
D. Confidence, integrity, action
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Access Control, Authentication, and Auditing • Chapter 1
3. Use of a certificate hierarchy under a CA provides digital certificates that
contain digital signatures.When using certificates, which part of AAA are we
A. Auditing
B. Access Control
C. Authentication
D. Accounting
4. You have been working with a team to design a security implementation.The
team has been divided into groups to plan and implement the three separate
AAA functions.Your team is in charge of verifying the conditions of connection, such as time of day, where the connection originates, and connection
points.While you are with the team, one of the members suggests that
CHAP be used.You gently (of course) suggest that this is not part of your
team role, but the other member disagrees.What role are you working on?
A. Auditing
B. Access control
C. Authorization
D. Authentication
5. Access controls set the conditions of entry into the system or remote resource.
Authentication verifies the identity of the entity that is requesting the access to
the resource.What does auditing accomplish (pick all that apply)?
A. Tracks logon/logoff events
B. Tracks resource access
C. Tracks trends
D. Tracks authentication
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Domain 1.0 • General Security Concepts
Access Control
6. Which of the following correctly defines the acronyms MAC, DAC, and
A. Media access control, discretionary access control, and remote-based
access control
B. Mandatory access control, discretionary access control, and role-based
access control
C. Mandatory access control, distributed access control, and role-based
access control
D. Media access control, distributed access control, and remote-based access
7. Which of the following would be used and controlled by the user in the setting of access levels on resources that they control?
D. A and C
8. You’ve been tasked with developing an access control policy that will allow
the creation of the tightest security possible.This policy must be enforceable,
testable, and may not be altered by users or administrators.Which type of
access control will you have to use?
D. A and C
9. You are working on a plan to implement access controls.You need to be able
to refine the permissions for access so that access to certain documents is available to some users, but not to others. At the same time, you need the flexibility
to modify those access levels if the user’s job description changes, and you have
been informed that there are to be cuts in administrative support for IT
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Access Control, Authentication, and Auditing • Chapter 1
administrators. Based on these requirements, which type of access control
should you implement?
D. Groups
10. Which of the following would have control over access to resources controlled by DACs?
A. Administrators
B. Users
C. Owner of the resource
D. None of the above
11. You have been besieged by attacks on your network. Among the problems
occurring, you have been the victim of a number of Trojan Horse-type
attacks. One of your co-workers has mentioned that a particular access control method implementation can limit the effects of this type of attack.Which
of these types would have helped?
D. None of the above
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12. When implementing a username/password policy, Joe wanted to make sure
that he properly protected the network he was going to work with.Which of
the following combinations would be most appropriate if he was to follow
the recommendations of industry for creation of passwords to provide a
medium level of security in his network?
A. Alphanumeric characters, 10 characters
B. Alphabetic characters, numbers, special characters, 14 characters
C. Alphabetic characters, numbers, special characters, 8 characters
D. Alphabetic characters, numbers, special characters, upper/lower case,
6 characters
13. If you were discussing authentication methods with co-workers and saw the
diagram shown, what authentication protocol would you be discussing?
(User, Service, or Machine)
Resource Server
or Storage
Key Distribution
Center (KDC)
D. Kerberos
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Access Control, Authentication, and Auditing • Chapter 1
14. During logon authentication using Kerberos, a certain item is created during
the logon process. In #2 and #3, the item being created is….
locally while user or
service is logged on
1: During logon,
credential validated
by KDC
Key Distribution
Center (KDC)
(User, Service, or Machine)
2: KDC, after
issues a
A. Session ticket
B. Ticket
D. Resource access ticket
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15. In the following diagram, what part of Kerberos authentication that is being
created in #2 and #3?
Key Distribution
Center (KDC)
returned to requesting
client or service
presented to target
server or resource
1: TGT Presented
4: Session
allowed for session
(User, Service, or Machine)
Resource Server
or Storage
A. Ticket
C. KDC access ticket
D. Session ticket
16. When auditing, it is important to secure the log files. Of the following, which
are reasons for securing the log files? (Pick all that apply)
A. Prevent damage
B. Prevent changes
C. Prevent removal or deletion
D. Prevent unauthorized disclosure
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Access Control, Authentication, and Auditing • Chapter 1
17. When establishing an Audit policy, which of the following could be tracked?
(Pick all that apply)
A. Logon/logoff events
B. Track trends
C. Resource access
D. Attack attempts and trails
18. You have been asked to develop an audit plan for your company.You have
been told that there have been constant deletions of files that are being
worked on by a team, and that they have had to redo the work a number of
times.What type of auditing would you implement to track the access to this
A. Logon/logoff success
B. object/file access success
C. object/file access failure
D. Logon/logoff failure
Removing Non-Essential Services
19. Which of the following are a benefit of removing unused or unneeded services and protocols?
A. More machine resource availability
B. More network throughput
C. Less need for administration
D. More security
20. Which is the most important reason for the removal of unused, unnecessary,
or unneeded protocols, services, and applications?
A. Increased security
B. Increased performance
C. Less need for administration
D. Less machine resource use.
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. D
11. A
2. C
12. C
3. C
13. D
4. B
14. C
5. A, B, C, and D
15. D
6. B
16. A, B, C, and D
7. B
17. A, B, C, and D
8. A
18. B
9. D
19. A, B, and D
10. C
20. A
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Chapter 2
Domain 1.0 Objectives in this Chapter:
Social Engineering
Vulnerability Scanning
Malicous Code Attacks
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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One of the more exciting and dynamic aspects of network security relates to
attacks. A great deal of media attention and many vendor product offerings have
been targeting attacks and attack methodologies.This is perhaps the reason that
CompTIA has been focusing many questions in this particular area.While there
are many different varieties and methods of attack, they can generally all be
grouped into several categories:
By the general target of the attack (application, network, or mixed)
By whether the attack is active or passive
By how the attack works (for example, via password cracking, or by
exploiting code and cryptographic algorithms)
It’s important to realize that the boundaries between these three categories
aren’t fixed. As attacks become more complex, they tend to be both applicationbased and network-based, which has spawned the new term “mixed threat applications.” An example of such an attack can be seen in the Nimda worm, which
targeted Windows IIS machines in 2001.This program used an automated attack
against an application (IIS in this case) to compromise the host.The compromised machine would then launch a network attack by scanning entire subnets
looking for additional targets. An enormous amount of bandwidth was consumed
in the course of this scanning, causing many network switches and routers to
cease to function properly. So, as attackers get more sophisticated, we can expect
to see more and more combined attacks in the future. In this chapter, we’ll focus
on some of the specific types of each attack, such as:
Active attacks These include Denial of Service (DoS), Distributed
Denial of Service (DDoS), buffer overflow, SYN attack, spoofing, Man in
the Middle (MITM), replay,Transmission Control Protocol/Internet
Protocol (TCP/IP) hijacking, wardialing, dumpster diving, and social
engineering attacks.
Passive attacks These include vulnerability scanning, sniffing, and
Password attacks These include password guessing, brute force, and
dictionary-based password attacks.
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Attacks • Chapter 2
Head of the Class…
Code and Cryptographic Attacks These include backdoors, viruses,
Trojans, worms, software exploitation, and weak keys and mathematical
Attack Methodologies in Plain English
In this section, we’ve listed network attacks, application attacks, and
mixed threat attacks, and within those are included buffer overflows,
DDoS attacks, fragmentation attacks, and theft of service attacks. While
the list of descriptions might look overwhelming, generally the names are
self-explanatory. For example, consider a DoS, or denial of service attack.
As its name implies, this attack is designed to do just one thing—render
a computer or network non-functional so as to deny service to its legitimate users. That’s it. So, a denial of service could be as simple as unplugging machines at random in a data center, or as complex as organizing an
army of hacked computers to send packets to a single host in order to
overwhelm it and shut down its communications. Another term that has
caused some confusion is a mixed threat attack. This simply describes any
type of attack that is comprised of two different, smaller attacks. For
example, an attack that goes after Outlook clients, and then sets up a
bootleg music server on the victim machine is classified as a mixed threat
Active Attacks
Active attacks can be described as attacks in which the attacker is actively
attempting to cause harm to a network or system.The attacker isn’t just listening
on the wire, but is attempting to breach or shut down a service. Active attacks tend
to be very visible because the damage caused is often very noticeable. Some of the
more well known active attacks are DoS/DDoS, buffer overflows, SYN attacks and
IP spoofing; these and many more will be detailed in the following section.
To understand a DDoS attack and its consequences, you first need to grasp the
fundamentals of DoS attacks.The progression from understanding DoS to DDoS
is quite elementary, though the distinction between the two is important. Given
its name, it should not come as a surprise that a DoS attack is aimed squarely at
ensuring that the service a computing infrastructure usually delivers is negatively
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affected in some way.This type of attack does not involve breaking into the target
system. Rather, a successful DoS attack reduces the quality of the service delivered by some measurable degree, often to the point where the target infrastructure of the DoS attack cannot deliver a service at all.
A common perception is that the target of a DoS attack is a server, though this
is not always the case.The fundamental objective of a DoS attack is to degrade
service, whether it is hosted by a single server or delivered by an entire network
infrastructure. A DoS attack can also be effectively launched against a router.
A DoS attack attempts to reduce the ability of a site to service clients,
whether those clients are physical users or logical entities such as other computer
systems.This can be achieved by either overloading the ability of the target network or server to handle incoming traffic or by sending network packets that
cause target systems and networks to behave unpredictably. Unfortunately for the
administrator, “unpredictable” behavior usually translates into a hung or crashed
Some of the numerous forms of DoS attacks can be difficult to detect or
deflect.Within weeks or months of the appearance of a new attack, subtle
“copycat” variations begin appearing elsewhere. By this stage, not only must
defences be deployed for the primary attack, but also for its more distant cousins.
Most DoS attacks take place across a network, with the perpetrator seeking to
take advantage of the lack of integrated security within the current iteration of
Internet Protocol (IP), IP version 4 (IPv4). Hackers are fully aware that security
considerations have been passed on to higher-level protocols and applications. IP
version 6 (IPv6), which may help rectify some of these problems, includes a
means of validating the source of packets and their integrity by using an authentication header. Although the continuing improvement of IP is critical, it does
not resolve today’s problems because IPv6 is not yet in widespread use.
DoS attacks do not only originate from remote systems, but can also be
launched against the local machine. Local DoS attacks are generally easier to
locate and rectify because the parameters of the problem space are well defined
(local to the host). A common example of a locally based DoS attack is the fork
bomb that repeatedly spawns processes to consume system resources.
Although DoS attacks do not by definition generate a risk to confidential or
sensitive data, they can act as an effective tool to mask more intrusive activities that
could take place simultaneously.While administrators and security officers are
attempting to rectify what they perceive to be the main problem, the real penetration could be happening elsewhere. In the confusion and chaos that accompany
system crashes and integrity breaches, experienced hackers can slip in undetected.
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Attacks • Chapter 2
The financial and publicity-related implications of an effective DoS attack are
hard to measure—at best they are embarrassing, and at worst they are a deathblow.
Companies reliant on Internet traffic and e-purchases are at particular risk from
DoS and DDoS attacks.The Web site is the engine that drives e-commerce, and
customers are won or lost on the basis of the site’s availability and speed. In the
world of e-commerce, a customer’s allegiance is fleeting. If a site is inaccessible or
unresponsive, an alternate virtual storefront is usually only a few clicks away. A
hacker, regardless of motive, knows that the best way to hurt an e-business is to
affect its Internet presence in some way. Unfortunately, DoS attacks can be an efficient means of achieving this end; the next sections cover these two elemental
types of DoS attacks:
Resource consumption attacks (such as SYN flood attacks and
amplification attacks)
Malformed packet attacks
Resource Consumption Attacks
Computing resources are, by their very nature, finite. Administrators around the
world bemoan the fact that their infrastructures lack network bandwidth, CPU
cycles, RAM, and secondary storage. Invariably, the lack of these resources leads
to some form of degradation of the services the computing infrastructure delivers
to clients.The reality of having finite resources is highlighted even further when
an orchestrated attack consumes these precious resources.
The consumption of resources involves the reduction of available resources,
whatever their nature, by using a directed attack. One of the more common
forms of a DoS attack targets network bandwidth. In particular, Internet connections and the supporting devices are prime targets of this type of attack, due to
their limited bandwidth and their visibility to the rest of the Internet community.
Very few businesses are in the fortunate position of having excessive Internet
bandwidth, and when a business relies on its ability to service client requests
quickly and efficiently, a bandwidth consumption attack can bring the company
to its knees.
Resource consumption attacks predominantly originate from outside the
local network, but you should not rule out the possibility that the attack is from
within.These attacks usually take the form of a large number of packets directed
at the victim, a technique commonly known as flooding.
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A target network can also be flooded when an attacker has more available
bandwidth than the victim and overwhelms the victim with pure brute force.
This situation is less likely to happen on a one-to-one basis if the target is a
medium-sized e-commerce site. Such companies generally have a larger “pipe”
than their attackers. On the other hand, the availability of broadband connectivity
has driven high-speed Internet access into the homes of users around the world.
This has increased the likelihood of this type of attack, as home users replace
their analog modems with DSL and cable modem technologies.
Another way of consuming bandwidth is to enlist the aid of loosely configured
networks, causing them to send traffic directed at the victim. If enough networks
can be duped into this type of behavior, the victim’s network can be flooded with
relative ease.These types of attacks are often called amplification attacks.
Other forms of resource consumption can include the reduction of connections available to legitimate users and the reduction of system resources available
to the host operating system itself. “Denial of service” is a very broad term, and
consequently various types of exploits can fit the description due to the circumstances surrounding their manifestation. A classic example is the Melissa virus,
which proliferated so swiftly that it consumed network resources, resulting in a
DoS in some cases.
DDoS Attacks
Though some forms of DoS attacks can be amplified by multiple intermediaries,
the first step of a DoS exploit still originates from a single machine. However,
DoS attacks have evolved beyond single-tier (SYN flood) and two-tier (Smurf)
attacks. DDoS attacks advance the DoS conundrum one more painful step forward. Modern attack methodologies have now embraced the world of distributed
multi-tier computing. One of the significant differences in the methodology of a
DDoS attack is that it consists of two distinct phases. During the first phase, the
perpetrator compromises computers scattered across the Internet and installs specialized software on these hosts to aid in the attack. In the second phase, the
compromised hosts (referred to as zombies) are then instructed through intermediaries (called masters) to commence the attack.
Hundreds, possibly thousands, of zombies can be co-opted into the attack by
diligent hackers. Using the control software, each of these zombies can then be
used to mount its own DoS attack on the target.The cumulative effect of the
zombie attack is to either overwhelm the victim with massive amounts of traffic
or to exhaust resources such as connection queues.
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Additionally, this type of attack obfuscates the source of the original attacker:
the commander of the zombie hordes.The multi-tier model of DDoS attacks and
their ability to spoof packets and to encrypt communications can make tracking
down the real offender a tortuous process.
The command structure supporting a DDoS attack can be quite convoluted
(see Figure 2.1), and it can be difficult to determine a terminology that describes
it clearly. Let’s look at one of the more understandable naming conventions for a
DDoS attack structure and the components involved.
Figure 2.1 A Generic DDoS Attack Tree
Attacker may install client
software on multiple
machines. Client software is
capable of waking daemons
installed on zombies and
commanding them to
commence targeted attacks.
Attacker can initiate attack
by sending messages to
compromised hosts with
DDoS client software
installed on them.
Target host becomes the
victim of multiple attacks
originating from multiple
Hacker compromises multiple
hosts to act as zombies included
in the coordinated attack.
Zombies are responsible for
contducting actual attack.
Software components involved in a DDoS attack include:
Client The control software used by the hacker to launch attacks.The
client directs command strings to its subordinate hosts.
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Daemon Software programs running on a zombie that receive
incoming client command strings and act on them accordingly.The
daemon is the process responsible for actually implementing the attack
detailed in the command strings.
Hosts involved in a DDoS attack include:
Master A computer that runs the client software.
Zombie A subordinate host that runs the daemon process.
Target The recipient of the attack.
In order to recruit hosts for the attack, hackers target inadequately secured
machines connected in some form to the Internet. Hackers use various inspection techniques—both automated and manual—to uncover inadequately secured
networks and hosts. Automated trawling for insecure hosts is usually scripted, and
can be detected by a company’s security infrastructure under the correct circumstances. Depending on the hackers’ level of competence, manual inspection can
be harder to identify because the attacker can adapt his approach accordingly, but
it is also much more time-consuming.
After the insecure machines have been identified, the attacker compromises
the systems. Hackers can gain access to a host in a startling variety of ways (usually through the root or administrative account), most of which are preventable.
The first task a thorough hacker undertakes is to erase evidence that the system
has been compromised and also to ensure that the compromised host will pass a
cursory examination.The tools used to ensure that these tasks will be successful
are sometimes collectively called rootkits.
Some of the compromised hosts become masters while others are destined for
zombification. Masters are installed with a copy of the client software and are used
as intermediaries between the attacker and the zombies. Masters receive orders
that they then trickle through to the zombies for which they are responsible.
Available network bandwidth is not a priority for hosts designated to be masters.The master is only responsible for sending and receiving short control messages, making lower bandwidth networks just as suitable as higher bandwidth
On the hosts not designated as masters, the hacker installs the software (called
a daemon) used to send out attack streams, and the host graduates to become a
zombie.The daemon runs in the background on the zombie, waiting for a message to activate the exploit software and launch an attack targeted at the designated victim. A daemon may be able to launch multiple types of attacks, such as
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UDP or SYN floods. Combined with the ability to use spoofing, the daemon
can prove to be a very flexible and powerful attack tool.
Despite its rather evil-sounding name, a daemon is defined as any program that runs on a continuous basis and handles requests for service
that come in from other computers. There are many legitimate and
useful daemon programs that have nothing to do with launching attacks
(for example, lpd, the line printer daemon that runs on a remote print
server to monitor for print requests). The term is more often used in reference to UNIX/Linux systems.
After the attacker has recruited what he deems to be a sufficient number of
zombies and has identified his victim, he can contact the masters (either via his
own methods or with a specially written program supplied with the DDoS program) and instruct them to launch a particular attack.The master then passes on
these instructions to multiple zombies who commence the DDoS attack. After
the attack network is in place, it can take only a few moments to launch a distributed attack.With similar speed, the hacker can also halt the attack.
The basic flow of the attack then becomes:
For hosts Attacker to Master to Zombie to Target
For software Attacker to Client to Daemon to Target
Know the difference between DoS and a DDoS attacks. A DoS attack is
simply any attack that makes a network or computing resource unavailable. A DDoS is very unique in that it orchestrates many packets to be
directed to one host from multiple machines called zombies. These are
easily confused terms, stemming from the same idea, but distinct in their
scope. DoS is a very general term describing any kind of attack that
knocks out a service, while DDoS is a term which describes one specific
type of DoS attack.
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The use and development of DDoS programs have piqued the interest of
governments, businesses, and security experts alike, in no small part because it
is a new class of attack that is extremely effective while simultaneously being hard
to trace.
In this exercise, we’ll be creating a DoS attack against a machine in a
network lab. The first example will be the ping of death attack, which,
while rather old, is still effective against unpatched UNIX and Windows
95 machines. To complete this part of the exercise, you’ll need two
machines, both running Windows 95. When both are connected to the
network, bring up a command shell by clicking on the Start button, then
on Run. Enter command into the box to launch the shell. At the
prompt, type ping -l 65510 <other.machine.ip> and hit Enter. You
should almost immediately see the other machine flash to the Windows
“blue screen,” informing you that an error has occurred. You can also try
pinging the machine to see if it will respond. This attack will also work
against Solaris 2.5 systems, and other older OS platforms.
The second DOS attack we’ll look at is called smbdie and is a newer
attack against Windows-based machines. This attack works by sending a
malicious server message block (SMB) packet to the victim machine.
Unable to process the packet properly, the system crashes. This attack
was released in mid-2002, so many systems may still be vulnerable.
To execute this attack, you’ll need the smbdie executable. It can be
found at, or by using a search engine
for the term smbdie. Once you’ve found it, you can choose to install it
on any Windows machine. You’ll also need a “victim” host running any
default installation of a Windows OS. The default Windows XP is vulnerable, but, because of the AutoUpdate function of XP, many systems may
already be patched.
Once you’ve installed and run the program, a window similar to
Figure 2.2 will appear.
It is simple to use this tool. You simply enter the IP address of the
victim machine, along with the NetBIOS name that you gave it at setup,
and click Kill. You should now have successfully launched a DoS against
your “victim,” and can test it by issuing a simple ping to verify that the
machine has crashed.
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Figure 2.2 SMBdie: A Windows Denial of Service Tool
Software Exploitation and Buffer Overflows
1.4.12 Despite their best intentions, programmers make mistakes.These mistakes often
lead to weaknesses in the software that can be exploited through buffer overflows,
one of the most common ways for an attacker to gain access to a system. As the
name suggests, this is nothing more than an attack that writes too much data to a
program’s buffer.The buffer is an area of temporary memory used by the program to store data or instructions.To create a buffer overflow attack, the attacker
simply writes too much data to that area of memory, overwriting what is there.
This extra data can be garbage characters, which would cause the program to fail;
more commonly, the extra data can be new instructions, which the victim computer will run.These instructions can contain information that will install software on the victim to allow the attacker access. Either way, an attacker can
generally gain access to a system very quickly and easily through buffer overflows.
There are many examples of buffer overflow attacks. One common buffer overflow attack is the ToolTalk Database attack for Solaris.While several years old
now, the ToolTalk database still installs as part of the default Solaris build.Tools
exist that will automatically compromise the host, and run whichever commands
are specified on the attacker’s command line.
Another type of software exploitation is found in a program’s failure to deal
with unexpected input.When a program asks a user for input, it looks for a certain response. A basic example of this would be if you were to use a program that
asked you to choose either Option 1 or Option 2.You would generate unexpected input if you were to enter a 3. Most programs will catch this error and tell
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you that you only have two choices, but some don’t have proper error handling
routines.This may sound like a really trivial and uncommon attack methodology,
because it is easy to catch from the programming standpoint. However, as mentioned earlier, mistakes do happen. For example, consider the lesson learned by an
early e-commerce site.Their shopping cart program would allow users to enter
negative numbers of items into their cart. A malicious user could order -2 books
at $50 each, and would be credited $100 on his or her credit card.This continued
for several days before an accountant caught the problem.
For the test you do not need to know exactly how a buffer overflow
works, only what a buffer overflow is and what its inherent risks are. We
recommend that security practitioners have a good understanding of
overflows, as they are very common. For more information on buffer
overflows, see Chapter 8 of Hack Proofing Your Network, Second Edition
(Syngress Publishing, ISBN: 1-928994-70-9).
SYN Attacks
A SYN attack exploits a basic weakness found in the TCP/IP protocol, and its
concept is fairly simple. As discussed above, a standard TCP session consists of the
two communicating hosts exchanging a SYN | SYN/ACK | ACK.The
expected behavior is that the initiating host sends a SYN packet, to which the
responding host will issue a SYN/ACK and wait for an ACK reply from the initiator.With a SYN attack, or SYN flood, the attacker simply sends only the SYN
packet, leaving the victim waiting for a reply.The attack occurs when the attacker
sends thousands and thousands of SYN packets to the victim, forcing them to
wait for replies that never come.While the host is waiting for so many replies, it
can’t accept any legitimate requests, so it becomes unavailable, thus achieving the
purpose of a DoS attack. For a graphical representation of a SYN attack, refer to
Figure 2.3.
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Figure 2.3 SYN Attack Diagram
Thousands of
SYN Packets
Sending Only
SYN Packets
Awaiting SYN/ACK Reply
Spoofing means providing false information about your identity in order to gain
unauthorized access to systems, or, in even simpler terms, pretending to be
someone you are not.The most classic example of spoofing is IP spoofing.TCP/IP
requires that every host fills in its own source address on packets, and there are
almost no measures in place to stop hosts from lying. Spoofing, by definition, is
always intentional. However, the fact that some malfunctions and misconfigurations can cause the exact same effect as an intentional spoof causes difficulty in
determining whether an incorrect address indicates a spoof.This means it’s often
easy for a spoofer to explain away his or her actions.
There are different types of spoofing attacks.These include blind spoofing
attacks in which the attacker can only send and has to make assumptions or
guesses about replies, and informed attacks in which the attacker can monitor, and
therefore participate in, bidirectional communications.Theft of all the credentials
of a victim (that is, the username and password) is not usually considered
spoofing, but gives the attacker much of the same power.
Spoofing is not always malicious. Some network redundancy schemes rely on
automated spoofing in order to take over the identity of a downed server.This is
due to the fact that the networking technologies never accounted for the need
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for one server to take over for another, and so have a hard-coded idea of one
address, one host.
Unlike the human characteristics we use to recognize each other, which we
find easy to use and hard to mimic, computer information is easy to spoof. It can
be perfectly stored, categorized, copied, and replayed.
Technologies and methodologies exist that can help safeguard against
spoofing of these capability challenges.These include:
Using firewalls to guard against unauthorized transmissions
Not relying on security through obscurity, the expectation that using
undocumented protocols will protect you
Using various cryptographic algorithms to provide differing levels of
Knowledge of TCP/IP is really helpful when dealing with spoofing and
sequence attacks. Having a good grasp of the fundamentals of TCP/IP
will make the attacks seem less abstract. Additionally knowledge of not
only what these attacks are, but how they work, will better prepare you
to answer test questions.
Subtle attacks are far more effective than obvious ones. Spoofing has an
advantage in this respect over a straight vulnerability exploit.The concept of
spoofing includes pretending to be a trusted source, thereby increasing chances
that the attack will go unnoticed.
If the attacks use just occasional induced failures as part of their subtlety, users
will often chalk it up to normal problems that occur all the time. By careful
application of this technique over time, users’ behavior can often be manipulated.
One major class of spoofing attacks disable security, then spoof the channel
that informs the user that security has been enabled. By simply drawing the right
pixels in the right places, one can make it appear that Secure Sockets Layer (SSL)
encryption has been activated. But then, the SSL pixels aren’t what really matters—a site just needs to look good. People don’t necessarily know that a welldesigned site could be ripped off by just anyone; most expensive-looking things
are inherently difficult to duplicate.
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When an attacker creates a spoofed system, they often just recreate as much
of the original as necessary to create an illusion of the real thing.With this
façade, they’ve managed to build enough to establish their trick, but have avoided
a lot of the complexities that may have been involved with the original system.
In closing, identity is one of the most critical needs in network security;
unfortunately it is also the most often unappreciated need. As we’ve discussed,
TCP/IP, as designed, does not adequately manage identity issues, so we must rely
on other means by which to recognize electronic identities. As it stands, online
identity is easy to claim but difficult to verify.
Address Resolution Protocol (ARP) spoofing can be quickly and easily
done with a variety of tools, most of which are designed to work on
UNIX operating systems. One of the best all-around suites is a package
called dsniff. It contains an ARP spoofing utility and a number of other
sniffing tools that can be beneficial when spoofing.
To make the most of dsniff you’ll need a Layer 2 switch, into which
all of your lab machines are plugged. It is also helpful to have various
other machines doing routine activities such as Web surfing, checking
POP mail, or using Instant Messenger software.
1. To run dsniff for this exercise, you will need a UNIX-based
machine. To download the package and to check compatibility,
visit the dsniff Web site at
2. After you’ve downloaded and installed the software, you will see
a utility called arpspoof. This is the tool that we’ll be using to
impersonate the gateway host. The gateway is the host that
routes the traffic to other networks.
3. You’ll also need to make sure that IP forwarding is turned on in
your kernel. If you’re using *BSD UNIX, you can enable this with
the sysctl command (sysctl –w net.inet.ip.forwarding=1). After
this has been done, you should be ready to spoof the gateway.
4. Arpspoof is a really flexible tool. It will allow you to poison the
ARP of the entire local area network (LAN), or target a single
host. Poisoning is the act of tricking the other computers into
thinking you are another host. The usage is as follows:
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home# arpspoof –i fxp0
This will start the attack using interface fxp0 and will intercept
any packets bound for The output will show you the
current ARP traffic.
5. Congratulations, you’ve just become your gateway.
You can leave the arpspoof process running, and experiment in
another window with some of the various sniffing tools which dsniff
offers. Dsniff itself is a jack-of-all-trades password grabber. It will fetch
passwords for Telnet, FTP, HTTP, IM, Oracle, and almost any other password that is transmitted in the clear. Another tool, mailsnarf, will grab
any and all e-mail messages it sees, and store them in a standard
Berkeley mbox file, for later viewing. Finally, one of the more visually
impressive tools is WebSpy. This tool will grab URL strings sniffed from a
specified host, and display them on your local terminal, giving the
appearance of surfing along with the victim.
You should now have a good idea of the kind of damage an attacker
can do with ARP spoofing and the right tools. This should also make
clear the importance of using encryption to handle data. Additionally,
any misconceptions about the security or sniffing protection provided by
switched networks should now be alleviated thanks to the magic of ARP
Head of the Class…
Why is Spoofing So Easy?
Spoofing is really easy, and this is a result of some inherent flaws in TCP/IP.
TCP/IP basically assumes that all computers are telling the truth. There is
little or no checking done to verify that a packet really comes from the
address indicated in the IP header. When the protocols were being
designed in the late 1960s, engineers didn’t anticipate that anyone would
or could use the protocol maliciously. In fact, one engineer at the time
described the system as flawless because “computers don’t lie.” There are
ways to combat spoofing, however. One really easy way to defeat harmful
spoofing attacks is to disable source routing in your network at your firewall, at your router, or both. Source routing is, in short, a way to tell your
packet to take the same path back that it took while going forward.
Disabling this will prevent attackers from using it to get responses back
from their spoofed packets.
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Man in the Middle Attacks
As you have probably already begun to realize, the TCP/IP protocols were not
designed with security in mind and contain a number of fundamental flaws that
simply cannot be fixed due to the nature of the protocols. One issue that has
resulted from TCP/IP’s lack of security is the Man-in-the-Middle attack.To fully
understand how a MITM attack works, let’s quickly review how TCP/IP works.
The Transmission Control Protocol/Internet Protocol was formally introduced in 1974 by Vincent Cerf.The original purpose of TCP/IP was not to provide security; it was to provide high-speed communication network links.
A TCP/IP connection is formed with a three-way handshake. As seen in Figure
2.4, a host (Host A) that wants to send data to another host (Host B) will initiate
communications by sending a SYN packet.The SYN packet contains, among other
things, the source and destination IP address as well as the source and destination
port numbers. Host B will respond with a SYN/ACK.The SYN from Host B
prompts Host A to send another ACK and the connection is established.
Figure 2.4 A Standard TCP/IP Handshake
Host A
Host B
If a malicious individual can place himself between Host A and Host B, for
example compromising an upstream router belonging to the ISP of one of the
hosts, he can then monitor the packets moving between the two hosts. It is then
possible for the malicious individual to analyze and change packets coming and
going to the host. It is quite easy for a malicious person to perform this type of
attack on Telnet sessions, but, the attacker must first be able to predict the right
TCP sequence number and properly modify the data for this type of attack to
actually work—all before the session times out waiting for the response.
Obviously, doing this manually is hard to pull off; however, tools designed to
watch for and modify specific data have been written and work very well.
There are a few ways in which you can prevent MITM attacks from happening. First, use a TCP/IP implementation that generates TCP sequence numbers that are as close to truly random as possible.
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Damage & Defense…
Random TCP Sequence Numbers
It is important to note that random TCP sequence numbers do not make
a connection secure if that connection is in cleartext. Thus, encryption is
probably the best option. For Web-based transactions, SSL should be used
and any type of remote administration should be performed via Secure
Shell (SSH), at a minimum. If the data is encrypted, an attacker must first
crack the encryption, then modify the packets, re-encrypt the data, and
finally send it on to the waiting host, all before the session times out or
the sending computer resends. The risk of such an attack actually being
carried out is quite low.
Replay Attacks
Replay attacks, while possible in theory, are quite unlikely due to multiple factors
such as the level of difficulty of predicting TCP sequence numbers.To perform a
replay attack, a malicious person must first capture an amount of sensitive traffic,
then simply replay it back to the host in an attempt to replicate the transaction.
For example, consider an electronic money transfer. User A transfers a sum of
money to Bank B. Malicious User C captures User A’s network traffic, then
replays the transaction in an attempt to cause the transaction to be repeated multiple times. Obviously, this attack has no benefit to User C but could result in
User A losing money. It has been proven, especially in older versions of Windows
NT and some other operating systems, that the formula for generating random
TCP sequence numbers isn’t truly random or even that difficult to predict, which
makes this attack possible.
Another potential scenario for a replay attack is this: An attacker replays the
captured data with all potential sequence numbers, in hopes of getting lucky and
hitting the right one, thus causing the user’s connection to drop, or in some cases,
to insert arbitrary data into a session.
As with MITM attacks, more random TCP sequence numbers and encryption like SSH or IPSec can help defend against this problem.
TCP/IP Hijacking
TCP/IP hijacking, or session hijacking, is a problem that has appeared in most
TCP/IP-based applications, ranging from simple Telnet sessions to Web-based
e-commerce applications. In order to hijack a TCP/IP connection, a malicious user
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must first have the ability to intercept a legitimate user’s data, then insert himself
into that session. A tool known as Hunt ( is
very commonly used to monitor and hijack sessions. It works especially well on
basic Telnet or FTP sessions.
Lately, a more interesting and malicious form of session hijacking has surfaced.This involves Web-based applications (especially e-commerce and other
applications that rely heavily on cookies to maintain session state).The first scenario involves hijacking a user’s cookie, which is normally used to store login
credentials and other sensitive information, and using that cookie to then access
that user’s session.The legitimate user will simply receive a “session expired” or
“login failed” message and probably will not even be aware that anything suspicious happened.The other issue with Web server applications that can lead to session hijacking is incorrectly configured session timeouts. A Web application is
typically configured to timeout a user’s session after a set period of inactivity. If
this timeout is too large, it leaves a window of opportunity for an attacker to
potentially use a hijacked cookie or even predict a session ID number and hijack
a user’s session.
In order to prevent these types of attacks, as with other TCP/IP-based
attacks, the use of encrypted sessions are key; in the case of Web applications,
unique and pseudo-random session IDs and cookies should be used along with
SSL encryption.
Wardialing, which gets its name from the film WarGames, is the act of dialing large
blocks of telephone numbers, via modem, searching for a computer with which
to connect.The attacker in this case uses a program known as a war dialer to automate this process.These programs are usually quite flexible and will dial a given
block of numbers at a set interval, logging whatever they may happen to find.
While this technique was previously heavily used, advances in telecom technology make it easier now to identify war dialers, therefore making it slightly
more of a risk to potential attackers.
From the viewpoint of someone in charge of securing a large corporate
infrastructure, it makes sense to war dial all known company lines to check for
modems that may be connected without your knowledge.Though the practice is
on a decline, installation of unauthorized modems by employees still represents a
huge threat to enterprise security.
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For more information on wardialing, refer to Chapters 4 and 6.
Dumpster Diving
Dumpster diving is the process of physically digging through a victim’s trash in an
attempt to gain information. Often it is easy to find client or product information, internal memos, and even password information that have been placed in
wastebaskets. In one infamous example, a major clothing company had simply
discarded photos and information about their upcoming clothing lineup. It didn’t
take long for the carelessly discarded information to wind up in the hands of
competitors, doing great damage to the victim company’s plans for a unique
product launch. It is important to make sure that your organization has a method
of securely disposing of the hard copies of confidential information. Even a $15
paper shredder can be enough to help protect your assets. Dumpster diving is
closely related to the next topic, social engineering.
Social Engineering
Social engineering is often overlooked in security plans and scenarios, which is
unfortunate because it is one of the most dangerous and easily used methods to
infiltrate a victim network.The concept is nothing more than creative lying.The
lies are often backed up by materials found in dumpster diving, which involves
digging through the victim’s trash, looking for important documents, phone lists,
and so forth. Knowing a few important names, for example, can make the
attacker seem more authentic and can allow him to pose as someone he is not,
perhaps asking for classified information over the telephone.This information can
be something as trivial as someone’s telephone number, or as confidential as
someone’s server password and login ID.
Unfortunately, you can’t firewall employees, but you can make them aware of
policies regarding disclosure of information, especially over the telephone or via
e-mail.The human factor can often be the weakest link in the security of a network. However, the positive side is that most employees do not wish to harm the
company, and will follow disclosure procedures if they are made aware of the
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It’s very important to recognize the threat that social engineering poses.
Kevin Mitnick made headlines for his various forays into networks, and a
majority of his information and strategies were based on social engineering.
The best way to see the success that can be had with social engineering
is to try it! With permission from your employer, make phone calls to
random employees, and do some information gathering. Have a list of
questions handy, and if necessary, practice what you will say. The smoother
and more confident your delivery, the more successful you will be.
Be careful to not ask sensitive questions without a proper introduction. Avoid asking questions such as “Hi, I’m from tech support; what is
your password, please?” Instead, try a different approach to first gain
trust. For example, get the number of a pay phone that accepts
incoming calls. Telephone your victim and prepare a story about needing
to verify passwords on the server, or something of that nature. Now,
inform the victim that “for security reasons” you’d like him or her to call
you back at the following number, and give the pay phone number.
When the victim calls back, be certain to answer the telephone professionally, and have the victim give you his or her password or other
important information. It is important to establish some kind of trust or
authority before requesting the information.
Social engineering takes practice (and a certain amount of talent) and
every situation is different, so there isn’t really any right or wrong way to
do it. As stated earlier, the victim must believe you are who you say you
are. Try to think of plausible situations, and, if possible, know the names
of other people in the organization that you are social engineering.
Familiarity means comfort, and comfort means trust. With these tips in
mind, along with some practice, you are likely to be able to obtain the
information you request.
Passive Attacks
During a passive attack, the direct opposite of an active attack, the attacker isn’t
directly affecting the victim network. Rather, the attacker is passively listening for
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something to occur, or trying to gather information. Some passive attacks can be
likened to eavesdropping on someone’s conversation, or using binoculars to spy
on someone.There are quite a few interesting ways that passive attacks can occur,
which will be described in detail in the following sections.
Vulnerability Scanning
Vulnerability scanning is important to both attackers and those responsible for security hosts and networks.This refers to the act of probing a host in order to find
an exploitable service or process.There are a number of tools that can assist in
vulnerability scanning. A basic example is a tool called Nmap. It is a port scanner,
which sends packets to a host in order to generate a list of services the host is
running, and it will also return the OS type.With this information, an attacker
can get a better idea of what type of attack may be suitable for that particular
host. For example, it would not make sense to launch an IIS attack against a
UNIX machine, so knowing the OS and installed services means an attacker can
better search for an exploitthat will work.
A more sophisticated vulnerability scanning tool is Nessus. It is a freeware
tool, which can be set up to scan multiple types of architectures for vulnerabilities
using a list of known attack types. It has several modes of operation, but in its
default mode, it will generate a very readable output detailing what services are
currently exploitable, and which may be exploitable. It also offers suggestions on
how to improve the security of a host. It’s a great tool for evaluating the security
of your systems, and can be downloaded from
For this exercise, you will need a copy of the Nmap port scanning tool.
The UNIX version and links to a Windows version can be found at Nmap is a powerful port scanning utility that can be
used to gain information about a single host or an entire network; it can
even determine OS types.
The basic command used with nmap is nmap <ipaddress>. If you
are running as the unprivileged user, this will default to a TCP scan,
which essentially establishes a full TCP connection to each port on the
target system.
There are a number of useful options, some of which will require you
to run as root.
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Consider Nmap –sS –O –v <ipaddress>: This scan only sends the
SYN packets, and thus is considered a stealth scan. The –O specifies that
we’d like Nmap to determine the OS type, and the –v requests the verbose mode, so we see exactly what the program is doing, while it’s
doing it.
You may notice that it takes a really long time to scan hosts. This is
because Nmap scans all ports by default. You may wish to shorten the
scan time by limiting it to certain ports. This can be done via the –p command. For example Nmap –sS –v –p ‘1-1024’ will use a SYN scan to scan
only ports 1-1024.
Nmap can also be used to scan networks for responding hosts. This
function is called the ping scan and can be envoked with the –sP option.
There are many more things that can be done with Nmap, so make
sure you have a test lab environment ready and start trying the many different options.
Sniffing and Eavesdropping
Sniffing means eavesdropping on a network. A sniffer is a tool that enables a
machine to see all packets that are passing over the wire (or through the air on a
wireless network), even the ones not destined for that host.This is a very powerful technique for diagnosing network problems, but it can also be used maliciously to scan for passwords, e-mail, or any other type of data sent in the clear.
Tcpdump is the most common UNIX sniffing tool, and does come with many
Linux distributions. Snoop is the Solaris equivalent.These two programs are command-line-based, and will simply begin dumping all of the packets they see, in a
readable format.They are fairly basic in their functionality, but can be used to
gain information about routing, hosts, and traffic types. For more detailed command line scanning, Snort, a freeware tool, offers many more functions than tcpdump, such as the ability to dump the entire application layer, and to generate
alerts based on types of traffic seen. Even more advanced, Ethereal is a fully
graphical sniffing program that has many advanced features. One of the more
powerful features of Ethereal is the ability to reassemble TCP streams and sessions. After capturing an amount of data, an attacker can easily reassemble Web
pages viewed, files downloaded or e-mail sent, all with the click of the mouse.
The threat from sniffing is yet another argument for the use of encryption to
protect any kind of sensitive data on a network.
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Another type of eavesdropping is established by using Trojan horse programs.
Tools like SubSeven and Back Orifice can log all user keystrokes and capture
screens that can be secretly sent to an attacker’s machine.These will be discussed
in more detail later in this chapter.
Password Attacks
1.4.11 Password attacks are extremely common, as they are easy to perform and often
result in a successful intrusion.There are two basic types of password guessing
that can be performed: brute force or dictionary-based attacks. Each of these methods
is explained in detail in the following sections.
Brute Force Attacks
Brute force, in its simplest definition, refers to trying as many password combinations as possible until hitting on the right one. It is a method commonly used to
obtain passwords, especially if the encrypted password list is available.While the
exact number of characters in a password is usually unknown, most passwords can
be estimated to be between four and 16 characters. Since only about 100 different
values can be used for each character of the password, there are only about 1004 to
10016 likely password combinations.Though massively large, the number of possible
password combinations is finite and is therefore vulnerable to brute force attack.
Before specific methods for applying brute force can be discussed, a brief
explanation of password encryption is required. Most modern operating systems
use some form of password hashing to mask the exact password (see Chapter 9 for
more information regarding hashing). Because passwords are never stored on the
server in cleartext form, the password authentication system becomes much more
secure. Even if someone who is unauthorized somehow obtains the password list,
he will not be able to make immediate use of it, making it more likely that
system administrators will have time to change all of the relevant passwords
before any real damage is done.
Passwords are generally stored in what is called hashed format.When a password is entered into the system, it passes through a one-way hashing function,
such as Message Digest 5 (MD5), and the output is recorded. Hashing functions
are one-way encryption only, and once data has been hashed, it cannot be
restored. A server doesn’t need to know what your password is. It needs to know
that you know what it is.When you attempt to authenticate, the password you
provided is passed through the hashing function and the output is compared to
the stored hash value. If these values match, then you are authenticated.
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Otherwise, the login attempt fails, and is logged by the system (assuming logging
of such events is configured).
Brute force attempts to discover passwords usually involve stealing a copy of
the username and hashed password listing and then methodically encrypting possible passwords using the same hashing function. If a match is found, then the
password is considered cracked. Some variations of brute force techniques involve
simply passing possible passwords directly to the system via remote login
attempts. However, these variations are rarely seen anymore, due to account
lockout features implemented on most business servers (which prevent further
logon attempts after a specified number of incorrect entries) and the fact that
they can be easily spotted and traced by system administrators.They also tend to
be extremely slow.
Dictionary-Based Attacks
Appropriate password selection minimizes—but cannot completely eliminate—a
password’s ability to be cracked. Simple passwords such as any individual word in
a language make the weakest passwords because they can be cracked with an elementary dictionary attack. In this type of attack, long lists of words of a particular
language called dictionary files are searched to find a match to the encrypted password. More complex passwords that include letters, numbers, and symbols require
a different brute force technique that includes all printable characters and generally take much longer to run.
Malicous Code Attacks
Code attacks are carefully crafted programs written by attackers and designed to do
damage.Trojan horses, viruses, and malware are all examples of this kind of attack.
These programs are written to be independent and do not always require user
intervention or for the attacker to be present for their damage to be done.This section will discuss these types of attacks and will give an in-depth look at each.
Malware is malicious software.While it has been around for many years, users in
the past were required to physically transport the software between machines,
often through floppy diskettes or other removable media to which the program
wrote itself without the user’s knowledge.This limitation has changed dramatically
with the widespread use of the Internet, and through programs such as e-mail
clients that accept HTML mail, which make it very easy for users to run programs
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e-mailed to them without their knowledge.Two common types of malware are
viruses and Trojan horses.Viruses self-replicate and spread without user interaction,
and the really advanced ones can modify themselves to avoid detection. A Trojan
horse (or Trojan) is a program that appears to do one thing but does something
else instead of or in addition to its claimed use.Trojan horses typically trick a user
into running them by promising that they do something great, such as make the
e-mail transfer faster, or offering a money-making opportunity.
A computer virus is defined as a self-replicating computer program that interferes
with a computer’s hardware or operating system or application software.Viruses
are designed to replicate and to elude detection. Like any other computer program, a virus must be executed to function (it must be loaded into the computer’s
memory) and then the computer must follow the virus’s instructions.Those
instructions constitute the payload of the virus.The payload may disrupt or change
data files, display a message, or cause the operating system to malfunction.
Damage & Defense…
End-User Virus Protection
As a user, you can prepare for a virus infection by creating backups of the
legitimate original software and data files on a regular basis. These
backups will help to restore your system, should that ever be necessary.
Activating the write-protection notch on a floppy disk (after you have
backed up the software and files) will help to protect against a virus on
your backup copy.
You can also help to prevent against a virus infection by using only
software that has been received from legitimate, secure sources. Always
test software on a “test” machine (not connected to your productivity
network) prior to installing it on any other machines to help ensure that
it is virus-free.
Using that definition, let’s explore in more depth exactly what a virus does
and what its potential dangers are.Viruses spread when the instructions (executable
code) that run programs are transferred from one computer to another. A virus
can replicate by writing itself to floppy disks, hard drives, legitimate computer programs, or even across networks.The positive side of a virus is that a computer
attached to an infected computer network or one that downloads an infected program does not necessarily become infected. Remember, the code has to actually
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be executed before your machine can become infected. However, chances are
good that if you download a virus to your computer and do not explicitly execute
it, the virus may contain the logic to trick your operating system into running the
viral program. Other viruses exist that have the ability to attach themselves to otherwise legitimate programs.This could occur when programs are created, opened,
or even modified.When the program is run, so is the virus.
Numerous different types of viruses can modify or interfere with your code.
Unfortunately, developers can do little to prevent these attacks from occurring. As a
developer, you cannot write tighter code to protect against a virus. It simply is not
possible.You can, however, detect modifications that have been made, or perform a
forensic investigation.You can also use encryption and other methods for protecting
your code from being accessed in the first place. Let’s take a closer look at the different categories that a virus could fall under and the definitions of each:
Parasitic Parasitic viruses infect executable files or programs in the
computer.This type of virus typically leaves the contents of the host file
unchanged but appends to the host in such a way that the virus code is
executed first.
Bootstrap sector Bootstrap sector viruses live on the first portion of
the disk, known as the boot sector (this includes both hard and floppy
disks).This virus replaces either the programs that store information
about the disk’s contents or the programs that start the computer.This
type of virus is most commonly spread via the physical exchange of
floppy disks.
Multi-partite Multi-partite viruses combine the functionality of the
parasitic virus and the bootstrap sector viruses by infecting either files or
boot sectors.
Companion Instead of modifying an existing program, a companion
virus creates a new program with the same name as an already existing
legitimate program. It then tricks the OS into running the companion
program, which delivers the virus payload.
Link Link viruses function by modifying the way the OS finds a program, tricking it into first running the virus and then the desired program.This virus is especially dangerous because entire directories can be
infected. Any executable program accessed within the directory will
trigger the virus.
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Data file A data file virus can open, manipulate, and close data files.
Data file viruses are written in macro languages and automatically execute when the legitimate program is opened. A well known type of data
file virus is the macro virus.
Trojan Horses
A Trojan horse closely resembles a virus, but is actually in a category of its own.
The Trojan horse is often referred to as the most elementary form of malicious
code. A Trojan horse is used in the same manner as it was in Homer’s Iliad; it is a
program in which malicious code is contained inside of what appears to be
harmless data or programming. It is most often disguised as something fun, such
as a cool game.The malicious program is hidden, and when called to perform its
functionality, can actually ruin your hard disk.
Not all Trojan horses are that malicious in content, but they can be, and it is
usually the intent of the program to seek and destroy with the goal of causing as
much damage as possible. One saving grace of a Trojan horse, if there is one, is
that it does not propagate itself from one computer to another (self-replication is
a characteristic of the worm).
A common way for you to become the victim of a Trojan horse is for
someone to send you an e-mail with an attachment that purports to do something useful. It could be a screensaver or a computer game, or even something as
simple as a macro quiz.To the naked eye, it will most likely not appear that anything has happened when the attachment is launched.The reality is that the
Trojan has now been installed (or initialized) on your system.What makes this
type of attack scary is the possibility that it may be a remote control program.
After you have launched this attachment, anyone who uses the Trojan horse as a
remote server can now connect to your computer. Hackers have advanced tools
to determine what systems are running remote control Trojans. After the specially
designed port scanner on the hacker’s end finds your system, all of your files are
accessible to that hacker.Two common Trojan horse remote control programs are
Back Orifice and NetBus.
Back Orifice consists of two key pieces: a client application and a server application.The client application runs on one machine and the server application runs
on a different machine.The client application connects to the other machine using
the server application. However, the only way for the server application of Back
Orifice to be installed on a machine is for it to be deliberately installed.This
means the hacker either has to install the server application on the target machine
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or trick the user of the target machine into doing so.This is the reason this server
application is commonly disguised via a Trojan horse. After the server application
has been installed, the client machine can transfer files to and from the target
machine, execute an application on the target machine, restart or lock up the
target machine, and log keystrokes from the target machine. All of these operations
are of value to a hacker.
While it isn’t necessary to have installed backdoor or virus software on
a test machine in order to pass this exam, it can be useful in gaining a
greater understanding of the concept. Reading about a topic is one thing,
but seeing it running in the wild is another. Hands-on experience can make
the concepts seem more tangible, while giving insight into not just what
malware is, but how it actually works. The added familiarity can ease
nerves on the test day. However, be sure you get this hands-on experience
in a controlled test environment; do not install these programs on
machines that are connected to a production network or the Internet.
The server application is a single executable file, just over 122 kilobytes in
size.The application creates a copy of itself in the Windows system directory and
adds a value containing its filename to the Windows registry under the key:
The specific registry value that points to the server application is configurable. By configuring the value to run at startup, the hacker ensures that the
server application always starts whenever Windows starts, and therefore is always
functioning. One additional benefit of Back Orifice to the hacker is that the
application will not appear in the Windows task list, rendering it invisible to the
casual observer.
Another common remote control Trojan horse is named the SubSeven Trojan.
This Trojan is also sent as an e-mail attachment and after execution can display a
customized message that often misleads the victim. Actually, the customized message is intended to mislead the victim.This particular program will allow someone
to have nearly full control of the victim’s computer with the ability to delete
folders and/or files. It also uses a function that displays something like a continuous screen cam, which allows the hacker to see screen shots of the victim’s computer, and the hacker can remotely control the mouse pointer, sniff traffic off the
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victim’s network, and even eavesdrop through the victim computer’s microphone.
Version 2.2 of SubSeven was designed to run on Windows NT and 2000 as well
as the 9x operating systems.
Damage & Defense…
Back Orifice Limitations
The Back Orifice Trojan horse server application will function only in
Windows 95 or Windows 98. The server application does not work in
Windows NT. The updated version of Back Orifice, BO2k will now run on
the newer Windows operating systems like Windows 2000, ME, and XP.
Additionally, the target machine (the machine hosting the server application) must have TCP/IP network capabilities.
Possibly the two most critical limitations to the Back Orifice Trojan
horse are that the attacker must know the IP address of the target
machine and that there cannot be a firewall between the target machine
and the attacker. A firewall makes it virtually impossible for the two
machines to communicate.
In August of 2000, a new Trojan horse was discovered, known as the QAZ
Trojan horse.This is the Trojan that was used to hack into Microsoft’s network and
allowed the hackers to access source code.This particular Trojan spreads within a
network of shared computer systems, infecting the Notepad.exe file.What makes
this Trojan so malicious is that it will open port 7597 (part of a block of unassigned
ports) on the network, allowing a hacker to gain access at a later time through the
infected computer. QAZ Trojan was originally spread through e-mail and/or IRC
chat rooms; it eventually was spread through LANs. If the user of an infected
system opens Notepad, the virus is run. QAZ Trojan will look for individual systems that share a networked drive and then seek out the Windows folder and infect
the Notepad.exe file on those systems.The first thing that QAZ Trojan does is to
rename Notepad.exe to, and then the Trojan creates a virus-infected file
Notepad.exe.This new Notepad.exe has a length of 120,320 bytes. QAZ Trojan
then rewrites the System Registry to load itself every time the computer is booted.
A network administrator monitoring open ports may notice unusual traffic on
TCP port 7597 if a hacker has connected to the infected computer.This Trojan was
particularly insidious because most users had been told that text files were safe from
viruses, so they didn’t hesitate running a program associated with Notepad.
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While the concepts behind worms, viruses, logic bombs and Trojan
horses are very similar, it’s important to be sure you can quickly differentiate. There is often a fine line between a virus and a worm, so be sure
to know the specific differences between them.
Logic Bombs
A logic bomb is a type of malware that can be compared to a time bomb.They are
designed to do their damage after a certain condition is met.This can be the
passing of a certain date or time, or it can be based on the deletion of a user’s
account. Often attackers will leave a logic bomb behind when they’ve entered a
system to try to destroy any evidence that system administrators might find. One
well-known logic bomb was known as the Chernobyl virus. It spread via infected
floppy disks or through infected files, and replicated itself by writing to an area
on the boot sector of a disc.What made Chernobyl different from other viruses is
that it didn’t activate until a certain date, in this case, April 26, the anniversary of
the Chernobyl disaster. On that day, the virus caused havoc by attempting to
rewrite the victim’s system BIOS and by erasing the hard drive. Machines that
were the unfortunate victims of this virus required new BIOS chips from the
manufacturer to repair the damage.While most logic bombs aren’t this well publicized, they can easily do similar or greater damage.
Another example of a well-known logic-bomb type virus was the
Michelangelo virus, which was set to go off on March 6, the birthday of the
famous Renaissance painter, and delete the data from hard disks. It was discovered
in 1991; antivirus software will catch most of the known varieties of this malware.
A worm is a self-replicating program that does not alter files but resides in active
memory and duplicates itself by means of computer networks.Worms use automated functionality found in operating systems and are invisible to the user. Often,
worms aren’t even noticed on systems until the network resources are completely
consumed, or the victim PC’s performance is degraded to unusable levels. Some
worms are not only self-replicating but also contain a malicious payload.
There are many ways worms can be transmitted, but the most common are
through e-mail or via Internet chat rooms. A well-known and now infamous
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worm known as the Lovebug originated in May 2000.The swiftness with which
this worm moved wreaked havoc on networks and systems around the world, and
puzzled many network administrators. Initial analysis of the worm showed that it
was written in Visual Basic and came attached to e-mail as an attachment named
Love-Letter-For-You.txt.vbs.This filename fooled many people because, by
default,Windows hides known file extensions. So, to most windows users, this
actually looked like Love-Letter-For-You.txt, which would normally be benign.
When users clicked on the attachment, the worm used the Microsoft Outlook
Address book to replicate itself, mailing copies of itself to everyone listed.The
worm then contacted one of four Web pages in the Philippines, where users were
prompted to download a “fix” titled WIN-BUGSFIX.EXE.This unfortunately
wasn’t a fix at all, but a Trojan horse that collected usernames and passwords from
the victim computer and sent them back to the attacker’s e-mail address.
Security experts and network administrators were startled by the speed at
which this worm spread.Within 12 hours after the worm had first been detected in
Europe, it had been spread to an estimated 500,000 computers worldwide.This
trend of rapid spreading was seen again with the Nimda worm (whose name
comes from “admin” spelled backward) and the Code Red worm in 2001.
Attacking a weakness in Microsoft’s IIS Web Server, these two worms replicated
themselves on the victim machines and begin scanning the network for additional
vulnerable machines.While Nimda and Code Red didn’t themselves do much
damage to host machines, they certainly set another precedent for the danger of
worms, and are not harmless. Nimda creates open network shares on infected computers, and also creates a Guest account with Administrator privileges, thus allowing
access to the system and opening it up to whatever a knowledgeable hacker wants
to do to it. Code Red (and its variant, Code Red II) degrades system performance
and causes instability by spawning multiple threads and using bandwidth.
Back Door
There are different types of back doors.Trojans, rootkits, and even legitimate programs can be used as a back door. A back door is essentially any program or
deliberate configuration designed to allow for unauthenticated access to a system.
Sometimes this is done in stealth and other times not.Types of backdoors can
include legitimate programs like Virtual Network Computing (VNC)
(available at, and PC Anywhere (available at, and malicious programs specifically written to provide
back door access like SubSeven and T0rnkit.
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It is important to understand the different types of backdoors. A Trojan is a
program that appears to be useful but in reality has malicious intent, as described
in the “Trojan Horses” section earlier. A rootkit is a bit different. A rootkit is a
collection of programs that an intruder can use to mask his presence. A typical
rootkit, like T0rnkit, will replace commonly used programs with versions modified to specifically hide the presence of the attacker while giving the attacker
remote access to the system. Because of their stealthy nature, rootkits are more
difficult to detect than the average back door.
Be less concerned with the specific functions of the different back door
programs available and concentrate on the different types and their general use. Knowing what a back door is used for is more important on the
test than knowing each of the types.
Most common antivirus software will detect specific malicious backdoors, but
unfortunately cannot help you when a legitimate program is configured to allow
back door access.You will only detect such a scenario by being aware of what
services are running on your system. Personal firewalls that block outgoing and
incoming connections based on user configurable rule-sets are much more effective in blocking legitimate programs configured as back doors.
Another kind of back door is one that is left in or written into a program by
the programmers.This is generally done within a program by creating a special
password that will allow access. For example, Award BIOS used to have a back
door password, which would bypass a password-protected machine. By entering
CONDO at the password screen, the security mechanism would be immediately
bypassed.This kind of back door can also be left by system administrators, to
make maintenance “easier.” Often, new administrators will bind a root shell to a
high port on a UNIX host, giving them immediate root level access by just
Telneting to that port. Other, craftier back doors can replace existing programs,
such as the telnetd program.There is a back-door version of telnetd that will, with
a preset username and password, grant root access to attackers. Malicious programmers have also written back-door code into some older versions of SSH1,
which would e-mail the passwords of those logging in to specified e-mail
account.This is why it is always important to verify the MD5 checksum of software when downloading it from the Web.
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Summary of Exam Objectives
In this chapter, we covered a number of different attacks and attack scenarios.
The Security+ exam will focus on these attack sections, so be mindful of this
while reviewing and make certain you are able to differentiate the attack types.
Specifically, pay attention to social engineering, malware, Denial of Service, and
TCP/IP-based attacks. Make certain you know why DoS attacks are effective and
what some of the common defense methods are.
In the DoS/DDoS section, we reviewed the fundamentals of a DoS attack,
and why they are so easy to perform but difficult to defend.We also covered the
difference between a DoS attack and a DDoS attack and the different components of a DDoS attack, such as client, daemon, master, and zombie.The next
section covered buffer overflow attacks, and described how attackers use flawed
application code to inject their own malicious code into a system.
We then moved on to different TCP/IP-based attacks such as spoofing
(defined as providing false information about your identity in order to gain access
to systems), and ways to detect spoofed addresses/hosts. Still in the category of
TCP/IP-based attacks, we then covered, at a high level, how a TCP/IP connection is made and how this makes possible attacks such as Man-in-the-Middle
(MITM), replay, and TCP/IP session hijacking.
We then discussed social engineering, providing steps on how to both use and
defend against it.We discussed dumpster diving and how it can be used to
strengthen a social engineering attack. Social engineering is an important concept
for this exam, so be certain you understand it.
Password attacks, both brute force and dictionary-based, were covered. One
common password attack that was not covered in very much detail is a form of
brute force: simply guessing! Many users seem to use birthdates or important
dates in history, social security numbers, or other easily guessed numbers or words
as a password.
The final sections of the chapter covered malware, viruses,Trojan horses, logic
bombs, and worms. Each of these are likely to be in the exam, so be sure to
know the differences between them, but don’t worry too much about knowing
the specific versions of each.
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Exam Objectives Fast Track
Active Attacks
; Active attacks can take many shapes, but the three most common forms
are network-based, application-based and mixed threat attacks.
; Network-based attacks include DDoS attacks (which utilize many dif-
ferent computers to attack a single host), spoofing (where attackers pretend to be someone they’re not), session hijacking (where attackers steal
users’ sessions), and MITM attacks (where attackers sandwich themselves
between the user and server in an attempt to steal information).
; Application-based attacks are any attacks against the applications
themselves.The most common forms of these are buffer overflow
attacks, where the attacker sends too much data to the application,
causing it to fail, and execute “attacker-supplied” malicious code.
; Mixed-threat attacks are those that are comprised of both network- and
application-based attacks. Many worms fall into this category, as they
have the ability to compromise hosts by using buffer overflows, and
generate enormous amounts of network traffic by scanning for new
vulnerable hosts.
; Social engineering is a potentially devastating technique based on lying
in order to trick employees into disclosing confidential information.
; Using a technique known as dumpster diving, attackers can learn a lot
about a company; this knowledge can then be used to lend an air of
credibility to their claims to be someone they’re not, as they quiz
employees for such information as system usernames and passwords.
Passive Attacks
; Vulnerability scanning is the act of checking a host or a network for
potential services that can be attacked. Scanning tools like Nessus can
give a full picture of vulnerable applications, while others like Nmap can
be used stealthily to gain a more general picture of the security of the
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; Packet sniffers such as tcpdump or Ethereal can be used to view all traffic
on a network.This is helpful for administrators to diagnose network
problems, but can also be used by attackers to harvest valuable information
sent in the clear. Protect yourself by encrypting sensitive data, and using
more secure management tools like SSH, rather than Telnet.
Password Attacks
; Password attacks are extremely common, as they are easy to perform and
often result in a successful intrusion.
; Brute force, in its simplest definition, refers to simply trying as many
password combinations as possible until hitting on the right one.
; Simple passwords, such as any individual word in a language, make the
weakest passwords because they can be cracked with an elementary
dictionary attack. In this type of attack, long lists of words of a particular
language called dictionary files are searched for a match to the encrypted
Code Attacks
; Viruses are programs that automatically spread, requiring no user interven-
tion, and generally cause damage.Viruses have a long history in computing, and take many different forms.Today’s antivirus software is effective
in catching most viruses before they can spread or cause damage.
; Trojan horses are different from viruses in that they require the user to
run them.They usually come hidden, disguised as some kind of
interesting program, or sometimes even as a patch for a virus or
common computer problem. Installing back doors or deleting files are
common behaviors for Trojan horses. Most antiviral software can now
catch and disable Trojan horses.
; One of the biggest new threats to security today is the worm.Worms,
which are basically network viruses, spread without user knowledge and
wreak havoc on computers and systems by consuming vast resources. So
far, there haven’t been any major worm outbreaks with damaging
payloads, though it’s likely only a matter of time.
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Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: Is it safe for me to install backdoors or Trojan horses like SubSeven or
NETbus onto my computer to learn how they work?
A: Yes and no.While it can be good to learn how they work, it’s important to
use a machine that is set up for testing purposes only and isn’t connected to
any networks.
Q: Why is a DoS attack different from a DDoS attack?
A: A DDoS attack is a type of Denial of Service attack which uses an “army” of
hacked machines to shut down service to another victim machine.The two
are often confused—a DoS attack is nothing more than any attack that denies
service to users or networks, while a DDoS attack is just one form of DoS.
Q: How can my applications be protected against buffer overflow attacks?
A: It’s impossible to provide 100% protection, but a good start is making sure
you are current with patches from the software vendor. Another approach is
to perform code reviews, looking for overlooked flaws in the code that could
potentially be exploitable.
Q: Is there any way to protect against dumpster diving?
A: Having a policy in place that requires shredding of any discarded company
documents will provide a decent amount of protection against dumpster
diving. Remember, any document with employee names, phone numbers, or
e-mail addresses could be potentially used against you by a social engineer.
Q: What can be done to guard against the dangers of social engineering?
A: A policy forbidding the disclosure of information over the phone is a good
place to start.Warn employees that they need to be able to verify the identity
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of any person requesting information. Let them know that they will not be
reprimanded for strictly enforcing this policy. Some employees worry that if a
“boss” asks for information, they should give it immediately. Additionally,
create an environment where information is obtained in appropriate ways,
rather than blindly over the telephone or via e-mail.
Q: My company has a firewall, do I need to worry about worms?
A: Yes. Many users these days have laptop computers that are connected to a
number of different networks. Each new network is a new vector for worm
attack. Many companies stand to face outages caused by worms brought in on
employee laptops.
Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
Active Attacks
1. The component of a DDoS attack that sends commands to DDoS zombie
agents is known as a _____.
A. System Commander
B. Console
C. Master
D. Rootkit
2. The act of attempting to appear to be someone you’re not in order to gain
access to a system is known as which of the following?
A. Spoofing
C. Replay
D. Sniffing
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3. Which of the following is most likely to make systems vulnerable to
MITM attacks?
A. Weak passwords
B. Weak TCP sequence numbers
C. Authentication misconfiguration on routers
D. Use of the wrong operating systems
4. Which of the following is the best way to protect your organization from
revealing sensitive information through dumpster diving?
A. Establish a policy requiring employees to change passwords every 30 to
60 days.
B. Teach employees the value of not disclosing restricted information over
the telephone to unknown parties.
C. Add a new firewall to the network.
D. Shred all sensitive documentation.
5. Which of the following attacks involves a SYN flood?
A. DoS
B. TCP hijacking
C. Replay
6. Buffer overflows can allow attackers to do which of the following?
A. Speak with employees to get sensitive information
B. Run code on a remote host as a privileged user
C. Write viruses that cause damage to systems
D. Crash server hard disks
7. Sending multiple packets with which of the following TCP flags set can
launch a common DoS attack?
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8. Which of the following is the best definition of IP spoofing?
A. Sending thousands of packets to a victim host in an attempt to shut
it down
B. Cracking the encryption of a password scheme
C. Pretending to be someone you are not to gain access to a system
D. Sending fragmented TCP/IP packets through a firewall to trick stateful
inspection filters
9. Wardialing requires which of the following?
A. An active TCP connection
B. A modem and a phone line
C. A connection to the Internet
D. Knowledge of UNIX systems
10. Which of the following can be classified as denial of service attacks? (Select
all that apply.)
A. Unplugging the main router for a network
B. Using zombies to send a SYN flood to a host
C. Using a buffer overflow to crash a Web server
D. Capturing packets from an unprotected network link
Passive Attacks
11. Packet sniffing will help with which of the following? (Select all that apply.)
A. Capturing e-mail to gain classified information
B. Launching a DDoS attack with zombie machines
C. Grabbing passwords sent in the clear
D. Developing a firewall deployment strategy
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12. Which of the following are vulnerability scanning tools?
A. Ethereal
B. libnet
C. Nessus
D. tcpdump
Password Attacks
13. Which of the following is true of brute force attacks?
A. They are always the fastest way to break any password.
B. They try all possible combinations of a password.
C. They are efficient and quiet on networks.
D. They will create a buffer overflow attack on a victim host.
Code Attacks
14. Software or a specific configuration or coding that allows unauthenticated
access to a system is known as which of the following?
A. Operating system
B. Back door
C. Logic bomb
D. Social engineering
15. Which of the following is the most common reason that an attacker would
place a back door in a system?
A. To spread viruses
B. To provide an interactive login without authentication or logging
C. To remove critical system files
D. To run a peer-to-peer file-sharing server
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. C
9. B
2. A
10. A, B, and C
3. B
11. A and C
4. D
12. C
5. A
13. B
6. B
14. B
7. D
15. B
8. C
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Communication Security
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Chapter 3
Remote Access and E-mail
Domain 2.0 Objectives in this Chapter:
The Need for Communication Security
Remote Access Security
E-mail Security
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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Domain 2.0 • Communication Security
The Security+ exam covers communication security. Data transmissions, particularly via e-mail or remote access methods, are typically an entity’s most exploited
vulnerability. Remote access is a common problem in today’s networks because
more businesses operate from remote offices. More people are connecting to the
workplace via the Internet or by “dialing in” through a public switched telephone network (PSTN).This chapter covers the technologies a Security+
technician needs to address including virtual private networks (VPNs) and Pointto-Point Tunneling Protocol/Layer 2 Tunneling Protocol (PPTP/L2TP) protocols
that aid in protecting communications, and other technologies used for remote
access such as Remote Authentication Dial-in User Service (RADIUS) and
Terminal Access Controller Access Control System+ (TACACS+). Each of these
terms are defined later in this chapter.
Do not confuse remote access with remote control. Remote access is the
process of creating a connection from a remote location (such as a home
office, hotel room, etc.) whereas remote control programs such as
PCAnywhere or VNC are used for emulating PC consoles remotely.
Technologies like e-mail are so ingrained in society that it is almost impossible to meet someone without an e-mail address. E-mail servers are exposed to
the Internet, so they must be protected and secure. For the Security+ exam, you
need to know how to protect personal e-mail vulnerabilities with Pretty Good
Privacy (PGP) as well as spam and e-mail relay vulnerabilities.
The Need for Communication Security
The need for communications-based security can be traced back thousands of
years to the days of ancient Egypt. Hieroglyphics were used by the Egyptians to
communicate, assuming that only those familiar with the meaning of the drawings would be able to decipher the messages.
As time went on, society became more complex and so did communications
security. Although the technologies have changed, the underlying reasoning
behind securing communications has not—that people need a secure method of
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transmitting messages. As recently as five years ago, the general consensus was that
all a user had to do to protect their network was install a firewall in front of their
Internet connection and load anti-virus software on their network.Today, things
are quite different. Hacking tools can be found on the Internet and used by
novice hackers, known as “script kiddies” and “click kiddies.” Books (such as
Syngress’ Hack Proofing Your Network, Second Edition ISBN: 1-928994-70-9) are
available at local bookstores that provide information on how different types of
attacks are carried out. Hacking has become so popular that underground networks for passing information and techniques now exist. In today’s environment,
a security professional must be extremely diligent in the protection of their assets.
Communications-Based Security
Security professionals are tasked with providing confidentiality, integrity, and
availability to information passing over public (and private) networks. In terms of
network security, there are three methods of passing communications to a centralized network:
On-site connection to the local network
Remote access
Because more people are using the Internet, many companies offer their
employees the opportunity to work from home.This creates a dilemma for security professionals, because they have to be able to meet the needs of the users and
still keep the company’s network secure. Remote access servers and VPNs are
commonplace in most networks today. Ensuring that the implementation of these
technologies is secure is as important as making sure they work properly.
Almost everyone today has a mobile phone, many people have personal digital assistants (PDAs), and a growing number of people are adding wireless network interface cards (NICs) to their laptops and desktops. Since these devices
work over “open air,” ways must be found to secure their transmissions.
Now that users have these tools for connecting to networks, they need software applications to communicate with each other. One of the most popular
ways to communicate is through e-mail.The problem is, e-mail is based on relatively old technology and because it is older, there is not much security in place
to protect it.
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The good news is there are many tools available to assist users in securing
communications. Later in this chapter is a discussion of two of the three categories: securing remote access and securing messaging.
Remote Access Security
The movie WarGames is a story about a high school student who hacks into a
Department of Defense mainframe by war dialing the server (dialing phone numbers in a pattern such as 617-555-0001 through 617-555-9999), and tracking
which numbers answer with a modem.This very nearly starts World War III.
Looking back on this movie two decades later, it is funny how easy they made it
look to hack into a “secure” system.
The truth is that although technology has made huge strides in the past 20
years, there are still many holes in remote access security. Remote Access Service
(RAS) servers, Network Access Servers (NAS),Virtual Private Networks (VPNs),
authentication servers such as RADIUS,TACACS, and TACACS+, and other
technologies have been designed to keep out unauthorized users.
It is the responsibility of the security professional to ensure that everything
has been done to secure their networks. Security professionals must find the balance between offering users the ability to work from remote locations, and
ensuring that the network is protected. One area of remote access that has grown
exponentially is wireless networking. Let’s begin our discussion of remote access
security by discussing this growing arena.
In Chapter 4, users will become familiar with wireless local area networks
(WLANs) and the Institute of Electrical and Electronics Engineers (IEEE) 802.11
standard for wireless networking. It is so simple to implement wireless networking technology, that most novice users can install it themselves.What most
novice users do not realize is that as soon as they transmit their first piece of data
across their new network they have opened up a can of worms!
This is where the 802.1x standard enters. 802.1x is a Wired Equivalent
Privacy (WEP) protocol designed to enhance the level of security offered on a
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The Dangers of a Wide-Open WLAN
My first experience with wireless security issues was while I was working
as a networking consultant at a boarding school. A staff member set up
an access point on the school’s network. Consequently, a student working
on a laptop (with wireless NIC installed) was able to access the school’s
network! The caller’s concern was that if one student accessed the WLAN,
how many others have? The message is: know your network, know what
is attached to it, and make sure you have security measures in place to
protect it.
When a wireless user (or supplicant) wants to access a wireless network, 802.1x
forces them to authenticate to a centralized authority called an authenticator.
802.1x uses the Extensible Authentication Protocol (EAP) for passing messages
between the supplicant and the authenticator.When communication begins, the
authenticator places the user into an unauthorized state.While in this unauthorized
state, the only messages that can be transmitted are EAP start messages. At this
point, the authenticator sends a request to the user asking for their identity.The
client then returns their identity to the authenticator, which in turn forwards it
to the authentication server, which is running an authentication service such as
The argument can be made that wireless technologies are part of a local
area network (LAN), not a remote access technology. For the Security+
exam, think of wireless as being a “remote access” because there is no
direct physical (cabled) connection from a laptop or personal digital
assistant (PDA).
The authentication server authenticates the user and either accepts or rejects
the user based on the credentials provided. If the user provides the correct credentials, the authenticator changes the user’s state to “authorized” thus allowing
the user to move freely within the WLAN. Figure 3.1 depicts how the authentication process works.
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Figure 3.1 The 802.1x Authentication Process
Access Point
Wireless User
1. Authenticator places user in
an unauthorized state.
4. Authenticator forwards credentials
to authentication server.
2. Authenticator sends request
for user credentials.
5. Authentication server verifies
credentials. If credentials are valid,
allows users onto WLAN.
3. User responds with their
username and password.
EAP was originally defined under RFC 2284 and then redefined under the
Internet Engineering Task Force (IETF) Internet draft dated September 13, 2002.
EAP is an authentication protocol designed to support several different authentication mechanisms. It runs directly over the data link layer and does not require
the use of Internet Protocol (IP).
You can read more on the IETF Internet draft on EAP at
EAP comes in several different forms:
EAP over IP (EAPoIP)
Message Digest Algorithm/Challenge-Handshake Authentication
Protocol (EAP-MD5-CHAP)
Transport Layer Security (EAP-TLS)
Tunneled Transport Layer Security (EAP-TTLS)
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Light Extensible Authentication Protocol (LEAP) Cisco
Each form of EAP has its own characteristics, but for the purpose of the
Security+ exam you will only need to know what it is and its different formats.
802.1x is not without its share of vulnerabilities.Wireless Encryption Protocol
(WEP) uses a stream cipher known as the RC4 encryption algorithm. A stream
cipher operates by expanding a short key into a key stream.The sender combines
the key stream with the original message (known as the plaintext message) to produce ciphertext.The receiver has a copy of the same key, and uses it to generate an
identical key stream.The receiver then applies the key to the ciphertext, and
views the plaintext message.
Ciphers will be covered in greater detail in Chapter 9.
This mode of operation makes stream ciphers vulnerable to attacks. If an
eavesdropper intercepts two ciphertext encrypted with the same key stream, they
can obtain the eXclusive OR (XOR) of the two plaintexts. Knowledge of this
XOR can enable statistical attacks to recover the plaintexts.
One particular vulnerability was discovered by the Fluhrer, Mantin, and
Shamir group.The attack (known as the Fluhrer, Mantin, and Shamir attack), is
exploited because of how keys are passed between the mobile user and the access
point.The Fluhrer, Mantin, and Shamir attack involves guesswork and creativity,
since you have to guess the first byte of plaintext data being transmitted.When
data is encrypted before transmission, a piece of data called the initialization
vector (IV) is added to the secret key. Fluhrer, Mantin, and Shamir discovered that
the IV was transmitted in the clear, and they recovered the 128-bit secret key
used in a production network.
There are also tools available for download on the Internet, which can be
used to exploit the vulnerabilities of WEP.Two of the most common tools are
AirSnort and WEPCrack.
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AirSnort ( or
is a tool used to recover encryption keys during the authentication process.
AirSnort passively monitors transmissions and recreates the encryption key once it
has collected enough packets. For AirSnort to be effective, it must collect between 5
and 10 million packets. Collecting this many packets takes time. In an 8-hour day,
the average person produces approximately 250,000 packets.To collect the minimum of 5 million packets would take about three weeks. Once AirSnort has
enough packets, it recreates the encryption password in less than one second.
While AirSnort is known for capturing packets and recreating secret keys,
WEPCrack simply breaks the secret keys.WEPCrack was the first software
package able to break the security of WEP technology.WEPCrack is available for
download at:
Damage & Defense…
Protecting Against AirSnort and WEPCrack
Although both of these tools pose serious risk to a wireless network, they
are easily detected. Most Intrusion Detection Systems (IDSs) are able to
detect attacks on wireless networks. IDS solutions are available in both
commercial and freeware versions. The Cisco IDS 4200 series is a great
commercial hardware solution, starting around $6000. If this price is high
for your organization, there are other free IDS solutions, such as Snort
( that are just as effective, and almost as easy to implement. Whether commercial or freeware, the key is to make sure the IDS is
up-to-date and functional. Implementing technologies such as VPNs,
Secure Internet Protocol (IPSec), Secure Sockets Layer (SSL), and Kerberos,
also greatly increase the reliability of the wireless network.
Wireless technologies will be covered in greater detail in Chapter 4.
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A VPN provides users with a secure method of connectivity through a public internetwork such as the Internet. Most companies use dedicated connections to connect to remote sites, but when users want to send private data over the Internet
they should provide additional security by encrypting the data using a VPN.
When a VPN is implemented properly, it provides improved wide-area security, reduces costs associated with traditional WANs, improves productivity, and
improves support for users who telecommute. Cost savings are twofold. First,
companies save money by using public networks (such as the Internet) instead of
paying for dedicated circuits (such as point-to-point T1 circuits) between remote
offices. Secondly, telecommuters do not have to pay long-distance fees to connect
to RAS servers.They can simply dial into their local Internet Service Provider
(ISPs) and create a virtual tunnel to their office. A tunnel is created by wrapping
(or encapsulating) a data packet inside another data packet and transmitting it over
a public medium.Tunneling requires three different protocols:
Carrier Protocol The protocol used by the network (IP on the
Internet) that the information is traveling over
Encapsulating Protocol The protocol (PPTP, L2TP, IPSec, Secure
Shell [SSH]) that is wrapped around the original data
Passenger Protocol The original data being carried
For the Security+ exam you need to remember the three protocols used
in a VPN tunnel. Think of a letter being sent through the mail: the letter
is the passenger, which is encapsulated in an envelope, and addressed in
a way that the carrier—the post office—can understand.
Essentially, there are two different types of VPNs: site-to-site and remote access.
Site-to-Site VPN
Site-to-site VPNs are normally established between corporate offices that are separated by a physical distance extending further than normal LAN media covers.
VPNs are available in software (such as Windows VPN available on Windows NT
and Windows 2000) and hardware (firewalls such as Nokia/Checkpoint and
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SonicWALL) implementations. Generally speaking, software implementations are
easier to maintain. However, hardware implementations are considered more
secure, since they are not impacted by OS vulnerabilities. For example, Company
XYZ has offices in Boston and Phoenix. As seen in Figure 3.2), both offices connect to the Internet via a T1 connection.They have implemented VPN-capable
firewalls in both offices, and established an encryption tunnel between them.
Figure 3.2 A Site-To-Site VPN Established Between Two Remote Offices
Firewall with VPN tunnel
Firewall with VPN tunnel
The Internet
Local Area Network
Local Area Network
The first step in creating a site-to-site VPN is selecting the protocols to
be used. Common protocols associated with VPN are PPTP, L2TP, SSH, and
IPSec. PPTP and L2TP are used to establish a secure tunnel connection between
two sites.
Once a tunnel is established, encryption protocols are used to secure data
passing through the tunnel.As data is passed from one VPN to another, it is encapsulated at the source and unwrapped at the target.The process of establishing the
VPN and wrapping and unwrapping the data is transparent to the end-user.
Most commercially available firewalls come with a VPN module that can be
set up to easily communicate with another VPN-capable device. Microsoft has
implemented site-to-site VPN tools on the Windows 2000 platform using either
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Damage & Defense…
Routing and Remote Access Service (RRAS) or the newest rendition of
Microsoft’s Proxy server, Microsoft ISA Server 2000.
Whichever product or service is chosen, it is important to ensure that each
end of the VPN is configured with identical protocols and settings.
Issues With Site-To-Site VPNs
Keeping communications secure while transferring data over a public
medium (such as the Internet) is only part of securing remote sites via
VPN. A common mistake that network security professionals make is setting up a site-to-site VPN, then disregarding other types of security.
Access control (such as Windows NTFS permissions) should also be implemented so that users on remote networks cannot access the local network freely. The same policies and restrictions that are in place at the
main office should also be in place at the remote office. In some cases,
this can be difficult—especially if the remote office is another company,
say a vendor or a partner. Your IT policies may vary from those of your
vendor or partner. If this is the case, both parties should come to some
agreement on policies that will apply to both. (Policies are covered in
detail in Chapter 12).
Remote Access VPN
A remote access VPN, known as a private virtual dial-up network (PVDN), differs from a site-to-site VPN in that end users are responsible for establishing the
VPN tunnel between their workstation and their remote office. An alternative to
connecting directly to the corporate VPN is connecting to an enterprise service
provider (ESP) that ultimately connects them to the corporate VPN.
In either case, users connect to the Internet or an ESP through a point of
presence (POP using their particular VPN client software (see Figure 3.3). Once
the tunnel is set up, users are forced to authenticate with the VPN server, usually
by username and password.
A remote-access VPN is a great solution for a company with several
employees working in the field.The remote-access VPN allows these employees
to transmit data to their home offices from any location. RRAS offers an easy
solution for creating a remote access VPN.
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Figure 3.3 A Remote-Access VPN Solution Using Regular Internet POPs
Analog Modem
Cable Modem
VPN Tunnel
DSL Modem
Local Area Network
Server Server
As noted in the discussion about 802.1x, users need a centralized entity to handle
authentication. Initially, RADIUS was created by Livingston Enterprises to
handle dial-in authentication.Then its usage broadened into wireless authentication and VPN authentication. RADIUS is the most popular of all the access control, authentication, and auditing (AAA) servers, including TACACS,TACACS+,
and DIAMETER. An RAS must be able to authenticate a user, authorize the
authenticated user to perform specified functions, and log (account for) the
actions of users for the duration of the connection.
When users dial into a network, RADIUS is used to authenticate usernames
and passwords. A RADIUS server can either work alone or in a distributed environment (known as distributed RADIUS) where RADIUS servers are configured
in a tiered (hierarchical) structure.
In a distributed RADIUS environment, a RADIUS server forwards the
authentication request to an enterprise RADIUS server using a protocol called
proxy RADIUS.The enterprise RADIUS server handles verification of user credentials and responds back to the service provider’s RADIUS server.
One of the reasons tha RADIUS is so popular is that it supports a number of
protocols including:
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Point-to-Point Protocol (PPP)
Password Authentication Protocol (PAP)
Challenge Handshake Authentication Protocol (CHAP)
Authentication Process
RADIUS authentication consists of five steps:
1. Users initiate a connection with an ISP RAS or corporate RAS.
Once a connection is established, users are prompted for a username
and password.
2. The RAS encrypts the username and password using a shared secret, and
passes the encrypted packet to the RADIUS server.
3. The RADIUS server attempts to verify the user’s credentials against a
centralized database.
4. If the credentials match those found in the database, the server responds
with an access-accept message. If the username does not exist or the password is incorrect, the server responds with an access-reject message.
5. The RAS then accepts or rejects the message and grants the appropriate
See Chapter 9 for a discussion of shared secrets and other cryptography
terms and concepts.
Certain “flavors” of RADIUS servers and Web servers can be compromised by
buffer overflow attacks. A buffer overflow attack occurs when a buffer is flooded
with more information than it can hold.The extra data overflows into other
buffers, which may be accessible to hackers.
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Head of the Class…
Sometimes You Just Get Lucky…
Once we lock a door, curiosity leads someone to try and see what is
behind it. This is the “cat-and-mouse game” that is network security.
Many vulnerabilities found in network security are discovered by hackers
trying to access systems they are not authorized to use. Sometimes,
“white hat” hackers—security consultants hired to test system vulnerabilities—discover vulnerabilities in their testing. Unlike “black hat” hackers,
whose intentions are malicious, (and “gray hat” hackers whose intentions
are not malicious), white hat hackers generally work with companies to
fix issues before they become public knowledge. In 2001, RADIUS bufferoverflow attacks were discovered by Internet Security Systems while
testing the vulnerabilities of the wireless networks.
RADIUS is not the only centralized RAS.TACACS is also used in authenticating remote users.TACACS has gone through three major “generations”,
TACACS, XTACACS, and TACACS+. For the Security+ exam, you need to
know about TACACS and TACACS+; however, for continuity purposes, XTACACS will also be discussed.
As stated previously,TACACS is the “old man” of centralized remote access
authentication.TACACS was first developed during the days of ARPANET,
which was the basis for the Internet.TACACS is detailed in RFC 1492, which
can be found at Although
TACACS offers authentication and authorization, it does not offer any
accounting tools. As mentioned earlier, a good RAS must fit all the criteria of the
AAA model. Similar to RADIUS, a dial-up user connects to a RAS that prompts
the user for their credentials.The credentials are then passed to the TACACS
server, which either permits or denies access to the network.
Initially,TACACS utilized the User Datagram Protocol (UDP) to handle
communications.The problem with UDP is that it does not provide packet
sequencing.Therefore, services such as TACACS must make sure that the entire
message has arrived and is intact.To overcome this shortcoming, Cisco Systems
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developed Extended TACACS (or XTACACS). In XTACACS, the transport protocol was changed from UDP to Transmission Control Protocol (TCP), ensuring
that messages would be divided into packets and reassembled when received at
the intended destination. XTACACS was a step in the right direction, but it did
not provide all of the functionality needed for a centralized remote access
authentication solution.
The previous information on XTACACS is provided for historical background only. XTACACS is rarely deployed in modern installations, and is
not a topic of the Security+ exam.
Cisco decided to develop a proprietary version of TACACS known as TACACS+.
The driving factor behind TACACS+ was to offer networking professionals the
ability to manage all remote access components from a centralized location.
TACACS+ is also credited with separating the AAA functions.TACACS+ is considered proprietary because its packet formats are completely different from those
in TACACS or XTACACS, making TACACS+ incompatible with previous versions. Unlike previous versions of TACACS that used one database for all AAA,
TACACS+ uses individual databases for each.TACACS+ was the first revision to
offer secure communications between the TACACS+ client and the TACACS+
server. Like XTACACS,TACACS+ uses TCP as its transport.TACACS+ continues to gain popularity because it is easy to implement and reasonably priced.
Make sure you understand the difference between TACACS and
TACACS+. The most important thing to remember is that TACACS uses
UDP as its transport protocol while TACACS+ uses TCP. Also, TACACS+
is a proprietary version owned by Cisco.
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One of the biggest complaints regarding TACACS+ is that it does not offer protection against replay attacks. Replay attacks occur when a hacker intercepts an
encrypted packet and impersonates the client using the information obtained
from the decrypted packet.
Packets must have the correct sequence number.When files are sent over a
network using TCP/IP, they are split into segments suitable for routing.This is
known as packet sequencing. At the receiving end, the TCP/IP organizes the file
into its original format before it was sent. Packet sequencing (along with time
stamping) is the general method of preventing replay attacks; however,TACACS+
sessions always start with a sequence number of 1. If a packet cannot be reorganized in the proper sequence at the receiving end, the entire message (or file) is
unusable. Other common weaknesses of TACACS+ include:
Head of the Class…
Birthday Attacks The pool of TACACS+ session IDs is not very large,
therefore, it is reasonable that two users could have the same session ID
Buffer Overflow Like RADIUS,TACACS+ can fall victim to buffer
overflow attacks.
Packet Sniffing The length of passwords can be easily determined by
“sniffing” a network.
Lack of Integrity Checking A attacker can alter accounting records
during transmission because the accounting data is not encrypted during
Decisions To Be Made: RADIUS versus TACACS+
Both RADIUS and TACACS+ get the job done. Both provide exceptional
user authentication, both are transparent to the end user, and both have
their share of problems.Specifically, the two issues that differentiate them
are separation of duties and the need for reliable transport protocols.
In terms of separation of duties, RADIUS lumps all of the AAA functions
into one user profile, whereas TACACS+ separates them.
We know that TACACS+ uses TCP for its transport protocol. Both
RADIUS and TACACS, on the other hand, use UDP. If reliable transport and
sensitivity to packet disruption is important, TACACS+ is the better fit.
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As mentioned earlier, there are several standard tunneling protocol technologies
in use today.Two of the most popular are PPTP and L2TP, which are Layer 2
(Data Link Layer) encapsulation (tunneling) protocols using ports 1723 and 1701,
respectively. However, PPTP and L2TP do use different transport protocols:
PPTP uses TCP and L2TP uses UDP.
Create a mental grid for remembering the difference between PPTP and
L2TP. PPTP | 1723 | TCP, L2TP | 1701 | UDP.
PPTP’s popularity is mainly because it was the first encapsulation protocol on the
market, designed by engineers at Microsoft.Thus it is supported in all Windows
OSs (L2TP is not supported in Windows 9x/ME or NT 4.0, although these OSs
(except Windows 95) can create L2TP connections using the Microsoft L2TP/
IPSec VPN client add-on. PPTP establishes point-to-point connections between
two computers by encapsulating the PPP packets being sent. Although PPTP has
helped improve communications security, there are several issues with it.
PPTP encrypts the data being transmitted, but does not encrypt the
information being exchanged during negotiation. In Microsoft implementations, Microsoft Point-to-Point Encryption (MPPE) protocol is
used to encrypt the data.
PPTP is protocol-restrictive, meaning it will only work over IP networks
PPTP cannot use the added benefit of IPSec
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Head of the Class…
PPTP Clients
When you say PPTP to most IP professionals, the first thing that they think
of is Microsoft. This is typically because has Microsoft played such a large
role in the development of PPTP, but also because of the fact that
Microsoft was one of the first to implement PPTP in an operating system,
specifically Windows NT 4.0. Besides Microsoft OSs, PPTP clients are also
available for UNIX, Linux, and Macintosh OSs. You can find a great opensource (UNIX/Linux) VPN client at while lists some of the
clients available for various Mac OS versions. Since PPTP is an industry
standard, there is not a compatibility issue between the different versions.
Microsoft has made it easy to create VPN client connections in their
newer OSs. In Windows 2000, users can create VPN connections as easily
as they can create dial-up connections to the Internet. Let’s walk through
the steps of creating a VPN client connection.
1. Click Start| Settings| Network and Dial-up Connections.
2. Click the Make New Connection icon.
3. At the Network Connection Wizard screen (Figure 3.4), click Next.
Figure 3.4 Network Connection Wizard Welcome Screen
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4. Select Connect to a private network through the Internet
(Figure 3.5) and click Next.
Figure 3.5 Selecting the Network Connection Type
5. When prompted to select a public network, select Do not dial
the initial connection and click Next.
6. Next, you will be prompted to select the destination address
(Figure 3.6). Type and click Next.
Figure 3.6 Selecting the Destination Address
7. On the Connection Availability screen, select For all users and
click Next.
8. Click Next again.
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9. Name the VPN connection and click Finish to complete the
wizard setup.
10. To begin the VPN connection, double-click on the new icon.
As with TACACS+, Cisco believed they could design a better tunneling protocol, which was the creation of the Layer 2 Forwarding (L2F) protocol.
Unfortunately, L2F was not much better than PPTP. Specifically, L2F provided
encapsulation (tunneling) but it did not encrypt the data being encapsulated.
To use the features of both PPTP and L2F, L2TP was developed through a
joint venture between Microsoft and Cisco. L2TP was a major improvement, but
still did not offer encryption.To remedy this, L2TP was designed to use IPSec for
encryption purposes.The differences between PPTP and L2TP that you need to
know for the Security+ exam are:
L2TP requires IPSec in order to offer encryption.
L2TP offers RADIUS and TACACS+, where PPTP does not.
L2TP is often implemented as a hardware solution, where PPTP is not.
L2TP can run on top of protocols such as IP, IPX, and SNA, where
PPTP can work only on IP networks.
Using L2TP with IPSec provides per-packet data origin authentication
(proof that the data was sent by an authorized user), data integrity
(proof that the data was not modified in transit), replay protection (prevention from resending a stream of captured packets), and data confidentiality (prevention from interpreting captured packets without an
encryption key).
L2TP/IPSec connections require two levels of authentication: computerlevel authentication using certificates or pre-shared keys for IPSec sessions,
and user-level authentication using PPP authentication protocol for the
L2TP tunnel.
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Punching a Hole in the Firewall
One of the most common mistakes made when setting up VPN tunnels
using PPTP or L2TP is forgetting to allow the associated ports through the
firewall. Make sure the appropriate ports are open: port 1723 for PPTP
and port 1701 for L2TP. For additional security, most (if not all) firewall
packages will allow you to specify the source and destination within their
rule base. If this is the case, you can further lock down VPN access by
specifying the IP addresses (or subnets) of those users you want grant
PPTP or L2TP access. Further more, you can also specify the destination IP
address for the VPN users. This can be useful if you have different VPN
hosts on your network, and you only want to allow VPN users access to
certain VPN tunnels.
Some advantages of the L2TP/IPSec combination over PPTP are:
IPSec provides per-packet data origin, data integrity, replay protection,
and data confidentiality. In contrast, PPTP only provides per-packet data
L2TP/IPSec connections require two levels of authentication: computerlevel authentication and user-level authentication.
PPP frames exchanged during user-level authentication are never sent
unencrypted because the PPP connection process for L2TP/IPSec
occurs after the IPSec security association (SA) is established.
Make sure you understand the differences between PPTP and L2TP
including pros, cons, and protocols related to each.
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SSH is a cryptographically secure replacement for standard Telnet, rlogin, rsh, and
rcp commands. SSH consists of both a client and a server that use public key
cryptography to provide session encryption. It also provides the ability to forward
arbitrary ports over an encrypted connection.
SSH has received wide acceptance as the secure mechanism for access to
remote systems interactively. SSH was conceived and developed by Finnish developer,Tatu Ylonen.When the original version of SSH became a commercial venture, the license became more restrictive. A public specification was created,
resulting in development of a number of versions of SSH-compliant client and
server software that do not contain the restrictions (most significantly, those that
restrict commercial use).
SSH deals with the confidentiality and integrity of information being passed
between a client and host. Since programs such as Telnet and rlogin transmit
usernames and passwords in cleartext, sniffing a network is easy. By beginning an
encrypted session before the username and password are transmitted, confidentiality is guaranteed. SSH protects the integrity of the data being transmitted by
the use of session keys.The client keeps a list of user keys for servers with which it
previously established secure sessions. If the key matches, the secure session is
established and the integrity of the data being transmitted is confirmed. Using
SSH helps protect against different types of attacks including packet sniffing, IP
spoofing, and manipulation of data by unauthorized users.
How SSH Works
When a client wants to establish a secure session with a host, the client initiates
communication by requesting an SSH session. Once the server receives the
request from the client, the two perform a handshake, which includes the verification of the protocol version. Next, session keys are exchanged between the client
and server. Once session keys have been exchanged and verified against a cache of
host keys, the client can begin the secure session. Figure 3.7 depicts the SSH
authentication process.
The IPSec protocol, as defined by the IETF, is “a framework of open standards
for ensuring private, secure communications over Internet Protocol networks,
through the use of cryptographic security services.”This means that IPSec is a set
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of standards used for encrypting data so that it can pass securely through a public
medium, such as the Internet. Unlike other methods of secure communications,
IPSec is not bound to any particular authentication method or algorithm, which
is why it is considered an “open standard.” Also, unlike older security standards
that were implemented at the application layer of the OSI model, IPSec is implemented at the network layer.
Figure 3.7 SSH Communications are Established in Four Steps
Wireless User
1. Client requests SSH session with host.
2. Client and host perform handshake.
3. Client and host exchange and verify session keys.
4. Client begins secure session.
Remember that IPSec is implemented at the network layer, not the application layer.
The advantage to IPSec being implemented at the network layer (versus the
application layer) is that it is not application-dependent, meaning users do not
have to configure each application to IPSec standards. IPSec also has the ability to
be implemented in two different modes of operation:
Transport Mode IPSec implemented in transport mode (Figure 3.8)
specifies that only the data (or payload) be encrypted during transfer.The
advantage to this is speed—since the IP headers are not encrypted, the
packets are smaller.The downside to transport mode is that a hacker can
sniff the network and gather information about end parties.Transport
mode is used in host-to-host VPNs.
Tunnel Mode Unlike transport mode where only the data is
encrypted, in tunnel mode (Figure 3.9) both the data and the IP headers
are encrypted.The advantage is that neither the payload nor any information about end parties can be sniffed.The disadvantage is speed, since
the size of the encrypted packet increases.Tunnel mode is used in hostto-gateway or gateway-to-gateway VPNs.
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Figure 3.8 Using IPSec in Transport Mode Only Encrypts the Data
IP Header
Data Payload
Figure 3.9 Using IPSec in Tunnel Mode Encrypts Both the Data and
IP Headers
IP Header
Data Payload
IPSec is made up of two separate security protocols. Authentication header
(AH) protocol is responsible for maintaining the authenticity and integrity of the
payload. AH authenticates packets by signing them, which ensures the integrity of
the data. Since the signature is specific to the packet being transmitted, the
receiver is assured of the data source. Signing packets also provides integrity, since
the unique signature prevents the data from being modified. Encapsulating security payload (ESP) protocol also handles the authenticity and integrity of payloads, but also adds the advantage of data confidentiality through encryption. AH
and encapsulating security payload can be used together or separately. If used
together, the entire packet is authenticated.
An easy way to remember the difference between AH and ESP is to use
the E in ESP to remember “Encryption.”
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IPSec Authentication
To ensure the integrity of data being transmitted using IPSec, there has to be a
mechanism in place to authenticate end users and manage secret keys.This mechanism is called Internet Key Exchange (IKE). IKE is used to authenticate the two
ends of a secure tunnel by providing a secure exchange of a shared key before
IPSec transmissions begin.
For IKE to work, both parties must use a password known as a pre-shared key.
During IKE negotiations, both parties swap a hashed version of a pre-shared key.
When they receive the hashed data, they attempt to recreate it. If they successfully recreate the hash, both parties can begin secure communications.
IPSec also has the ability to use digital signatures. A digital signature is a certificate signed by a trusted third party called a certificate authority (CA) that
offers authentication and nonrepudiation, meaning the sender cannot deny that the
message came from them.Without a digital signature, one party can easily deny
they were responsible for messages sent.
Although public key cryptology (“User A” generates a random number and
encrypts it with “User B’s” public key, and User B decrypts it with their private key
[described in Chapter 10]) can be used in IPSec, it does not offer nonrepudiation.The most important factor to consider when choosing an authentication
method is that both parties must agree on the method chosen. IPSec uses an SA to
describe how parties will use AH and encapsulating security payload to communicate.The security association can be established through manual intervention or
by using the Internet Security Association and Key Management Protocol
(ISAKMP).The Diffie-Hellman key exchange protocol, described in detail in
Chapter 9, is used for secure exchange of pre-shared keys.
The advantage to using IKE over the manual method is that the SA can be established when needed, and can be set to expire after a certain amount of time. RFC
2408 describes ISAKMP as a framework for establishing, negotiating, modifying,
and deleting security associations between two parties. By centralizing the management of security associations, ISAKMP reduces the amount of duplicated functionality within each security protocol. ISAKMP also reduces the amount of time
required for communications setup, by negotiating all of the services at once.
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Head of the Class…
Deciding on Encryption and Authentication Methods
As mentioned earlier, IPSec is a general framework for secure communications. It does not require a particular encryption or authentication
method to function. Some of the more common authentication hashes
are MD5, SHA, HMAC, and HAVAL. Likewise, some of the more common
encryption methods include DES, 3DES, and IDEA. (These algorithms will
be discussed further in Chapter 9.) When the parties decide on the type
of authentication and encryption to be used, they establish an SA
between them. Without an SA, communications cannot be established.
For the Security+ exam remember the three Is: IPSec, IKE, and ISAKMP.
So far, we have discussed the vulnerabilities specific to the different types of RAS,
however, there are also many vulnerabilities that are common to all methods.
Some of the more common types are eavesdropping (sniffing), data modification,
identity spoofing, and user error.
Eavesdropping, is simply attaching to a network in a manner that allows you to
“hear” all the traffic being passed over the wire.This is known as a passive attack,
since data is observed but not modified.
A sniffer can be attached to a network to pick up information that is passed
in cleartext. Protocols such as Telnet, rlogin, and POP3 are often victim to
sniffing since usernames and passwords are sent in cleartext. Sniffing is also considered a passive attack since the data is observed but not modified.
Data Modification
Data modification is just as it sounds. Data is intercepted by a third party, modified,
and sent to the party originally intended to receive it.This type of attack is known
as a man-in-the-middle (MITM) attack. A good example of this is a program called
sshmitm. Sshmitm implements a man-in-the-middle attack against SSH-secured
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traffic by listening to traffic between a client and host. Sshmitm intercepts the
requests from the client and replies with a fake server response. It then takes the
original request from the client and forwards it to the host, and then intercepts the
response from the host. At this point, the attacker has the ability to send messages to
the client and server as if they were from the expected originator.
As discussed in the section on IPSec, digital signatures can be used to remedy
data modification because they offer nonrepudiation. Nonrepudiation is a way to
guarantee that senders cannot deny they sent a message. Nonrepudiation also
means that recipients cannot deny receiving a message. Additional details
regarding nonrepudiation are found in Chapter 9.
Identity Spoofing
Since information about senders and receivers is stored in IP packet headers,
it is easy to construct packets to look like they came from a different sender.
Normally, hackers will listen on a public network (such as the Internet) and
examine packets until they believe they have found a trusted host that is allowed
to pass data through a firewall. Once a hacker finds this address, they can begin
creating packets and sending them to a target network.
User Vulnerabilities and Errors
Users who write passwords on sticky notes and put them on their monitor, leave
their workstations unlocked, or allow other people to watch while they enter
usernames and passwords, are the easiest victims for hackers. It is the security professional’s responsibility to educate end users and perform due diligence to ensure
these types of user errors are at a minimum. For the Security+ exam, you need to
know that the best way to keep these types of attacks to a minimum is to educate
users of the consequences.
Administrator Vulnerabilities and Errors
One of the biggest mistakes security professionals make is not fixing known security issues with remote access methods. Keeping up with security patches, hardening RASs, and being aware of flaws in different remote access methods is vital.
Most vendors have Web sites where they post patches for their products.
Larger companies such as Microsoft, Sun, Oracle, and Cisco also have e-mail
notification systems that notify users when new problems are discovered, and
what actions to take to remedy them.There are also several white papers in existence that explain the steps used to harden OSs. Hardening an OS simply means
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that all of the applications, services, and protocols not required for the operation
of a host will be disabled or completely removed. Any host that is accessible to
the Internet (or any public access) should be hardened prior to production.
Since users will not likely be able to track and fix vulnerabilities daily, they
should make sure to review their core applications (Windows, Linux, Microsoft
Office, SQL, Oracle, etc) monthly to see if there are new patches being released.
The top ten items to remember about RAS:
1. 802.1x uses EAP for passing messages between the supplicant
and the authenticator.
2. VPN tunneling requires a carrier protocol, an encapsulation protocol, and a passenger protocol.
3. There are two types of VPNs: site-to-site and remote access.
4. Know your ports (PPTP, L2TP, SSH).
5. Know your transport protocols (RADIUS and TACACS use UDP,
TACACS+ uses TCP, etc).
6. TACACS+ was the first revision to offer secure communications
between the TACACS+ client and the TACACS+ server.
7. SSH is a cryptographically secure replacement for standard
Telnet, rlogin, rsh, and rcp commands.
8. Know the steps SSH uses to establish secure connections.
9. IPSec uses IKE to manage keys. A SA can be established either
manually or through the use of ISAKMP.
10. Understand what types of vulnerabilities apply to all items
(802.1x, VPN, RADIUS, etc.) as well as remote access as a whole.
E-mail Security
Before continuing, let’s look at how e-mail is sent and where it goes.The term
e-mail is short for electronic mail and is, quite simply, an electronic letter that is sent
over a network. Mail clients are programs used to create, send, receive, and view
e-mails. Most current mail clients allow messages to be formatted in plain text or
Hypertext Markup Language (HTML).This means that e-mails can be simple
text or they can include formatted text, images, sounds, backgrounds, and other
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When sending e-mail messages, many stops occur along the way to its destination.The first stop is an e-mail server, which, in Figure 3.10, belongs to an
ISP. An e-mail server can also be a corporate mail server running applications
such as Microsoft Exchange, Lotus Notes, or Sendmail.When the message reaches
the e-mail server, the e-mail server looks at the address where the message is
being sent.This e-mail address is in the form of mailbox@domain (for example, Note that it ends by denoting the top-level domain
(such as .com, .net, .org, .ca, and so on). For example, if an e-mail address is, the e-mail server sees that the top-level domain is
Figure 3.10 How E-mail Gets from Sender to Recipient
.com Server
Name Server
Sender ISP
Mail Server
Receiver ISP
Mail Server
E-mail Receiver
E-mail servers use a number of different servers to locate the IP address of a
recipient’s domain. An IP address is a unique number that identifies computers on
the Internet, to ensure messages get to the correct destination. Because mybuddy@ is a .com domain, the ISP’s server contacts a Domain Name
System (DNS) server authorized to find IP addresses of name servers in the .com
domain.The e-mail server then sends out several requests to the name servers to
find the IP address of the recipient’s domain ( DNS
server looks up the mail exchange (MX) record for, and
responds to the e-mail server with the IP address. After the e-mail server has the
IP address, it sends the message.When the e-mail server at gets the
e-mail message, it will be placed in the recipient’s mailbox, based on the mailbox
account name.
To make the e-mail process clearer, think of e-mailing in terms of sending
physical interoffice mail from one department to another. Mail is given to a
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delivery person who looks at the envelope’s destination. From the address, the
delivery person knows that the recipient is on the third floor.The delivery person
goes to the third floor and asks someone where the specific department is.When
the department is found, the delivery person contacts the department to find
where the department’s mailroom is. Once in the mailroom, the delivery person
places the message in the recipient’s mailbox.To deliver the mail, several steps had
to be taken to locate the recipient.
In terms of e-mail, the process is more complicated. E-mail is broken into
smaller pieces of data called packets, and the packets are routed through numerous
devices called routers. Routers connect networks (or subnets) together and are
used to find the fastest route between two networks. Individual packets making
up one e-mail message may travel along different routes before reaching their
destination where an e-mail server puts the packets back together in their original form using sequencing information in the packet headers.
While this may seem like a long and arduous process it actually takes very
little time.
To protect yourself and your data, use encryption. Encryption scrambles the contents of a message and its attachments, and then puts the contents back together on
the recipient’s end. Anyone attempting to view the data in between will be unable
to decipher the content. Secure/Multipurpose Internet Mail Extensions (S/MIME)
and PGP are two excellent ways to protect e-mail. For the Security+ exam, you
need to understand both S/MIME and PGP. However, there are other e-mail
encryption products including HushMail ( and ShyFile
( available.There are also companies who offer secure e-mail services, such as SecureNym (
It is extremely important to encrypt your e-mail. Services like Hotmail,
Yahoo!, Excite, and others reserve the right to view e-mail messages
stored in any accounts on which they are providing services at no
charge. Courts have upheld the rights of employers to monitor employee
e-mails, and public employees’ e-mail can be accessed by the press under
the Freedom of Information Act.
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Before discussing S/MIME, its parent product, Multi-Purpose Internet Mail
Extensions (MIME) should be discussed. MIME is an extension of Simple Mail
Transfer Protocol (SMTP) that provides the ability to pass different kinds of data
files on the Internet, including audio, video, images, and other files as attachments.The MIME header is inserted at the beginning of the e-mail, and then the
mail client (such as Microsoft Outlook) uses the header to determine which program will be used on the attached data. For example, if an audio file is attached
to an e-mail, Outlook will look at the file associations for audio files and use an
audio player, such as Winamp, to open the file.
RFC 1847 and RFC 2634 offer additional information about multi-part/
signed MIME and the specifications for S/MIME.
Since MIME does not offer any security features, developers at RSA Security
created S/MIME. S/MIME, like MIME, is concerned with the headers inserted
at the beginning of an e-mail. However, instead of determining the type of program to use on a data file, S/MIME looks to the headers to determine how data
encryption and digital certificates must be handled. Messages are encrypted using
a symmetric cipher (method of encrypting text), and a public-key algorithm is
used for key exchange and digital signatures. S/MIME can be used with three
different symmetric encryption algorithms: DES, 3DES, and RC2. Free versions
of S/MIME are available for Microsoft Outlook Express as well as for Netscape
Communicator. However, newer versions of Outlook Express and Microsoft
Outlook come with S/MIME installed.
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Head of the Class…
Screensaver versus S/MIME
Like S/MIME, PGP is encryption software used to encrypt e-mail messages and
files. Freeware and commercial versions of PGP are available on the Web, and also offers a free version. A commercial version can be downloaded from the PGP Corporation at the software is
installed, plug-ins for Microsoft Outlook, Outlook Express, ICQ, Netscape, and
other programs can be installed, allowing users to encrypt, decrypt, and sign messages sent through these e-mail packages.
Head of the Class…
Hacking tools come in all shapes and sizes, but this has to be one of the
strangest. A screensaver was developed that could crack 40-bit encryption
S/MIME keys (encryption “strength” is based on the number of bits in the
key) in less than one hour. At the time that this vulnerability was discovered,
it took the screensaver a little more than a month to crack the keys using a
first generation Intel Pentium processor running at 166Mhz. Bruce Schneier
developed the screensaver to combat the S/MIME vendors who were marketing their software as a “secure solution.” This has since been repaired in
newer versions, but it shows the level of creativity that hackers possess. To
learn more about this vulnerability, see
technology/0,1282,7220,00.html. You can also download the screensaver
cracker at to test it yourself.
A Note About Phil Zimmermann, the Creator of PGP
Philip R. Zimmermann created PGP in 1991. According to his home page,
despite the lack of funding, staff, or a company to stand behind it, PGP
became the most widely used e-mail encryption software in the world.
After settling some issues with the US Government, Mr. Zimmerman
founded his company in 1996; Network Associates Inc. (NAI) eventually
acquired PGP Inc. in December 1997.Mr. Zimmerman was asked to stay
on with NAI until 2000 as Senior Fellow. In August 2002, PGP was
acquired by PGP Corporation, where Mr. Zimmermann is a consultant.
Before founding PGP Inc., Mr. Zimmermann was a software engineer with
more than 20 years of experience, specializing in cryptography and data
security, data communications, and real-time embedded systems. You
can learn more about Mr. Zimmerman and his work with PGP at
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How PGP Works
PGP uses a combination of public and private keys to secure e-mail. It uses
public key cryptography, which uses a “secret key” to encrypt and decrypt a message.The sender uses a public key to encrypt the message, while the recipient
deciphers it using another version of the key. PGP encryption and key exchange
is designed in the “web of trust” model, meaning that the reliability of PGP is
directly related to how much you trust the other users whom you hold keys for.
When PGP is run on Microsoft Outlook, Outlook compares a digital signature with public keys that are stored on a key ring.This is a collection of public
keys located locally on a desktop or laptop that is already installed on Outlook
and used to decrypt the e-mail received.
For the Security+ exam, remember that a key ring is always held locally.
Think of your own personal key ring with the keys to your home or car,
since you normally keep your keys with you.
If Outlook cannot find the proper public key to decrypt a message, users will
be prompted to acquire the public key from a key authority. If Outlook already
has the public key, it will decrypt the message so that it can be read. Users should
realize, however, that once decrypted, an e-mail message will remain decrypted
while stored on a machine. PGP is a well-respected method of encrypting e-mail.
Plug-ins are available for both Microsoft Outlook and Microsoft Outlook
Express, so users can send, encrypt, decrypt, and digitally sign any messages sent
or received with this software. Once PGP has been installed on a system, using
PGP with either of these e-mail programs is quite easy. Exercise 3.02 provides
instruction for installing PGP for use with Microsoft Outlook Express.
PGP Interface Integration
When the PGP plug-in is installed, it is integrated with the installation of
Outlook or Outlook Express.When a message is opened or sent, several new
buttons appear on the right of the toolbar: Encrypt Message, Decrypt PGP
Message, and Launch PGPKeys (see Figure 3.11).
When you click the Launch PGPKeys button, the PGPKeys tool is
invoked. Using this tool, you can perform a variety of tasks, including creating
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new keys used for encrypting and decrypting messages.This is the same key generator used when PGP was first installed.
Figure 3.11 Microsoft Outlook Express 6 Toolbar with PGP Buttons
When the Encrypt Message button is clicked, the e-mail and any attachments will be flagged as needing to be encrypted. Upon hitting the Send button,
PGP will encrypt the message and place it in the Outbox to be sent.When the
e-mail is encrypted, it will change in appearance to anyone viewing the message.
Similar to the following example, the e-mail becomes hashed (transforming a
string of characters into a fixed-length value that represents the original string),
so that no one can understand it until it is decrypted:
-----BEGIN PGP MESSAGE----Version: PGPfreeware 7.0.3 for non-commercial use <>
When a person receives a message encrypted with PGP, they need to decrypt
it before it can be read. Upon opening the message and clicking on the Decrypt
PGP Message button, a dialog box appears asking for a password.This is the
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Damage & Defense…
password that the user chose when setting up PGP on their machine.The user
needs to have the public key from the person who sent the e-mail or the message
cannot be deciphered.This protects the e-mail from being read by an unauthorized person. After the correct password is entered, the message and any file
attachments are restored to their original format.
Weaknesses in PGP
PGP vulnerabilities can be exploited through the use of chosen ciphertext.
In a chosen ciphertext attack, a hacker creates a message and sends it to
a targeted user with the expectation that this user will send the message
to yet other users. When the targeted user distributes the message in an
encrypted form, the hacker listens to the transmitted messages and figures out the key from the newly created ciphertext.
The vulnerability in PGP works in the same way. A nonsense message
is sent to a targeted party, with the expectation that the targeted party
will respond to the attacker’s message. Once the target responds to the
message, the attacker can discover the key used to encrypt messages that
have been sent to and from the targeted party.
Most PGP distributors are aware of this type of attack and have
released newer versions that account for this flaw.
Installing PGP on a Microsoft Windows OS is fairly easy. For this exercise,
you will walk through the steps of installing PGP. The first step is to
obtain a copy of the PGP software. You can download a free copy at
1. Download the PGP software from the link provided, and unzip it
to a temporary directory called drive:PGP.
2. Open the PGP directory to which you unzipped the contents, and
launch PGPFreeware7.0.3.exe. Note that 7.0.3 is the latest version
of the PGP software at the time this book was written, and version 8.0 for Windows and Macintosh OS X is expected to be available in November 2002. The PGP setup begins (Figure 3.12).
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Figure 3.12 The Initial Setup Splash Screen for the PGP Software
This exercise will not work on Windows XP; PGP 7.0.3 does not support
it. NAI states that version 7.1 of their commercial product will run on
Windows XP, but they do not support it. It is expected that version 8.0
will be fully XP compatible.
3. Click Next at the initial welcome screen.
4. Read through the license agreement, and click Yes to continue.
5. Read through the PGP readme screen, and click Next to continue.
6. If this is the first time you have used PGP, you need to create a
new key ring. At the User Type screen, click on the “No, I’m a
new user” radio button and click Next (Figure 3.13).
7. You will then be prompted to select an installation directory. Use
the default location provided for your installation and click Next
to continue.
8. At this point in the installation, you can select the plug-ins you
want to use. For this example, you will be installing the PGP Key
Management Plug-in for Microsoft Outlook Express, and the PGP
Documentation (Figure 3.14). Click Next once you have selected
your plug-ins.
9. Verify your current setting, and click Next.
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Figure 3.13 Make Sure to Select the Proper Radio Tab to Create a
New Key Ring.
Figure 3.14 Select the PGP Plug-ins That You Want to Install
10. Click Next again to bypass the splash screen. PGP will begin
11. At this point during the installation, you may be asked to restart
your computer.
12. After the installation is complete, the Key Generation Wizard
appears. Click Next to begin creating a key.
13. Enter the full name and e-mail address that you want associated
with the key (Figure 3.15). Click Next to continue.
14. Next, create a passphrase that PGP can use to protect your PGP
key. You can see what you are typing by unchecking the Hide
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Typing checkbox. Confirm your passphrase by entering it again
(Figure 3.16), and click Next.
Figure 3.15 Enter in the Name and Password to Associate With the
Figure 3.16 Enter in a Strong Passphrase for Your PGP Key
15. PGP will now begin generating your key. Click Next once the PGP
key has been generated.
16. The Key Generator Wizard will inform you that the process is
complete. Click Finish.
17. PGP will start the necessary services. You may be asked to restart
your computer at this time.
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You must understand the importance of a passphrase for the Security+
exam. Passphrases are collections of words and characters used as an
alternative to a password for identification. In PGP, passphrases are used
to encrypt or decrypt messages.
18. Once your computer has restarted (if necessary), you will notice
that there is now a padlock in your system tray. Click on the padlock icon from the PGP pull-down list.
19. From the pull-down list, select PGP Keys to view the list of known
keys on your key ring.
20. At this point, you can right-click on your key (Figure 3.14) and
select Key Properties to review specific information about your
PGP key.
21. Once you have collected others users’ keys, you may begin
exchanging secure messages.
E-mail has become one of the most popular (and faster) means of communication used today. Users that need to get information and ideas to others quickly
use e-mail rather than the postal service, telephones, and other methods. Since
e-mail is so popular, there are vulnerabilities within the e-mail delivery system.
Some are technical, such as SMTP relay abuse and e-mail client vulnerabilities
(like Microsoft Outlook), and some are non-technical, such as spam and e-mail
The solution to most of these issues is being proactive regarding the vulnerabilities. Cracking down on open SMTP relay servers, implementing fixes for
client software, keeping antivirus signature files up to date, and being aware of
e-mail hoaxes constitute the best defense.
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SMTP Relay
One feature of SMTP is the SMTP relay. Relay simply means that any SMTP
message accepted by one SMTP server will automatically be forwarded to that
server’s destination domain. Often, an organization will configure a single SMTP
host (such as a firewall) to relay all inbound and outbound e-mail.
This feature must be carefully configured and tightly controlled. Most e-mail
server programs (Microsoft Exchange, Sendmail, etc.) have the ability to limit the
addresses that SMTP e-mail can be relayed from.
An improperly configured e-mail server may end up being used to forward
spam to a recipient (or group of recipients) throughout the Internet. Using an
open SMTP relay gives “spammers” free reliable delivery of their messages
(Figure 3.17).What then happens is the recipient(s) of the spam messages will see
a company’s domain name and assume it came from that e-mail server.Eventually
the domain name will be placed into a DNS-based Blackhole List (DNSBL) to
block e-mail from those sources. Once the domain name has been placed into
one of these lists, companies subscribing to the lists will no longer accept e-mail
from that domain.
Figure 3.17 How SMTP Relay Works
1. Spammer composes
e-mail and sends it to
open SMTP relay server.
Mail Server
2. SMTP server receives
message, and forwards
it to e-mail servers of
3. End-user e-mail servers
deliver messages to enduser mailboxes.
Open SMTP Relay
Mail Server
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Protecting Yourself Against Relaying
There are fixes for open SMTP relay issues. If there were not, every e-mail server
would eventually end up on the DNSBL! Implementing these fixes vary from
e-mail server to e-mail server, based on the e-mail application that is running.
However, the underlying fix is always the same—limiting the domains a server is
allowed to relay.
Microsoft Exchange 2000 makes restricting SMTP relay easy. By default,
Exchange 2000 does not allow unauthorized relaying, so to allow an Exchange
2000 server to relay messages, a user must provide a valid username and password.Hackers can sniff network traffic to capture user credentials and generate
attacks.This can be easily resolved by removing the ability to relay messages even
if a user is authenticated. Unfortunately, this also limits the ability to send and
receive messages remotely, as users will not be able to access their e-mail via
POP3 services.
Sendmail, which is the e-mail server application for UNIX, can also fall
victim to SMTP relay attacks.Version 8.9 of Sendmail was the first to disable
SMTP relaying. For example, in version 8.8, changes can be made to Sendmail
configuration files to restrict e-mail so that it has to originate or terminate at the
local server.The file /etc/sendmail.cR would be reconfigured to look like this:
# anything terminating locally is ok
R< $+ @ $=w >
$@ OK
R< $+ @ $=R >
$@ OK
# anything originating locally is ok
$: $(dequote "" $&{client_name} $)
$@ OK
$@ OK
$@ OK
# anything else is bogus
$#error $: "550 Relaying Denied"
The easiest way to prevent SMTP relay is to properly configure and test the
server during the build process. If you are not sure if your server is configured
properly, there is an easy way to test it.
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Do not try this from your internal network, since your server will allow
you to relay from the trusted internal domain.
1. Open a command prompt window (assuming you are using a
Windows OS).
2. At the command prompt, type Telnet <servername> 25.This will
open up a Telnet session with the SMTP server using SMTP port 25.
3. You will receive a response from the e-mail server giving the name of
the server, the e-mail software being used, and the date and time usually
in the format of 220 Microsoft ESMTP Sendmail
8.11.6/SuSE Linux Mon, Oct 7, 2002 08:50:00.
4. Type HELLO will get a response from the e-mail
server, saying “Hello” back to you.
5. Type in a fake “from” address in the format of mail from: e-mail server will respond with the
“Sender OK” response.
6. Type rcpt to: server should respond
with “unable to relay for” If not, your server
can be used for SMTP relay.
Head of the Class...
Spam and SMTP Relay
Later in this chapter, you will read about unsolicited e-mails known as
spam. Many times, companies that use spam (those selling illegal goods,
pyramid schemes, pornography Web sites, or other unsolicited products)
search the Internet for SMTP servers that do not restrict SMTP relay services. When they find an e-mail server that is not restricted, they exploit
that server to distribute spam e-mails to the connected world.
Many large companies have e-mail administrators who manage
e-mail servers. If the e-mail administrator of one company is given the
address or domain of another company’s e-mail server as a potential
spam distributor, the other administrator will block all incoming e-mail
from that company. “Black hole” software is available that contains a list
of exploited SMTP relay servers.
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If your e-mail server does not respond with the “unable to relay” notification,
go back through the configurations to make sure the necessary steps were taken
to prevent relaying.
E-mail and Viruses
Damage & Defense…
Microsoft Outlook is the “whipping boy” when it comes to e-mail vulnerabilities, mostly due to the fact that Outlook has many features. Any time you add
features to a software package, you create opportunity for those features to be
exploited. Most e-mail oriented viruses—ILOVEYOU, Melissa, Anna
Kornakova—were distributed using weaknesses found in the Outlook client.
Viruses are often spread as e-mail attachments. Attachments might be compressed files (such as ZIP files), programs (such EXE files), or documents. Once
the file is executed, the virus is released. Executing the file can be done by
opening or viewing the file, installing and/or running an program attached to the
file, opening an attached document, or decompressing a file.
Many e-mail software programs provide a “Preview” pane that allows users to
view message contents without actually opening it.This is a problem when
viewing HTML e-mail, which appears as a Web page and may contain malicious
content.Viewing HTML documents has the same effect as opening an HTML
message. Computers can then fall prey to any scripts, applets, or viruses within
the message. For protection, e-mail software should be set to view plaintext messages or antivirus software that scans email before opening it should be installed.
Plugging the Holes
The good news about these security holes in Microsoft Outlook, is that
there are ways to solve them without having to upgrade all of your e-mail
packages to newer versions (such as Outlook XP).
.com/downloads/9798/Out98sec.aspx offers a cumulative fix for all of the
problems in Outlook 97/98, and provides links to patches for Outlook
2000. As mentioned earlier, the patches that Microsoft has released have
been considered by some to be a problem because they completely block
attachments of certain file formats, such as executables. Third party software such as that available at, allows users to specify
the attachment types to be blocked and the types be allowed through.
Most virus protection software packages, such as Norton, McAfee, or
Trend Micro, also offer solutions for fixing these holes without having to
make modifications to the Outlook product.
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Antivirus software provides real-time scans of systems regularly. For example,
Norton AntiVirus, McAfee Viruscan, and Trend Micro PC-cillin scan every four
seconds for new e-mail messages with attachments. If HTML content is part of
the message, real-time scans also detect viruses embedded in the message.
Antivirus software is important because of the damage that can be caused by
viruses. One of the most infamous was the Melissa virus. In 1999, a file called was posted to a newsgroup called file supposedly contained a
listing of sexually orientated Web sites and the usernames and passwords required
to access them illegally. However, when the file was downloaded, opened, and the
program inside was run, these users became the first to be infected with the
Melissa virus.
The Melissa virus exploited a security vulnerability in Outlook.The virus
accessed the address book and sent the virus to every address listed. It is estimated
that Melissa crippled computers at 300 companies and caused nearly $400 million
in damages.
The creator of this virus was arrested. In December 1999, David Smith
pleaded guilty to federal and state charges, and was sentenced to five years in
prison. Even though antivirus programs are able to detect and remove this virus,
it is interesting to note that it continues to infect systems and be distributed.This
is because it still reaches people who do not have antivirus software on their
system with updated signature files.
For more information about the Melissa virus and other situations where
viruses have lead to criminal action, see Scene of the Cybercrime:
Computer Forensics Handbook (Syngress Publishing, ISBN: 1-931836-65-5)
by Debra Littlejohn Shinder.
Even if antivirus software is installed on a system, there is no guarantee it will
actually catch the virus. As seen in the case of the Melissa virus, when people
downloaded the file called from the newsgroup they were infected
with the virus. Regardless of whether these people had antivirus software
installed, the signature files for the software did not have any data on the Melissa
virus. Until a virus is known and an antivirus solution is created, a virus can
infect any computer using antivirus software.
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Another common reason why a computer with antivirus software can be
infected with viruses is because the signature files have not been updated.
Antivirus software manufacturers release new signature files regularly, and it is up
to users to download and update them.To make this simple, many manufacturers
provide features to automatically update the signature files via Internet.
Spam Spam is unsolicited e-mail, much like the advertisements and other junk e-mail
that frequently fills home mailboxes. Spam is junk e-mail that rarely is of any
interest to users, is never requested, and is sent by people you do not know.
The origin of the name is ambiguous at best and goes back to the early days
of the Internet and Bulletin Board Systems (BBSs) run on individual computers
to which people dialed in directly). Some believe it came from computer users at
the University of California who made a derogatory comparison between the
processed lunchmeat product made by Hormel and e-mail that nobody wants.
Others believe the term comes from the song by British comedy group Monty
Python, which was about the ubiquity of spam.Whatever the exact source, spam
is something that is not likely to disappear from the Internet anytime soon.
Spam often comes from lists of e-mail addresses or software that sends thousands or millions of messages. Many legitimate businesses avoid soliciting customers this way, because people do not like receiving spam. Also, many ISPs
specify that bulk e-mail is a violation of the contract between themselves and
their customers, so they can shut down sites or disable the accounts of customers
who send spam. Furthermore, the FTC warns that many states have laws regulating the sending of unsolicited commercial e-mail, making “spamming” illegal.
Spam is considered to be a Denial of Service (DoS) attack since it has the ability
to disable e-mail servers by overloading e-mail storage with junk messages.
E-mail users can deal with spam in a number of ways. One method is to read
the spam message to see if there is a method of removing addresses from the
mailing list. Legitimate companies will remove users from their mailing lists; however, many spam mailers use these links to verify that the e-mail addresses the
message was sent to are “live” addresses. Users may be removed from the list, but
their e-mail is almost always sold again as it has been confirmed as a “live” address.
Another method of avoiding spam is by disabling cookies. Cookies are small
text files sent by some Web sites that contain information about the user, and are
stored in a folder on the users computer. Cookies are commonly associated with
Internet browsers that access Web pages, but, because many e-mail programs
allow users to accept messages in HTML format, HTML e-mails may contain
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cookies as well. Plain-text messages are safer than HTML messages because plaintext messages are not capable of storing cookies and other damaging content.
Users can also contact companies they routinely deal with and ask them not
to share or sell their information. Generally, privacy policies outline whether
companies share or sell client information. If they do share or sell information,
the user has to decide whether or not to use those sites.
Spam filters are programs that analyze the contents of messages to see if they
have the common elements of spam. If a message does contain some of those
elements, the spam filter deals with the message in a specific way. For example,
users can configure the filter to add the word spam to the subject line, so they
know that the message is spam. Users can also configure the filter to delete suspected spam. Examples of products that can be used include MailWasher
( and EmTec Software’s Spam Detective, which runs on
Windows systems and is available at However,
before investing in such software, users should visit the Web site of their ISP.
Many ISPs offer spam detection and elimination services, in which spam-like email is deleted on the server.This saves the ISP the cost of using bandwidth to
send users e-mail they do not want.
Hoaxes E-mail hoaxes are those e-mails sent around the Internet about concerned par-
ents desperately searching for their lost children, gift certificates being offered
from retail stores for distributing e-mails for them, and dangerous viruses that
have probably already infected the user’s computer.
There are a lot of different ways to separate hoaxes from real information.
Most of the time, it comes down to common sense. If users receive e-mail that
says it originated from Bill Gates who is promising to give $100 to everyone who
forwards the e-mail, it is probably a hoax.The best rule of thumb is timeless—if
something seems too good to be true, it probably is. If a user is still not sure of the
validity of an e-mail message, there are plenty of sites on the Internet that specialize in hoaxes. One of the more popular sites is
Virus hoaxes are a little different.Virus hoaxes are warnings about viruses that
do not exist. In these cases, the hoax itself becomes the virus because wellmeaning people forward it to everyone they know. Some virus hoaxes are dangerous, advising users to delete certain files from their computer to “remove the
virus,” when those files are actually very important OS files. In other cases, users
are told to e-mail information such as their password (or password file) to a specified address so the sender can “clean” the system of the virus. Instead, the sender
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will use the information to hack into the users system and may “clean” it of its
valuable data.
How do users know whether a virus warning is a hoax? Since users should
never take a chance with viruses, the best place to go is to the experts—the
antivirus companies. Most antivirus companies have information on their Web
sites that list popular e-mail hoaxes.The most important thing to remember
about e-mail hoaxes is to never follow any instructions within the e-mail that
instructs users to delete a certain file or send information to an unknown party.
The top ten items about e-mail security to remember for the Security+
exam are:
1. S/MIME looks to the headers to determine how data encryption
and digital certificates are to be handled.
2. S/MIME messages are encrypted using a symmetric cipher
(method of encrypting text), and a public-key algorithm is used
for key exchange and digital signatures.
3. PGP uses a combination of public and private keys to secure
4. PGP uses public key cryptography, which uses a “secret key” to
encrypt and decrypt messages.
5. Using an open SMTP relay server gives a spammer free reliable
delivery of their messages.
6. Fixes for SMTP relay are available for Microsoft and UNIX e-mail
7. New e-mail servers that come with SMTP relay are disabled by
8. Spam is unsolicited e-mail messages, much like the advertisements and other junk e-mail that frequently fills home mailboxes.
9. Users must know the methods for reducing the amount of spam
they receive.
10. Virus hoaxes are warnings about viruses that do not exist; in
these cases, the hoax itself becomes the virus because wellmeaning people forward it to everyone they know.
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Summary of Exam Objectives
Secure communications are a necessity in today’s world, and there are many tools
available to users to protect information and networks from being compromised.
Knowing how these tools, work and how certain tools differ from other tools
should be your goal when studying for the Security+ exam.
Although technology has made huge strides in remote access security, there
are still many problems.Technologies such as RAS servers, NAS,VPN, authentication servers like RADIUS,TACACS, and TACACS+, and others were designed
to address these problems.
It is the security professional’s responsibility to ensure that everything possible
has been done to secure their networks. Security professionals have to find the
balance between offering users the ability to work from remote locations, and
ensuring that the network is protected.The 802.1x protocol is a WEP protocol
used for securing the transfer of messages between a user and an access point.
When a wireless user (or supplicant) wants to access a wireless network, 802.1x
forces them to authenticate to a centralized authority called an authenticator.
802.1x uses the EAP for passing messages between the supplicant and the
authenticator.The authenticator sends a request to the user requesting their identity.The client returns their identity to the authenticator, which is forwarded to
an authentication server for verification.
VPNs use secure tunnels to allow remote users to connect to a network.
VPNs can be configured in two forms: site-to-site VPNs or remote access VPNs.
VPNs use either PPTP or L2TP as the tunneling protocol. A tunnel is created by
wrapping (or encapsulating) a data packet inside another packet and transmitting
it over a public medium. PPTP is a Layer 2 (Data Link Layer) encapsulation (tunneling) protocol using port 1723 and TCP for its transport protocol. L2TP is also
a Layer 2 encapsulation protocol, but uses port 1701 and UDP.
A RAS authenticates a user, which means they determine who a user is. A
RAS also authorizes the functions the authenticated user may perform. A RAS
logs the actions of the user for the duration of the connection.RADIUS was
designed to handle the authentication and authorization of dial-in users.
RADIUS is the most popular of all the AAA servers, which include
developed during the days of ARPANET. Although TACACS offers authentication and authorization, it does not offer any accounting tools.TACACS+ is a
proprietary version of TACACS that was developed by Cisco.TACACS+ is considered proprietary because the packet formats are completely different from
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those in either TACACS or XTACACS, making it incompatible with previous
versions.TACACS+ is credited with separating the AAA functions. Unlike previous versions (as well as RADIUS) that used one database for AAA,TACACS+
uses individual databases for AAA.TACACS+ was the first revision to offer secure
communications between the TACACS+ client and the TACACS+ server.
Another difference between RADIUS and TACACS is that TACACS+ uses TCP
as its transport instead of UDP.
Another tool that can be used to secure remote communications is SSH. SSH
is a cryptographically secure replacement for standard Telnet, rlogin, rsh, and rcp
commands. It consists of both a client and server that use public-key cryptography to provide session encryption. It also provides the ability to forward arbitrary ports over an encrypted connection. SSH is concerned with the
confidentiality and integrity of the information being passed between the client
and the host. Using SSH helps protect against many different types of attack
including packet sniffing, IP spoofing, and the manipulation of data by unauthorized users.
IPSec is “a framework of open standards for ensuring private, secure communications over Internet Protocol networks, through the use of cryptographic
security services.”
IPSec can be implemented in either tunnel mode or transport mode. IPSec
uses IKE to manage keys and authenticate the two ends of a secure tunnel before
IPSec transmissions begin.IPSec is made up of two separate security protocols:
the (AH) and the ESP. IPSec offers nonrepudiation through the use of digital
There are several vulnerabilities that can be exploited in RAS. Eavesdropping
is simply attaching yourself to a network in a manner that allows users to “hear”
all of the traffic being passed over the wire. In data modification, data is intercepted by a third party (one that is not part of the initial communication), modified, and sent through to the originally intended recipient. In an IP spoof attack,
a hacker will listen on a public network (such as the Internet) and examine
packets until they believe they have found a trusted host that is allowed to pass
data through the firewall. Once the hacker finds this address, they can begin creating packets and sending them to the target network as if from a trusted address.
Users who write passwords on sticky notes and put them on their monitor, leave
their workstation without locking it with a screensaver, or allow other people to
watch while they are entering their usernames or passwords, are often the easiest
victims of these attacks.
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Keeping up with security patches, hardening remote access systems, and being
aware of flaws in different remote access methods must be part of the security
professional’s daily routine.
E-mail is one of the most common means of communications used in many
parts of the world. Because e-mail travels across multiple routers, servers, and
mediums, more parties than just the recipient might be able to access the messages or data attached to an e-mail.To protect yourself and your data, you should
consider using encryption. Encryption scrambles the contents of a message and
attachments, and then puts the contents back together on the recipient’s end.
Anyone attempting to view the data in between will generally be unable to decipher the content. S/MIME was developed from MIME. MIME is an extension
of SMTP that provides the ability to pass different kinds of data files over the
Internet including audio, video, images, and other types of files MIME does not
offer any security features by itself. Developers at RSA Security created S/MIME
to address the security flaws of regular SMTP e-mail transfers. S/MIME deals
with determining how data encryption and digital certificates are to be handled.
Messages are encrypted using a symmetric cipher (method of encrypting text),
and a public key algorithm is used for key exchange as well as digital signatures.
S/MIME can be used with the DES, 3DES, and RC2 encryption algorithms.
Philip R. Zimmermann is the creator of PGP. PGP is a third-party application that can be installed to interact with e-mail client software.When PGP is
installed, plug-ins for Microsoft Outlook, Outlook Express, ICQ, Netscape, and
other programs can also be installed, allowing users to encrypt, decrypt, and sign
messages sent through these e-mail packages. PGP uses a combination of public
and private keys to secure e-mail. PGP encryption and key exchange is designed
in the “web of trust” model.When PGP is run, the digital signature is compared
with public keys that are stored on a local key ring.
As with RAS, e-mail security is susceptible to its own types of vulnerabilities.
SMTP relay is one of the most commonly exploited vulnerabilities. SMTP relay
is a feature of e-mail servers that allows a message to be accepted by one SMTP
server and automatically forwarded to its destination domain by that server.
SMTP relay must be tightly controlled, otherwise the SMTP server may be
forwarding e-mail for another organization. Most e-mail server programs
(Microsoft Exchange, Sendmail, etc.) have the ability to limit the addresses that
SMTP e-mail can be relayed from.
E-mail has become the most popular means of transferring viruses.Viruses are
generally spread through e-mail as attachments. Executing these viruses can be
done by opening or viewing the file, by installing and/or running an attached
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program, by opening an attached document, or by decompressing a file.Viewing
HTML documents in the preview pane has the same effect as opening the
HTML message itself. Antivirus software should provide real-time scans of user’s
systems, and should check e-mail attachments on a regular basis.
Spam is unsolicited e-mail, much like the advertisements and other junk mail
that that frequently fills home mailboxes. Spam filters are programs that analyze
the contents of messages to see if they have the common elements of spam. Spam
is considered to be a DoS attack since it has the ability to disable e-mail servers
by overloading the e-mail storage with junk messages.
Regarding hoaxes, if something seems too good to be true, it probably is. If
users are not sure of the validity of an e-mail message, they should check their
antivirus provider’s Web site to see if it is a hoax or a real threat. Users should
never follow any instructions within an e-mail that tells users to delete certain
files or send information to an unknown party.
Exam Objectives Fast Track
The Need for Communication Security
; Potentially sensitive data is being transmitted over public networks.
; Users want the ability to work from home.
; Hackers have tools readily available on the Internet.
; Hacking is such a popular pastime that underground networks for
passing information and techniques now exist.
; 802.1x is a WEP protocol.
; 802.1x uses the EAP for passing messages between the supplicant and
the authenticator.
; RADIUS and TACACS use UDP, and TACACS+ uses TCP
; PPTP uses port 1723, and L2TP uses port 1701
; IPSec uses AH and the ESP
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; In data modification, data is intercepted by a third party (one that is not
part of the initial communication), modified, and sent through to the
party it was originally intended for.
; Using SSH helps protect against many different types of attacks
including packet sniffing, IP spoofing, and the manipulation of data by
unauthorized users.
E-mail Security
; PGP and S/MIME are used for encrypting e-mail.
; Spam is unsolicited advertisements sent via e-mail.
; Hoaxes should be verified at reputable sites (such as anti-virus companies)
before action is taken.
; When PGP is installed, plug-ins for Microsoft Outlook, Outlook Express, ICQ,
Netscape, and other programs can then be installed, allowing users to encrypt,
decrypt, and sign messages sent through these e-mail packages.
; Users should never follow any instructions within an e-mail that tells
them to delete a certain file or send information to an unknown party.
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Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: Why is it important to secure communications?
A: Important data is transmitted over public media every day, and making sure
unauthorized users are not reading it can be crucial to users, companies,
governments, and so on.
Q: In reality, how easy is it for someone to hack into my network?
A: It all depends on how secure your network is. If you have the correct tools in
place (firewalls, secure VPNs, and so on), you make it very difficult for a
hacker to penetrate your network. Any network can be hacked.The purpose
of network security is to make it so difficult and time consuming that hackers
will be discouraged. In reality, there is no such thing as “hackproofing” a network—security measures only slow hackers down; they never guarantee that a
network cannot be penetrated.
Q: Why is wireless networking such a security concern?
A: Wireless networks run over the open-air using standardized frequencies and
protocols.Wireless network transmissions use radio signals that can be picked
up by anyone with the right reception equipment.Therefore, anyone within
range can potentially listen in on a user network for data.There is no need to
make a physical connection. By adding WEP protocols like 802.1x, users
make it more difficult for hackers to listen to the airwaves.
Q: If I have to choose between L2TP and PPTP for my VPN, which should I use?
A: That is a matter of opinion. Some older Microsoft OSs (such as Windows 95)
can only handle PPTP, and others (Windows 9x/ME/NT 4.0) require that
users download an add-on L2TP/IPSec client to use L2TP, while the newer
ones (Windows 2000/XP and .NET 2003) can use both.There are PPTP and
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L2TP client implementations for Linux and Macintosh, as well. On the server
side, if users have the option of using both PPTP and L2TP, it’s always safer to
go with both because of the OS limitations.
Q: Which is better, S/MIME or PGP?
A: Functionally, they are about the same. However, PGP seems to get more
“press” and has become more popular because of it. It is not always a matter
of “which is better” as much as it is “which one is more widely used.”This is
because both the sender and recipient of an encrypted message must have
compatible software in order for the recipient to be able to decrypt the
encrypted messages.
Q: Can you recommend a good spam filter?
A: Lyris MailShield (formerly EmTec Software’s Spam Detective) is a decent
spam filter.The program is available at
and there are three versions available: desktop, workgroup, and server.The
downside to MailShield is that the evaluation copy is only good for seven
days. Licenses are expensive at $500 for 10 licensed seats for the desktop version. A less expensive choice is MailWasher ( which is a
free download that never expires, but includes advertising on the software that
is removed if users register it for a “contribution” of $20. Registration also
includes free upgrades for life. MailWasher runs on Windows 95/98/ME,
Microsoft NT 4.0, 2000, and Microsoft XP Home and Pro Editions.
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Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
The Need For Communication Security
1. The use of VPNs and __________________ have enabled users to be able to
C. Wireless NICs
2. PDAs, cell phones, and certain network cards have the ability to use
_____________ networks. Choose the BEST answer.
A. Wired
B. Private
C. Wireless
D. Antique
3. There are three recognized levels of hacking ability in the Internet community.The first is the skilled hacker, who writes the programs and scripts that
script kiddies use for their attacks. Next comes the script kiddie, who knows
how to run the scripts written by the skilled hackers. After the script kiddies
come the _______________, who lack the basic knowledge of networks and
security to launch an attack themselves.
A. Web kiddies
B. Clickers
C. Click kiddies
D. Dunce kiddies
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Remote Access Security
4. Bob is trying to set up VPN access to his network. He is sure that he has
configured both his server and his clients correctly, but he cannot connect to
the server from home. Assuming the server and clients are set up correctly,
what else could be stopping Bob from accessing his VPN server?
A. Bob has not contacted his ISP to let them know he is going to use a
B. Bob needs to get a newer version of his VPN client.
C. Bob must inform the VPN server of his home IP address before he can
connect to the VPN server.
D. Bob has to open up the correct ports on his firewall.
5. Choose the correct set of terms:When a wireless user, also known as the
___________ wants to access a wireless network, 802.1x forces them to
authenticate to a centralized authority called the ____________.
A. Authenticator; supplicant
B. Supplicant; authenticator
C. Supplicant; negotiator
D. Contact; authenticator
6. Steve’s boss has asked him to find ways to cut back on WAN communications
costs but still wants to keep communications between offices secure. Steve
goes back to his office and looks over his network diagrams (on the following
page) and decides on a solution.Which of the following answers is the BEST
solution for Steve?
A. Drop all of the connection speeds on the private frame relay from a
1.544Mb to 128Kb.
B. Remove the private frame relay connections, and implement a remote
access VPN.
C. Remove the private frame relay connections, and implement a site-tosite VPN.
D. Only allow the Internet T1’s to run during normal business hours,
which will lower connection costs.
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Frame Relay
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7. IPSec implemented in _____________ specifies that only the data will be
encrypted during the transfer.
A. Tunnel mode
B. Unauthorized state mode
C. Transfer mode
D. Transport mode
8. One of the biggest differences between TACACS and TACACS+ is that
TACACS uses _________ as its transport protocol and TACACS+ uses
_________ as its transport protocol.
9. The __________ protocol was created from by combining the features of
PPTP and L2F.
A. IPSec
10. SSH is concerned with the confidentiality and __________ of the information being passed between the client and the host.
A. Integrity
B. Availability
C. Accountability
D. Speed
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11. IPSec is made up of two basic security protocols:The AH protocol and the
_________________ protocol.
E-Mail Security
12. You are a consultant working with a high-profile client.They are concerned
about the possibility of sensitive e-mail being read by unauthorized persons.
After listening to their issues, you recommend that they implement either
S/MIME or PGP to _________ their messages. Select the BEST answer.
A. Encapsulate
B. Encrypt
C. Authorize
D. Identify
13. When PGP is implemented on an e-mail client, it compares a digital signature with public keys that are stored on a ____________.
A. Key chain
B. Key ring
C. Web-of-trust
D. Ring-of-trust
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14. Melanie has become frustrated with all of the spam e-mail she receives.
Although she knows she will never be completely rid of spam, what TWO
courses of action can she take that would BEST be reduce the amount she
A. Tell her network administrator to block all incoming spam e-mail at the
e-mail server.
B. Disable cookies in her Web browser.
C. Send threatening e-mails back to the people sending the spam e-mail.
D. Scan the e-mails to see if there is a “remove” option to be removed from
the mailing list.
E. There is nothing Melanie can do, spam is just a fact of life on the
15. Julie, an employee at ACME Company, Inc., receives e-mail from a friend
warning her of an extremely dangerous virus that is circulating through the
Internet. Julie forwards the e-mail to her e-mail administrator so he is aware
of the problem.What should the administrator do first?
A. Forward the e-mail to all company employees, telling them to follow the
instructions for removing the virus that were included in the original
B. Check his antivirus company’s Web site to find out if it is actually a
virus, and if it is, what course of action should be taken to remove it.
C. Follow the instructions on removing the virus on his own computer.
16. Most ISPs offer their customers a service to block _____.
A. Hoaxes
B. SMTP relay
C. Viruses
D. Spam
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17. S/MIME uses a/an ________________ for key exchange as well as digital
A. Symmetric cipher
B. Asymmetric cipher
C. Public-key algorithm
D. Mimic algorithm
18. PGP can fall victim to a _________________ attack, which occurs when a
hacker creates a message and sends it to a targeted userid with the expectation that this user will then send the message out to other users.When a targeted user distributes a message to others in an encrypted form, a hacker can
listen to the transmitted messages and figure out the key from the newly created ciphertext.
A. Birthday
B. Ciphertext
C. Sniffer
D. Brute-force
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. D
10. A
2. C
11. C
3. C
12. B
4. D
13. B
5. B
14. B and D
6. C
15. B
7. D
16. D
8. B
17. C
9. D
18. B
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Domain 2.0 Objectives in this Chapter:
Wireless Concepts
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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This chapter thoroughly discusses what you need to know about wireless technologies for the Security+ exam as well as to be an efficient security analyst.
Wireless networks can be very insecure if specific measures are not taken to
properly manage them; however, securing them is not impossible.
Although the concepts of wireless in this chapter go above and beyond
what is covered on the Security+ exam, it is our belief that as a security
analyst you will need to know this information as you progress forward.
Therefore, we have highlighted areas you will definitely be expected to
know for the Security+ exam.
Wireless Concepts
This section covers some of the most popular wireless technologies used today
for wireless networking. In the past five years, two wireless network technologies
have seen considerable deployment:Wireless Application Protocol (WAP) networks and Wireless Local Area Network (WLAN) networks based on the
Institute of Electrical and Electronic Engineers (IEEE) 802.11 specification.
While these are not the only wireless networking technologies available, they are
the most popular and must be understood to pass the wireless objectives on the
Security+ certification exam.
Understanding Wireless Networks
Connecting to a wireless network is often transparent to users; from their perspective it is no different than connecting to a copper-based or fiber-based Ethernet
network, with the exception that no wires are involved.Windows XP supports
automatic configuration and seamless roaming from one wireless network to
another through its Wireless Zero Configuration service (seen in Figure 4.1).The
ease with which users can connect to wireless networks contradicts the complexity of the technology and the differences between the two kinds of networks.
Furthermore, because the experience of using a wireless network is identical
to that of using an Ethernet network, there is a tendency to treat both kinds of
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networks the same.They are, in fact, quite different from one another, and an
understanding of those differences is critical to providing an informed and effective implementation of a secure wireless network.
Figure 4.1 Viewing the Wireless Zero Configuration Service
Overview of Wireless
Communication in a Wireless Network
Wireless networks, like their wired counterparts, rely on the manipulation of
electrical charge to enable communication between devices. Changes or oscillations in signal strength from 0 to some maximum value (amplitude) and the rate
of those oscillations (frequency) are used singularly or in combination with each
other to encode and decode information.
Two devices can communicate with each other when they understand the
method(s) used to encode and decode information contained in the changes to
the electrical properties of the communications medium being used. A network
adapter can decode changes in the electric current it senses on a wire and convert
them to meaningful information (bits) that can subsequently be sent to higher
levels for processing. Likewise, a network adapter can encode information (bits) by
manipulating the properties of the electric current for transmission on the communications medium (in the case of wired networks, this would be the cable).
Radio Frequency Communications
The primary difference between wired and wireless networks is that wireless networks use a special type of electric current known as radio frequency (RF),
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which is created by applying alternating current (AC) to an antenna to produce
an electromagnetic field (EM). Devices for broadcasting and reception use the
resulting RF field. In the case of wireless networks, the medium for communications is the EM field, the region of space that is influenced by electromagnetic
radiation. (Unlike audio waves, radio waves do not require a medium such as air
or water to propagate.) As with wired networks, amplitude decreases with distance, resulting in the degradation of signal strength and the ability to communicate. However, the EM field is also dispersed according to the properties of the
transmitting antenna, and not tightly bound as is the case with communication
over a wire.The area over which the radio waves propagate from an electromagnetic source is known as the fresnel zone.
A fresnel zone calculator is available at
Like the waves created by throwing a rock into a pool of water, radio waves
are affected by the presence of obstructions and can be reflected, refracted,
diffracted, or scattered, depending on the properties of the obstruction and its
interaction with the radio waves. Reflected radio waves can be a source of interference on wireless networks.The interference created by bounced radio waves is
called multipath interference.
When radio waves are reflected, additional wave fronts are created.These different wave fronts may arrive at the receiver at different times and be in phase or
out of phase with the main signal.When the peak of a wave is added to another
wave (in phase), the wave is amplified.When the peak of a wave meets a trough
(out of phase), the wave is effectively cancelled. Multipath interference can be the
source of hard-to-troubleshoot problems. In planning for a wireless network,
administrators should consider the presence of common sources of multipath
interference.These include metal doors, metal roofs, water, metal vertical blinds,
and any other source that is highly reflective to radio waves. Antennas may help
to compensate for the effects of multipath interference, but must be carefully
chosen. Many wireless access points (APs) have two antennas for precisely this
purpose. However, a single omnidirectional antenna may be of no use at all for
this kind of interference.
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Another source of signal loss is the presence of obstacles.While radio waves
can travel through physical objects, they are degraded according to the properties
of the object they travel through. For example, a window, is fairly transparent to
radio waves, but may reduce the effective range of a wireless network by between
50 percent and 70 percent, depending on the presence and nature of the coatings
on the glass. A solid core wall can reduce the effective range of a wireless network by up to 90 percent or greater.
EM fields are also prone to interference and signal degradation by the presence of other EM fields. In particular, 802.11 wireless networks are prone to
interference produced by cordless phones, microwave ovens, and a wide range of
devices that use the same unlicensed Industrial, Scientific and Medical (ISM) or
Unlicensed National Information Infrastructure (UNII) bands.To mitigate the
effects of interference from these devices and other sources of electromagnetic
interference, RF-based wireless networks employ spread spectrum technologies.
Spread spectrum provides a way to “share” bandwidth with other devices that
may be operating in the same frequency range. Rather than operating on a single,
dedicated frequency such as is the case with radio and television broadcasts, wireless networks use a “spectrum” of frequencies for communication.
Spread Spectrum Technology
Conceived of by Hedy Lamarr and George Antheil in 1940 as a method of
securing military communications from jamming and for eavesdropping during
WWII, spread spectrum defines methods for wireless devices to use to send a
number of narrowband frequencies over a range of frequencies simultaneously for
communication.The narrowband frequencies used between devices change
according to a random-appearing, but defined pattern, allowing individual frequencies to contain parts of the transmission. Someone listening to a transmission
using spread spectrum would hear only noise, unless their device understood in
advance what frequencies were used for the transmission and could synchronize
with them.
Two methods of synchronizing wireless devices are:
Frequency hopping spread spectrum (FHSS)
Direct sequence spread spectrum (DSSS)
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Frequency Hopping Spread Spectrum
As the name implies, FHSS works by quickly moving from one frequency to
another according to a psuedorandom pattern.The frequency range used by
the frequency hop is relatively large (83.5 MHz), providing excellent protection
from interference.The amount of time spent on any given frequency is known
as dwell time and the amount of time it takes to move from one frequency to
another is known as hop time. FHSS devices begin their transmission on one frequency and move to other frequencies according to a pre-defined psuedorandom
sequence and then repeat the sequence after reaching the final frequency in the
pattern. Hop time is usually very short (200 to 300 µs) and not significant relative
to the dwell time (100 to 200 ms). In general, the longer the dwell time, the
greater the throughput and the more susceptible the transmission is to narrowband interference.
The frequency hopping sequence creates a channel, allowing multiple channels to coexist in the same frequency range without interfering with each other.
As many as 79 FCC-compliant FHSS devices using the 2.4 GHz ISM band can
be co-located together. However, the expense of implementing such a large
number of systems limits the practical number of co-located devices to well
below this number.Wireless networks that use FHSS include HomeRF and
Bluetooth, which both operate in the unlicensed 2.4 GHz ISM band. FHSS is less
subject to EM interference than DSSS, but usually operates at lower rates of data
transmission (usually 1.6 Mbps, but can be as high as 10 Mbps) than networks
that use DSSS.
Head of the Class…
Bluetooth uses the same 2.4 GHz frequency that the IEEE 802.11 wireless
networks use but, unlike those networks, Bluetooth can select from up to
79 different frequencies within a radio band. Unlike 802.11 networks
where the wireless client can only be associated with one network at a
time, Bluetooth networks allow clients to be connected to seven networks
at the same time. However, one of the main reasons that Bluetooth never
succeeded like the 802.11 standard did is because of its low bandwidth
capabilities and a lack of range.
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Direct Sequence Spread Spectrum
DSSS works somewhat differently.With DSSS, the data is divided and simultaneously transmitted on as many frequencies as possible within a particular frequency
band (the channel). DSSS adds redundant bits of data known as chips to the data
to represent binary 0s or 1s.The ratio of chips to data is known as the spreading
ratio:The higher the ratio, the more immune to interference the signal is, because
if part of the transmission is corrupted, the data can still be recovered from the
remaining part of the chipping code.This method provides greater rates of transmission than FHSS, which uses a limited number of frequencies, but fewer channels in a given frequency range. And, DSSS also protects against data loss through
the redundant, simultaneous transmission of data. However, because DSSS floods
the channel it is using, it is also more vulnerable to interference from EM devices
operating in the same range. In the 2.4 to 2.4835 GHz frequency range
employed by 802.11b, DSSS transmissions can be broadcast in any one of 14 22
MHz-wide channels.The number of center-channel frequencies used by 802.11
DSSS devices depends on the country. For example, North America allows 11
channels operating in the 2.4 to 2.4835 GHz range, Europe allows 13, and Japan
allows 1. Because each channel is 22-MHz-wide, they may overlap each other. Of
the 11 available channels in North America, only a maximum of three (1, 6, and
11) may be used concurrently without the use of overlapping frequencies.
When comparing FHSS and DSSS technologies, it should be noted that
FHSS networks are not inherently more secure than DSSS networks,
contrary to popular belief. Even if the relatively few manufacturers of
FHSS devices were not to publish the hopping sequence used by their
devices, a sophisticated hacker armed with a spectrum analyzer and a
computer could easily determine this information and eavesdrop on the
Wireless Network Architecture
The seven-layer open systems interconnect (OSI) networking model defines the
framework for implementing network protocols.Wireless networks operate at the
physical and data link layers of the OSI model.The Physical layer is concerned with
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the physical connections between devices, such as how the medium and low bits
(0s and 1s) are encoded and decoded. Both FHSS and DSSS are implemented at
the Physical layer.The Data Link layer is divided into two sublayers, the Media
Access Control (MAC) and Logical Link Control (LLC) layers.
The MAC layer is responsible for such things as:
Framing data
Error control
Collision detection and avoidance
The Ethernet 802.3 standard, which defines the Carrier Sense Multiple
Access with Collision Detection (CSMA/CD) method for protecting against data
loss as result of data collisions on the cable, is defined at this layer.
Head of the Class…
Nitty Gritty Details
Wireless networks and wireless networking in general are tested on the
Security+ exam, and as the test is revised in the future, the Security+
exam wireless content will continue to grow as the networking world and
corporate enterprises embrace more of the technology. Unfortunately, we
(the authors of this book) have to balance our goal of providing a broad
education with providing the specific knowledge needed to pass the
Security+ exam. The explanation of wireless, how it works, and what you
can do with it, is strictly background information to further your understanding of the technology. Security+ exam questions are not based on
FHSS and DSSS technologies, so if this information seems overly technical,
do not panic! It is important, however, to know this information as a
security analyst. It is our mission to teach you everything you need to
know to transition from the Security+ exam to the real world of security
In contrast to Ethernet 802.3 networks, wireless networks defined by the 802.11
standard do not use CSMA/CD as a method to protect against data loss resulting
from collisions. Instead, 802.11 networks use a method known as Carrier Sense
Multiple Access with Collision Avoidance (CSMA/CA). CSMA/CD works by
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detecting whether a collision has occurred on the network and then retransmitting the data in the event of such an occurrence. However, this method is not
practical for wireless networks because it relies on the fact that every workstation
can hear all the other workstations on a cable segment to determine if there is a
In wireless networks, usually only the AP can hear every workstation that is
communicating with it (for example, workstations A and B may be able to communicate with the same AP, but may be too far apart from each other to hear
their respective transmissions). Additionally, wireless networks do not use fullduplex communication, which is another way of protecting data against corruption and loss as a result of collisions.
APs are also referred to as wireless access points. This is a more precise
term that differentiates them from other network access points (such as
dial-in remote access points) but in this chapter, we will use the acronym
AP to avoid confusion with the Wireless Application Protocol (also known
as WAP).
CSMA/CA solves the problem of potential collisions on the wireless network
by taking a more active approach than CSMA/CD, which kicks in only after a
collision has been detected. Using CSMA/CA, a wireless workstation first trys to
detect if any other device is communicating on the network. If it senses it is clear
to send, it initiates communication.The receiving device sends an acknowledgment (ACK) packet to the transmitting device indicating successful reception. If
the transmitting device does not receive an ACK, it assumes a collision has
occurred and retransmits the data. However, it should be noted that many collisions can occur and that these collisions can be used to compromise the confidentiality of Wired Equivalent Privacy (WEP) encrypted data.
CSMA/CA is only one way in which wireless networks differ from wired
networks in their implementation at the MAC layer. For example, the IEEE standard for 802.11 at the MAC layer defines additional functionality, such as virtual
collision detection (VCD), roaming, power saving, asynchronous data transfer, and
The fact that the WEP protocol is defined at the MAC layer is particularly
noteworthy and has significant consequences for the security of wireless networks.
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This means that data at the higher levels of the OSI model, particularly
Transmission Control Protocol/Internet Protocol (TCP/IP) data, is also encrypted.
Because much of the TCP/IP communications that occur between hosts contain a
large amount of frequently repeating and well-known patterns,WEP may be vulnerable to known plaintext attacks, although it does include safeguards against this
kind of attack.
Make sure you completely understand WEP and its vulnerabilities. WEP is
discussed in more detail later in this chapter.
Wireless Local Area Networks
Wireless local area networks (WLANs) are covered by the IEEE 802.11 standards.
The purpose of these standards is to provide a wireless equivalent to IEEE 802.3
Ethernet-based networks.The IEEE 802.3 standard defines a method for dealing
with collisions (CSMA/CD), speeds of operation (10 Mbps, 100 Mbps, and
faster), and cabling types (CAT–5 twisted pair and fiber).The standard ensures the
interoperability of various devices despite different speeds and cabling types.
As with the 802.3 standard, the 802.11 standard defines methods for dealing
with collision and speeds of operation. However, because of the differences in the
media (air as opposed to wires), the devices being used, the potential mobility of
users connected to the network, and the possible wireless network topologies, the
802.11 standard differS significantly from the 802.3 standard. As mentioned earlier, 802.11 networks use CSMA/CA as the method to deal with potential collisions, instead of the CSMA/CD used by Ethernet networks, because not all
stations on a wireless network can hear collisions that occur on a network.
In addition to providing a solution to the problems created by collisions that
occur on a wireless network, the 802.11 standard must deal with other issues specific to the nature of wireless devices and wireless communications in general.
For example, wireless devices need to be able to locate other wireless devices,
such as APs, and communicate with them.Wireless users are mobile and therefore
should be able to move seamlessly from one wireless zone to another. Many
wireless-enabled devices such as laptops and hand-held computers, use battery
power and should be able to conserve power when not actively communicating
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with the network.Wireless communication over the air needs to be secure to
mitigate both passive and active attacks.
The Wireless Application Protocol (WAP) is an open specification designed to
enable mobile wireless users to easily access and interact with information and services.WAP is designed for hand-held digital wireless devices such as mobile
phones, pagers, two-way radios, smartphones and other communicators. It works
over most wireless networks and can be built on many operating systems (OSs)
including PalmOS,Windows CE, JavaOS, and others.The WAP operational model
is built on the World Wide Web (WWW) programming model with a few
enhancements and is shown in Figure 4.2.
Figure 4.2 WAP 2.0 Architecture Programming Model
Request (URL)
Response (Content)
Push (Content)
WAP browsers in a wireless client are analogous to the standard WWW
browsers on computers.WAP URLs are the same as those defined for traditional
networks and are also used to identify local resources in the WAP-enabled client.
The WAP specification added two significant enhancements to the above programming model: push and telephony support (Wireless Telephony Application
[WTA]).WAP also provides for the use of proxy servers, as well as supporting
servers that provide functions such as PKI support, user profile support, and provisioning support.
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The wireless transport layer security (WTLS) protocol is an attempt by the WAP
Forum to introduce a measure of security into the WAP.The WTLS protocol is
based on the Transport Layer Security (TLS) protocol that is itself a derivative of
the Secure Sockets Layer (SSL) protocol. However, several changes were made to
these protocols to adapt them to work within WAP.These changes include:
Support for both datagram- and connection-oriented protocols
Support for long round-trip times
Low-bandwidth, limited memory, and processor capabilities
WTLS is designed to provide privacy as well as reliability for both the client
and the server over an insecure network and is specific to applications that utilize
WAP.These applications tend to be limited by memory, processor capabilities, and
low bandwidth environments.
Make sure you fully understand WTLS for the Security+ exam.
IEEE 802.11
The original IEEE 802.11 standard was developed in 1989 and defines the operation of wireless networks operating in the 2.4 GHz range using either DSSS or
FHSS at the physical layer of the OSI model.The standard also defines the use of
infrared for wireless communication.The intent of the standard is to provide a
wireless equivalent for standards, such as 802.3, that are used for wired networks.
DSSS devices that follow the 802.11 standard communicate at speeds of 1 Mbps
and 2 Mbps and generally have a range of approximately 300 feet. Because of the
need for higher rates of data transmission and to provide more functionality at
the MAC layer, the 802.11 Task Group developed other standards. (In some cases
the 802.11 standards were developed from technologies that preceded them.)
The IEEE 802.11 standard provides for all the necessary definitions and constructs for wireless networks. Everything from the physical transmission specifications to the authentication negotiation is defined by this standard.Wireless traffic,
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like its wired counterpart, consists of frames transmitted from one station to
another.The primary feature that sets wireless networks apart from wired networks is that at least one end of the communication pair is either a wireless client
or a wireless AP.
IEEE 802.11b
The most common standard used today for wireless networks, the IEEE 802.11b
standard defines DSSS networks that use the 2.4 GHz ISM band and communicate at speeds of 1, 2, 5.5, and 11 Mbps.The 802.11b standard defines the operation of only DSSS devices and is backward compatible with 802.11 DSSS devices.
The standard is also concerned only with the PHY and MAC layers: Layer 3 and
higher protocols are considered payload.There is only one frame type used by
802.11b networks, and it is significantly different from Ethernet frames.The
802.11b frame type has a maximum length of 2346 bytes, although it is often
fragmented at 1518 bytes as it traverses an AP to communicate with Ethernet
networks.The frame type provides for three general categories of frames: management, control, and data. In general, the frame type provides methods for wireless devices to discover, associate (or disassociate), and authenticate with one
another; to shift data rates as signals become stronger or weaker; to conserve
power by going into sleep mode; to handle collisions and fragmentation; and to
enable encryption through WEP. Regarding WEP, it should be noted that the
standard defines the use of only 64-bit (also sometimes referred to as 40-bit to
add to the confusion) encryption, which may cause issues of interoperability
between devices from different vendors that use 128-bit or higher encryption.
Remember that IEEE 802.11b functions at 11 Mbps.
IEEE 802.11a
In spite of its nomenclature, IEEE 802.11a is a more recent standard than
802.11b.This standard defines wireless networks that use the 5 GHz UNII bands.
802.11a supports much higher rates of data transmission than 802.11b.These rates
are 6, 9, 12, 16, 18, 24, 36, 48, and 54 Mbps, although higher rates are possible
using proprietary technology and a technique known as rate doubling. Unlike
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802.11b, 802.11a does not use spread spectrum and Quadrature Phase Shift
Keying (QPSK) as a modulation technique at the physical layer. Instead it uses a
modulation technique known as Orthogonal Frequency Division Multiplexing
(OFDM).To be 802.11a compliant, devices are only required to support data
rates of 6, 12, and 24 Mbps—the standard does not require the use of other data
rates. Although identical to 802.11b at the MAC layer, 802.11a is not backward
compatible with 802.11b because of the use of a different frequency band and
the use of OFDM at the Physical layer, although some vendors are providing
solutions to bridge the two standards at the AP. However, both 802.11a and
802.11b devices can be easily co-located because their frequencies will not interfere with each other, providing a technically easy but relatively expensive migration to a pure 802.11a network. At the time of this writing, 802.11a-compliant
devices are becoming more common, and the prices for them are falling quickly.
However, even if the prices for 802.11b and 802.11a devices were identical,
802.11a would require more APs and be more expensive than an 802.11b network to achieve the highest possible rates of data transmission, because the higher
frequency 5 GHz waves attenuate more quickly over distance.
IEEE 802.11g
To provide both higher data rates (up to 54 Mbps) in the ISM 2.4 GHz bands
and backward compatibility with 802.11b, the IEEE 802.11g Task Group members along with wireless vendors are working on the 802.11g standard specifications. 802.11g has been approved as a standard, but the specifications for the
standard are still in draft form and are due for completion in late 2002.To achieve
the higher rates of transmission, 802.11g devices use OFDM in contrast to
QPSK, which is used by 802.11b devices as a modulation technique. However,
802.11g devices are able to automatically switch to QPSK to communicate with
802.11b devices. At the time of this writing, there are no 802.11g devices on the
market, although Cisco has announced that its 802.11g-compliant Aironet 1200
will be available in 2003. 802.11g appears to have advantages over 802.11a in
terms of providing backward compatibility with 802.11b; however, migrating to
and co-existence with 802.11b may still prove problematic because of interference in the widely used 2.4 GHz band. Because of this, it is unclear whether
802.11g will be a popular alternative to 802.11a for achieving higher rates of
transmission on wireless networks.
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Ad-Hoc and Infrastructure Network Configuration
The 802.11 standard provides for two modes for ad-hoc and infrastructure wireless clients to communicate.The ad-hoc mode is geared for a network of stations
within communication range of each other. Ad-hoc networks are created spontaneously between the network participants. In infrastructure mode, APs provide
more permanent structure for the network. An infrastructure consists of one or
more APs as well as a distribution system (that is, a wired network) behind the
APs that tie the wireless network to the wired network. Figures 4.3 and 4.4 show
an ad-hoc network and an infrastructure network, respectively.
Figure 4.3 Ad-Hoc Network Configuration
To distinguish different wireless networks from one another, the 802.11 standard defines the Service Set Identifier (SSID).The SSID is considered the identity element that “glues” various components of a wireless local area network
(LAN) together.Traffic from wireless clients that use one SSID can be distinguished from other wireless traffic using a different SSID. Using the SSID, an AP
can determine which traffic is meant for it and which is meant for other wireless
802.11 traffic can be subdivided into three parts:
Control frames
Management frames
Data frames
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Figure 4.4 Infrastructure Network Configuration
Wireless Client
Basic Service Set (BSS)
Wireless Client
Wireless Client
Wireless Client
Basic Service Set (BSS)
Extended Service Set (ESS)
Control frames include such information as Request to Send (RTS), Clear to
Send (CTS), and ACK messages. Management frames include beacon frames,
probe request/response, authentication frames, and association frames. Data frames
are 802.11 frames that carry data, which is typically considered network traffic,
such as Internet Protocol (IP) encapsulated frames.
The IEEE 802.11 standard covers the communication between WLAN components. RF poses challenges to privacy in that it travels through and around physical
objects. Because of the nature of the 802.11 wireless LANs, the IEEE working
group implemented a mechanism to protect the privacy of the individual transmissions, known as the Wireless Equivalent Privacy (WEP) protocol. Because WEP utilizes a cryptographic security countermeasure for the fulfillment of its stated goal of
privacy, it has the added benefit of becoming an authentication mechanism.This
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benefit is realized through a shared-key authentication that allows for encryption
and decryption of wireless transmissions. Up to four keys can be defined on an AP
or a client, and they can be rotated to add complexity for a higher security standard
in the WLAN policy.
WEP was never intended to be the absolute authority in wireless security.
The IEEE 802.11 standard states that WEP provides for protection from “casual
eavesdropping.” Instead, the driving force behind WEP was privacy. In cases that
require high degrees of security, other mechanisms should be utilized such as
authentication, access control, password protection, and virtual private networks
Despite its flaws,WEP still offers a level of security provided that all its features
are used properly.This means taking great care in key management, avoiding default
options, and ensuring adequate encryption is enabled at every opportunity.
Proposed improvements in the 802.11 standard should overcome many of the
limitations of the original security options, and should make WEP more appealing
as a security solution. Additionally, as WLAN technology gains popularity and
users clamor for functionality, both the standards committees and the hardware
vendors will offer improvements. It is critically important to keep abreast of
vendor-related software fixes and changes that improve the overall security posture
of a wireless LAN.
Most APs advertise that they support WEP in 40-bit encryption, but often
the 128-bit option is also supported. For corporate networks, 128-bit
encryption-capable devices should be considered as a minimum.
With data security enabled in a closed network, the settings on the client for
the SSID and the encryption keys must match the AP when attempting to associate with the network or it will fail.The next few paragraphs discuss WEP and
its relation to the functionality of the 802.11 standard, including a standard definition of WEP, the privacy created, and the authentication.
WEP provides security and privacy in transmissions held between the AP and
the clients.To gain access, an intruder must be more sophisticated and have specific intent to gain access. Some of the other benefits of implementing WEP
include the following:
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All messages are encrypted using a CRC-32 checksum to provide some
degree of integrity.
Privacy is maintained via the RC4 encryption.Without possession of the
secret key, the message cannot be easily decrypted.
WEP is extremely easy to implement. All that is required is to set the
encryption key on the APs and on each client.
WEP provides a basic level of security for WLAN applications.
WEP keys are user-definable and unlimited.WEP keys can, and should,
be changed often.
Do not confuse WAP and WEP. While it may seem that WEP is the privacy
system for WAP, you should remember that WTLS is the privacy mechanism for WAP and WEP is the privacy mechanism for 802.11 WLANs.
Creating Privacy with WEP
WEP provides for three implementations: no encryption, 40-bit encryption, and
128-bit encryption. Clearly, no encryption means no privacy.When WEP is set to no
encryption, transmissions are sent in the clear and can be viewed by any wireless
sniffing application that has access to the RF signal propagated in the WLAN
(unless some other encryption mechanism, such as IPSec, is being used). In the
case of the 40- and 128-bit varieties (just as with password length), the greater the
number of characters (bits), the stronger the encryption.The initial configuration
of the AP includes the setup of the shared key.This shared key can be in the form
of either alphanumeric or hexadecimal strings, and must be matched on the client.
WEP uses the RC4 encryption algorithm, a stream cipher developed by Ron
Rivest (the “R” in RSA).The process by which WEP encrypts a message is
shown in Figure 4.5. Both the sender and the receiver use the stream cipher to
create identical psuedorandom strings from a known-shared key.This process
entails having the sender logically XOR the plaintext transmission with the
stream cipher to produce ciphertext.The receiver takes the shared key and identical stream and reverses the process to gain the plaintext transmission.
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Figure 4.5 WEP Encryption Process in IEEE 802.11
Initialization Vector (IV)
Secret Key
Key Sequence
Integrity Algorithm
The steps in the process are as follows:
1. The plaintext message is run through an integrity check algorithm (the
802.11 standard specifies the use of CRC-32) to produce an integrity
check value (ICV).
2. This value is appended to the end of the original plaintext message.
3. A “random” 24-bit initialization vector (IV) is generated and prepended
to (added to the beginning of) the secret key (which is distributed
through an out-of-band method) that is then input to the RC4 Key
Scheduling Algorithm (KSA) to generate a seed value for the WEP
pseudorandom number generator (PRNG).
4. The WEP PRNG outputs the encrypting cipher-stream.
5. This cipher-stream is then XOR’d with the plaintext/ICV message to
produce the WEP ciphertext.
6. The ciphertext is then prepended with the IV (in plaintext), encapsulated, and transmitted.
A new IV is used for each frame to prevent the reuse of the key from weakening the encryption.This means that for each string generated, a different value
will be used for the RC4 key. Although this is a secure policy in itself, its implementation in WEP is flawed because of the nature of the 24-bit space. It is so
small with respect to the potential set of IVs, that in a short period of time all
keys are reused.When this happens, two different messages are encrypted with
the same IV and key and the two messages can be XOR’d with each other to
cancel out the keystream, allowing an attacker who knows the contents of one
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message to easily figure out the contents of the other. Unfortunately, this weakness is the same for both the 40- and 128-bit encryption levels, because both use
the 24-bit IV.
To protect against some rudimentary attacks that insert known text into the
stream to attempt to reveal the key stream,WEP incorporates a checksum into
each frame. Any frame not found to be valid through the checksum is discarded.
There are two authentication methods in the 802.11 standard:
Open authentication
Shared-key authentication
Open authentication is more precisely described as device-oriented authentication and can be considered a null authentication—all requests are granted.
Without WEP, open authentication leaves the WLAN wide open to any client
who knows the SSID.With WEP enabled, the WEP secret key becomes the indirect authenticator.The open authentication exchange, with WEP enabled, is
shown in Figure 4.6.
Figure 4.6 Open Authentication
Authentication Request
Authentication Response
Wired Network
Association Request/Response
Wireless Client
WEP Key : 654321
WEP Data Frame to Wired Network
WEP Key : 123456
Key Mismatch
Frame Discarded
Open authentication can also require the use of a WEP key. Do not
assume that just because the Security+ exam discusses open authentication that a WEP key should not be set.
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The shared-key authentication process shown in Figure 4.7 is a four-step process that begins when the AP receives the validated request for association. After
the AP receives the request, a series of management frames are transmitted
between the stations to produce the authentication.This includes the use of the
cryptographic mechanisms employed by WEP as a validation.The four steps
break down in the following manner:
1. The requestor (the client) sends a request for association.
2. The authenticator (the AP) receives the request, and responds by producing a random challenge text and transmitting it back to the requestor.
3. The requestor receives the transmission, encrypts the challenge with the
secret key, and transmits the encrypted challenge back to the authenticator.
4. The authenticator decrypts the challenge text and compares the values
against the original. If they match, the requestor is authenticated. On the
other hand, if the requestor does not have the shared key, the cipher
stream cannot be reproduced, therefore the plaintext cannot be discovered, and theoretically the transmission is secured.
Figure 4.7 Shared-Key Authentications
Authentication Request
Authentication Response
Wireless Client
Client WEP Key : 12345
Authentication Request
(Encrypted Challenge)
Response (Success)
Wired Network
AP WEP Key : 12345
One of the greatest weaknesses in shared-key authentication is that it provides
an attacker with enough information to try and crack the WEP secret key.The
challenge, which is sent from authenticator to requestor, is sent in the clear.The
requesting client then transmits the same challenge, encrypted using the WEP
secret key, back to the authenticator. An attacker who captures both of these
packets now has two pieces of a three-piece puzzle: the cleartext challenge, and
the encrypted ciphertext of that challenge.The algorithm RC4 is also known. All
that is missing is the secret key.To determine the key, the attacker may simply try a
brute–force search of the potential key space using a dictionary attack. At each
step, the attacker tries to decrypt the encrypted challenge with a dictionary word
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as the secret key.The result is then compared against the authenticator’s challenge.
If the two match, then the secret key has been determined. In cryptography, this
attack is termed a known-plaintext attack and is the primary reason why shared-key
authentication is actually considered slightly weaker than open authentication.
While the Security+ exam does not cover the authentication process in
great detail, it is important to remember the two authentication mechanisms in the 802.11 standard: open and shared-key.
802.1x Authentication
The current IEEE 802.11b standard is severely limited because it is available only
for the current open and shared-key authentication scheme which is non-extensible.To address the weaknesses in the authentication mechanisms discussed
above, several vendors (including Cisco and Microsoft) adopted the IEEE 802.1x
authentication mechanism for wireless networks.The IEEE 802.1x standard was
created for the purpose of providing a security framework for port-based access
control that resides in the upper layers of the protocol stack.The most common
method for port-based access control is to enable new authentication and key
management methods without changing current network devices.The benefits
that are the end result of this work include the following:
There is a significant decrease in hardware cost and complexity.
There are more options, allowing administrators to pick and choose
their security solutions.
The latest and greatest security technology can be installed and should
still work with the existing infrastructure.
You can respond quickly to security issues as they arise.
When a client device connects to a port on an 802.1x-capable AP, the AP
port determines the authenticity of the devices. Before discussing the workings of
the 802.1x standard, the following terminology must be defined:
Port A single point of connection to a network.
Port Access Entity (PAE) Controls the algorithms and protocols that
are associated with the authentication mechanisms for a port.
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Authenticator PAE Enforces authentication before allowing access to
resources located off of that port.
Supplicant PAE Tries to access the services that are allowed by the
Authentication Server Used to verify the supplicant PAE. It decides
whether or not the supplicant is authorized to access the authenticator.
Extensible Authentication Protocol Over LAN (EAPoL) 802.1x
defines a standard for encapsulating EAP messages so that they can be
handled directly by a LAN MAC service. 802.1x tries to make authentication more encompassing, rather than enforcing specific mechanisms on
the devices. Because of this, 802.11x uses Extensible Authentication
Protocol (EAP) to receive authentication information.
Extensible Authentication Protocol Over Wireless (EAPoW)
When EAPOL messages are encapsulated over 802.11 wireless frames,
they are known as EAPoW.
802.1x typically is covered in the access control, authentication, and
auditing sections of the Security+ exam, but is relevant to wireless networks because of the fact that it is quickly becoming the standard
method of securely authenticating on a wireless network. Also, do not
confuse 802.1x with 802.11x.
The 802.1x standard works in a similar fashion for both EAPoL and EAPoW.
As shown in Figure 4.8, the EAP supplicant (in this case, the wireless client)
communicates with the AP over an “uncontrolled port.”The AP sends an EAP
Request/Identity to the supplicant and a Remote Authentication Dial-In User
Service (RADIUS)-Access-Request to the RADIUS access server.The supplicant then responds with an identity packet and the RADIUS server sends a challenge based on the identity packets sent from the supplicant.The supplicant
provides its credentials in the EAP-Response that the AP forwards to the
RADIUS server. If the response is valid and the credentials validated, the
RADIUS server sends a RADIUS-Access-Accept to the AP, which then allows
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the supplicant to communicate over a “controlled” port.This is communicated by
the AP to the supplicant in the EAP-Success packet.
Figure 4.8 EAP over LAN (EAPoL) Traffic Flow
Access Point
RADIUS server
Access Blocked
EAPoL Start
Access Allowed
Head of the Class…
So what exactly are 802.1x and 802.11x?
Wireless provides convenience and mobility, but also poses massive security challenges for network administrators, engineers, and security administrators. Security for 802.11 networks can be broken down into three
distinct components:
The authentication mechanism
The authentication algorithm
Data frame encryption
Current authentication in the IEEE 802.11 standard is focused more on
wireless LAN connectivity than on verifying user or station identity. Since
wireless can potentially scale very high in the sheer number of possible
users, it is important to consider a centralized way to have user authentication. This is where the IEEE 802.1x standard comes into play.
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User Identification and Strong Authentication
With the addition of the 802.1x standard, clients are identified by username, not
by the MAC addresses of the devices.This design not only enhances security, but
also streamlines the process of authentication, authorization, and accountability
(AAA) for the network. 802.1x was designed to support extended forms of
authentication using password methods (such as one-time passwords, or GSS_API
mechanisms like Kerberos) and non-password methods (such as biometrics,
Internet Key Exchange [IKE], and Smart Cards).
Dynamic Key Derivation
The IEEE 802.1x standard allows for the creation of per-user session keys.WEP
keys do not have to be kept at the client device or at the AP when using 802.1x.
These WEP keys are dynamically created at the client for every session, thus
making it more secure.The Global key, like a broadcast WEP key, can be
encrypted using a Unicast session key, and then sent from the AP to the
client in a much more secure manner.
Mutual Authentication
802.1x and EAP provide for a mutual authentication capability.This makes the
clients and the authentication servers mutually authenticating end points, and
assists in the mitigation of attacks from man-in-the-middle (MITM) types of
devices. Any of the following EAP methods provide for mutual authentication:
TLS Requires that the server supply a certificate and establish that it
has possession of the private key.
IKE Requires that the server show possession of a preshared key or
private key (this can be considered certificate authentication).
GSS_API (Kerberos) Requires that the server can demonstrate
knowledge of the session key.
Per-Packet Authentication
EAP can support per-packet authentication and integrity protection, but it is not
extended to all types of EAP messages. For example, negative acknowledgment
(NACK) and notification messages cannot use per-packet authentication and
integrity. Per-packet authentication and integrity protection works for the following (packet is encrypted unless otherwise noted):
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TLS and IKE derive session key
TLS ciphersuite negotiations (not encrypted)
IKE ciphersuite negotiations
Kerberos tickets
Success and failure messages that use a derived session key (through WEP)
EAP was designed to support extended authentication. When implementing EAP, dictionary attacks can be avoided by using non-passwordbased schemes such as biometrics, certificates, OTP, smart cards, and
token cards. Using a password-based scheme should require the use of
some form of mutual authentication so that the authentication process is
protected against dictionary attacks.
It is helpful to write out a table showing the various authentication
methods used in 802.11 networks (for example, open authentication,
shared-key authentication, and 802.1x authentication) with the various
properties each of these authentication methods require. This will help
keep them straight in your mind when taking the test.
Common Exploits of Wireless Networks
In general, attacks on wireless networks fall into four basic categories: passive
attacks, active attacks, MITM attacks, and jamming.
Passive Attacks on Wireless Networks
A passive attack occurs when someone eavesdrops on network traffic. Armed
with a wireless network adapter that supports promiscuous mode, eavesdroppers
can capture network traffic for analysis using easily available tools such as
Network Monitor in Microsoft products,TCPDump in Linux-based products, or
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Head of the Class…
AirSnort (developed for Linux, but Windows drivers can be written). A passive
attack on a wireless network may not be malicious in nature. In fact, many in the
wardriving community claim their wardriving activities are benign or “educational” in nature.Wireless communication takes place on unlicensed public frequencies—anyone can use these frequencies.This makes protecting a wireless
network from passive attacks more difficult.
Passive attacks are by their very nature difficult to detect. If an administrator is
using dynamic host control protocol (DHCP) on a wireless network (this is not
recommended), they may or may not notice that an authorized MAC address has
acquired an IP address in the DHCP server logs. Perhaps the administrator
notices a suspicious-looking car with an antenna sticking out of its window. If
the car is parked on private property, the driver could be asked to move or possibly be charged with trespassing. But, the legal response is severely limited. Only
if it can be determined that a wardriver was actively attempting to crack encryption on a network or otherwise interfere or analyze wireless traffic with malicious
intent, would they be susceptible to criminal charges. However, this also depends
on the country or state in which the activity took place.
The Legal Status of Wardriving and Responsibility
of Wireless Network Owners and Operators
Standard disclaimer: The law is a living and dynamic entity. What appears
to be legal today may become illegal tomorrow and vice versa. And what
may be legal in one country or state may be illegal in another.
Furthermore, the legal status of any particular activity is complicated by
the fact that such status arises from a number of different sources, such
as statutes, regulations, and case law precedents. The following text summarizes some of the current popular thinking regarding the legal status
of wardriving and related activities in the U.S. However, you should not
assume that the following in any way constitutes authoritative legal
advice or is definitive with regard to the legal status of wardriving.
If wardriving is defined as the benign activity of configuring a wireless device to receive signals (interference) from other wireless devices,
and then moving around to detect those signals without the presence
of an ulterior or malicious motive on the part of the wardriver, then
wardriving is probably legal in most jurisdictions. Most of this thinking
is based on Part 15 of the FCC regulations, which can be found at According to
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these regulations, wireless devices fall under the definition of Class B
devices, which must not cause harmful interference, and must accept any
interference they receive, including interference that harms operations.
(In Canada, the situation is identical, except that Class B devices are
known as Category I devices. For more information on Canadian regulations regarding low-power radio devices, see the Industry Canada Web
site at In other words, simply
accepting a signal from another wireless device could be considered a
type of interference that the device must be able to accept.
So far, wardriving appears legal; however, this is only because there
are no laws written to specifically address situations involving the computer-related transmission of data. On the other hand, cordless phones
use the same ISM and UNII frequencies as wireless networks, but wiretap
laws exist that make it illegal to intercept and receive signals from cordless phones without the consent of all the parties involved, unless the
interception is conducted by a law enforcement agency in possession of
a valid warrant. (In Canada, the situation is a little different and is based
on a reasonable expectation of privacy.)
No one has been charged with violating FCC regulations regarding
wardriving and the passive reception of computer-related data over the
ISM or UNII bands. However, in the wake of September 11, 2001, both the
federal and state governments passed new criminal laws addressing
breach of computer network security. Some of these laws are written in
such a way that makes any access to network communications illegal
without authorization. Although many of the statutes have not yet been
tested in court, it is safest to take the conservative path and avoid intentionally accessing any network that you do not have permission to access.
The issue gets more complicated when considering the implications
of associating with a wireless network. If a wireless network administrator
configures a DHCP server on a wireless network to allow any wireless station to authenticate and associate with the network, wireless users in the
vicinity may find that the wireless station automatically received IP address
configuration and associated with the wireless network, simply by being in
close proximity to the network. That is, without any intent on their part,
the person using a wireless-equipped computer can use the services of the
wireless network, including access to the Internet. Assume the person used
this automatic configuration to gain access to the Internet through the
wireless network. Technically, this could be considered theft of service in
some jurisdictions although the person has been, for all intents and purposes, welcomed on to the wireless network. Regardless of this “welContinued
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come,” however, if the laws in that jurisdiction prohibit all unauthorized
access, the person may be charged. Most such statutes set the required
culpable mental state at “intentional or knowing”. Thus, if the person
knows they are accessing a network, and does not have permission to do
so, the elements of the offense are satisfied.
Where a wardriver crosses the line from a “semi-legal” to an illegal
activity is when they collect and analyze data with malicious intent and
cause undesirable interference with the operation of a network. Cracking
WEP keys and other encryption on a network is almost universally illegal.
In this case, it is presumed that malicious intent to steal data or services
or interfere with operations can be established, since it requires a great
deal of effort, time, and planning to break into an encrypted network.
The onus to exercise due care and diligence to protect a wireless network falls squarely on the administrator, just as it is the responsibility of
corporate security personnel to ensure that tangible property belonging
to the company is secure and safe from theft. That is, it is up to the
administrator to ensure that the network’s data is not radiating freely in
such a way that anyone can receive it and interpret it using only licensed
wireless devices. This much is clear: administrators who do not take care
to protect their wireless networks put their companies at risk.
Passive attacks on wireless networks are extremely common, almost to the
point of being ubiquitous. Detecting and reporting on wireless networks has
become a popular hobby for many wireless wardriving enthusiasts. In fact, this
activity is so popular that a new term, “war plugging,” has emerged to describe
the behavior of people who wish to advertise the availability of an AP and the
services they offer, by configuring their SSIDs with text such as “Get_food_here.”
Wardriving Software
Most wardriving enthusiasts use a popular freeware program called NetStumbler,
which is available from NeStumbler program works
primarily with wireless network adapters that use the Hermes chipset because of
its ability to detect multiple APs that are within range and WEP. (A list of supported adapters is available at the NetStumbler Web site.) The most common card
that uses the Hermes chipset for use with NetStumbler is the ORiNOCO gold
card. Another advantage of the ORiNOCO card is that it supports the addition
of an external antenna, which can greatly extend the range of a wireless network.
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One disadvantage of the Hermes chipset is it does not support promiscuous
mode, so it cannot be used to sniff network traffic. For that purpose, a wireless
network adapter is needed that supports the PRISM2 chipset.The majority of
wireless network adapters targeted to the consumer market use this chipset (for
example, the Linksys WPC network adapters). Sophisticated wardrivers arm
themselves with both types of cards, one for discovering wireless networks and
another for capturing the traffic.
Wardrivers often make their own Yagi-type (tubular or cylindrical)
antennas. Instructions for doing so are easy to find on the Internet, and
effective antennas have been made out of such items as Pringles potato
chip cans. Another type of antenna that can be easily made is a dipole,
which is basically a piece of wire of a length that is a multiple of the
wavelength, cut in the center, and attached to a piece of cable that is
connected to the wireless network interface card (NIC).
In spite of the fact that NetStumbler is free, it is a sophisticated and featurerich product that is excellent for performing wireless site surveys. Not only can it
provide detailed information on the wireless networks it detects, but it can also
be used in combination with a global positioning system (GPS) to provide exact
details on the latitude and longitude of the detected wireless networks. Figure 4.9
shows the interface of a typical NetStumbler session.
As can be seen in Figure 4.9, NetStumbler displays information on the SSID,
the channel, and the manufacturer of the wireless AP.There are a few noteworthy
things about this session.The first is that some of the APs are still configured with
the default SSID supplied by the manufacturer, which should always be changed
to a non-default value upon setup and configuration. Another is that at least one
network uses a SSID that may provide a clue about the entity that implemented
it. Again, this is not a good practice when configuring SSIDs. Finally, you can see
which of these networks implemented WEP.
If the network administrator was kind enough to provide a clue about the
company in the SSID or is not encrypting traffic with WEP, the potential eavesdropper’s job is made a lot easier. Using a tool such as NetStumbler is only a preliminary step for an attacker. After discovering the SSID and other information,
an attacker can connect to a wireless network and sniff and capture network
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traffic.This network traffic can reveal a lot of information about the network and
the company that uses it. For example, looking at network traffic, an attacker can
determine what domain name system (DNS) servers are being used, the default
home pages configured on browsers, network names, logon traffic, and so on.The
attacker can use this information to determine if a network is of sufficient
interest to proceed further with other attacks. Furthermore, if a network is using
WEP, given enough time the attacker can capture a sufficient amount of traffic to
crack the encryption.
Figure 4.9 Discovering Wireless LANs Using NetStumbler
NetStumbler works on networks that are configured as open systems.This
means that the wireless network indicates that it exists and will respond with the
value of its SSID to other wireless devices when they send out a radio beacon
with an “empty set” SSID. However, this does not mean that a wireless network
can be easily compromised if other security measures have been implemented.
To defend against the use of NetStumbler and other programs that detect a
wireless network easily, administrators should configure the wireless network as a
closed system.This means that the AP will not respond to “empty set” SSID beacons
and will consequently be “invisible” to programs such as NetStumbler, which rely
on this technique to discover wireless networks. However, it is still possible to capture the “raw” 802.11b frames and decode them using programs such as ethereal
and Wild Packet’s AiroPeek to determine the information. RF spectrum analyzers
can also be used to discover the presence of wireless networks. Notwithstanding
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this weakness of closed systems, administrators should choose wireless APs that support this feature.
Active Attacks on Wireless Networks
Once an attacker has gained sufficient information from a passive attack, they can
launch an active attack against the network.There are a potentially large number
of active attacks that can be launched against a wireless network. For the most
part, these attacks are identical to the kinds of active attacks encountered on
wired networks.These include, but are not limited to, unauthorized access,
spoofing, Denial of Service (DoS), and flooding attacks, as well as the introduction of malware (malicious software) and the theft of devices.With the rise in
popularity of wireless networks, new variations of traditional attacks specific to
wireless networks have emerged along with specific terms to describe them, such
as “drive-by spamming” in which a spammer sends out hundreds of thousands of
spam messages using a compromised wireless network.
Because of the nature of wireless networks and the weaknesses of WEP, unauthorized access and spoofing are the most common threats to wireless networks.
Spoofing occurs when an attacker is able to use an unauthorized station to
impersonate an authorized station on a wireless network. A common way to protect a wireless network against unauthorized access is to use MAC filtering to
allow only clients that possess valid MAC addresses access to the wireless network.The list of allowable MAC addresses can be configured on the AP, or it can
be configured on a RADIUS server with which the AP communicates. However,
regardless of the technique used to implement MAC filtering, it is relatively easy
to change the MAC address of a wireless device through software. In Windows,
this is accomplished with a simple edit of the registry; in UNIX it is accomplished through a root shell command. MAC addresses are sent in the clear on
wireless networks, so it is also relatively easy to discover authorized addresses.
WEP can be implemented to provide more protection against authentication
spoofing through the use of shared-key authentication. However, as discussed earlier, shared-key authentication creates an additional vulnerability. Because sharedkey authentication makes visible both a plaintext challenge and the resulting
ciphertext version of it, it is possible to use this information to spoof authentication to a closed network.
Once an attacker has authenticated and associated with a wireless network,
they can run port scans, use special tools to dump user lists and passwords, impersonate users, connect to shares, and, in general, create havoc on the network
through DoS and flooding attacks. DoS attacks can be traditional in nature, such
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as a ping flood, SYN, fragment, or Distributed DoS (DDoS), or they can be specific
to a wireless network through the placement and use of rogue access points that
prevent wireless traffic from being forwarded properly (similar to router spoofing
on wired networks).
MITM Attacks on Wireless Networks
Placing a rogue AP within range of a wireless station is a wireless-specific variation of a MITM attack. If the attacker knows the SSID in use by the network
and the rogue AP has enough strength, wireless users will have no way of
knowing that they are connecting to an unauthorized AP. Using a rogue AP, an
attacker can gain valuable information about a wireless network, such as authentication requests, the secret key being used, and so on. Often, an attacker will set
up a laptop with two wireless adapters, in which one card is used by the rogue
AP and the other is used to forward requests through a wireless bridge to the
legitimate AP.With a sufficiently strong antenna, the rogue AP does not have to
be located in close proximity to the legitimate AP. For example, an attacker can
run a rogue AP from a car or van parked some distance away from a building.
However, it is also common to set up hidden rogue APs (under desks, in closets,
and so on) close to and within the same physical area as the legitimate AP.
Because of their undetectable nature, the only defense against rogue APs is vigilance through frequent site surveys (using tools such as NetStumbler and
AiroPeek), and physical security.
Frequent site surveys also have the advantage of uncovering unauthorized APs
that company staff members may have set up in their own work areas, thereby
compromising the entire network.This is usually done with no malicious intent,
but for the convenience of the user, who may want to be able to connect to the
network via their laptop in areas that do not have wired outlets. Even if a company does not use or plan to use a wireless network, they should consider conducting regular wireless site surveys to see if anyone has violated company
security policy by placing an unauthorized AP on the network.
Wireless Vulnerabilities
Wireless technologies are inherently more vulnerable to attack because of the
nature of the network transmissions.Wireless network transmissions are not physically constrained within the confines of a building or its surroundings, thus
allowing attackers ready access to the information in wireless networks. As wireless network technologies have emerged, they have become the focus of analysis
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by security researchers and hackers. Security researchers and hackers realize that
wireless networks can be insecure and can often be exploited as a gateway into
the relatively secure wired networks beyond them.This section covers the vulnerabilities that have been found in the WTLS and WEP security protocols.
WAP Vulnerabilities
WTLS has been criticized for many of its weaknesses, which include weak
encryption algorithms, the susceptibility of the protocol to chosen plaintext
attacks, message forgery, and others. Another problem with WTLS is the possibility of the compromise of the WAP gateway.This puts all of the data that passes
through the gateway at risk.
Markku-Juhani Saarinen published detailed descriptions of these and
other weaknesses in his paper Attacks against the WAP WTLS Protocol,
which is available at
The primary weaknesses associated with WAP stem from problems in the
WTLS protocol specification.These include such problems as:
The use of predictable IVs, leading to chosen-plaintext attacks
40-bit DES encryption
Susceptibility to probable plaintext attacks
Unauthenticated alert messages
The WAP Forum is currently working on a new version of WAP that may
address these and other weaknesses in WTLS.The draft titled The WAP Transport
Layer E2E Security Specification describes an architecture where the WAP gateway’s
role is minimized.
The Security+ exam covers WAP and its security mechanism, WTLS.
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WEP Vulnerabilities
As does any standard or protocol,WEP has some inherent disadvantages.The
focus of security is to allow a balance of access and control while juggling the
advantages and disadvantages of each implemented countermeasure for security
gaps. Some of WEP’s disadvantages include:
The RC4 encryption algorithm is a known stream cipher.This means it
takes a finite key and attempts to make an infinite psuedorandom key
stream in order to generate the encryption.
Altering the secret must be done across the board; all APs and clients
must be changed at the same time.
Used on its own,WEP does not provide adequate WLAN security.
WEP has to be implemented on every client and every AP, to be effective.
WEP is part of the IEEE 802.11 standard defined for wireless networks in
1999.WEP differs from many other kinds of encryption employed to secure network communication, in that it is implemented at the MAC sublayer of the Data
Link layer (Layer 2) of the OSI model. Security can be implemented at many different layers of the model. For example, Secure Internet Protocol (IPSec) is
implemented at the Network layer (Layer 3) of the OSI model. Point-to-Point
Tunneling Protocol (PPTP) creates a secure end-to-end tunnel by using the
Network layer (GRE) and Transport layer protocols to encapsulate and transport
data. HTTP-S and Secure Shell (SSH) are Application layer (Layer 7) protocols
for encrypting data. Because of the complexity of the 802.11 MAC and the
amount of processing power it requires, the 802.11 standard made 40-bit WEP an
optional implementation only.
Vulnerability to Plaintext Attacks
From the outset, knowledgeable people warned that WEP was vulnerable because
of the way it was implemented. In October 2000, Jesse Walker, a member of the
IEEE 802.11 working group, published his now famous paper, “Unsafe at Any
Key Size: An Analysis of WEP Encapsulation.”The paper points out a number of
serious shortcomings of WEP and recommends that WEP be redesigned. For
example,WEP is vulnerable to plaintext attacks because it is implemented at the
data link layer, meaning that it encrypts IP datagrams. Each encrypted frame on a
wireless network contains a high proportion of well-known TCP/IP information,
which can be revealed fairly accurately through traffic analysis, even if the traffic
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is encrypted. If a hacker can compare the ciphertext (the WEP-encrypted data) to
the plaintext equivalent (the raw TCP/IP data), they have a powerful clue for
cracking the encryption used on the network. All they would have to do is plug
the two values (plaintext and ciphertext) into the RC4 algorithm used by WEP
to uncover the keystream used to encrypt the data.
Vulnerability of RC4 Algorithm
As discussed in the previous paragraph, another vulnerability of WEP is that it
uses RC4, a stream cipher developed by RSA to encrypt data. In 1994, an
anonymous user posted the RC4 algorithm to a cipherpunk mailing list, which
was subsequently re-posted to a number of Usenet newsgroups with the title
“RC4 Algorithm Revealed.” Until August 2001, it was thought that the underlying algorithm used by RC4 was well designed and robust, so even though the
algorithm was no longer a trade secret, it was still thought to be an acceptable
cipher to use. However, Scott Fluhrer, Itsik Mantin, and Adi Shamir published a
paper entitled, “Weaknesses in the Key Scheduling Algorithm of RC4” that
demonstrated that a number of keys used in RC4 were weak and vulnerable to
compromise.The paper designed a theoretical attack that could take advantage of
these weak keys. Because the algorithm for RC4 is no longer a secret and
because there were a number of weak keys used in RC4, it is possible to construct software that is designed to break RC4 encryption relatively quickly using
the weak keys in RC4. Not surprisingly, a number of open-source tools have
appeared, which do precisely this.Two such popular tools for cracking WEP are
AirSnort and WEPCrack.
Some vendors, such as Agere (which produces the ORiNOCO product line),
responded to the weakness in key scheduling by modifying the key scheduling in
their products to avoid the use of weak keys, making them resistant to attacks
based on weak key scheduling.This feature is known as WEPplus.
Stream Cipher Vulnerability
WEP uses an RC4 stream cipher, which differs from block ciphers such as DES
or AES, which perform mathematical functions on blocks of data, in that the data
or the message is treated as a stream of bits.To encrypt the data, the stream cipher
performs an Exclusive OR (XOR) of the plaintext data against the keystream to
create the ciphertext stream. (An XOR is a mathematical function used with
binary numbers. If the bits are the same the result of the XOR is “0”; if different,
the result of the XOR is “1”.)
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If a keystream were always the same, it would be relatively easy to crack the
encryption if an attacker had both the plaintext and the ciphertext version of the
message (known as a plaintext attack).To create keystreams that are statistically
random, a key and a PRNG are used to create a keystream that is XOR’d against
the plaintext message to generate the ciphertext.
In the case of WEP, a number of other elements are involved to encrypt and
decrypt messages.To encrypt an 802.11 frame, the following process occurs:
1. A cyclic redundancy check (CRC), known as an ICV, is calculated
for the message and appended to the message to produce the plaintext
2. RC4 is used to create a pseudorandom keystream as a function of a 24bit IV and the shared secret WEP key.The IV and the shared secret WEP
key are used to create the RC4 key schedule. A new IV is used for every
frame to be transmitted.
3. The resulting keystream is XOR’d with the plaintext message to create a
4. The IV is concatenated with the ciphertext in the appropriate field and
bit set to indicate a WEP-encrypted frame.
To decrypt the ciphertext, the receiving station does the following:
1. Checks the bit-denoting encryption.
2. Extracts the IV from the frame to concatenate it with the shared secret
WEP key.
3. Creates the keystream using the RC4 key schedule.
4. XOR’s the ciphertext with the keystream to create the plaintext.
5. Performs an integrity check on the data using the ICV appended to the
end of the data.
A central problem with WEP is the potential for reuse of the IV. A wellknown vulnerability of stream ciphers is the reuse of an IV and key to encrypt
two different messages.When this occurs, the two ciphertext messages can be
XOR’d with each other to cancel out the keystream, resulting in the XOR of
the two original plaintexts. If the attacker knows the contents of one of these
plaintext messages, they can easily obtain the plaintext of the other message.
Although there are 16,777,216 possible combinations for the IV, this is actually a relatively small number. On a busy wireless network, the range of possible
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combinations for the IV can be exhausted in a number of hours (remember, each
frame or packet uses a different IV). Once an attacker has collected enough
frames that use duplicate IVs, they can use the information to derive the shared
secret key. In the absence of other solutions for automatic key management and
out-of-band or encrypted dynamic key distribution, shared secret WEP keys have
to be manually configured on the APs and wireless client workstations. Because
of the administrative burden of changing the shared secret key, administrators
often do not change it frequently enough.
Head of the Class…
More Information on WEP
There are many excellent resources available on the Internet that you can
consult if you wish to learn more about WEP and its weaknesses. You may
want to start with Jesse Walker’s famous whitepaper entitled “Unsafe at
Any Key Size; An Analysis of WEP Encapsulation,” which started the initial
uproar about the weaknesses of WEP. This paper can be found at Another excellent source of information is “Intercepting Mobile
Communications: The Insecurity of 802.11” by Nikita Borisov, Ian Goldberg,
and David Wagner. This paper can be found at
papers/wep-mob01.pdf. “Your 802.11 Wireless Network Has No Clothes,”
by William A. Arbaugh, Narendar Shankar, and Y.C. Justin Wan covers similar ground to the previous two papers, but also introduces important information on problems with access control and authentication mechanisms
associated with wireless networks. This paper can be found at
To make matters worse, hackers do not have to wait until the 24-bit IV key
space is exhausted to find duplicate IVs (remember, these are transmitted in the
frame of the message). In fact, it is almost certain that hackers will encounter a
duplicate IV in far fewer frames or discover a number of weak keys.The reason is
that upon reinitialization, wireless PC cards reset the IV to “0”.When the wireless client begins transmitting encrypted frames, it increments the IV by “1” for
each subsequent frame. On a busy network, there are likely to be many instances
of wireless PC cards being reinitialized, thereby making the reuse of the loworder IVs a common occurrence. Even if the IVs were randomized rather than
being used in sequence, this would not be an adequate solution because of the
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birthday paradox.The birthday paradox predicts the counterintuitive fact that
within a group as small as 23 people, there is a 50 percent chance that two
people will share the same birthday.
It does not really matter whether a wireless network is using 64- or 128-bit
encryption (in reality, these constitute 40- and 104-bit encryption once the 24
bits for the IV is subtracted). Both use a 24-bit long IV. Given the amount of
traffic on a wireless network and the probability of IV collisions within a relatively short period of time, a 24-bit IV is far too short to provide meaningful
protection against a determined attacker.
Should You Use WEP?
The existence of these vulnerabilities does not mean WEP should not be used.
One of the most serious problems with wireless security is not that it is insecure,
but that a high percentage of wireless networks discovered by wardrivers are not
using WEP. All wireless networks should be configured to use WEP, which is
available for free with wireless devices. At the very least,WEP prevents casual
wardrivers from compromising a network and slows down knowledgeable and
determined attackers.The following section looks at how to configure APs and
Windows XP wireless clients to use static WEP keys.
The level of knowledge about WEP presented in this chapter is crucial to
functioning in a wireless environment, and should be something you
know well if you plan to work in such an environment. However, for the
Security+ exam, focus on what WEP is, its basic definition, and its basic
Security of 64-Bit versus 128-Bit Keys
To a nontechnical person it may seem that a message protected with a 128-bit
encryption scheme would be twice as secure as a message protected with a 64-bit
encryption scheme. However, this is not the case with WEP. Since the same IV
vulnerability exists with both encryption levels, they can be compromised within
similar time limits.
With 64-bit WEP, the network administrator specifies a 40-bit key—typically
10 hexadecimal digits (0 through 9, a through f, or A through F). A 24-bit IV is
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appended to the 40-bit key, and the RC4 key scheme is built from these 64 bits
of data.This same process is followed in the 128-bit scheme.The administrator
specifies a 104-bit key—this time 26 hexadecimal digits (0 through 9, a through
f, or A through F).The 24-bit IV is added to the beginning of the key, and the
RC4 key schedule is built.
Because the vulnerability stems from capturing predictably weak IVs, the size
of the original key does not make a significant difference in the security of the
encryption.This is due to the relatively small number of total IVs possible under
the current WEP specification. Currently, there are a total of 16,777,216 possible
IV keys. Because every frame or packet uses an IV, this number can be exhausted
within hours on a busy network. If the WEP key is not changed within a strictly
defined period of time, all possible IV combinations can be intercepted off of an
802.11b connection, captured, and made available for cracking within a short
period of time.This is a design flaw of WEP, and bears no correlation to whether
the wireless client is using 64-bit WEP or 128-bit WEP.
Acquiring a WEP Key
As mentioned previously, programs exist that allow an authenticated and/or unassociated device within the listening area of the AP to capture and recover the
WEP key. Depending on the speed of the machine listening to the wireless conversations, the number of wireless hosts transmitting on the WLAN, and the
number of IV retransmissions due to 802.11 frame collisions, the WEP key could
be cracked within a couple of hours. However, if an attacker attempts to listen to
a WEP-protected network at a time of low network traffic volume, it would take
significantly longer to get the data necessary to crack WEP.
As a minimum requirement, static WEP keys should be configured on APs
and wireless clients. If the hardware is Wi–Fi compliant, a minimum of
64-bit encryption can be set (a 40-bit key with a 24-bit IV). However, if
available on the hardware, 128-bit encryption should be selected (a 104bit key with a 24-bit IV). Some vendors now provide 256-bit WEP.
However, this is proprietary technology and, because it is not standard,
may not be interoperable between the different vendors.
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Most APs allow for configuration of up to four different WEP keys for
use on a wireless network. However, only one of these WEP keys can be
used at one time. The reason for configuring up to four WEP keys is to
provide an easy means for rolling over keys according to a schedule.
Figure 4.10 shows the WEP Key configuration property for a Linksys
Figure 4.10 Configuring WEP Keys on a Linksys WAP11
A number of wireless devices, such as the Linksys WAP11 shown in
Figure 4.10, allow the use of a passphrase to generate the WEP keys.
This helps simplify the process of generating new keys. However, potential attackers may know the algorithm for generating the keys from a
passphrase, so it is necessary to choose hard-to-guess passphrases if
using this method to generate keys.
The Linksys WAP11 allows administrators to create WEP keys using
hexadecimal digits only. Other APs give the choice of creating WEP keys
using either ASCII characters or HEX digits. The advantage of using ASCII
characters is that there are fewer of them to type in: 13 characters versus
26 hexadecimal digits to create a 104-bit key length. The convenience of
using ASCII characters is even more apparent when the wireless client is
Windows XP with Service Pack 1 (SP1) installed. SP1 changes the wireless
interface so that the WEP keys have to be configured using ASCII characters. If an AP only supports the use of hexadecimal digits for the WEP
key, the hexadecimal digits have to be converted to ASCII characters to
configure the Windows XP SP1 clients.
Once the AP is configured with the WEP keys, the wireless interface
is configured with the WEP key corresponding to the one WEP key currently being used by the AP. (Remember, both the wireless client and the
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AP have to use the same WEP key as a kind of shared secret. If there is
no available mechanism to automate the distribution and configuration
of dynamic WEP keys, they must be manually configured.) Windows XP
allows for the configuration of only one WEP key per SSID profile. Figure
4.11 shows the property page for configuring WEP keys on Windows XP.
Figure 4.11 Configuring a Static WEP Key on Windows XP
To configure static WEP keys in Windows XP:
1. Open Network Connections | Wireless Network Connection
Properties and click on the Wireless Networks tab.
2. If the wireless network has already been detected, select the
appropriate network denoted by the SSID in the Preferred
Networks dialog box and click Properties. Otherwise, click the
Add button below the Preferred Networks dialog box.
3. In the Wireless Network Properties page (Figure 4.11), enter the
SSID, if required, and select Data Encryption (WEP enabled).
4. Deselect the box indicating The key is provided for me automatically. (This is used if the software and/or hardware allows for
the automatic distribution of dynamic WEP keys (for example,
802.1x authentication using EAP-TLS.)
5. Enter the Network key. The length of the key entered determines
the Key Length (for example, 5 or 13 ASCII characters), so it is not
necessary to indicate the length.
6. Select the Key format, if necessary.
7. Select the Key index the AP is using. This is an important, if
under-documented, point: The same key index must be used on
the wireless client adapter as is used on the AP itself. If using the
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WEP key that corresponds to the first key configured on the AP,
select 0 as the Key index; select 1 as the key index if using the
second key configured on the AP; and so on.
Figure 4.11 also shows the option Network authentication (shared
mode). This option should be selected if the AP was configured to use
shared-key authentication. Figure 4.12, shows the interface for configuring shared-key authentication on the Linksys WAP11 AP.
Damage & Defense…
Figure 4.12 Configuring Shared-Key Authentication on WAP11 AP
WEP Key Compromise
Because casual attackers are now capable of WEP key retrieval, keeping
the same static WEP key in a production role for an extended period of
time does not make sense. A static WEP key could be published into the
underground by a hacker and still be used in a production WLAN six
months later if there are no policies in place mandating regular change of
keys. One of the easiest ways to mitigate the risk of WEP key compromise
is to regularly change the WEP key on all APs and wireless clients.
Although this is an easy task for administrators of small WLANs, it
becomes extremely daunting on a large enterprise-size network. Both
Cisco Systems and Funk Software have released access control servers that
implement rapid WEP rekeying on both APs and the end-user clients. Even
if a WEP key is discovered, utilizing this form of software within a specified period of time will render that particular key to be invalid.
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Armed with a valid WEP key, an intruder can successfully negotiate association with an AP and gain entry to the target network. Unless other mechanisms
like MAC filtering are in place, this intruder can roam across the network and
potentially break into servers or other systems.
Addressing Common Risks and Threats
The advent of wireless networks has not created new legions of attackers. Many
attackers utilize the same attacks for the same objectives they used in wired networks. Unless administrators protect their wireless infrastructure with proven
tools and techniques, and establish standards and policies that identify proper
deployment and security methodology, the integrity of wireless networks will be
Finding a Target
Utilizing new tools created for wireless networks and the existing identification
and attack techniques and utilities originally designed for wired networks,
attackers have many avenues into a wireless network.The first step in attacking a
wireless network involves finding a network to attack.The most popular software
developed to identify wireless networks was NetStumbler (
NetStumbler is a Windows application that listens for information, such as the
SSID, being broadcast from APs that have not disabled the broadcast feature.
When it finds a network, it notifies the person running the scan and adds it to
the list of found networks.
As people began to drive around their towns and cities looking for wireless
networks, NetStumbler added features such as pulling coordinates from Global
Positioning System (GPS) satellites and plotting the information on mapping
software.This method of finding networks is reminiscent of the method hackers
used to find computers when they had only modems to communicate.They ran
programs designed to search through all possible phone numbers and call each
one, looking for a modem to answer.This type of scan was typically referred to as
wardialing; driving around looking for wireless networks is known as wardriving. has a Web site where people can upload the output of their
war drives for inclusion into a database that graphs the location of wireless networks ( See Figure 4.13 for the output of discovered and uploaded wireless networks as of October 2002.
Similar tools are available for Linux and other UNIX-based operating
systems.These tools contain additional utilities that hackers use to attack hosts
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and networks once access is found. A quick search on or for “802.11” reveals several network identification
tools, as well as tools used to configure and monitor wireless network connections.
Figure 4.13 Networks Discovered with NetStumbler
Installing NetStumbler is simple: You just go to,
select the downloads link in the main menu, and click on the Network
Stumbler link on the downloads page. Once the installer has been
downloaded, double-click on it and follow the instructions to install
With NetStumbler installed, double-click on the icon to start it up. If
you do not have a wireless card inserted in your machine you will get the
screen shown in Figure 4.14.
Notice the error message at the bottom of NetStumbler’s screen. If
this occurs, insert a wireless network card or, if your system has a wireless network card on the mini-PCI bus, make sure it has been enabled.
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Figure 4.14 NetStumbler Main Screen
Once the wireless network card has been installed or enabled,
NetStumbler automatically begins picking up wireless network and
clients, as shown in Figure 4.15.
Figure 4.15 Wireless Networks and Clients Detected by NetStumbler
In this example, there are two APs in the area. Both are identified as
Cisco Aironet APs with WEP enabled. One AP is on channel 6 while the
other is on channel 1. The SSIDs are visible as 020020141 and stattest.
On the left side of the NetStumbler screen, it is possible to limit the display of the various wireless devices based on whether certain attributes
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are on or off. For example, if you wish to only see APs that have WEP
turned off, select the Encryption Off filter. This is shown in Figure 4.16.
Figure 4.16 NetStumbler with Filtering for Wireless Networks without
Additional information about an individual AP or client can be found
by selecting its MAC address either under the Channels or the SSIDs
menu in NetStumbler, as shown in Figure 4.17.
Figure 4.17 Additional Information from NetStumbler
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This information shows the strength of the device’s signal. The black
lines in the field indicate when the signal was lost. The closer the green
area gets to zero, the stronger the signal. By using NetStumbler, an
attacker can determine where an AP or a client is located, as well as
what characteristics have been enabled on the wireless network. This
same tool can be used by network administrators for site surveys of their
Finding Weaknesses in a Target
Reports show that more than half of the wireless networks found to date do not
have encryption enabled.When an attacker finds such a network they have complete access to any resources the wireless network is connected to.The attacker
can scan and attack any machines local to the network, or use those machines as
agents to launch attacks on remote hosts.
If an attacker finds a network with WEP enabled, they will need to identify
several items to reduce the time it takes to get onto the wireless network. First,
utilizing the output of NetStumbler or another network discovery tool, the
attacker will identify the SSID, network, MAC address, and any other packets that
might be transmitted in cleartext. Generally, NetStumbler results include vendor
information, which an attacker can use to determine which default keys to
attempt on the wireless network.
If the vendor information has been changed or is unavailable, the attacker
might still be able to use the SSID and network name and address to identify the
vendor or owner of the equipment. (Many people use the same network name as
the password, or use the company initials or street address as their password.) If
the SSID and network name and address have been changed from the default setting, a final network-based attempt could be to use the MAC address to identify
the manufacturer.
If none of these options work, there is still the possibility of a physical review.
Many public areas are participating in the wireless revolution. An observant
attacker might be able to use physical and wireless identification techniques such
as finding antennas, APs, and other wireless devices that are easily identified by
the manufacturer’s casing and logo.
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Exploiting Those Weaknesses
A well-configured wireless AP will not stop a determined attacker. Even if the
network name and SSID are changed and the secret key is manually reconfigured
on all workstations on a regular basis, the attacker can still take other avenues to
compromise the network.
If easy physical access is available near the wireless network (for example, a
parking lot or garage next to the building being attacked), the only thing an
attacker needs is patience and AirSnort or WEPCrack.When these applications
have captured enough “weak” packets (IV collisions, for example), the attacker is
able to determine the secret key currently in use on the network. Quick tests
have shown that an average home network can be cracked in an overnight session.To ensure network protection, the WEP key would have to be changed at
least two times per day!
If none of these network tools help determine which default configurations
to try, the next step is to scan the traffic for any cleartext information that may
be available. Some brands of wireless equipment, such as those made by Lucent,
have been known to broadcast the SSID in cleartext even when WEP and closed
network options are enabled. Using tools such as Ethereal (
and tcpdump ( allows attackers to sniff traffic and analyze it
for any cleartext hints they may find.
As a last option, attackers might go directly after the equipment or install
their own.The number of laptops or accessories stolen from travelers is rising
each year. Criminals simply looking to sell the equipment perpetrated these thefts
at one time, but as criminals become more savvy, they also go after the information contained within the machines. Access to the equipment allows for the
determination of valid MAC addresses that can access the network, the network
SSID, and the secret keys to be used.
An attacker does not need to become a burglar in order to acquire this information. A skilled attacker can utilize new and specially designed malware and
network tricks to determine the information needed to access the wireless network. A well-scripted Visual Basic script, which could arrive in e-mail (targeted
spam) or through an infected Web site, can extract the information from the
user’s machine and upload it to the attacker’s.
With the size of computers so small today, it would not take much for an
attacker to create a small AP of their own that could be attached to a building or
office, and which looks just like another telephone box. Such a device, if placed
properly, will attract much less attention than someone camping in a car in the
parking lot will.
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Originally conceived as a legitimate network and traffic analysis tool, sniffing
remains one of the most effective techniques in attacking a wireless network,
whether it is to map the network as part of a target reconnaissance, to grab passwords, or to capture unencrypted data.
Sniffing is the electronic form of eavesdropping on the communications that
computers transmit across networks. In early networks, the equipment that connected machines allowed every machine on the network to see the traffic of all
others.These devices, repeaters and hubs, were very successful in connecting
machines, but allowed an attacker easy access to all traffic on the network because
the attacker only needed to connect to one point to see the entire network’s traffic.
Wireless networks function similarly to the original repeaters and hubs. Every
communication across a wireless network is viewable to anyone who happens to
be listening to the network. In fact, a person who is listening does not even need
to be associated with the network in order to sniff.
Hackers have many tools available for attacking and monitoring wireless
networks, such as AiroPeek ( for
Windows, Ethereal for Windows, and UNIX or Linux and tcpdump or ngrep
( for a UNIX or Linux environment.These tools
work well for sniffing both wired and wireless networks.
All of these software packages function by putting the network card in promiscuous mode.When the NIC is in this mode, every packet that goes past the interface is captured and displayed within the application window. If an attacker
acquires a WEP key, they can utilize features within AiroPeek and Ethereal to
decrypt either live or post-capture data.
By running NetStumbler, hackers are able to find possible targets. Figure 4.18
shows the output from NetStumbler with several networks that could be
Once a hacker has found possible networks to attack, one of their first tasks is
to identify the target. Many organizations are “nice” enough to include their
names or addresses in the network name.
Even if the network administrator has configured his equipment in such a
way as to hide this information, there are tools available that can determine this
information. Utilizing any of the mentioned network sniffing tools, an attacker
can easily monitor the unencrypted network. Figure 4.19 shows a network sniff
of the traffic on a wireless network. From this session, it is simple to determine
the DNS server and the default search domain and default Web home page.With
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this information, an attacker can easily identify a target and determine if it is
worth attacking.
Figure 4.18 Discovering Wireless LANs with NetStumbler
Figure 4.19 Sniffing with Ethereal
If the network is encrypted, the hacker will start by determining the physical
location of the target. NetStumbler has the ability to display the signal strength of
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the discovered networks (see Figure 4.20). Utilizing this information, the attacker
only needs to drive around and look for a location where the signal strength
increases and decreases to determine the home of the wireless network.
Figure 4.20 Using Signal Strength to Find Wireless Networks
To enhance their ability to locate the positions of a wireless network, an
attacker can use directional antennas to focus the wireless interface in a specific
direction. An excellent source for wireless information, including information on
the design of directional antennas, is the Bay Area Wireless Users Group
Keep in mind that the most popular wireless network security scanning
tools are Ethereal, NetStumbler, AiroPeek, and Kismet. This will help you
analyze wireless networks in the field. Each tool has its benefits, so you
may want to try them all if you have access to them.
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Protecting Against Sniffing and Eavesdropping
As networking technology matured, wired networks were able to upgrade from
repeaters and hubs to a switched environment.These switches would send only
the traffic intended for a specific host over each individual port, making it difficult (although not impossible) to sniff the entire network’s traffic. Unfortunately,
this is not an option for wireless networks due to the nature of wireless communications.
The only way to protect wireless users from attackers who might be sniffing is
to utilize encrypted sessions wherever possible: SSL for e-mail connections, SSH
instead of Telnet, and Secure Copy (SCP) instead of File Transfer Protocol (FTP).
To protect a network from being discovered with NetStumbler, it is important to turn off any network identification broadcasts and, if possible, close down
the network to any unauthorized users.This prevents tools such as NetStumbler
from finding the network. However, the knowledgeable attacker will know that
just because the network is not broadcasting information, does not mean that the
network cannot be found.
All an attacker needs to do is utilize one of the network sniffers to monitor
for network activity. Although not as efficient as NetStumbler, it is still a functional way to discover and monitor networks. Even encrypted networks show
traffic to the sniffer. Once they have identified traffic, the attacker can then utilize
the same identification techniques to begin an attack on the network.
Spoofing (Interception)
and Unauthorized Access
The combination of weaknesses in WEP and the nature of wireless transmission
has revealed spoofing to be a real threat to wireless network security. Some wellpublicized weaknesses in user authentication using WEP have made authentication spoofing just one of an equally well-tested number of exploits by attackers.
One definition of spoofing is the ability of an attacker to trick network
equipment into thinking that the address from which a connection is coming is a
valid machine from its network. Attackers can accomplish this in several ways, the
easiest of which is to simply redefine the MAC address of the attacker’s wireless
or network card to be a valid MAC address.This can be accomplished in
Windows through a simple Registry edit. Several wireless providers also have
options available to define the MAC address for each wireless connection from
within the client manager application that is provided with the interface.
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There are several reasons that an attacker would spoof. If a network allows
only valid interfaces through MAC or IP address filtering, an attacker would need
to determine a valid MAC or IP address to be able to communicate on the network. Once that is accomplished, the attacker could then reprogram their interface with that information, allowing them to connect to the network by
impersonating a valid machine.
IEEE 802.11 networks introduce a new form of spoofing: authentication
spoofing. As described in their paper “Intercepting Mobile Communications:The
Insecurities of 802.11,” Borisov, Goldberg, and Wagner identified a way to utilize
weaknesses within WEP and the authentication process to spoof authentication into
a closed network.The process of authentication, as defined by IEEE 802.11, is very
simple. In a shared-key configuration, the AP sends out a 128-byte random string
in a cleartext message to the workstation that is attempting to authenticate.The
workstation then encrypts the message with the shared key and returns the
encrypted message to the AP. If the message matches what the AP is expecting, the
workstation is authenticated onto the network and access is allowed.
As described in the paper, if an attacker has knowledge of both the original
plaintext and ciphertext messages, it is possible to create a forged encrypted message. By sniffing the wireless network, an attacker is able to accumulate many
authentication requests, each including the original plaintext message and the
returned ciphertext-encrypted reply. From this, the attacker can easily identify the
keystream used to encrypt the response message.The attacker could then use it to
forge an authentication message that the AP accepts as a proper authentication.
The wireless hacker does not need many complex tools to succeed in
spoofing a MAC address. In many cases, these changes are either features of the
wireless manufacturers or can be easily changed through a Windows Registry
modification or through Linux system utilities. Once a valid MAC address is
identified, the attacker needs only to reconfigure his device to trick the AP into
thinking he is a valid user.
The ability to forge authentication onto a wireless network is a complex process.There are no known “off-the-shelf ” packages available that provide these services. Attackers need to either create their own tool or take the time to decrypt
the secret key by using AirSnort or WEPCrack.
If an attacker is using Windows 2000, and their network card supports reconfiguring the MAC address, there is another way to reconfigure this information.
A card supporting this feature can be changed through the System Control Panel.
Once an attacker is utilizing a valid MAC address, they are able to access any
resource available from the wireless network. If WEP is enabled, the attacker will
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have to either identify the WEP secret key or capture the key through malware
or stealing the user’s notebook.
Protecting Against Spoofing
and Unauthorized Attacks
Protecting against these attacks involves adding several additional components to
the wireless network.The following are examples of measures that can be taken:
Using an external authentication source such as RADIUS or SecurID,
will prevent an unauthorized user from accessing the wireless network
and the resources with which it connects.
Requiring wireless users to use a VPN to access the wired network also
provides a significant stumbling block to an attacker.
Another possibility is to allow only SSH access or SSL-encrypted traffic
into the network.
Many of WEP’s weaknesses can be mitigated by isolating the wireless
network through a firewall and requiring that wireless clients use a VPN
to access the wired network.
Network Hijacking and Modification
Numerous techniques are available for an attacker to “hijack” a wireless network
or session. And unlike some attacks, network and security administrators may be
unable to tell the difference between the hijacker and a legitimate “passenger.”
Many tools are available to the network hijacker.These tools are based on
basic implementation issues within almost every network device available today.
As TCP/IP packets go through switches, routers, and APs, each device looks at
the destination IP address and compares it with the IP addresses it knows to be
local. If the address is not in the table, the device hands the packet off to its
default gateway.
This table is used to coordinate the IP address with the MAC addresses that
are known to be local to the device. In many situations, this is a dynamic list that
is compiled from traffic passing through the device and through Address
Resolution Protocol (ARP) notifications from new devices joining the network.
There is no authentication or verification that the request received by the device
is valid.Thus, a malicious user is able to send messages to routing devices and APs
stating that his MAC address is associated with a known IP address. From then
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on, all traffic that goes through that router destined for the hijacked IP address
will be handed off to the hacker’s machine.
If the attacker spoofs as the default gateway or a specific host on the network,
all machines trying to get to the network or the spoofed machine will connect to
the attacker’s machine instead of to the gateway or host to which they intended
to connect. If the attacker is clever, they will only use this to identify passwords
and other necessary information and route the rest of the traffic to the intended
recipients. If they do this, the end users will have no idea that this “man-in-themiddle” has intercepted their communications and compromised their passwords
and information.
Another clever attack can be accomplished using rogue APs. If an attacker can
put together an AP with enough strength, end users may not be able to tell
which AP is the authorized one that they should be using. In fact, most will not
even know that another is available. Using this technique, an attacker is able to
receive authentication requests and information from the end workstation
regarding the secret key and where they are attempting to connect.
Rogue APs can also be used to attempt to break into more tightly configured
wireless APs. Utilizing tools such as AirSnort and WEPCrack requires a large
amount of data to be able to decrypt the secret key. A hacker sitting in a car in
front of a house or office is noticeable, and thus will generally not have enough
time to finish acquiring enough information to break the key. However, if an
attacker installs a tiny, easily hidden machine in an inconspicuous location, it
could sit there long enough to break the key and possibly act as an external AP
into the wireless network it has hacked.
Attackers who wish to spoof more than their MAC addresses have several tools
available. Most of the tools available are for use in a UNIX environment and can
be found through a simple search for “ARP Spoof ” at http://packetstormsecurity
.com.With these tools, hackers can easily trick all machines on a wireless network
into thinking that the hacker’s machine is another valid machine.Through simple
sniffing on the network, an attacker can determine which machines are in high use
by the workstations on the network. If the attacker then spoofs the address of one
of these machines, they might be able to intercept much of the legitimate traffic on
the network.
AirSnort and WEPCrack are freely available.While it would take additional
resources to build a rogue AP, these tools run from any Linux machine.
Once an attacker has identified a network for attack and spoofed their MAC
address to become a valid member of the network, they can gain further information that is not available through simple sniffing. If the network being attacked
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is using SSH to access the hosts, stealing a password might be easier than
attempting to break into the host using an available exploit.
By ARP spoofing the connection with the AP to be that of the host from
which the attacker wants to steal the passwords, an attacker can cause all wireless
users who are attempting to SSH into the host to connect to the rogue machine
instead.When these users attempt to sign on with their passwords, the attacker is
able to, first, receive their passwords, and second, pass on the connection to the
real end destination. If an attacker does not perform the second step, it increases
the likelihood that the attack will be noticed, because users will begin to complain that they are unable to connect to the host.
Protection against Network
Hijacking and Modification
There are several different tools that can be used to protect a network from IP
spoofing with invalid ARP requests.These tools, such as arpwatch, notify an
administrator when ARP requests are detected, allowing the administrator to take
the appropriate action to determine whether someone is attempting to hack into
the network.
Another option is to statically define the MAC/IP address definitions.This
prevents attackers from being able to redefine this information. However, due to
the management overhead in statically defining all network adapters’ MAC
addresses on every router and AP, this solution is rarely implemented.There is no
way to identify or prevent attackers from using passive attacks, such as from
AirSnort or WEPCrack, to determine the secret keys used in an encrypted wireless network.The best protection available is to change the secret key on a regular
basis and add additional authentication mechanisms such as RADIUS or dynamic
firewalls to restrict access to the wired network. However, unless every wireless
workstation is secure, an attacker only needs to go after one of the other wireless
clients to be able to access the resources available to it.
Denial of Service and Flooding Attacks
The nature of wireless transmission, and especially the use of spread spectrum
technology, makes wireless networks especially vulnerable to denial of service (DoS)
attacks.The equipment needed to launch such an attack is freely available and
very affordable. In fact, many homes and offices contain the equipment that is
necessary to deny service to their wireless networks.
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A DoS attack occurs when an attacker has engaged most of the resources a
host or network has available, rendering it unavailable to legitimate users. One of
the original DoS attacks is known as a ping flood. A ping flood utilizes misconfigured equipment along with bad “features” within TCP/IP to cause a large
number of hosts or devices to send an ICMP echo (ping) to a specified target.
When the attack occurs, it uses a large portion of the resources of both the network connection and the host being attacked.This makes it very difficult for
valid end users to access the host for normal business purposes.
In a wireless network, several items can cause a similar disruption of service.
Probably the easiest way to do this is through a conflict within the wireless spectrum, caused by different devices attempting to use the same frequency. Many
new wireless telephones use the same frequency as 802.11 networks.Through
either intentional or unintentional uses of another device that uses the 2.4 GHz
frequency, a simple telephone call can prevent all wireless users from accessing the
Another possible attack is through a massive number of invalid (or valid)
authentication requests. If the AP is tied up with thousands of spoofed authentication attempts, authorized users attempting to authenticate would have major
difficulties in acquiring a valid session.
As demonstrated earlier, an attacker has many tools available to hijack network connections. If a hacker is able to spoof the machines of a wireless network
into thinking that the attacker’s machine is their default gateway, not only will
the attacker be able to intercept all traffic destined for the wired network, but
they will also be able to prevent any of the wireless network machines from
accessing the wired network.To do this, a hacker needs only to spoof the AP and
not forward connections on to the end destination, preventing all wireless users
from doing valid wireless activities.
Not much effort is needed to create a wireless DoS attack. In fact, many users
create these situations with the equipment found in their homes and offices. In a
small apartment building, you could find several APs as well as many wireless
telephones, all of which transmit on the same frequency.These users could easily
inadvertently create DoS attacks on their own networks as well as on those of
their neighbors.
A hacker who wants to launch a DoS attack against a network with a flood
of authentication strings also needs to be a well-skilled programmer.There are
not many tools available for creating this type of attack, but (as discussed earlier
regarding attempts to crack WEP) much of the programming required does not
take much effort or time. In fact, a skilled hacker should be able to create such a
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tool within a few hours.Then this simple application, when used with standard
wireless equipment, could render a wireless network unusable for the duration of
the attack.
Creating a hijacked AP DoS attack requires additional tools that can be found
on many security Web sites. See the earlier section “Sample Hijacking Tools” for a
starting point to acquiring some of the ARP spoofing tools needed.These tools
are not very complex and are available for almost every computing platform
Many apartments and older office buildings do not come prewired for the
high-tech networks used today.To add to the problem, if many individuals are
setting up their own wireless networks without coordinating the installations,
problems can occur that will be difficult to detect.
Only a limited number of frequencies are available to 802.11 networks. In
fact, once the frequency is chosen, it does not change until manually reconfigured. Considering these problems, it is not hard to imagine the following situation occurring:
A man goes out and purchases a wireless AP and several network cards for his
home network.When he gets home and configures his network, he is extremely
happy with how well wireless networking works. Suddenly, none of the machines
on the wireless network are able to communicate. After waiting on hold for 45
minutes to get through to the tech support line of the vendor who made the
device, he finds that the network has magically started working again, and hangs up.
Later that week, the same problem occurs, except this time he decides to wait
on hold.While waiting, he goes outside and begins discussing his frustration with
his neighbor. During the conversation, his neighbor’s kids come out and say that
their wireless network is not working.
So, they begin to do a few tests (while still waiting on hold). First, the man’s
neighbor turns off his AP (which is usually off to “protect” their network).When
this is done, the original person’s wireless network starts working again.Then
they turn on the neighbor’s AP again and his network stops working again.
At this point, a tech support representative finally answers and the caller
describes what has happened.The tech-support representative informs the user
that he needs to change the frequency used in the device to another channel. He
explains that the neighbor’s network is utilizing the same channel, causing the
two networks to conflict. Once the caller changes the frequency, everything starts
working properly.
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Protecting Against DoS and Flooding Attacks
There is little that can be done to protect against DoS attacks. In a wireless environment, an attacker does not have to even be in the same building or neighborhood.With a good enough antenna, an attacker is able to send these attacks from
a great distance away.
This is one of those times when it is valid to use NetStumbler in a nonhacking context. Using NetStumbler, administrators can identify other networks
that may be in conflict. However, NetStumbler will not identify other DoS
attacks or other non-networking equipment that is causing conflicts (such as
wireless telephones, wireless security cameras, amateur TV systems, RF-based
remote controls, wireless headsets, microphones and audio speakers, and other
devices that use the 2.4 GHz frequency).
IEEE 802.1x Vulnerabilities
The IEEE 802.1x standard is still relatively new in relation to the IEEE 802.11
standard, and the security research community is only recently beginning to seriously evaluate the security of this standard. One of the first groups to investigate
the security of the 802.1x standard was the Maryland Information Systems Security
Lab (MISSL) at the University of Maryland at College Park.This group, led by
Dr.William Arbaugh, was the first to release a paper (
Projects/wireless/ix.pdf) documenting flaws in the IEEE 802.1x standard. In this
paper, the group noted that 802.1x is susceptible to several attacks, due to the following vulnerabilities:
The lack of the requirement of strong mutual authentication.While
EAP-TLS does provide strong mutual authentication it is not required
and can be overridden.
The vulnerability of the EAP Success message to a MITM attack.
The lack of integrity protection for 802.1x management frames.
These flaws provide for avenues of attack against wireless networks.While the
networks are not as vulnerable as they would be without EAP and 802.1x, the
“silver-bullet” fix which designers had hoped for was not provided in the form
of 802.1x.
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Site Surveys A site survey is part of an audit done on wireless networks. Site surveys allow
system and network administrators to determine the extent to which their wireless networks extend beyond the physical boundaries of their buildings.Typically,
a site survey uses the same tools an attacker uses, such as a sniffer and a WEP
cracking tool (for 802.11 network site surveys).The sniffer can be either
Windows-based such as NetStumbler or UNIX/Linux-based such as Kismet. For
WEP cracking, AirSnort is recommended.
Other tools that can be useful are a directional antenna such as a Yagi antenna
or a parabolic dish antenna. Directional and parabolic dish antennae allow for the
reception of weak signals from greater distances by providing better amplification
and gain on the signal.These antennae allow wireless network auditors the ability
to determine how far an attacker can realistically be from the source of the wireless network transmissions in order to receive from and transmit to the network.
Finally, another tool that is useful for site surveys is a GPS locator.This provides for the determination of the geographical latitude and longitude of areas
where wireless signal measurements are taken. Using GPS, auditors can create a
physical map of the boundaries of the wireless network.
Site surveys are not covered extensively in the Security+ exam. However,
there may be a question about some of the tools used to conduct these
surveys. Remember that the tools used to conduct site surveys and audits
are essentially the same tools an attacker uses to gain access to a wireless network. Be prepared in case an Security+ exam question asks
whether a particular tool is used in wireless network site surveys.
Additional Security Measures
for Wireless Networks
Although 802.1x authentication provides good security through the use of
dynamically generated WEP keys, security administrators may wish to add more
layers of security. Additional security for wireless networks can be introduced
through the design of the network itself. As stated previously, a wireless network
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should always be treated as an untrusted network.This has implications for the
design and topology of the wireless network.
Using a Separate Subnet for Wireless Networks
Many wireless networks are set up on the same subnets as the wired network.
Also, to make life easier for administrators and users alike, both wired and wireless
clients are often configured as DHCP clients and receive IP address configurations from the same DHCP servers.There is an obvious security problem with
this approach as this configuration makes it easy for hackers to acquire valid IP
address configurations that are on the same subnet as the corporate networks,
which can pose a significant threat to the security of the network.
The solution is to place wireless APs on their own separate subnets, in effect
creating a kind of Demilitarized Zone (DMZ) for the wireless network.The
wireless subnet could be separated from the wired network by either a router or
a full-featured firewall, such as an ISA server.There are a number of advantages to
this approach.When a wireless network is placed on a separate subnet, the router
can be configured with filters to provide additional security for the wireless network. Furthermore, through the use of an extended subnet mask on the wireless
network, the number of valid IP addresses can be limited to approximately the
number of valid wireless clients. Finally, in the case of potential attack on the
wireless network, the router can be quickly shut down to prevent any further
access to the wired network until the threat has been removed.
If you have to support automatic roaming between wireless zones, you will
still want to use DHCP on the wireless subnets. However, if you do not need to
support automatic roaming, you may want to consider not using DHCP and
manually configuring IP addresses on the wireless clients.This will not prevent a
hacker from sniffing the air for valid IP addresses to use on the wireless subnet,
but it will provide another barrier for entry and consume time. Additionally, if a
hacker manually configures an IP address that is in use by another wireless client,
the valid user will receive an IP address conflict message, providing a crude
method for detecting unauthorized access attempts.
Using VPNs for Wireless Access to Wired Network
In high security networks, administrators may wish to leverage the separate
subnet by only allowing access to the wired network through a VPN configured
on the router or firewall. For wireless users to gain access to a wired network,
they would first have to successfully authenticate and associate with the AP and
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then create a VPN tunnel for access to the wired network. Some vendors, such as
Colubris, offer VPN solutions built into wireless devices.These devices act as
VPN-aware clients that forward only VPN traffic from the wireless network to
the wired network, or they can provide their own VPN server for wireless clients.
However, it is not necessary to use a proprietary hardware-based solution. One
solution is to use freeware known as Dolphin from that will
turn a PC into an appliance that encrypts wireless traffic with IPSec. Figure 4.21
below shows a network topology for this level of security.
Figure 4.21 Using a VPN for Wireless Access to Wired Network
Wireless Network
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For more information on this technology, see
When a VPN is required for access to a corporate network from a wireless
network subnet, all traffic between the two networks is encrypted within the
VPN tunnel. If using static WEP, a VPN ensures a higher degree of confidentiality
for traffic. Even if the WEP encryption is cracked, the hacker would still have to
crack the VPN encryption to see the corporate traffic, which is much more difficult. If a wireless laptop is stolen and the theft unreported, the thief would have
to know the user credentials to gain access to the VPN.
It is important to ensure that the user does not configure the VPN connection to save the username and password. Although this makes it
more convenient for the user, who does not have to type the account
name and password each time they use the VPN connection, it provides
a thief with the credentials needed to access the VPN.
Of course, this kind of configuration is still vulnerable to attack. If, for
example, an attacker has somehow acquired user names and passwords (or the
user has saved them in the VPN connection configuration), they can still access
the wired network through the VPN. Another consideration is the additional
overhead of encryption used in the VPN tunnel. If also using WEP, the combined
loss of bandwidth as a result of the encryption could easily be noticeable. Again,
administrators have to compare the benefits of implementing a VPN for wireless
clients in a DMZ against the cost of deployment in terms of hardware, software,
management, loss of bandwidth, and other factors.
Setting up this kind of configuration can be a relatively complex undertaking,
depending on a number of factors. If, for example, 802.1x authentication is being
used, it is important to ensure that 802.1x-related traffic can pass between the
wireless and wired network without a VPN tunnel. If using ISA server to separate
networks, you would have to publish the RADIUS server on the corporate network to the wireless network.
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Temporal Key Integrity Protocol
As noted earlier, the use of WEP in combination with 802.1x authentication and
EAP-TLS, while providing a much higher standard of security, does not mitigate
all the potential threats to the confidentiality and integrity of the data. As an
interim solution until the IEEE 802.11i standard is implemented and finalized,
many vendors are using or considering using a temporary solution called
Temporal Key Integrity Protocol (TKIP) to enhance the security of wireless networks.The TKIP standard was not finalized at the time of this writing, but some
vendors are already implementing it (for example, Cisco, which initially developed TKIP as a proprietary technology for use in its products).
TKIP can be used with or as an alternative to 802.1x authentication.TKIP
comprises a set of algorithms that enhance WEP. It provides more security than
WEP through the use of key mixing, an extended IV, a message integrity check
(MIC), and rekeying. A primary advantage of TKIP is that it can be implemented
through firmware updates of current devices (another reason to only purchase
devices capable of firmware updates).TKIP addresses the problem of static WEP
keys by changing the temporal key used for the encryption process every 10,000
packets. Additionally, the use of TKIP addresses another vulnerability of static
WEP: the use of the same shared key by all the wireless devices.TKIP ensures
that each wireless station uses a different key for the encryption process.TKIP
accomplishes this by using a 128-bit temporal key that is shared between the wireless workstations and the AP.The temporal key is then combined with the MAC
address of each of the wireless devices to provide the encryption key used for
RC4 encryption on the wireless network by that device.This also reduces the
vulnerability to attacks based on the fact that the IV is sent in the clear in standard WEP implementations, by adding another layer of encryption.
Message Integrity Code (MIC)
Another vulnerability of WEP is that it is relatively easy for a knowledgeable and
determined attacker to modify (flip) bits in an intercepted message, recalculate
the appropriate CRC (also known as the Integrity Checksum value or ICV), and
then send the altered message to the AP. Because the CRC is spoofed, the AP
will accept the altered message and reply to it, providing information that the
attacker can use to crack the WEP encryption.This form of attack is described in
a paper entitled “Intercepting Mobile Communications:The Insecurity of
802.11” by Nikita Borisov, Ian Goldberg, and David Wagner.
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MIC, which is also part of the TKIP algorithms, provides a much stronger
mechanism for checking messages for evidence of tampering by adding a MIC
value that is encrypted and sent with the message. Upon receipt, the MIC value
is decrypted and compared with the expected value. MIC is, in reality, a form of
Message Authentication Code, often referred to as MAC, which is a standard
cryptographic term. However, because “MAC” is used quite frequently with
regard to Media Access Control addresses, “MIC” is used to differentiate the two.
To add to the confusion, MIC is variously referred to as Message Integrity
Code or Message Integrity Check. As with TKIP, MIC is a technology originally developed by Cisco (which uses the term “Check”) for use in its
products, and is not widely available at the time of this writing.
IEEE 802.11i Standard
The negative response to the weaknesses of WEP has been vociferous and strong.
To address the criticisms leveled at WEP and to provide a stronger standardsbased security mechanism that vendors can implement in their products, the
IEEE 802.11i task group is working on the upcoming 802.11i standard. Although
the standard is not finalized, some things about its final form are fairly certain.
The standard will take the best of the technology available today for securing
wireless networks and combine them into a single, coherent standard.The following are expected to be included in the standard:
The 802.11i standard will require the use of 802.1x authentication based
on EAP.
The 802.11i standard will also likely require the use of TKIP and MIC.
For new devices, the 802.11i standard will also require the use of
Advanced Encryption Standard (AES) as a replacement for the compromised RC4 algorithm.
AES provides much stronger encryption than RC4. However, because of the
additional processing power required for AES encryption, the addition of a coprocessor will likely be necessary in wireless device hardware.When this technology becomes available in the marketplace, replacing legacy wireless devices
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Head of the Class…
could result in a significant expenditure. As with all other security measures,
administrators and managers will have to compare the costs of implementation
against the threats the implementation will mitigate.
Implementing Wireless Security:
Common Best Practices
Wireless security is a large, complex topic. Administrators wishing to
implement wireless networks should exercise due care and due diligence
by becoming as familiar as possible with the operation and vulnerabilities
of wireless networks and the available countermeasures for defending
them. Installing a wireless network opens up the current wired network
to new threats. The security risks created by wireless networks can be mitigated, however, to provide an acceptably safe level of security in most situations. In some cases, the security requirements are high enough that
the wireless devices will require proprietary security features. This might
include, for example, the ability to use TKIP and MIC, which is currently
only available on some Cisco wireless products, but may be available on
other products in the near future. In many cases, however, standardsbased security mechanisms that are available on wireless products from a
wide range of vendors will be sufficient.
Even though many currently implemented wireless networks support
a wide range of features that can be potentially enabled, the sad fact is
that most administrators do not use them. The media is full of reports of
the informal results of site surveys conducted by wardrivers. These reports
provide worrisome information, for example, that most wireless networks
are not using WEP and that many wireless networks are using default
SSIDs. There is no excuse for not minimizing the security threats created
by wireless networks through the implementation of security features
that are available on most wireless networks. The following is a summary
of common best practices that can be employed on many current and
future wireless networks.
Carefully review the available security features of wireless
devices to see if they fulfill your security requirements. The
802.11 and Wi–Fi standards specify only a subset of features
that are available on a wide range of devices. Over and above
these standards, there is a great deal of divergence of supported features.
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At a minimum, wireless APs and adapters should support
firmware updates, 128-bit WEP, MAC filtering, and the disabling of SSID broadcasts.
Wireless vendors are continually addressing the security weaknesses of wireless networks. Check the wireless vendors’ Web
sites frequently for firmware updates and apply them to all
wireless devices. You can leave your network exposed if you
fail to update even one device with the most recent firmware.
In medium- to high-security environments, wireless devices
should support EAP-based 802.1x authentication and, possibly,
TKIP. Another desirable feature is the ability to remotely
administer a wireless AP over a secure, encrypted channel.
Being able to use IPSec for communications between the AP
and the RADIUS server is also desirable.
Always use WEP. While it is true that WEP can be cracked,
doing so requires knowledge and time. Even 40-bit WEP is
better than no WEP.
Rotate static WEP keys frequently. If this is too much of an
administrative burden, consider purchasing devices that support
dynamic WEP keys.
Change the default administrative password used to manage
the AP frequently. The default passwords for wireless APs are
well known. If possible, use a password generator to create a
difficult and sufficiently complex password.
Change the default SSID of the AP. The default SSIDs for APs
from different vendors are well known, such as “tsunami” and
“Linksys” for Cisco and Linksys APs, respectively.
Do not put any kind of identifying information in the SSID,
such as company name, address, products, divisions, and so
on. Doing so provides too much information to potential
hackers and lets them know whether your network is of sufficient interest to warrant further effort.
If possible, disable SSID broadcasts. This will make your network invisible to site survey tools such as NetStumbler.
However, this will cause an administrative burden if you are
heavily dependent on Windows XP clients being able to automatically discover and associate with the wireless network.
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If possible, avoid the use of DHCP for your wireless clients,
especially if SSID broadcasts are not disabled. By using DHCP,
casual wardrivers can potentially acquire IP address configurations automatically.
Do not use shared-key authentication. Although it can protect
your network against specific types of DoS attacks, other kinds
of DoS attacks are still possible. Shared-key authentication
exposes your WEP keys to compromise.
Enable MAC filtering. It is true that MAC addresses can be
easily spoofed, but your goal is to slow down potential
attackers. If MAC filtering is too much of an administrative
burden, consider using port-based authentication available
through 802.1x.
Consider placing your wireless network in a Wireless
Demilitarized Zone (WDMZ), separated from the corporate
network by a router or a firewall.
In a WDMZ, restrict the number of hosts on the subnet
through an extended subnet mask, and do not use DHCP.
Learn how to use site survey tools such as NetStumbler, and
conduct frequent site surveys to detect the presence of rogue
APs and vulnerabilities in your own network.
Do not place the AP near windows. Try to place it in the center
of the building so that interference will hamper the efforts of
wardrivers and others trying to detect your traffic. Ideally, your
wireless signal would radiate only to the outside walls of the
building and not beyond. Try to come as close to that ideal as
If possible, purchase an AP that allows you to reduce the size of
the wireless zone (cell sizing) by changing the power output.
Educate yourself as to the operation and security of wireless
Educate users about safe computing practices in the context
of the use of both wired and wireless networks.
Perform a risk analysis of your network.
Develop relevant and comprehensive security policies and
implement them throughout your network.
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Wireless LANs are attractive to many companies and home users because of the
increased productivity that results from the convenience and flexibility of being
able to connect to the network without using wires.WLANs are especially
attractive as they can reduce the cost of having to install cabling to support users
on the network. For these and other reasons,WLANs have become very popular
in the past few years. However,WLAN technology has often been implemented
poorly and without due consideration being given to the security of the network. For the most part, these poor implementations result from a lack of understanding of the nature of wireless networks and the measures that can be taken to
secure them.
WLANs are inherently insecure because of their very nature: they radiate
radio signals containing network traffic that can be viewed and potentially compromised by anyone within range of the signal.With the proper antennas, the
range of WLANs is much greater than is commonly assumed. Many administrators wrongly believe that their networks are secure because the interference created by walls and other physical obstructions combined with the relative low
power of wireless devices will contain the wireless signal sufficiently. Often, this is
not the case.
There are a number of different types of wireless networks that can be potentially deployed including HomeRF, Bluetooth, 802.11b, and 802.11a.The most
common type of WLAN used today is based on the IEEE 802.11b standard.
The 802.11b standard defines the operation of WLANs in the 2.4 to 2.4835
GHz unlicensed ISM band. 802.11b devices use direct sequence spread spectrum
(DSSS) to achieve transmission rates of up to 11 Mbps. All 802.11b devices are
half-duplex devices, which means that a device cannot send and receive at the
same time. In this, they are like hubs and therefore require mechanisms for contending with collisions when multiple stations are transmitting at the same time.
To contend with collisions, wireless networks use CSMA/CA.
The 802.11a and forthcoming 802.11g standards define the operation of
wireless networks with higher transmission rates. 802.11a devices are not compatible with 802.11b because they use frequencies in the 5 GHz band. Furthermore,
unlike 802.11b networks, they do not use DSSS. 802.11g uses the same ISM frequencies as 802.11b and is backward-compatible with 802.11b devices.
The 802.11 standard defines the 40-bit WEP protocol as an optional component to protect wireless networks from eavesdropping.WEP is implemented in
the MAC sublayer of the Data Link layer (Layer 2) of the OSI model.
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WEP is insecure for a number of reasons.The first is that, because it encrypts
well-known and deterministic IP traffic in layer 3, it is vulnerable to plaintext
attacks.That is, it is relatively easy for an attacker to figure out what the plaintext
traffic is (for example a DHCP exchange) and compare that with the ciphertext,
providing a powerful clue for cracking the encryption.
Another problem with WEP is that it uses a relatively short (24-bit) IV to
encrypt the traffic. Because each transmitted frame requires a new IV, it is possible
to exhaust the entire IV keyspace in a few hours on a busy network, resulting in
the reuse of IVs.This is known as IV collisions. IV collisions can also be used to
crack the encryption. Furthermore, IVs are sent in the clear with each frame,
introducing another vulnerability.
The final stake in the heart of WEP is the fact that it uses RC4 as the
encryption algorithm.The RC4 algorithm is well known and recently it was discovered that it uses a number of weak keys. AirSnort and WEPcrack are two
well-known open-source tools that exploit the weak key vulnerability of WEP.
Although WEP is insecure, it does potentially provide a good barrier, and its
use will slow down determined and knowledgeable attackers.WEP should always
be implemented.The security of WEP is also dependent on how it is implemented. Because the IV keyspace can be exhausted in a relatively short amount
of time, static WEP keys should be changed on a frequent basis.
The best defense for a wireless network involves the use of multiple security
mechanisms to provide multiple barriers that will slow down attackers, making it
easier to detect and respond to attacks.This strategy is known as defense-in-depth.
Securing a wireless network should begin with changing the default configurations of the wireless network devices.These configurations include the default
administrative password and the default SSID on the AP.
The SSID is a kind of network name, analogous to an Simple Network
Management Protocol (SNMP) community name or a VLAN ID. For wireless
clients to authenticate and associate with an AP, they must use the same SSID as
the one in use on the AP. It should be changed to a unique value that does not
contain any information that could potentially be used to identify the company
or the kind of traffic on the network.
By default, SSIDs are broadcast in response to beacon probes and can be
easily discovered by site survey tools such as NetStumbler and Windows XP. It is
possible to turn off SSID on some APs. Disabling SSID broadcasts creates a closed
network. If possible, SSID broadcasts should be disabled, although this will interfere
with the ability of Windows XP to automatically discover wireless networks and
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associate with them. However, even if SSID broadcasts are turned off, it is still
possible to sniff the network traffic and see the SSID in the frames.
Wireless clients can connect to APs using either open system or shared-key
authentication.While shared-key authentication provides protection against some
DoS attacks, it creates a significant vulnerability for the WEP keys in use on the
network and should not be used.
MAC filtering is another defensive tactic that can be employed to protect
wireless networks from unwanted intrusion. Only the wireless station that possess
adapters that have valid MAC addresses are allowed to communicate with the AP.
However, MAC addresses can be easily spoofed and maintaining a list of valid
MAC addresses may be impractical in a large environment.
A much better way of securing WLANs is to use 802.1x. 802.1x was originally developed to provide a method for port-based authentication on wired networks. However, it was found to have significant application in wireless networks.
With 802.1x authentication, a supplicant (a wireless workstation) needs to be
authenticated by an authenticator (usually a RADIUS server) before access is
granted to the network itself.The authentication process takes place over a logical
uncontrolled port that is used only for the authentication process. If the authentication process is successful, access is granted to the network on the logical controlled port.
802.1x relies on EAP to perform authentication.The preferred EAP type for
802.1x is EAP-TLS. EAP-TLS provides the ability to use dynamic per-user, session-based WEP keys, eliminating some of the more significant vulnerabilities
associated with WEP. However, to use EAP-TLS, you must deploy a PKI to issue
digital X.509 certificates to the wireless clients and the RADIUS server.
Other methods that can be used to secure wireless networks include placing
wireless APs on their own subnets in WDMZs.The WDMZ can be protected
from the corporate network by a firewall or router. Access to the corporate network can be limited to VPN connections that use either PPTP or L2TP.
New security measures continue to be developed for wireless networks.
Future security measures include TKIP and MIC.
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Exam Objectives Fast Track
Wireless Concepts
; The most predominant wireless technologies consist of WAP and IEEE
802.11 WLAN.
; WEP is the security method used in IEEE 802.11.WLANs and WTLS
provide security in WAP networks.
; WEP provides for two key sizes: 40-bit and 104-bit.These keys are
concatenated to a 24-bit IV to provide either a 64- or 128-bit key for
; WEP uses the RC4 stream algorithm to encrypt its data.
; 802.11 networks use two types of authentication: open system and
; There are two types of 802.11 network modes: ad hoc and
infrastructure. Ad hoc 802.11 networks are peer-to-peer in design and
can be implemented by two clients with wireless network cards.The
infrastructure mode of 802.11 uses APs to provide wireless connectivity
to a wired network beyond the AP.
; To protect against some rudimentary attacks that insert known text into
the stream to attempt to reveal the key stream,WEP incorporates a
checksum in each frame. Any frame not found to be valid through the
checksum is discarded.
; Used on its own,WEP does not provide adequate WLAN security.
; WEP must be implemented on every client as well as every AP to
be effective.
; WEP keys are user definable and unlimited.They do not have to be
predefined and can and should be changed often.
; Despite its drawbacks, you should implement the strongest version of
WEP available and keep abreast of the latest upgrades to the standards.
; The IEEE 802.1x specification uses the EAP to provide for client
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Wireless Vulnerabilities
; Examining the common threats to both wired and wireless networks
provides a solid understanding in the basics of security principles and
allows the network administrator to fully assess the risks associated with
using wireless and other technologies.
; Threats can come from simple design issues, where multiple devices
utilize the same setup, or intentional DoS attacks, which can result in the
corruption or loss of data.
; Malicious users are not the source of all threats.They can also be caused
by a conflict of similar resources, such as with 802.11b networks and
cordless telephones.
; With wireless networks going beyond the border of the office or home,
chances are greater that users’ actions may be monitored by a third party.
; Electronic eavesdropping, or sniffing, is passive and undetectable to
intrusion detection devices.
; Tools that can be used to sniff networks are available for Windows (such
as Ethereal and AiroPeek) and UNIX (such as tcpdump and ngrep).
; Sniffing traffic allows attackers to identify additional resources that can
be compromised.
; Even encrypted networks have been shown to disclose vital information
in cleartext, such as the network name, that can be received by attackers
sniffing the WLAN.
; Any authentication information that is broadcast can often be replayed
to services requiring authentication (NT Domain,WEP authentication,
and so on) to access resources.
; The use of VPNs, SSL, and SSH helps protect against wireless
; Due to the design of TCP/IP, there is little that you can do to prevent
MAC/IP address spoofing. Static definition of MAC address tables can
prevent this type of attack. However, due to significant overhead in
management, this is rarely implemented.
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; Wireless network authentication can be easily spoofed by simply
replaying another node’s authentication back to the AP when attempting
to connect to the network.
; Many wireless equipment providers allow for end users to redefine the
MAC address for their cards through the configuration utilities that
come with the equipment.
; External two-factor authentication such as RADIUS or SecurID should
be implemented to additionally restrict access requiring strong
authentication to access the wireless resources.
; Due to the design of TCP/IP, some spoof attacks allow for attackers to
hijack or take over network connections established for other resources
on the wireless network.
; If an attacker hijacks the AP, all traffic from the wireless network gets
routed through the attacker, so the attacker can then identify passwords
and other information that other users are attempting to use on valid
network hosts.
; Many users are susceptible to these MITM attacks, often entering their
authentication information even after receiving many notifications that
SSL or other keys are not what they should be.
; Rogue APs can assist the attacker by allowing remote access from wired
or wireless networks.These attacks are often overlooked as just faults in
the user’s machine, allowing attackers to continue hijacking connections
with little fear of being noticed.
; Many wireless networks that use the same frequency within a small
space can easily cause network disruptions and even DoS for valid
network users.
; If an attacker hijacks the AP and does not pass traffic on to the proper
destination, all users of the network will be unable to use the network.
; Flooding the wireless network with transmissions can prevent other
devices from utilizing the resources, making the wireless network
inaccessible to valid network users.
; Wireless attackers can utilize strong and directional antennas to attack
the wireless network from a great distance.
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; An attacker who has access to the wired network can flood the wireless
AP with more traffic than it can handle, preventing wireless users from
accessing the wired network.
; Many new wireless products utilize the same wireless frequencies as
802.11 networks. A simple cordless telephone can create a DoS situation
for the network.
Site Surveys
; Tools used in site surveys include wireless Sniffers, directional or
parabolic dish antennae, and GPS receivers.
; Wireless sniffers that can be used in a site survey include the Windows-
based NetStumbler and the UNIX/Linux-based Kismet or Ethereal.
; Site surveys are used to map out the extent to which wireless networks
are visible outside the physical boundaries of the buildings in which
their components are installed.
Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: Is 128-bit WEP more secure than 64-bit WEP?
A: Not really.This is because the WEP vulnerability has more to do with the
24-bit initialization vector than the actual size of the WEP key.
Q: If I am a home user, can I assume that if I use MAC filtering and WEP, my
network is secure?
A: You can make the assumption that your home network is more secure than it
would be if it did not utilize these safeguards. However, as shown in this
chapter, these methods can be circumvented to allow for intrusion.
Q: Where can I find more information on WEP vulnerabilities?
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A: Besides being one of the sources who brought WEP vulnerabilities to light, has links to other Web sites that cover WEP
Q: If I have enabled WEP, am I now protected?
A: No. Certain tools can break all WEP keys by simply monitoring the network
traffic (generally requiring less than 24 hours to do so).
Q: Is there any solution available besides RADIUS to perform external user and
key management?
A: No. Plans are available from manufacturers to identify other ways of performing user/key management, but to date nothing is available.
Q: How can I protect my wireless network from eavesdropping by unauthorized
A: Because wireless devices are half-duplex devices, you cannot wholly prevent
your wireless traffic from being listened to by unauthorized individuals.The
only defense against eavesdropping is to encrypt Layer 2 and higher traffic
whenever possible.
Q: Are wireless networks secure?
A: By their very nature and by definition, wireless networks are not secure.They
can, however, be made relatively safe from the point of view of security
through administrative effort to encrypt traffic, to implement restrictive
methods for authenticating and associating with wireless networks, and so on.
Q: Why should I do frequent site surveys?
A: A site survey will reveal the presence of unauthorized APs. Some of these
APs could be placed to facilitate a MITM attack or to gain access to the
physical network from a safe location. On the other hand, the unauthorized
APs could have been purchased and implemented by departmental staff
without your knowledge but with no malicious intent.Wireless networks are
relatively inexpensive and easy to set up. It is natural for people to desire to
implement technology they think will make their lives easier without waiting
for knowledgeable staff in the IT department to implement it for them. Even
if your company does not have a wireless network, it may be a good idea to
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conduct wireless site surveys to protect your wired network if you suspect
there is a likelihood of employees installing their own APs to increase their
Q: My AP does not support the disabling of SSID broadcasts. Should I purchase
a new one?
A: Disabling SSID broadcasts adds only one barrier for the potential hacker.
Wireless networks can still be made relatively safe even if the AP does
respond with its SSID to a beacon probe. Disabling SSID broadcasts is a
desirable feature. However, before you go out and purchase new hardware,
check to see if you can update the firmware of your AP.The AP vendor may
have released a more recent firmware version that supports the disabling of
SSID broadcasts. If your AP does not support firmware updates, consider
replacing it with one that does.
Q: Why is WEP insecure?
A: WEP is insecure for a number of reasons.The first is that 24-bit IV is too
short. Because a new IV is generated for each frame and not for each session,
the entire IV key space can be exhausted on a busy network in a matter of
hours, resulting in the reuse of IVs. Second, the RC4 algorithm used by WEP
has been shown to use a number of weak keys that can be exploited to crack
the encryption.Third, because WEP is implemented at Layer 2, it encrypts
TCP/IP traffic, which contains a high percentage of well-known and predictable information, making it vulnerable to plaintext attacks.
Q: How can I prevent unauthorized users from authenticating and associating
with my AP?
A: There are a number of ways to accomplish this.You can configure your AP as
a closed system by disabling SSID broadcasts and choosing a hard-to-guess
SSID.You can configure MAC filtering to allow only those clients that use
valid MAC addresses access to the AP.You can enable WEP and shared-key
authentication. However, all of these methods do not provide acceptable levels
of assurance for corporate networks that have more restrictive security
requirements than are usually found in SOHO environments. For corporate
environments that require a higher degree of assurance, you should configure
802.1x authentication.
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Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
Wireless Concepts
1. Your supervisor has charged you with determining which 802.11 authentication method to use when deploying the new wireless network. Given
your knowledge of the 802.11 specification, which of the following is the
most secure 802.11 authentication method?
A. Shared-key
D. Open
2. What are the two WEP key sizes available in 802.11 networks?
A. 40-bit and 104-bit
B. 24-bit and 64-bit
C. 64-bit and 128-bit
D. 24-bit and 104-bit
3. Which of the following is a weakness in WEP related to the IV? (Select all
that apply)
A. The IV is a static value, which makes it relatively easy for an attacker to
brute force the WEP key from captured traffic.
B. The IV is transmitted in plaintext and can be easily seen in captured
C. The IV is only 24 bits in size, which makes it possible that two or more
data frames will be transmitted with the same IV, thereby resulting in an
IV collision that an attacker can use to determine information about the
D. There is no weakness in WEP related to the IV.
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4. Bill, the network administrator, wishes to deploy a wireless network and use
open authentication. His problem is that he also wants to make sure that the
network is not accessible by anyone. How can he authenticate users without
a shared-key authentication mechanism? (Choose the best answer)
A. Use MAC address filters to restrict which wireless network cards can
associate to the network.
B. Deploy a RADIUS server and require the use of EAP.
C. Set a WEP key on the APs and use it as the indirect authenticator
for users.
D. Use IP filters to restrict access to the wireless network.
5. The 802.1x standard specifies a series of exchanges between the supplicant
and the authentication server.Which of the following is not part of the
802.1x authentication exchange?
A. Association Request
B. EAPoL Start
C. RADIUS-Access-Request
D. EAP-Success
6. 802.1x provides for mutual authentication of the supplicant and the
authenticator.Which of the following 802.1x methods support mutual
7. The 802.11 standard defines two authentication methods.What are they?
A. Open and closed
B. Shared-key and private-key
C. Open and private-key
D. Open and shared-key
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8. To set up an ad hoc wireless network, what three elements must be agreed
upon by all of the participants in the network?
A. Whether WEP is enabled,WEP key, SSID, IP addresses to use
B. Whether WEP is enabled,WEP key, authentication method, IP addresses
to use
C. Whether WEP is enabled,WEP key, MAC addresses to use
D. None of the above
Wireless Vulnerabilities
9. The biggest weakness in WEP stems from which vulnerability?
A. The reuse of IV values.
B. The ability to crack WEP by statistically determining the WEP key
through the Fluhrer-Mantin-Shamir attack.
C. The ability to spoof MAC addresses thereby bypassing MAC
address filters.
D. All of the above.
10. The tool NetStumbler detects wireless networks based on what feature?
B. WEP key
C. MAC address
D. CRC-32 checksum
11. Some DoS attacks are unintentional.Your wireless network at home has
been having sporadic problems.The wireless network is particularly susceptible in the afternoon and the evenings.This is most likely due to which of
the following possible problems?
A. The AP is flaky and needs to be replaced.
B. Someone is flooding your AP with traffic in a DoS attack.
C. The wireless network is misconfigured.
D. Your cordless phone is using the same frequency as the wireless network
and whenever someone calls or receives a call the phone jams the wireless network.
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12. The 802.1x standard requires the use of an authentication server to allow
access to the wireless LAN.You are deploying a wireless network and will
use EAP-TLS as your authentication method.What is the most likely vulnerability in your network?
A. Unauthorized users accessing the network by spoofing EAP-TLS
B. DoS attacks occurring because 802.11 management frames are not
C. Attackers cracking the encrypted traffic.
D. None of the above.
Site Surveys
13. Your manager has asked you to determine whether the wireless network is
accessible from outside the physical building.To do this, you will need to
conduct a site survey.What should you be concerned about when conducting a site survey?
A. Accessing other wireless networks around your building.
B. Being mistaken for a hacker trying to break into a wireless network.
C. Being arrested by the police.
D. All of the above.
14. When conducting a site survey of a wireless network, which is the most
important element to gauge to determine the level of security in the wireless network?
A. The distance the signal travels.
B. The visibility of the SSID in the beacon frames.
C. Whether or not WEP is enabled.
D. Whether there are other wireless networks in the area.
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15. What is the purpose of conducting a wireless network site survey?
A. To identify other wireless networks in the area.
B. To determine the extent to which your wireless network extends
beyond the physical boundary of the building.
C. To hack into other companies’ wireless networks.
D. None of the above.
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. D
9. B
2. C
10. A
3. B and C
11. D
4. C
12. B
5. A
13. D
6. D
14. C
7. D
15. B
8. A
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Chapter 5
Web Security
Domain 2.0 Objectives in this Chapter:
Web Security
FTP Security
Directory Services and LDAP Security
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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Security+ technicians must know how to configure, manage, and service security
on a Web platform. As discussed in the previous chapters,Web-based services and
e-mail rank highly when identifying possible threats, risks, and exploitation.
The problems associated with Web-based exploitation can affect a wide array
of users, including end users surfing Web sites, using instant messaging, and shopping online. End users can also have many problems with their Web browsers.
This chapter covers many of these issues, including:
How to recognize possible vulnerabilities
How to securely surf the Web
How to shop and conduct financial transactions online safely
Security+ technicians also need to know how to secure Web-based services
and servers. Earlier chapters covered securing e-mail services because they “need”
to be exposed to the Internet.The same precautions hold true for Web-based services; they also need to be exposed (unless they are intranet-only Web services),
thus increasing risk.
This chapter looks at File Transfer Protocol (FTP) based services. FTP is the
de facto standard used today to transfer files across the Internet, using either a
Web browser or an FTP client. Because of the highly exploitable nature of FTP,
this chapter looks at why it is insecure, how it can be exploited, and how to
secure it.The last section deals with Lightweight Directory Access Protocol
(LDAP), its inherent security vulnerabilities, and how it can be secured.
Web Security
When considering Web-based security for a network, knowledge of the entire
Internet and the Transmission Control Protocol/Internet Protocol (TCP/IP)
protocol stack is a must. So far, this book has exposed you to the inner workings
of TCP/IP and Internet communicationsThis chapter looks at Web-based security and topics including server and browser security, exploits,Web technologies
such as ActiveX, JavaScript, and CGI, and much more.
Web Server Lockdown
Web server(s) store all of the Hypertext Markup Language (HTML), Dynamic
Hyper Text Markup Language (DHTML), Active Server Pages (ASP), and
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Web Security • Chapter 5
eXtensible Markup Language (XML) documents, graphics, sounds, and other files
that make up Web pages. In some cases, it may also contain other data that a business does not want to share over the Internet (for example, businesses running
Microsoft’s Small Business Server often have a single physical server that performs
all server functions for the organization, including Web services). A dedicated Web
server, however, can serve as a pathway into the internal network unless security
is properly configured.Thus, it is vital that Web servers be secure.
The most popular types of Web server software include Microsoft’s
Internet Information Services (IIS), which is built into Windows NT, 2000,
and .NET/2003 server products as well as Windows 2000/XP Professional
operating systems (OSs), and Apache, which can be run on Linux/UNIX
machines or Windows machines. Other Web servers include Novell servers,
the CERN World Wide Web daemon, Spinner (distributed under the GPL
license), GoServe (a Web server for OS/2, MacHTTP (for Macintosh),
SerWeb (a Web server that runs on Windows 3.x), and many others.
Locking down a Web server follows a path that begins in a way that should
already be familiar: Applying the latest patches and updates from the vendor.
Once this task is accomplished, the network administrator should follow the
vendor’s recommendations for configuring Web services securely.The following
sections discuss typical recommendations made by Web server vendors and security professionals, including:
Managing access control
Handling directory and data structures
Eliminating scripting vulnerabilities
Logging activity
Performing backups
Maintaining integrity
Finding rogue Web servers
Stopping browser exploits
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For the Security+ exam, you will not need to know the step-by-step process of how to make a Web server secure, but you will be expected to
know the technical details of how a Web server can be exploited and the
details on how to fix the exploits. For example: Making sure that your
Web servers are completely patched with updates and hot fixes.
Managing Access Control
Many Web servers, such as IIS on Windows NT-based OSs, use a named user
account to authenticate anonymous Web visitors (by default, this account on IIS
servers is called IUSER_<computername>).When a Web visitor accesses a Web site
using this methodology, the Web server automatically logs that user on as the IIS
user account.The visiting user remains anonymous, but the host server platform
uses the IIS user account to control access.This account grants system administrators granular access control on a Web server so that all anonymous users have the
same level of access, whereas users accessing the services through their own user
accounts can have different levels of access.
These specialized Web user accounts (for anonymous users) must have their
access restricted so they cannot log on locally nor access anything outside the
Web root. Additionally, administrators should be very careful about granting these
accounts the ability to write to files or execute programs; this should be done
only when absolutely necessary. If other named user accounts are allowed to log
on over the Web (to give certain users a higher level of access than the anonymous account has), it is essential that these accounts not be the same user
accounts employed to log onto the internal network. In other words, if employees
log on via the Web using their own credentials instead of the anonymous Web
user account, administrators should create special accounts for those employees to
use just for Web logon. Authorizations over the Internet should always be considered insecure unless strong encryption mechanisms are in place to protect them.
Secure Sockets Layer (SSL) can be used to protect Web traffic; however, the protection it offers is not significant enough to protect internal accounts that are
exposed on the Internet.
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Handling Directory and Data Structures
Planning the hierarchy or structure of the Web root is an important part of
securing a Web server.The root is the highest level Web in the hierarchy that
consists of webs nested within webs.Whenever possible,Web server administrators
should place all Web content within the Web root. All the Web information (the
Web pages written in HTML, graphics files, sound files, and so on) is normally
stored in folders and directories on the Web server. Administrators can create virtual directories, which are folders that are not contained within the Web server
hierarchy (they can even be on a completely different computer) but appear to
the user to be part of that hierarchy. Another way of providing access to data that
is on another computer is mapping drives or folders.These methods allow administrators to store files where they are most easily updated or take advantage of
extra drive space on other computers. However, mapping drives, mapping folders,
or creating virtual directories can result in easier access for intruders if the Web
server’s security is compromised. It is especially important not to map drives from
other systems on the internal network.
If users accessing these Webs must have access to materials on another system,
such as a database, it is best to deploy a duplicate database server within the Web
server’s Demilitarized Zone (DMZ) or domain.The duplicate server should contain only a backup, not the primary working copy of the database.The duplicate
server should also be configured so that no Web user or Web process can alter or
write to its data store. Database updates should come only from the original protected server within the internal network. If data from Web sessions must be
recorded into the database, it is best to configure a sideband connection from the
Web zone back to the primary server system for data transfers. Administrators
should also spend considerable effort verifying the validity of input data before
adding it to the database server.
Eliminating Scripting Vulnerabilities
Maintaining a secure Web server means ensuring that all scripts and Web applications deployed on the Web server are free from Trojans, backdoors, or other malicious code. Many scripts are available on the Internet for the use of Web
developers. However, scripts downloaded from external sources are more susceptible to coding problems (both intentional and unintentional) than those developed in-house. If it is necessary to use external programming code sources,
developers and administrators should employ quality assurance tests to search for
out-of-place system calls, extra code, and unnecessary functions.These hidden
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segments of malevolent code are called logic bombs when they are written to execute in response to a specified trigger or variable (such as a particular date, lapse
of time, or something that the user does or does not do).
One scripting vulnerability to watch out for occurs within Internet Server
Application Programming Interface (ISAPI) scripts.The command RevertToSelf()
allows the script to execute any following commands at a system-level security
context.The RevertToSelf function is properly used when an application has been
running in the context of a client, to end that impersonation. However, in a
properly designed ISAPI script, this command should never be used. If this command is present, the code has been altered or was designed by a malicious or
inexperienced coder.The presence of such a command enables attacks on a Web
server through the submission of certain Uniform Resource Locator (URL)
syntax constructions.
We mentioned logic bombs in Chapter 2 in a very simplified manner.
Here, we look at logic bombs in a practical sense, as written into the
code itself. Remember that for the Security+ exam, a logic bomb is an
attack that, is set off or begins to run when a certain variable is met
within the code. Using the RevertToSelf() function is a practical example
of such an attack in action.
Logging Activity
Logging, auditing, or monitoring the activity on a Web server becomes more
important as the value of the data stored on the server increases.The monitoring
process should focus on attempts to perform actions that are atypical for a Web
user.These actions include, among others:
Attempting to execute scripts
Trying to write files
Attempting to access files outside the Web root
The more traffic a Web server supports, the more difficult it becomes to review
the audit trails. An automated solution is needed when time required to review log
files exceeds the time administrators have available for that task. Intrusion detection
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systems (IDSs) are automated monitoring tools that look for abnormal or malicious
activity on a system. An IDS can simply scan for problems and notify administrators
or can actively repel attacks once they are detected. IDSs are covered in depth in
Chapter 7,“Infrastructure Security:Topologies and IDS.”
Performing Backups
Unfortunately, every administrator should assume that the Web server will be compromised at some point and that the data hosted on it will be destroyed, copied, or
corrupted.This assumption will not become a reality in all cases, but planning for
the worst is always the best security practice. A reliable backup mechanism must be
in place to protect the Web server from failure.This mechanism can be as complex
as a real-time mirror server using clustering technology to back up the primary
Web server (and to which Web services will automatically failover if the primary
Web server goes down), or as simple as a daily backup to tape. Either way, a backup
is the only insurance available that allows a return to normal operations within a
reasonable amount of time. If security is as much maintaining availability as it is
maintaining confidentiality, backups should be part of any organization’s security
policy and backups of critical information (such as Web sites) should be stored offsite. Backups, disaster recovery planning, and how to continue on with business
after an attack are covered in depth in Chapter 12,“Operational and Organizational
Security: Security Policies and Disaster Recovery.”
Maintaining Integrity
Locking down the Web server is only one step in the security process. It is also
necessary to maintain that security over time. Sustaining a secure environment
requires that the administrator perform a number of tasks on a regular basis such as:
Continuously monitor the system for anomalies
Apply new patches when available
Adjust security configurations to match the ever-changing needs of the
internal and external Web community
If a security breach occurs, an organization should reevaluate previous security decisions and implementations. Administrators might have overlooked a security hole because of ignorance, or they might have simply misconfigured some
security control.
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Finding Rogue Web Servers
For a network administrator, the only thing worse than having a Web server and
knowing that it is not 100 percent secure even after locking it down, is having a
Web server on the network that they are not aware exists.These are sometimes
called rogue Web servers, and they can come about in two ways. It is possible that a
technically savvy user on the network has intentionally configured Web services
on their machine. More often, however, rogue Web servers are deployed unintentionally. Many OSs include Web server software and install it as part of the default
OS installation. If administrators are not careful, when they install Windows
(especially a member of the Server family) on a network computer, they can
create a new Web server without even realizing it.When a Web server is present
on a network without the knowledge of network administrators, the precautions
necessary to secure that system are not taken, thus making the system (and
through it, the entire network) vulnerable to every out-of-the-box exploit and
attack for that Web server.
In Exercise 5.01, you will learn how to find a rogue Web server running on
your system and disable it. In the exercise, you will learn how to run a few tests
to see if you have rogue Web servers on your network and how to find them.
Damage & Defense…
Hunting Down Rogue Web Servers
To check a system very quickly to determine if a local Web server is running without your knowledge, you can use a Web browser to access
http://localhost/. This is called the loopback URL. If no Web server is running, you should see an error stating that you are unable to access the
Web server. If you see any other message or a Web page (including a message advising that the page is under construction or coming soon), that
computer is running a Web server locally. Once you discover the existence
of such a server, you must either secure, remove, or disable it. Otherwise,
the system will remain insecure. Other ways to discover the existence of a
Web server is by checking services and running processes (for example,
Inetinfo.exe). but the quickest way to check on any platform (including
Windows 9x, which comes with rudimentary Web server software called
Personal Web Server [PWS]) is to quickly look at the loopback URL.
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1. At any workstation or server type: http://localhost. This is the loopback address found in your HOSTS file that maps to (the
loopback IP address). After entering this URL, you should see a
default Web page like the one shown in Figure 5.1. This indicates
you have a Web server running.
Figure 5.1 Viewing the Default Web Page with IIS
2. Another way to find out if IIS is installed and running is to go to
the Task Manager utility (found in the Taskbar properties) as seen
in Figure 5.2, and look for the Inetinfo.exe process running. This
is an indicator that IIS is running on your system. One way to disable the Web server is to open the Internet Service Manager (ISM)
found in the Administrative tools folder in the Control Panel and
find the running Web site. You can then right-click on it and
choose to stop the service from the context menu.
3. In Windows 2000/XP or .NET/2003, go to the Services MMC within
the Administrative tools folder in your Control Panel. If you find
W3SVC (The World Wide Web Publishing Service) running and it is
either set to Automatic or Manual, then it is installed and able to
run. If the Status is set to “Started” then you are currently running
a Web server. You might notice that the path to the executable
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shown in Figure 5.3 points to the inetinfo.exe process. You can
change the Startup type from Automatic (or Manual) to Disabled.
This will disable the service without removing it altogether (in case
you should want to run a Web server on this machine in the
Figure 5.2 Viewing the Inetinfo.exe Process in Task Manager
Figure 5.3 Viewing the W3SVC Service
4. Another quick way to see if you are running a rouge Web server
is to go to a command prompt and type netstat –na, as seen in
Figure 5.4. On the second line you can see that you have TCP port
80 LISTENING. This means that you are using the HTTP service on
your machine, which again, indicates that you have a Web server
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Figure 5.4 Using the netstat Command to See Port 80 in Use
Port 80 is the default port on which a Web server listens for requests
from Web clients. However, Web servers can also be configured to listen
on a different port, so the fact that this port is not listed does not guarantee that there is no Web server running.
5. Another way to check for a Web server is to go to the Control
Panel and open the Add/Remove Programs applet. If you navigate
to Add/Remove Windows Components, you can check to see if
you have IIS checked off (or, in Windows 9x, PWS), which would
also indicate that is the Web server software is installed. In Figure
5.5, you can see that IIS is deselected so that it is not installed.
The machine used for this screenshot is a Windows XP
Professional workstation. To completely remove the Web server,
make sure it is not checked at all; this means it will not be
installed (or will be uninstalled if it has already been installed).
Figure 5.5 Viewing IIS on a Windows XP Professional Workstation
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Stopping Browser Exploits
Web browsers are client software programs such as Microsoft Internet Explorer
(MSIE), Netscape, Opera, Mozilla, and others.These clients connect to servers
running Web server software such as IIS or Apache and request Web pages via a
URL, which is a “friendly” address that represents an IP address and particular
files on the server at that address. It is also possible to connect to a Web site by
typing the Web server’s IP address itself into the browser’s address box.The
browser receives files that are encoded (usually in HTML, but sometimes in other
markup languages such as XML) and must interpret the code or “markup” that
determines how the page will be displayed on the user’s monitor.This code can
be seen by selecting the View Source option from your browser.
HTML was originally designed as a simple markup language used to format
text size, style, color, and characteristics such as boldface or italic. However, as
Web users demanded more sophisticated Web pages,Web designers developed
ways to create interactive elements in pages.Today’s Web pages include Java,
ActiveX, and VB scripts that run in the browser and utilize other technologies
that allow for much more dynamic pages. Unfortunately, these new features
brought with them new vulnerabilities.
Browsers are open to a number of types of attack, which are discussed in the
following section.
Exploitable Browser Characteristics
Early browser programs were fairly simple, but today’s browsers are complex; they
are capable of not only displaying text and graphics but of playing sound files and
movies and running executable code. Browser software stores information about
the computer on which it is installed and about the user, which can be uploaded
to Web servers either deliberately by the user or in response to code on a Web
site (often without the user’s knowledge).
These characteristics all serve useful purposes. Support for running code (as
“active content” such as Java, JavaScript, and ActiveX) allows Web designers to
create pages that interact with users in sophisticated ways. For example, users can
complete and submit forms across the Web. Cookies are very small text files that
are placed on the user’s hard disk by the Web server.They allow users to set preferences on sites that will be retained the next time they visit the site. However,
hackers can exploit these characteristics in many ways. For example, a hacker can
program a Web site to run code that transfers a virus to the client computer
through the browser, erases key system files, or plants a back door program that
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then allows the hacker to take control of the user’s system. Chapter 8,
“Implementing System Security,” discusses active content and other browser
security issues and provides tips on how to disable these features when they are
not needed and make popular browsers more secure.
If you are interested in how cookies work, the specifications for the HTTP
cookie protocol are detailed in RFC 2109. A paper about various cookie
exploits, “Cookies – Exploitations and Invasion of Privacy” by Randall
Miller, is available on the SANS Institute Web site at
Web Spoofing
Web spoofing is a means by which an attacker is able to see and make changes to
Web pages that are transmitted to or from another computer (the target
machine).These pages can include confidential information such as credit card
numbers entered into online commerce forms and passwords that are used to
access restricted Web sites.The changes are not made to the actual Web pages on
their original servers, but to the copies of those pages that the spoofer returns to
the Web client who made the request.
As discussed earlier, the term spoofing refers to impersonation, or pretending
to be someone or something you are not.Web spoofing involves creating a
“shadow copy” of a Web site or even the entire Web. JavaScript can be used to
route Web pages and information through the attacker’s computer, which impersonates the destination Web server.The attacker can initiate the spoof by sending
e-mail to the victim that contains a link to the forged page or putting a link into
a popular search engine.
SSL does not necessarily prevent this sort of “man-in-the-middle” (MITM)
attack; the connection appears to the victim user to be secure because it is secure.
The problem is that the secure connection is to a different site than the one to
which the victim thinks they are connecting. Hyperlink spoofing exploits the fact
that SSL does not verify hyperlinks that the user follows, so if a user gets to a site
by following a link, they can be sent to a spoofed site that appears to be a legitimate site.
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For more technical details about Web and hyperlink spoofing, see the
paper by Frank O’Dwyer at and
the paper by Felten, Balfanz, Dean, and Wallach at
Web spoofing is a high-tech form of con artistry.The point of the scam is to
fool user’s into giving confidential information such as credit card numbers, bank
account numbers, or Social Security numbers to an entity that the user thinks is
legitimate, and then using that information for criminal purposes such as identity
theft or credit card fraud.The only difference between this and the “real-world”
con artist who knocks on a victim’s door and pretends to be from the bank,
requiring account information, is in the technology used to pull it off.
There are clues that will tip off an observant victim that a Web site is not
what it appears to be, such as the URL or status line of the browser. However, an
attacker can use JavaScript to cover their tracks by modifying these elements. An
attacker can even go so far as to use JavaScript to replace the browser’s menu bar
with one that looks the same but replaces functions that provide clues to the
invalidity of the page, such as the display of the page’s source code.
Later versions of browser software have been modified to make Web spoofing
more difficult. However, many people are still using MSIE or Netscape versions
3, both of which are highly vulnerable to this type of attack.
A common method of spoofing URLs is to exploit the ways in which
browsers read addresses entered into the address field. For example, anything on
the left side of an @ sign in a URL is ignored. Additionally, the % sign is
ignored. Finally, URLs do not have to be in the familiar format of a DNS name
(such as; they are also recognized when entered as an IP
address in decimal format (such as, hexadecimal format (such as
D8.EE.8.2C), or in Unicode.Thus, a spoofer can send an e-mailed link such as,” which to the
casual user appears to be a link to the PayPal Web site. However, it is really a link
(an IP address in hex format) to the spoofer’s own server.Which in this case was
a site in Russia.The spoofer’s site was designed to look like PayPal’s site, with
form fields requiring that the user enter their PayPal account information.This
information was collected by the spoofer and could then be used to charge purchases to the victim’s PayPal account.This site packed a double whammy—it also
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ran a script that attempted to download malicious code to the user’s computer.
Administrators should educate users to always beware of any link that contains
an @ sign, as it is designed to appear to be something it is not.
Web Server Exploits
Web server’s host Web pages that are made available to others across the Internet
or an intranet. Public Web servers (those accessible from the Internet) always pose
an inherent security risk because they must be available to the Internet to do
what they are supposed to do. Clients (Web browser software) must be able to
send transmissions to the Web server for the purpose of requesting Web pages.
However, allowing transmissions to come into the network to the Web server
makes the system—and the entire network, unless measures are undertaken to
isolate the Web server from the rest of the internal network—vulnerable to
Web server applications, like other software, can contain bugs that can be
exploited. For example, in 2001 a flaw was discovered in Microsoft’s IIS software
(included with Windows NT,Windows 2000, and Windows XP) that exploited the
code used for the indexing feature.The component was installed by default.When
it was running, hackers could create buffer overflows to take control of the Web
server and change Web pages or attack the system to bring it down. Microsoft
quickly released security patches to address the problem, but many companies do
not upgrade their software nor do they update it with available fixes, and new, different security holes are being found all the time in all major Web server programs.
Major flaws have been found in Apache Web servers’ PHP scripting language that,
if exploited by an attacker, can result in the attacker running arbitrary code on the
system. Security patches are available to address this issue.
Web server exploits are popular because firewalls are usually configured to
block most traffic that comes into an internal network from the Internet, but
HTTP traffic usually is not blocked.There are a large number of HTTP exploits
that can be used to access resources that are outside the webroot directory.These
include the Unicode Directory Transversal Exploit and the Double Hex
Encoding Exploit.These are used to “sneak” the “../” directory transversal strings
past the server’s security mechanisms, which generally block URLs that contain
the string.
It is not necessary for hackers to have sophisticated technical skills to exploit
unprotected Web servers. Scripts to carry out buffer overflow attacks, for example,
can be downloaded and executed by anyone.
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These are just a few examples of the ways that Web servers can be exploited,
making it vitally important that these machines be secured. In addition to best
configuration practices, there are software packages, such as Entercept
( that are designed specifically to protect Web servers from
common attacks.
Make sure you update your Web Servers with all the available updates
and hot fixes you can get, after testing them first on a non-production
test system. You need to know that service packs, hot fixes and updates
are critical to the security analyst survival when dealing with systems and
services, especially Web services which are generally exposed to the
SSL is a public key based protocol that was developed by Netscape and is supported by all popular Web browsers. It is widely used on the Internet for Web
transactions such as sending credit card data. It can be utilized for other protocols
as well, such as Telnet, FTP, LDAP, Internet Message Access Protocol (IMAP), and
Simple Mail Transfer Protocol (SMTP), but these are not commonly used.
Transport Layer Security (TLS), on the other hand, is an open, Internet
Engineering Task Force (IETF)-proposed standard based on SSL 3.0. RFC’s
2246, 2712, 2817, and 2818 define TLS.The name is misleading, since TLS happens well above the Transport layer.The two protocols are not interoperable, but
TLS has the capability to drop down into SSL 3.0 mode for backward compatibility, and both can provide security for a single TCP session.
SSL and TLS provide a connection between a client and a server, over which any
amount of data can be sent securely. Both the server and browser generally must
be SSL- or TLS-enabled to facilitate secure Web connections, while applications
generally must be SSL- or TLS-enabled to allow their use of the secure connection. However, a recent trend is to use dedicated SSL accelerators as virtual private network (VPN) terminators, passing the content on to an end server.The
Cisco CSS Secure Content Accelerator 1100 is an example of this technique.
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For the browser and server to communicate securely, each needs to have the
shared session key. SSL and TLS use public key encryption to exchange session
keys during communication initialization.When a browser is installed on a workstation, it generates a unique private/public key pair.
HTTP/S is simply HTTP over SSL. HTTP/S is the protocol responsible for
encryption of traffic from a client browser to a Web server. HTTP/S uses port
443 instead of HTTP port 80.
When a URL begins with “https://,” you know you are using HTTP/S.
Both HTTP/S and SSL use a X.509 digital certificate for authentication purposes from the client to the server. For highly detailed information about SSL
and HTTP/S, visit Netscape’s Web site at
SSL must be known and understood for the Security+ exam. Remember
key items like the port it uses (443) and its basic functionality.
SSL suffers from security vulnerabilities caused by small key sizes, expired
certificates, and other weaknesses that can plague any public key implementation.
Many servers running SSL on the Internet are still using an older, flawed version
(SSLv2), or they use 40-bit encryption, or their certificates are expired or selfsigned.There is an online resource at
check_server.html that allows you to check the strength of an SSL server.You
simply type in the URL of the server and SSL version numbers and certificate
information are returned (Figure 5.6).
It is important not to confuse HTTP/S with Secure HTTP (S-HTTP). Although
they sound alike, they are two separate protocols, used for different purposes.
S-HTTP is not widely used, but it was developed by Enterprise Integration
Technologies (ETI) to provide security for Web-based applications. Secure HTTP
is an extension to the HTTP protocol. It is a secure message-oriented communications protocol that can transmit individual messages securely (whereas SSL
establishes a secure connection over which any amount of data can be sent).
S-HTTP provides transaction confidentiality, authentication, and message
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integrity, and extends HTTP to include tags for encrypted and secure transactions. S-HTTP is implemented in some commercial Web servers and most
browsers. An S-HTTP server negotiates with the client for the type of encryption that will be used, several types of which exist.
Figure 5.6 Checking the Strength of an SSL Server
Unlike SSL, S-HTTP does not require clients to have public key certificates
because it can use symmetric keys to provide private transactions.The symmetric
keys are provided in advance using out-of-band communication.
S-HTTP is easily confused with HTTP/S. Do not make the mistake of confusing the two on the Security+ exam. S-HTTP is a security-enhanced version of HTTP developed and proposed as a standard by EIT. You can find
more information in RFC 2660 (
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Instant Messaging
As more and more people go online and more businesses and their employees
rely on communicating in real time, Instant Messaging (IM) will grow by leaps
and bounds. Instant Messaging involves using tools such as AOL instant messenger (AIM),Yahoo Messenger, or MSN’s Messenger that comes with Windows
XP.This technology allows you to communicate with other members of your
staff when used at work, or with friends and family when used at home.There
are even programs, such as Trillian, that allow users to consolidate their accounts
on different IM networks and connect to AIM,Yahoo Messenger, MSN
Messenger, ICQ, and IRC all within a single interface.
However, some businesses prohibit the use of IM programs. One reason is
practical: Incessant “chatting” can become a bigger time waster than gossiping at
the water fountain (and one that is less obvious for management to detect). But
an even more important reason is that IM technologies pose significant security
risks. Each of the messenger programs has been exploited and most of them
require a patch.The hacker community has discovered exploits, which range from
DoS attacks all the way to executing remote commands on a system. For the
Security+ exam, the following security issues that are related to using IM technology must be acknowledged:
IM technology is constantly exploited via buffer overflow attacks. Since the tech- nology was made for ease of use and convenience, not for secure communica-
tions, there are many ways to exploit IM technology.
IP Addressing Conventions
IP address exposure is prominent and, because an attacker can get this informa- tion from IM technology, provides a way that an attacker can isolate a user’s
home machine, crack into it, and then exploit it.
File Transfer
Since IM technology includes a file transfer capability, there is the possibility that massive exploits can occur in that arena if the firewall technology is not configured to block it. All kinds of worms and viruses can be downloaded (circumventing the firewall), which could cause huge problems on an internal network.
Companies’ Human Resources (HR) policies need to be addressed because there
is no way to really track IM communication out of the box.Thus, if an employee
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is communicating in an improper way, it might be more difficult to prove as
compared with improper use of e-mail or Web sites visited.
Make sure you fully understand the implications of using IM technology
on your network. Many exploits, attacks, and hoaxes can be performed
using Instant Messaging.
For companies that want to allow IM for business purposes but prevent abuse,
there are software products available, such as Akonix’s security gateway for public
instant messaging, Zantaz’s Digital Safe, and IMlogic’s IM Manager, that allow
companies to better control IM traffic and log and archive IM communications.
Web-based Vulnerabilities
Java, JavaScript, and ActiveX components are often overlooked as potential threats
to a Web site.These are client-side scripts and components, which run on the
computer of a visitor to your site. Because they are downloaded to and run on
the user’s computer, any problems will generally affect the user rather than the
Web site itself. However, the effect of an erroneous or malicious script, applet, or
component can be just as devastating to a site. If a client’s computer locks up
when one of these loads on their computer—every time they visits a site—it ultimately will have the same effect as the Web server going down: No one will be
able to use the site.
As shown in the sections that follow, a number of problems may result from
Java applets, ActiveX components, or client-side scripts such as JavaScript. Not all
of these problems affect the client, and they may provide a means of attacking a
site. Ultimately, however, the way to avoid such problems involves controlling
which programs are made available on a site and being careful about what is
included in the content.
Understanding Java-, JavaScript-,
and ActiveX-based Problems
Some Web designers use public domain applets and scripts for their Web pages,
even though they do not fully understand what the applet or script does. Java
applets are generally digitally signed or of a standalone format, but when they are
embedded in a Web page, it is possible to get around this requirement. Hackers can
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program an applet to execute code on a machine, so that information is retrieved
or files are destroyed or modified. Remember that an applet is an executable program and has the capability of performing malicious activities on a system.
Java is a programming language, developed by Sun Microsystems, which is used
to make small applications (applets) for the Internet as well as standalone programs. Applets are embedded into the Web page and are run when the user’s
browser loads the HTML document into memory. In programming such applets,
Java provides a number of features related to security. At the time the applet is
compiled, the compiler provides type and bytecode verification to check whether
any errors exist in the code. In this way, Java keeps certain areas of memory from
being accessed by the code.When the code is loaded, the Java Virtual Machine
(JVM) is used in executing it.The JVM uses a built-in Security Manager, which
controls access by way of policies. In Netscape’s JVM, however, a problem was
discovered where certain conditions caused the JVM not to check code that was
being loaded. Because all of the code was not being checked, this allowed code to
be run that circumvented Java’s type verification. Shortly after this problem was
identified in Netscape Communicator, a similar problem was identified in
Internet Explorer.
In looking at this identified problem, it is recognized that such problems
would affect the user’s computer and not the Web server itself. As is the case with
other Internet programming methods discussed in this section, Java runs on the
client side. Generally, this means that the client, rather than the Web server, will
experience any problems or security threats posed by the applets. However, if the
applet is designed to extract information from the client machine, usernames and
passwords may be obtained and used to hack your site. Also, if the client machine
is damaged in any way by a malicious applet, the user will only know that they
visited the site and experienced a problem and is likely to blame the administrator for the problem.This will have an impact on the public perception of the
site’s reliability and the image of the company.
ActiveX is Microsoft’s implementation of applets, which are embedded in HTML
documents using the <OBJECT> tag. ActiveX controls can provide a variety of
functions, such as allowing users to view multimedia on a Web page. If a user
accesses an HTML document with an ActiveX control, it will check whether the
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control is already on the user’s computer. If it is not, it will be downloaded, the
Web page will be displayed, and the ActiveX code will be loaded into memory
and executed.
As with Java and JavaScript, ActiveX runs on the client side, thus many of the
issues encountered will impact the user’s machine and not the server. An issue
with ActiveX was revealed in 1999 when the “Safe for Scripting” security hole
was revealed. Programmers could set the “Safe for Scripting” flag so that their
ActiveX controls would not be checked for an Authenticode signature before
being run. Microsoft’s Authenticode is used to authenticate the control through
code signing, which is discussed later.When Authenticode is used, the ActiveX
code is signed and authenticated by a trusted third party.This ensures that the
code has not been modified since the time it was created.When the “Safe for
Scripting” flag was enabled, the code checking was bypassed, and the control
could be run without the user being aware of a problem.Two controls shipped
with IE4 that had this problem were Scriptlet.typelib (which had the ability to
create, edit, and overwrite files on the user’s hard disk) and Eyedog.ocx (which had
the ability to gather information from the registry).This was a major security
issue, because hackers could benefit from this weakness to cause malicious code
to run.To deal with this, a patch that fixed the problem was made available
through Microsoft’s Web site.
JavaScript is different from ActiveX and Java, in that it is not compiled into a program. Despite this, JavaScript uses some of the same syntax and functions as Java.
JavaScript is not a full-fledged programming language (as Java is). It cannot create
standalone applications; instead, the script typically is part of an HTML document.When a user accesses an HTML document with JavaScript in it, it is run
through an interpreter.This is slower than if the program were already compiled
into a language that the machine can understand. For this reason, JavaScript is
slower than Java applets.There are both client-side and server-side versions of
Although JavaScript is different from ActiveX and Java in that it is a scripting
language, it is still possible that a hacker may use a script to acquire information
about a site or use code to attack a site or client computer. However, JavaScript is
generally less likely to cause crashes than Java applets.
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Remember that an applet is a program that has the capability of performing malicious activities on your system. The known security vulnerabilities in Java and ActiveX can be fixed by downloading security based
hot fixes from the browser creators’ Web site.
Preventing Problems with
Java, JavaScript, and ActiveX
Preventing problems with scripts, applets, and other components that are included
on a site is not impossible if precautions are taken beforehand. First, network
administrators should not include components that they do not fully understand
or trust. If they are not certain what a particular script is doing in a line of code,
then they should not add it to a page. Similarly, they should use applets and
ActiveX components that make their source code available. If an administrator
has a particular applet or component that they want to use but do not have the
code available, then they must ensure that it was created by a trusted source. For
example, some commercially available recordable CDs (CD-Rs) are filled with
various applets, scripts, and components.Well-known companies, who do not
want to tarnish their corporate image by selling products with dangerous code,
create many of these. Also, a number of companies such as Microsoft provide
code samples on their site, which can be used safely and successfully on a site.
The code for a Java applet resides in a separate file, whereas the script
for a JavaScript is embedded in the HMTL document, and anyone can see
it (or copy it) by using the View Source function in the browser.
Code should be checked or any flaws, because administrators do not want
end users to be the first to identify them. A common method for testing code is
to upload the Web page and component to the site, but do not link the page to
any other pages.This will keep users who are not aware of the page from
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accessing it.Then they can test it live on the Web, without the risk that end users
will access it before they are sure the code is good. However, when using this
method, the administrator should be aware that there are tools such as Sam Spade
( that can be used to crawl your Web site
to look for unlinked pages. Another method is to use a test server, which is a
computer that is configured the same as the Web server but separated from the
rest of the network.With a test server, if damage is done to a site, the real site will
be unaffected. After this is done, it is wise to access the site using the user account
that will normally be used to view the applet, component, or script. For example,
if the site is to be used by everyone, view it using the anonymous user account.
This will allow the administrator to effectively test for problems.
A common problem that hacker’s use to their advantage regards scripts and
programs that trust user input.This issue was mentioned in the discussion about
how a guest book could be used to have a SSI command run and possibly
damage a site. In that discussion, we saw that CGI programs written in Perl can
be used to run batch files. Scripting languages can also be used to run shell functions.With a properly written and executed script, the cmd.exe function could be
used to run other programs on a Windows NT,Windows 2000 or Windows XP
For best security, administrators should write programs and scripts so that
input passed from a client is not trusted.Tools such as Telnet or other programs
available on the Internet can be used to simulate requests from Web browsers. If
input is trusted, a hacker can pass various commands to the server through the
applet or component.
As discussed in a previous section, considerable information may be found in
Web pages. Because scripts can be embedded directly into the Web page, the
script can be displayed along with the HTML by viewing the source code.This
option is available through most browsers, and may be used to reveal information
that the administrator did not want made public. Passwords and usernames can be
found in the code in an HTML document. Scripts in Web pages may be used to
pass usernames and passwords to Access or SQL databases.Windows NT requires
such scripts to include the usernames and passwords to connect to such databases.
It is possible that the hierarchy may also show in such code. Displaying this information might open the system up to attack.
To protect a system and network, the administrator should ensure that permissions are correctly set and use other security methods available through the
OS on which the Web server is running. For example, the NTFS file system on
Windows NT,Windows 2000, and Windows XP supports access control lists
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Damage & Defense…
(ACLs), which can be configured to control who is allowed to execute a script.
By controlling access to pages using scripts, the network is better protected from
hackers attempting to access this information.
Limit Access and Back Up Your Site
Hackers may attack a site for different reasons. Some may simply poke
around, look at what is there, and leave, whereas others may modify or
destroy data on the site. Some malicious hackers may modify a site so
that sensitive material is not destroyed, but the effects are more akin to
graffiti. This was the case when data was modified on the Web site of the
Royal Canadian Mounted Police (RCMP). Cartoon images appeared on the
site, showing RCMP officers riding pigs rather than horses. Although the
images were quickly fixed by simply uploading the original content to the
server, this case illustrates the need to set proper permissions on directories and regularly back up a site.
Often, content is created on one computer and then transferred it to
the actual Web site (unless using a program such as Front Page that
allows you to work directly on the Web site). In many cases, the administrator may feel this is enough, since they will have a copy of the content
on the machine where it was originally created. By backing up content,
they are insuring that if a script, applet, or component is misused, the site
can be restored and repaired quickly.
Before a problem occurs (and especially after one happens), the
administrator should review permissions to determine if anonymous or
low-level users have more access than they should. If they can write to a
directory or execute files, they may find that this is too much access
(depending on the directory in question). In any case, administrators
should not give users any more access to a directory than they need, and
the directories lower in the hierarchy should be checked to ensure that
they do not have excessive permissions due to their location. In other
words, if a directory is lower in the hierarchy, it may have inherited the
same permissions as its parent directory, even though you do not want
the lower level directory to have such a high level of access.
Because of the possible damage a Java applet, JavaScript, or ActiveX component can do to a network in terms of threatening security or attacking machines,
many companies filter out applets completely. Firewalls can be configured to filter
out applets, scripts, and components so that they are removed from an HTML
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document that is returned to a computer on the internal network. Preventing
such elements from ever being displayed will cause the Web page to appear differently from the way its author intended, but any content that is passed through
the firewall will be more secure.
On the client side, many browsers can also be configured to filter content.
Changing the settings on a Web browser can prevent applets and other programs
from being loaded into memory on a client computer.The user accessing the
Internet using the browser is provided with the HTML content, but is not presented with any of these programmed features. Remember that although
JavaScripts are not compiled programs, they can still be used to attack a user’s
machine. Because JavaScript provides similar functionality to Java, it can be used
to gather information or perform unwanted actions on a user’s machine. For this
reason, administrators should take care in the scripts used on their site.
In creating applets, components, and scripts, keep in mind that not all
browsers support these components. Also, some scripts will run on Internet
Explorer or Netscape Navigator, but will not run on both or other browsers.To
make a Web site accessible to as wide an audience as possible, the administrator
should provide a secondary set of Web pages or add code that determines the
type and version of browser a user is using and allow execution based on this
type and version information. If the script or applet is not supported set up the
HTML code to allow it to be skipped over.To show this, look at the following
The first line is used to retrieve the name of the browser being used; the
second line is used to retrieve the version of the browser. By using these functions, you can determine whether a script or applet should run.This is done as
if (navigator.appName = = "Netscape") {
Insert code here;
} else if (navigator.appName = = "Microsoft Internet Explorer") {
Insert code here;
} else {
document.write ("Internet Explorer or Netscape is required to
view this page");
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Another method of keeping errors from occurring in the JavaScript is to use
comments, which will prevent errors in browsers that do not support a scripting
language.The following piece of HTML code illustrates how to do this:
<SCRIPT LANGUAGE="JavaScript 1.1">
<!-insert JavaScript here
// -- >
Looking at this line-by-line, notice that the first line specifies the language
being used in the script. If an older browser is being used that does not understand the script tag, it will ignore the script. If it does support the language, this
tag will inform the browser’s interpreter of what language is to be interpreted.
The next line shows an opening comment. If an older browser that does not
understand JavaScript reads this line, any JavaScript between the opening and
closing comments will be ignored. If JavaScript is supported, it will begin to process the script.
Although the best course of action is to only use applets and scripts that are
personally created, this may not be feasible.The administrator might not know
how to create Java applets, JavaScripts, or ActiveX components, or they might
need ones that perform tasks that are beyond their abilities to program. Although
it is a good idea to avoid applets and scripts created by untrustworthy or
unknown individuals, administrators may feel forced to do so.They should try to
find programmers in their own company who have the skills needed to script or
program, or purchase or acquire existing scripts and applets from an established
source. If the source code is available, or if they are using scripts, then they should
look over how it was created and determine what it actually does.This will save
considerable problems in the long run.
When studying for this section of the Security+ exam, focus on the basic
aspects of scripting exploits. You will not be expected to analyze a script
for errors, or to create any type of exploit; they are listed here to
enhance your understanding of the exploits. However, make sure that
you know the fundamentals of scripting exploits and that languages
such as JavaScript are constantly used to exploit systems on the Internet.
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Programming Secure Scripts
The previous section looked at client-side programs and scripts, which run on
the user’s machine.This section looks at server-side programs and scripts, which
run on the Web server rather than on the machine being used to browse a site.
Server-side programs and scripts provide a variety of functions, including
working with databases, searching a site for documents based on keywords, and
providing other methods of exchanging information with users.
A benefit of server-side scripts is that the source code is hidden from the
user.With JavaScript, all scripts are visible to the user, who only has to view the
source code through the browser. Although this is not an issue with some scripts,
server-side scripts should be used when the script contains confidential information.The last thing the administrator wants to do is reveal to the world how
information in a corporate database can be accessed.
The Common Gateway Interface (CGI) allows communication links between
Internet applications and a Web server, allowing users to access programs over the
Web.The process begins when a user requests a CGI script or program using
their browser. For example, the user might fill out a form on a Web page and
then submit it.The request for processing of the form is made to the Web server,
which executes the script or application on the server. After the application has
processed the input, the Web server returns output from the script or application
to the browser.
PERL is another scripting language that uses an interpreter to execute various functions and commands. It is similar to the C programming language in its
syntax. It is popular for Web-based applications, and is widely supported. Apache
Web Server is a good example of this support, as it has plug-ins that will load
PERL permanently into memory. By loading it into memory, the PERL scripts
are executed faster. Microsoft has offered an alternative to CGI and PERL in
Active Server Pages (ASP)—HTML documents with scripts embedded into
them.These scripts can be written in a number of languages, including JScript
and VBScript, and may also include ActiveX Data Object program statements. A
benefit of using ASP is that it can return output through HTML documents
extremely quickly. It can provide a return of information faster than using CGI
and PERL.
Unfortunately, using ASP can cause problems that are similar to those seen in
client-side scripting. Embedding the scripts into the Web pages allows curious
and malicious users to view ASP code. Depending on what is included in the
page, a hacker may be able to acquire usernames and passwords and identify vulnerabilities in the code.
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For more information about PERL, see the PERL FAQ on the Web site. For more information about CGI, see For more information
about ASP, see the ASP Resource Index at
Common to all of these methods is that the scripts and programs run on the
server.This means attacks using these methods will often affect the server rather
than the end user.Weaknesses and flaws can be used to exploit the script or program and access private information or damage the server. An example of this is
the PHF script that came with early versions of NCSA HTTPD server (version
1.5a-export or earlier) and Apache Web Server 1.0.3.The problem with this
script was that it did not properly parse and validate input.The PHF script is a
phone book script.Whenever a new line character (%0a) was used in the script,
any additional commands were also performed with the privileges of the user
account running the Web server.To deal with this problem, the script should be
removed from the Web server.
Testing and auditing programs before going live with them is very important.
In doing so, administrators may reveal a number of vulnerabilities or find problems, such as buffer overflows, which might have been missed if the code had
been made available on the site. It is best to use a server dedicated to testing only.
This server should have the same applications and configurations as the actual
Web server and should not be connected to the production network.
Any programs and scripts available on your site should be thoroughly
tested before they are made available for use on the Web. Determine
whether the script or program works properly by using it numerous
times. If you are using a database, enter and retrieve multiple records.
You should also consider having one or more members of your IT staff
try the script or program themselves, because this will allow you to analyze the effectiveness of the program with fresh eyes. They may enter
data in a different order or perform a task differently, causing unwanted
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Code Signing: Solution or More Problems? Code signing addresses the need for users to trust the code they download and
then load into their computer’s memory. After all, without knowing who provided the software, or whether it was altered after being distributed, malicious
code could be added to a component and used to attack a user’s computer.
Digital certificates can be used to sign the code and to authenticate that code
has not been tampered with, and that it is indeed the identical file distributed by
its creator.The digital certificate consists of a set of credentials for verifying identity and integrity.The certificate is issued by a certification authority and contains
a name, serial number, expiration date, copy of the certificate holder’s public key,
and a digital signature belonging to the certificate authority (CA).The elements
of the certificate are used to guarantee that the file is valid.
For more information about how digital certificates work, see Chapter
10, “Public Key Infrastructure.”
As with any process that depends on trust, code signing has its positive and
negative aspects.The following sections discuss these issues and show how the
process of code signing works.
Understanding Code Signing
Digital certificates are assigned through CAs. A CA is a vendor that associates a
public key with the person applying for the certificate. One of the largest organizations to provide such certificates is VeriSign (, which provides Authenticode certificates. An Authenticode certificate is used for software
publishing and timestamp services. It can be attached to the file a programmer is
distributing and allows users to identify that it is a valid, unadulterated file.
Digital certificates can be applied to a number of different file types. For
example, using VeriSign Authenticode, developers can sign such files as the
.EXE An executable program
.CAB Cabinet files commonly used for the installation and setup of
applications; contain numerous files that are compressed in the cabinet file
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.CAT Digital thumbprints used to guarantee the integrity of files
.OCX ActiveX controls
.DLL Dynamic link library files, containing executable functions
.STL Contains a certificate trust list
When a person downloads a file with a digital certificate, the status of that
certificate is checked through the CA. If the certificate is not valid, the user will
be warned. If it is found to be valid, a message will appear stating that the file has
a valid certificate.The message will contain additional information and will show
to whom the certificate belongs.When the user agrees to install the software, it
will begin the installation.
The Strengths of Code Signing
Digital signatures can be used to guarantee the integrity of files and that the
package being installed is authentic and unmodified.This signature is attached to
the file being downloaded, and identifies who is distributing the files and shows
that they have not been modified since being created.The certificate helps to
keep malicious users from impersonating someone else.
This is the primary benefit of code signing. It provides users with the identity
of the software’s creator. It allows them to know who manufactured the program
and provides them with the option of deciding whether to trust that person or
company.When the browser is about to download the component, a warning
message is displayed, allowing them to choose whether it is to be installed or
loaded into memory.This puts the option of running it in the user’s hands.
Problems with the Code Signing Process
A major problem with code signing is that you must rely on a third party for
checking authenticity. If a programmer provided fake information to a CA or
stole the identity of another individual or company, they could then effectively
distribute a malicious program over the Internet.The deciding factor here would
be the CA’s ability to check the information provided when the programmer
applied for the certificate.
Another problem occurs when valid information is provided to the CA, but
the certificate is attached to software that contains bad or malicious code. An
example of such a problem with code signing is seen in the example of Internet
Exploder, an ActiveX control that was programmed by Fred McLain.This programmer obtained an Authenticode certificate through VeriSign.When users
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running Windows 95 with Advanced Power Management ran the code for
Internet Exploder, it would perform a clean shutdown of their systems.The certificate for this control was later revoked.
Certificate Revocation Lists (CRLs), which store a listing of revoked certificates, can also be problematic.Web browsers and Internet applications rarely
check certificate revocation lists, so it is possible for a program to be used even
though its certificate has been revoked. If a certificate was revoked, but its status
was not checked, the software could appear to be okay even though it has been
These problems with code signing do not necessarily apply to any given CA.
Certificates can also be issued within an intranet using software such as Microsoft
Certificate Server (which is a component that comes with Windows 2000 and
.NET/2003 server products). Using this server software, users can create a CA to
issue their own digital certificates for use on a network.This allows technically
savvy individuals to self-sign their code with their own CA and gives the appearance that the code is valid and secure.Therefore, users should always verify the
validity of the CA before accepting any files.The value of any digital certificate
depends entirely on how much trust there is in the CA that issued it. By
ensuring that the CA is a valid and reputable one, administrators can avoid
installing a hacker’s code onto their system.
An additional drawback to code signing for applications distributed over the
Internet is that users must guess and choose whom they trust and whom they do
not.The browser displays a message informing them of who the creator is, a brief
message about the dangers of downloading any kind of data, and then leave it up to
the user whether to install it or not.The browser is unable to verify code.
Damage & Defense…
Problems with Code Signing
The possibility exists that code you download might have a valid certificate or use self-signed code that is malicious. Such code might use CAs
that have names similar to valid CAs, but are in no way affiliated with that
CA. For example, you may see code signed with the vendor name of
VerySign, and misread it as VeriSign, and thus allow it to be installed. It is
easy to quickly glance at a warning and allow a certificate, so remember
to read the certificate information carefully before allowing installation of
the code.
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You do not need to know the code signing-based problems and resolutions for the Security+ exam. You do need to know that code is problematic, that it can cause problems in the form of scripting and applets,
and that it must be dealt with in a specific way to make your systems,
network, and infrastructure safer and more secure.
JavaScript JavaScript is a scripting language developed by Netscape to allow executable code
to be embedded in Web pages. All major Web browsers support JavaScript.
JavaScript is used to manipulate browser window size, open and close windows,
manage forms, and alter browser settings. JavaScript itself is relatively secure.
However, improper implementations (such as vendor programming errors) have
enabled numerous attacks. Each vendor has patched most of these vulnerabilities,
but it is still possible to use JavaScript to perform a malicious activity if a hacker
can trick Web surfers into doing something they should not. Unfortunately, it is
usually easy for a malicious Web site to trick visitors into providing access or
enabling code execution when they should not. For information about specific
exploits that use JavaScript, see the JavaScript for Beginners Web site at
JavaScript is completely different from Java. Although both are objectoriented languages and use some of the same syntax, and both can be
used to add interactivity to Web sites, the similarity stops there. Java is
a full-fledged programming language that can be used to create standalone applications, whereas JavaScript is a much simpler (and less functional) scripting language that is used within a markup language (HTML).
Java can even function as a complete computing platform. For more
information about the differences between the two, see “Java vs.
JavaScript” at
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Head of the Class…
What Is Java?
Java is a programming language developed by Sun Microsystems and
designed to provide much of the functionality and “feel” of C++, while
being simpler to learn and use. It is fundamentally different from
JavaScript in that it uses a technique known as sandboxing to restrict its
capabilities. Small Java programs that execute locally are called application modules or applets. Each applet is checked to make sure it is coded
properly and is not corrupted before it is allowed to execute. Then a security monitor oversees the applet’s activity to prevent it from performing
actions that it should not be able to do, such as reading data, opening
network connections, or deleting files.
Java can also be used to create complete applications, including
applications that are used in a distributed client-server environment. A
major advantage of Java is that its applications are highly portable; and
they can run on any computer that has a JVM installed. Thus, programmers do not have to write several different versions of their applications
for different OS platforms.
Unfortunately, some implementations of Java have been compromised using various exploits. For example, in August 2000, CERT released
a security advisory warning that some versions of Netscape
Communicator contained Java classes that allowed unsigned Java applets
to access local and remote resources in violation of the security policies
for applets. Hostile applets can crash browsers and systems, kill other
applets, extract an e-mail address and send it to the applet’s distributor,
and perform other nasty acts. See the Hostile Applets page at An excellent paper on Java security
issues is located at
index.html. The transcript of a good discussion comparing ActiveX and
Java in terms of security issues is available from the Princeton Secure
Internet Programming team at
ActiveX ActiveX controls are Microsoft’s implementation of the Component Object Model
(COM). Microsoft designed ActiveX to replace the older Object Linking and
Embedding (OLE) model that was used in earlier versions of the Windows platform. ActiveX is an improvement on OLE, in that it adds extensibility to the model
and allows for distributed computing (DCOM) as well as better performance in
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local applications. ActiveX controls are commonly written in either Visual Basic or
C++. An ActiveX control is a component that functions as a self-sufficient program
object that can be downloaded as a small program or used by other application
programs. An ActiveX control functions similarly to a Java applet.
For more information about COM, DCOM, and related technologies such
as COM+, see the Microsoft Component Object Model home page at
ActiveX controls are apparent throughout the modern Windows platform and
add many of the new interactive features of Windows-based applications, and
especially Web applications. ActiveX controls fit nicely into HTML documents
and are therefore portable to many systems. ActiveX controls can be used in
applications to perform repetitive tasks or invoke other ActiveX controls that perform special functions. Once an ActiveX control is installed, it runs automatically
and does not need to be installed again. As a matter of fact, an ActiveX control
can be downloaded from a distant location via a URL link and run on a local
machine over and over without having to be downloaded again.This allows
ActiveX controls to be activated from Web pages. ActiveX controls run in “container” applications, such as the Internet Explorer Web browser application or the
Access database application.
The security issues involving ActiveX controls are very closely related to the
inherent properties of ActiveX controls. ActiveX controls do not run in a confined space or “sandbox” as Java applets do, so they pose much more potential
danger to applications. Also, ActiveX controls are capable of all operations that a
user is capable of, so controls can add or delete data and change the properties of
objects. Even though JavaScript and Java applets seem to have taken the Web programming community by storm, many Web sites and Web applications still
employ ActiveX controls to service users.
As evidenced by the constant news flashes about compromised Web sites,
many developers have not yet mastered the art of securing their controls, even
though ActiveX is a well-known technology.This section helps identify and avert
some of the security issues that may arise from using poorly coded ActiveX controls (many of which are freely available on the Internet).The following sections
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debunk common misconceptions about ActiveX and introduce the best practices
for rendering safe, secure, and functional ActiveX controls.
Dangers Associated with Using ActiveX
The primary dangers associated with using ActiveX controls stem from the way
Microsoft approaches security. By using their Authenticode technology to digitally sign an ActiveX control, Microsoft attempts to guarantee the user of the
origin of the control and that it has not been tampered with since it was created.
In most cases this works, but there are several things that Microsoft’s authentication system does not do, which can pose a serious threat to the security of an
individual machine and a network.
The first and most obvious danger is that Microsoft does not limit the access
that the control has after it is installed on a local machine.This is one of the key
differences between ActiveX and Java. Java uses a method known as sandboxing.
Sandboxing a Java applet ensures that the application is running in its own protected memory area, which isolates it from things like the file system and other
applications.This puts some serious limitations on what administrators can do
with a control.
For more information about sandboxing as part of the JVM’s security
mechanisms, see “Java’s Security Architecture” by Bill Venners at
ActiveX controls, on the other hand, have the same rights as the user who is
running them after they are installed on a computer. Microsoft does not guarantee
that the author is the one using the control, or that it is being used in the way it
was intended, or on the site or pages for which it was intended. Microsoft also
cannot guarantee that the owner of the site or someone else has not modified the
pages since the control was put in place. It is the exploitation of these vulnerabilities that poses the greatest dangers associated with using ActiveX controls.
For example, Scriptlet.Typelib is a Microsoft ActiveX control that developers
use to generate Type Libraries for Windows Script Components (WSCs). One of
the functions of this control is that it allows files to be created or modified on the
local computer. Obviously, this is an ActiveX control that should be protected
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from untrusted programs. According to the CERT Coordination Center
(CERT/CC), this control is incorrectly marked as “Safe for Scripting” when it is
shipped with Internet Explorer versions 4.0 and 5.0. As a result, a hacker could
write malicious code to access and execute this control without the user ever
knowing that it has happened.Two well-known viruses exploit this vulnerability:
.kak and BubbleBoy. Both are delivered through HTML-formatted e-mail and
affect the Windows Registry and other system files (Microsoft issued a patch for
both in 1999).
Because Scriptlet.Typelib is marked “Safe for Scripting,” the default security
settings of Internet Explorer, Outlook, and Outlook Express allow the control to
be used without raising any security alerts.The .kak virus uses this security hole
in an attempt to write an HTML Application (HTA) file into the Windows
startup directory. Once there, .kak waits for the next system startup or user login.
When this happens, the virus can go back to work and cause its intended
damage. It then goes through a series of writing and modifying several files.The
end result is that users end up with a new signature file that attaches itself to all
outgoing messages and includes the virus (see Figure 5.7).This is the method that
.kak uses to propagate itself.
Figure 5.7 Microsoft Outlook Express Options Dialog Box
The final insult comes when the day of the month and current hour are
checked. If it is 6:00 P.M. or later on the first day of any month, .kak displays a
dialog box saying “Not Today”; when this dialog box is closed, .kak calls a Win32
API function causing Windows to shut down. Because this code is in the HTA file
that runs at each startup and login, restarting an afflicted machine at or after 6:00
P.M. on the first day of any month results in the machine starting up, displaying the
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“Not Today” message, then shutting down.With the ability to create or modify files
and make registry entries and API calls, this control can be extremely dangerous.
ActiveX controls are a very serious threat to your system if they are not
from a trusted source. Remember that these are small programs that can
exploit your system if you do not have security set up correctly on your
Web browser.
Avoiding Common ActiveX Vulnerabilities
One of the most common vulnerabilities with ActiveX controls has to do with
the programmer’s perception, or lack thereof, of the capabilities of the control.
Every programmer that works for a company or consulting firm and writes a
control for a legitimate business use wants his controls to be as easy to use as possible. He takes into consideration the intended use of the control, and if it seems
OK, he marks it “Safe for Scripting.”This is a double-edged sword. If it is not
marked “safe,” users will be inundated with warnings and messages on the potential risk of using a control that is not signed or not marked as safe. Depending on
the security settings in the browser, they may not be allowed to run it at all.
However, after it is marked as safe, other applications and controls have the ability
to execute the control without requesting the user’s approval.You can see how
this situation could be dangerous. A good example of the potential effects of
ActiveX is the infamous Windows Exploder control.This was a neat little
ActiveX control written by Fred McLain (
that demonstrates what he calls “dangerous” technology. His control only performs a clean shutdown and power-off of the affected Windows system.This
might not seem so bad, but it was written that way to get the point across that
the control could be used to perform much more destructive acts. Programmers
have to be careful with ActiveX controls, and be sure that they know everything
their control is capable of before releasing it.
Another problem that arises as a result of lack of programmer consideration is
the possibility that a control will be misused and at the same time take advantage
of the users’ privileges. Just because the administrator has a specific use in mind
for a control does not mean that someone else cannot find a different use for the
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control.There are many people who are not trustworthy and will try to exploit
another’s creativity. Consider the Scriptlet.Typelib example in the previous section.
The programmers at Microsoft knew that their control worked fine for creating
Type Libraries for WSCs, but they never considered that someone else might use
their control to write HTA files or make Registry modifications.
Another common cause of vulnerabilities in ActiveX controls is the release of
versions that have not been thoroughly tested and contain bugs. One specific bug
that is often encountered in programs written in C++ is the buffer overflow bug.
This occurs a string is copied into a fixed-length array and the string is larger
than the array.The result is a buffer overflow and a potential application crash.
With this type of error, the key is that the results are unpredictable.The buffer
overflow may print unwanted characters on the screen, or it may kill the browser
and in turn lock up the system.This problem has plagued the UNIX/Linux
world for years, but recently has also become more noticeable on the Windows
platform. If you browse the top IT security topics at Microsoft TechNet
(, you will notice that one or
more issues involving this type of error are found monthly.This is not exclusively
a Microsoft problem, but it affects almost every vendor that writes code for the
Windows platform.To illustrate how far-reaching this type of problem is, in a
recent report found on the secureroot Web site (, Neal
Krawetz reported that he had identified a buffer overflow condition in the
Shockwave Flash plug-in for Web browsers. He states, “Macromedia’s Web page
claims that 90 percent of all Web browsers have the plug-ins installed. Because
this overflow can be used to run arbitrary code, it impacts 90 percent of all ‘Web’
enabled systems.” Now that is a scary thought! Although this is a very widespread
type of error, the solution is simple: Programmers must take the extra time
required to do thorough testing and ensure that their code contains proper
bounds checking on all values that accept variable length input.
Another vulnerability occurs when using older, retired versions of ActiveX
controls. Some may have had errors, some not. Some may have been changed
completely or replaced for some reason. After someone else has a copy of a control, it cannot be guaranteed that the current version will be used, especially if it
can be exploited in some way. Although users will get an error message when
they use a control that has an expired signature, a lot of people will install it
anyway. Unfortunately, there is no way to prevent someone from using a control
after it has been retired from service. After a control that can perform a potentially harmful task is signed and released, it becomes fair game for every hacker
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on the Internet. In this case, the best defense is a good offense.Thorough testing
before releasing a control will save much grief later.
Lessening the Impact of ActiveX Vulnerabilities
An ActiveX vulnerability is serious business for network administrators, end users,
and developers alike. For some, the results of misused or mismanaged ActiveX
controls can be devastating; for others, it is never taken into consideration.There
can be policies in place that disallow the use of all controls and scripts, but it has
to be done at the individual machine level, and takes a lot of time and effort to
implement and maintain.This is especially true in an environment where users
are more knowledgeable on how to change browser settings. Even when policy
application can be automated throughout the network, this might not be a feasible solution if users need to be able to use some controls and scripts. Other
options can limit the access of ActiveX controls, such as using firewalls and virus
protection software, but the effectiveness is limited to the obvious and known.
Although complete protection from the exploitation of ActiveX vulnerabilities is
difficult—if not impossible—to achieve, users from every level can take steps to
help minimize the risk.
Protection at the Network Level
For network administrators, the place to start is by addressing the different security settings available through the network OS such as.
Options such as security zones and SSL protocols to place limits on
Access to the CodeBaseSearchPath in the system Registry, which controls
where the system will look when it attempts to download ActiveX
The Internet Explorer Administration Kit (IEAK), which can be used to
define and dynamically manage ActiveX controls.
Although all of these are great, administrators should also consider implementing a firewall if they have not already done so. Some firewalls have the capability of monitoring and selectively filtering the invocation and downloading of
ActiveX controls and some do not, so administrators must be aware of the capabilities of the firewall they choose.
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Protection at the Client Level
One of the most important things to do as an end user is to keep the OS with all
its components and the virus detection software current. Download and install
the most current security patches and virus updates on a regular basis. Another
option for end users, as well as administrators, is the availability of security zone
settings in Internet Explorer, Outlook, and Outlook Express.These are valuable
security tools that should be used to their fullest potential.
Properly set security zones can dramatically reduce the potential vulnerability to ActiveX controls. There are five security zones:
Local Intranet zone
Trusted Sites zone
Restricted Sites zone
Internet zone
My Computer zone
The last zone, My Computer, is only available through the IEAK and
not through the browser interface. If you do not have access to the
IEAK, you can also access the security zone settings through the
Internet Settings\Zones] Registry key. The appropriate settings for this
key are shown in Table 5.1.
Table 5.1 Security Zone Settings in Internet Explorer, Outlook, and
Outlook Express
Registry Key Setting
Security Zone
My Computer zone
Local Intranet zone
Trusted Sites zone
Internet zone
Restricted Sites zone
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Complete the following steps to modify the security zone settings
through Internet Explorer 6:
1. From the Tools menu, select Internet Options. The Internet
Options dialog box appears (Figure 5.8).
Figure 5.8 The Internet Options Dialog Box
2. Select the Security tab. The Security Options panel appears
(Figure 5.9).
Figure 5.9 The Security Tab of the Internet Options Dialog Box
3. Select the zone you wish to change. For most users, this is the
Internet zone, but depending on your circumstances, you may
need to repeat these steps for the Local Intranet zone as well.
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4. Click the Custom Level button. The Security Settings panel
appears (Figure 5.10).
Figure 5.10 Security Settings Panel
5. Change one or more of the following settings for your desired
level of security:
Set Run ActiveX controls and plug-ins to administrator
approved, disable, or prompt.
Set Script ActiveX controls marked safe for scripting to disable
or prompt.
6. Click OK to accept these changes. A dialog box appears asking if
you are sure you want to make these changes (Figure 5.11).
Figure 5.11 Viewing a Warning about Zone Settings
7. Click Yes.
8. Click OK to close the Internet Options dialog box and save your
End users should exercise extreme caution when prompted to download or
run an ActiveX control.They should also make sure that they disable ActiveX
controls and other scripting languages in their e-mail applications, which is a
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measure that is often overlooked. A lot of people think that if they do not use a
Microsoft e-mail application, they are safe. But if an e-mail client is capable of
displaying HTML pages (for example, Eudora), chances are they are just as vulnerable using it as they would be using Outlook Express. As far as Netscape
browsers go, they are most likely safe from any potential ActiveX security threat
for now. In order to use ActiveX with a Netscape browser earlier than version 6,
a third party plug-in has to be installed.The best known plug-in for ActiveX support in Netscape is called ScriptActive, which is written by NCompass. (However,
NCompass is no longer providing this plug-in or supporting the Netscape
browser.) No standard plug-in or support exists for Netscape 6 with its new
Gecko engine. However, several ongoing development projects are working to
create new plug-ins or direct API support for ActiveX in Netscape.
Developer’s have the most important responsibility.They control the first line
of defense against ActiveX vulnerabilities.They must stay current on the tools
available to assist in securing the software.They must always consider the risks
involved in writing mobile code and follow good software engineering practices
and be extra careful to avoid common coding problems and easily exploited
coding mistakes. But most importantly, they must use good judgment and
common sense and test, test, test before releasing the code to the public.
Remember, after signing it and releasing it, it is fair game.
Hackers can usually create some creative way to trick a user into clicking
on a seemingly safe link or opening e-mail with a title like “In response
to your comments.”
Buffer Overflows A buffer is a sort of holding area for data.To speed processing, many software pro-
grams use a memory buffer to store changes to data, then the information in the
buffer is copied to the disk.When more information is put into the buffer than it
is able to handle, a buffer overflow occurs. Overflows can be caused deliberately by
hackers and then exploited to run malicious code.
There are two types of overflows: stack and heap.The stack and the heap are
two areas of the memory structure that are allocated when a program is run.
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Function calls are stored in the stack, and dynamically allocated variables are
stored in the heap. A particular amount of memory is allocated to the buffer.
Attackers can use buffer overflows in the heap to overwrite a password, a filename, or other data. If the filename is overwritten, a different file will be opened.
If this is an executable file, code will be run that was not intended to be run. On
UNIX systems, the substituted program code is usually the command interpreter,
which allows the attacker to execute commands with Superuser privileges. On
Windows systems, the overflow code can be used to send an HTTP request to
download malicious code of the attacker’s choice.
Buffer overflows are based on the way the C programming language works.
Many function calls do not check to ensure that the buffer will be big enough to
hold the data copied to it. Programmers can use calls that do this check to prevent overflows, but many do not.
Creating a buffer overflow attack requires that the hacker understand
assembly language as well as technical details about the OS to be able to write
the replacement code to the stack. However, the code for these attacks is often
published so that others, who have less technical knowledge, can use it. Some
types of firewalls, called stateful inspection firewalls, allow buffer overflow attacks
through, whereas application gateways (if properly configured) can filter out most
overflow attacks.
Buffer overflows constitute one of the top flaws for exploitation on the
Internet today. A buffer overflow occurs when a particular operation/function
writes more data into a variable (which is actually just a place in memory) than
the variable was designed to hold.The result is that the data starts overwriting
other memory locations without the computer knowing those locations have
been tampered with.To make matters worse, some hardware architectures (such as
Intel and Sparc) use the stack (a place in memory for variable storage) to store
function return addresses.Thus, the problem is that a buffer overflow will overwrite these return addresses, and the computer—not knowing any better—will
still attempt to use them. If the attacker is skilled enough to precisely control
what values are used to overwrite the return pointers, the attacker can control the
computer’s next operation(s).
The two flavors of buffer overflows referred to today are stack and heap. Static
variable storage (variables defined within a function) is referred to as stack,
because they are actually stored on the stack in memory. Heap data is the
memory that is dynamically allocated at runtime, such as by C’s malloc() function.
This data is not actually stored on the stack, but somewhere amidst a giant
“heap” of temporary, disposable memory used specifically for this purpose.
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Actually exploiting a heap buffer overflow is a lot more involved, because there
are no convenient frame pointers (as are on the stack) to overwrite.
Luckily, however, buffer overflows are only a problem with languages that
must pre-declare their variable storage sizes (such as C and C++). ASP, Perl, and
Python all have dynamic variable allocation—the language interpreter itself handles the variable sizes.This is rather handy, because it makes buffer overflows a
moot issue (the language will increase the size of the variable if there is too much
data). But C and C++ are still widely used programming languages (especially in
the UNIX world), and therefore buffer overflows are not likely to disappear anytime soon.
Making Browsers and
E-Mail Clients More Secure
There are several steps network administrators and users can take to make Web
browsers and e-mail clients more secure and protect against malicious code or
unauthorized use of information.These steps include the following:
Restricting the use of programming languages
Keeping security patches current
Becoming aware of the function of cookies
Restricting Programming Languages
Most Web browsers have options settings that allow users to restrict or deny the
use of Web-based programming languages. For example, Internet Explorer can be
set to do one of three things when a JavaScript, Java, or ActiveX element appears
on a Web page:
Always allow
Always deny
Prompt for user input
Restricting all executable code from Web sites, or at least forcing the user to
make choices each time code is downloaded, reduces security breaches caused by
malicious downloaded components.
A side benefit of restricting the Web browser’s use of these programming languages is that the restrictions set in the browser often apply to the e-mail client as
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well.This is true when the browser is Internet Explorer and the e-mail client is
Outlook or Outlook Express, and Netscape and Eudora also depend on the Web
browser settings for HTML handling.The same malicious code that can be
downloaded from a Web site could just as easily be sent to a person’s e-mail
account. If administrators do not have such restrictions in place, their mail client
can automatically execute downloaded code.
Keep Security Patches Current
New exploits for Web browsers and e-mail clients seem to appear daily. Product
vendors usually address significant threats promptly by releasing a patch for their
products.To maintain a secure system, administrators must remain informed about
their software and apply patches for vulnerabilities when they become available.
However, they must consider a few caveats when working with software
Patches are often released quickly, in response to an immediate problem,
so they may not have been thoroughly tested.This can result in failed
installations, crashed systems, inoperable programs, or additional security
It is extremely important to test new patches on non-production systems
before deploying them throughout a network.
If a patch cannot be deemed safe for deployment, the administrator
should weigh the consequences of not deploying it and remaining vulnerable to the threat against the possibility that the patch might itself
cause system damage. If the threat from the vulnerability is minimal, it is
often safer to wait and experience the problem that a patch is designed
to address before deploying a questionable patch.
Cookie Awareness A cookie is a kind of token or message that a Web site hands off to a Web browser
to help track a visitor between clicks.The browser stores the message on the visitor’s local hard disk in a text file.The file contains information that identifies the
user and their preferences or previous activities at that Web site. If the user revisits
the same Web site, the user’s browser sends the cookie back to the Web server.
Cookies are extremely useful in allowing a Web site to provide a seemingly continuous communications session with a visitor, such as maintaining a shopping
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cart, remembering search keywords, or customizing displayed data based on the
user’s preferences. However, because cookies contain identifying information, they
can also be used for less noble purposes.
Cookies have been discussed extensively in the popular press.These stories
sometimes grant cookies more power than they really have and assign them more
regard than they deserve. Cookies raise questions about privacy, but they are
unable to execute code or access files. Instead, cookies simply store data from
Web browsing sessions and send that same data back to a Web server. Cookies can
be delivered to a computer via Web pages or HTML-enabled e-mail. Malicious
or unscrupulous use of cookies occurs when they are used to track a user’s
surfing habits from one system to another, to grab a user’s logon information
from one site and send it to another, or to capture a user’s e-mail address and add
the user to mailing lists without the user’s knowledge. Fortunately, cookies can be
disabled in the same manner as programming languages, using the security settings in the browser.
Securing Web Browser Software
Although the same general principles apply, each of the popular Web browser
programs has a slightly different method to configure its security options.The
following sections demonstrate how to make changes to the settings of the three
most popular browsers—Microsoft Internet Explorer, Netscape, and Opera—and
turn off features that allow security holes to be exploited.
Securing Microsoft Internet Explorer
Securing Microsoft Internet Explorer (IE) involves applying the latest updates
and patches, modifying a few settings, and practicing intelligent surfing. Microsoft
seems to release an IE-specific security patch every week.This constant flow of
patches is due to both the oversights of the programmers who wrote the code
and to the focused attacks on Microsoft products by the malevolent cracker community. In spite of this negative attention, IE can still be employed as a relatively
secure Web browser—when it is configured correctly.
The first step in securing IE is to install the latest patches and updates. Users
can do so automatically through Windows Update or can install them manually.
Either way, only through patch application will most of the known vulnerabilities
of IE programming be resolved. For information about security patches available
for Microsoft’s latest browser software, see
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The second step is to configure IE for secure surfing. Users can do this
through the Internet Options applet. In IE version 6, this applet is accessed
through the Windows Control Panel or through the Tools menu of IE. If the
default settings are properly altered on the Security, Privacy, Content, and
Advanced tabs, IE security is improved significantly.
Zones are defined on the Security tab. A zone is nothing more than a named
collection of Web sites (from the Internet or a local intranet) that can be assigned
a specific security level. IE uses zones to define the threat level a specific Web site
poses to the system. IE offers four security zone options:
Internet Contains all sites not assigned to other zones.
Local Intranet Contains all sites within the local intranet or on the
local system.The OS maintains this zone automatically.
Trusted Sites Contains only sites manually added to this zone. Users
should add only fully trusted sites to this zone.
Restricted Sites Contains only sites manually added to this zone.
Users should add any sites that are specifically not trusted or that are
known to be malicious to this zone.
Each zone is assigned a predefined security level or a custom level can be created.The predefined security levels are offered on a slide controller with four settings—Low, Medium-Low, Medium, and High—with a description of the
content that will be downloaded under particular conditions.
Custom security levels can be defined to exactly fit the security restrictions of
an environment.There are over 20 individual security controls related to how
ActiveX, downloads, Java, data management, data handling, scripting, and logon
are handled.The most secure configuration is to set all zones to the High security
level. However, keep in mind that increased security means less functionality and
The Privacy tab, shown in Figure 5.12, defines how IE manages personal
information through cookies.
The Privacy tab offers a slide controller with six settings ranging from full
disclosure to complete isolation. A custom set of cookie controls can also be
defined by deciding whether first-party and third-party cookies are allowed or
denied, or whether a prompt will be initiated, as well as whether session cookies
are allowed. Individual Web sites can be defined whose cookies are either always
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allowed or always blocked. Preventing all use of cookies is the most secure configuration, but it is also the least functional. Many Web sites will not function
properly under this setting, and some will not even allow users to visit them
when cookies are disabled.
Figure 5.12 Cookie Options Can Be Set in IE via the Privacy Tab in
Internet Options
The Content tab, shown in Figure 5.13, gives access to the certificates that
are trusted and accepted by IE. If a certificate has been accepted that the administrator no longer trusts, they can peruse this storehouse and remove it.
Figure 5.13 You Can Configure Certificate Options in IE Using the Content
Tab in Internet Options
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The Content tab also gives access to IE’s AutoComplete capability.This feature is useful in many circumstances, but when it is used to remember usernames
and passwords to Internet sites, it becomes a security risk.The most secure configuration requires that AutoComplete be turned off for usernames and passwords, that prompting to save passwords is disabled, and that the current password
cache is cleared.
On the Advanced tab shown in Figure 5.14, several security-specific controls
are included at the bottom of a lengthy list of functional controls.These security
controls include the following (and more):
Check for certificate revocation
Do not save encrypted pages to disk
Delete temporary Internet files when the browser is closed
Use Secure Shell/Transport Layer Security (SSH/TLS)
Warn when forms are submitted insecurely
Figure 5.14 The Advanced Tab in IE’s Internet Options Allows You to
Configure Security Settings
The most secure configuration has all these settings enabled.
The final step in maintaining a secure IE deployment is to practice safe
surfing habits. Common sense should determine what users do, both online and
off.Visiting Web sites of questionable design is the virtual equivalent of putting
yourself in harm’s way in a dark alley, but Internet users do it all the time. Here
are some guidelines that should be followed to ensure safe surfing:
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Download software only from original vendor Web sites.
Always attempt to verify the origin or ownership of a Web site before
downloading materials from it.
Never assume anything presented online is 100 percent accurate.
Avoid visiting suspect Web sites—especially those that offer cracking
tools, pirated programs, or pornography—from a system that needs to
remain secure.
Always reject certificates or other dialog box prompts by clicking No,
Cancel, or Close when prompted by Web sites or vendors with which
you are unfamiliar.
For the Security+ exam, you will not be expected to know how to set
specific settings on your Web browser, but you will be expected to know
what will be exploited if you do not set such settings.
CGI Programmer’s working on a Web application already know that if they want their
site to do something such as gather information through forms or customize itself
to their users, they will have to go beyond HTML.They will have to do Web
programming; the most common form used today is the Common Gateway
Interface (CGI). CGI applies rules for running external programs in a Web
HTTP server. External programs are called gateways because they open outside
information to the server.
There are other ways to customize or add client activity to a Web site. For
example, JavaScript can be used, which is a client-side scripting language. If a
developer is looking for quick and easy interactive changes to their Web site, CGI
is the way to go. A common example of CGI is a “visitor counter” on a Web site.
CGI can do just about anything to make a Web site more interactive. CGI can
grab records from a database, use incoming forms, save data to a file, or return
information to the client side, to name a few features. Developers have numerous
choices as to which language to use to write their CGI scripts; Perl, Java, and
C++ are a just a few of the choices.
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Of course, security must be considered when working with CGI.Vulnerable
CGI programs are attractive to hackers because they are simple to locate, and
they operate using the privileges and power of the Web server software itself. A
poorly written CGI script can open a server to hackers.With the assistance of
whisker, a hacker could potentially exploit CGI vulnerabilities. whisker was
designed specifically to scan Web servers for known CGI vulnerabilities. Poorly
coded CGI scripts have been among the primary methods used for obtaining
access to firewall-protected Web servers. However, developers and Webmasters can
also use hacker tools to identify and address the vulnerabilities on their networks
and servers.
CGI is commonly exploited from the server side. CGI scripts are often
exploited on Web Servers.
What Is a CGI Script and What Does It Do?
Web servers use CGI to connect to external applications. It provides a way for
data to be passed back and forth between the visitor to a site and a program
residing on the Web server. In other words, CGI acts as a middleman, providing a
communication link between the Web server and an Internet application.With
CGI, a Web server can accept user input, and pass that input to a program or
script on the server. In the same way, CGI allows a program or script to pass data
to the Web server, so that this output can then be passed on to the user.
Figure 5.15 illustrates how CGI works.This graphic shows that there are a
number of steps that take place in a common CGI transaction. Each of these
steps is labeled numerically, and is explained in the paragraphs that follow.
In Step 1, the user visits the Web site and submits a request to the Web server.
For example, say the user has subscribed to a magazine and wants to change their
subscription information.The user enters an account number, name, and address
into a form on a Web page, and clicks Submit.This information is sent to the
Web server for processing.
In Step 2, CGI is used to process the data. Upon receiving the updated data,
the Web server identifies the submitted data as a CGI request. Using CGI, the
form data is passed to an external application. Because CGI communicates over
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the HTML, which is part of the TCP/IP protocol suite, the Web server’s CGI
support uses this protocol to pass the information on to the next step.
Figure 5.15 Steps Involved in a Common CGI Program
Internet User
Web Server
CGI Program
Once CGI has been used to pass the data to a separate program, the application program processes it.The program may save it to the database, overwriting
the existing data, or compare the data to existing information before it is saved.
What happens at this point (Steps 3 and 4) depends on the Internet application.
If the CGI application accepts input but does not return output, it may not
work.While many CGI programs will accept input and return output, some may
only do one or the other.There are no hard-and-fast rules regarding the behavior
of programs or scripts, as they perform the tasks they are designed to perform,
which is no different from non-Internet applications that are bought or programmed for use on a network.
If the application returns data, Step 5 takes place. For this example, assume
that it has read the data that was saved to the database, and returns this to the
Web server in the form of a Web page. In doing so, the CGI is again used to
return data to the Web server.
Step 6 finalizes the process, and has the Web server returning the Web page to
the user.The HTML document will be displayed in the user’s browser window.
This allows the user to see that the process was successful, and will allow the user
to review the saved information for any errors.
In looking at how CGI works, almost all of the work is done on the Web
server. Except for submitting the request and receiving the output Web page, the
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Head of the Class….
Web browser is left out of the CGI process.This is because CGI uses server-side
scripting and programs. Code is executed on the server, so it does not matter
what type of browser the user is using when visiting the site. Because of this, the
user’s Internet browser does not need to support CGI, or need special software
for the program or script to execute. From the user’s point of view, what has
occurred is no different from clicking on a hyperlink to move from one Web
page to another.
CGI Misconceptions
In discussing CGI programs and CGI scripts, it is not unusual for people to
state that CGI is a language used to create the Internet application; however, this could not be further from the truth. Programs are not written in
the CGI language, because there is no such thing. CGI is an interface, not
a language. As discussed later in this chapter, there are a number of languages that can be used in creating a CGI program, including Perl, C,
C++, Visual Basic, and others. CGI is not used to create the program
itself; it is the medium used to exchange information between the Web
server and the Internet application or script. The best way to think of CGI
is as a middleman that passes information between the Web server and
the Internet application. It passes data between the two in much the
same way a waiter passes food between a chef and the customer. One
provides a request, while the other responds to it. CGI is the means by
which each of the two receives what is needed from the other.
Typical Uses of CGI Scripts
CGI programs and scripts allow users to have a Web site that provides functionality that is similar to a desktop application. By itself, HTML can only be used to
create Web pages. It will show the text that was typed in when the page was created, and various graphics that you specified. CGI allows you to go beyond this,
and takes your site from providing static information to being dynamic and interactive.
CGI can be used in a number of ways. For example, CGI is used by eBay, the
online auction house. It uses CGI to process bids and process user logons to display a personal Web page of purchases and items being watched during the bidding process.This is similar to other sites that use CGI programs to provide
shopping carts, CGI programs that keep track of items a user has selected to buy.
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Once the users decide to stop shopping, these customers use another CGI script
to “check out” and purchase the items.
While sites such as eBay and e-commerce sites may use more complex CGI
scripts and programs for making transactions, there are also a number of other
common uses for CGI on the Web, including hit counters, which show the
number of users who have visited a particular site. Each time a Web page is
accessed, a CGI script is run that increments the counter number by one.This
allows Webmasters (and visitors) to view how often a particular page is viewed,
and the type of content that is being accessed most often.
Guestbooks and chatrooms are other common uses for CGI programs.
Chatrooms allow users to post messages and chat with one another online in real
time.This also allows users to exchange information without exchanging personal
information such as IP addresses, e-mail addresses, or other connection information.This provides autonomy to the users, while allowing them to discuss topics
in a public forum. Guest books allow users to post their comments about the site
to a Web page. Users enter their comments and personal information (such as
their name and/or e-mail address). Upon clicking Submit, the information is
appended to a Web page and can usually be viewed by anyone who wishes to
view the contents of the guest book.
Another popular use for CGI is comment or feedback forms, which allow
users to voice their concerns, praise, or criticisms about a site or a company’s
product. In many cases, companies use these for customer service so that customers have an easy way to contact a company representative. Users enter their
name, e-mail address, and comments on this page.When they click Send, the
information is sent to a specific e-mail address or can be collected in a specified
folder on the Web server for perusal by the Webmaster.
In looking at the HTML content of a typical form page, there is very little
involved in terms of the Web page itself. In the following code, a form has been
created on a Web page.The POST method is used to pass information that is
entered into the various fields to a CGI program called field
information is placed into variables called name (for the person’s name), e-mail (for
the e-mail address they entered), and feedback (for their personal comments). After
the program processes the data it receives, an e-mail message is sent to the address All of this is specified through the various values
attributed to the form fields.
<TITLE>Send Comments</TITLE>
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<H2>Comment Form</H2>
<FORM METHOD="post" ACTION="/cgi-bin/">
<B>Name:&nbsp; </B><INPUT NAME="name" SIZE=50 TYPE="text"> <BR>
<B>E-mail:&nbsp; </B><INPUT NAME="e-mail" SIZE=50 TYPE="text"> <BR>
<INPUT TYPE="hidden" NAME="submitaddress" VALUE="">
You will not need to be proficient in CGI scripting for the exam. It is
important to understand how CGI works in order to understand the vulnerabilities of CGI. CGI exploitation is very common and is something
you may see in the future as a Security+ technician.
While the HTML takes the data and serves as an instrument to use CGI to pass
the variables, the script itself does the real work. In this case, the script is written in
Perl. In the code, comments begin with the pound symbol (#) and are ignored
during processing.The code in the Perl script called is as follows:
# The following specifies the path to the PERL interpreter.
# It must show the correct path, or the script will not work.
# The following is used to accept the form data, which is used
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# in processing.
read(STDIN, $buffer, $ENV{'CONTENT_LENGTH'});
@pairs = split(/&/, $buffer);
foreach $pair (@pairs) {
($name, $value) = split(/=/, $pair);
$value =~ tr/+/ /;
$value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
$FORM{$name} = $value;
# The following code is used to send e-mail to the
# specified e-mail address.
open (MESSAGE,"| /usr/lib/sendmail -t");
print MESSAGE "To: $FORM{submitaddress}\n";
print MESSAGE "From: $FORM{name}\n";
print MESSAGE "Reply-To: $FORM{email}\n";
print MESSAGE "Subject: Feedback from $FORM{name} at
print MESSAGE "The user commented:\n\n";
print MESSAGE "$FORM{feedback}\n";
close (MESSAGE);
# The following code creates a Web page that confirms
# e-mail was sent.
sub thank_you {
print "Content-type: text/html\n\n";
print "<HTML>\n";
print "<HEAD>\n";
print "<TITLE>Thank You!</TITLE>\n";
print "</HEAD>\n";
print "<BODY BGCOLOR=#FFFFCC TEXT=#000000>\n";
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print "<H1>Thank You!</H1>\n";
print "\n";
print "<P>\n";
print "<H3>Your feedback has been sent.<BR>\n";
print "<P>\n";
print "</BODY>\n";
print "</HTML>\n";
The beginning of the code specifies the location of the Perl interpreter. In
the case of the Web server on which this script was run, the Perl interpreter
resides in the directory /usr/local/bin/perl.The program requires this, because the
interpreter is used to compile the script at the time it is executed (that is, when
the user clicks Send).Without this line of code, the script will not be able to
compile and will be unable to run.
The next section of the program is used to accept the data from the form on
the Web page.This is so that the data can be processed, and used in the next section, where the data in each variable is put into an e-mail message. Once this is
done, the final section of script is executed. Here, a Web page is produced and
returned to the user who initially entered the data.This HTML document confirms that the feedback was sent, so that the user knows the task is done and they
can continue browsing the site.
Break-ins Resulting from Weak CGI Scripts
One of the most common methods of hacking a Web site is to find and use
poorly written CGI scripts. Using a CGI script, a hacker can acquire information
about a site, access directories and files they would not normally be able to see or
download, and perform various other unwanted and unexpected actions. One of
the most publicized attacks with a CGI program occurred by request, as part of
the “Crack-A-Mac” contest.
In 1997, a Swedish consulting firm called Infinit Information AB offered a
100,000 kroner (approximately US$15,000) cash prize to the first person who
could hack their Web server.This system ran the WebStar 2.0 Web server on a
Macintosh 8500/150 computer. After an incredible number of hacking attempts,
the contest ended with no one collecting the prize.This led to Macintosh being
considered one of the most secure platforms for running a Web site.
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About a month later, the contest started again.This time, the Lasso Web server
from Blue World was used. As with the previous Web server, no firewall was used.
In this case, a commercial CGI script was installed so that the administrator could
log on remotely to administer the site.The Web server used a security feature that
prevented files from being served that had a specific creator code, and a password
file for the CGI script used this creator code so that users would be unable to
download the file. Unfortunately, another CGI program was used on the site that
accessed data from a FileMaker Pro database, and (unlike the Web server) did not
restrict what files were made available. A hacker managed to take advantage of
this, and—after grabbing the password file—logged in and uploaded a new home
page for the site.Within 24 hours of the contest being won, a patch was released
for the security hole.
Damage & Defense…
Beware of User Input
One of the most common methods of exploiting CGI scripts and programs is used when scripts allow user input, but the data that users are
submitting is not checked. Controlling what information users are able to
submit will dramatically reduce your chances of being hacked through a
CGI script. This not only includes limiting the methods by which data can
be submitted through a form (by using drop-down lists, check boxes and
other methods), but also by properly coding your program to control the
type of data being passed to your application. This would include input
validation on character fields, such as limiting the number of characters
to only what is needed. An example would be a zip code field being limited to five or nine numeric characters.
Although the Web server, the Macintosh platform, and programs on the
server had been properly configured and had suitable security, the combination of
these with the CGI scripts created security holes that could be used to gain
access. Not only does this case show how CGI programs can be used to hack a
site, it also shows the need for testing after new scripts are added, and shows why
administrators should limit the CGI programs used on a Web site.
When a new script is added to a site, the system should be tested for security
holes. As seen in the preceding example, the combination of elements on the
system led to the Web site becoming vulnerable. One tool that can be used to
find such holes is a CGI scanner such as whisker, which is discussed later in this
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Another important point to remember is that as a Web site becomes more
complex, it becomes more likely that a security hole will appear. As new folders
are created, the administrator might overlook the need to set the correct policies;
this vulnerability can be used to navigate into other directories or access sensitive
data. A best practice is to try to keep all CGI scripts and programs in a single
directory. In addition, with each new CGI script that is added, the chances
increase that vulnerabilities in a script (or combination of scripts) may be used to
hack the site. For this reason, the administrator should only use the scripts they
definitely need to add to the site for functionality, especially for a site where
security is an issue.
CGI Wrappers
Wrapper programs and scripts can be used to enhance security when using CGI
scripts.They can provide security checks, control ownership of a CGI process,
and allow users to run the scripts without compromising the Web server’s security. In using wrapper scripts, however, it is important to understand what they
actually do before implementing them on a system.
CGIWrap is a commonly used wrapper that performs a number of security
checks.These checks are run on each CGI script before it executes. If any one of
these fails, the script is prohibited from executing. In addition to these checks,
CGIWrap runs each script with the permissions of the user who owns it. In
other words, if a user ran a script wrapped with CGIWrap, which was owned by
a user named “bobsmith,” the script would execute as if bobsmith was running it.
If a hacker exploited security holes in the script, they would only be able to
access the files and folders to which bobsmith has access.This makes the owner
of the CGI program responsible for what it does, but also simplifies administration over the script. However, because the CGI script is given access to whatever
its owner can access, this can become a major security risk if the administrator
accidentally leaves an administrator account as owner of a script. CGIWrap can
be found on SourceForge’s Web site,
whisker is a tool that used to scan Web sites for vulnerabilities in CGI scripts and
programs. It is a CGI script itself, which is written in Perl, and can easily be
installed on a site. Once it is there, administrators can scan their own network for
problems, or specify other sites to analyze.
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whisker is different from most available CGI scanners in a number of ways.
For example, it will not run checks on a system that does not apply to the Web
server being used.This is because it begins its scan by querying the type and version of Web server being used.This means that this tool will not look for vulnerabilities and files exclusive to IISs on non-Microsoft Web servers.
Another benefit of whisker is that it allows the administrator to specify multiple directories where CGI scripts may be stored. Although CGI programs will
generally reside in the cgi-bin directory, this may not always be the case. A number
of Webmasters mistakenly place their scripts in the same directory as their HTML
documents, which have read permission for all users.This permission allows users
to view the Web pages and anything else in that directory.While this is a security
risk, many CGI scanners will not recognize that the scripts exist, because they are
only looking in the cgi-bin directory. In addition, many Web servers allow administrators to specify a different name for the directory storing these scripts and
programs.Thus, they can name the cgi-bin directory anything they would like.
When a CGI scanner is run, it will again fail in finding a cgi-bin directory, and
return a message that no scripts exist or that no vulnerabilities were found.
Because whisker allows the administrator to specify multiple directories, they can
specify where whisker will look, and properly scan the CGI scripts for vulnerabilities that could be exploited.
whisker is a free CGI script available at Because it is
written in Perl, it can be opened using a viewer and analyzed to find out exactly
what it does. In addition, once installed, the administrator will need to open it to
make some modifications.To use whisker, they will need to open the file called, and modify the first line:
This line points to the Perl interpreter on the Web server, and may reside in a
location that is different from the path shown here. If the Perl interpreter resides
in the usr/bin/perl directory, it will not need to be changed.
Once this is done, the administrator uploads the file to the Web server so that
it resides in a directory that is accessible via a Web browser. Once the file is on
the server, the administrator will need to open a Web browser to access it.This is
done by entering the Web site’s URL into the address bar of the Web browser,
followed by the directory containing whisker, and the filename For
example, if the site is, and the administrator places whisker into
a directory called whisker, they would enter the URL
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whisker/ into the address bar of the browser. Upon pressing Enter, the
script will execute, and display the screen shown in Figure 5.16.
Figure 5.16 whisker
In the field labeled “Target host to scan,” the administrator enters the host
(Web server) they would like to scan.They can enter the URL (for example, or the IP address (for example, in this field.
This does not have to be the URL or IP address of the site on which whisker is
installed.They can enter any Web site into this field, and whisker will scan it for
The second field on the Whisker CGI Scan Form is used to specify which
port to scan. By default, a Web server uses port 80 for HTTP requests. However,
this can be changed on the Web server so that a different port is used.
Below this field are three check boxes that allow administrators to specify
what information will be displayed in the results of their scan.The options available are:
Use Virtual Hosts This option allows administrators to scan virtual
hosts when possible.Virtual hosts are additional domain names that use
the same IP address.This is common for ISPs that provide site hosting
for multiple Web sites. Rather than everyone using the same domain
name (for example,, each site hosted on that physical
machine can use a different domain name even though the server uses a
single IP address.
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Display Supporting Information This check box specifies that the
administrator wants additional information displayed with the results. For
example, if an Apache Web server were being run, the supporting information would show that “Apache prior to 1.2.5 had various problems.”
It will reveal the paths of various files, their purposes, where additional
information can be found, and so forth.
Verbose Results This option is used to provide detailed information
on what was acquired from the scan.
Because these are check boxes, they can be combined to control the information returned from the scan.
Below this, administrators can specify the request methods.There are four
possible request methods that can be used by whisker to retrieve information:
Get w/ byte-range
Get w/ socket close
The default method used by whisker is “Head.”This method is the same as
the GET method, but it does not return document bodies; it only returns HTTP
headers. GET is a method that retrieves data that is specified in a URL.The
responding site returns the data that is requested. In this case, the information
would be the results of tests performed by whisker.
Damage & Defense…
Acquiring and Using whisker
A CGI programmer who uses the alias Rain Forest Puppy developed
whisker. Although it is excellent for exposing security risks on your own
site, the alias should also indicate the fact that this tool is also excellent
for exposing vulnerabilities for hacking purposes. Not only can you scan
your own system, but you can also specify other URLs to scan. While it is
valuable in testing your own site for security holes, you should realize that
others might use it on your site to see where problems (and opportunities) are. whisker is available for download from
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Once the administrator has specified the site, information to be displayed, and
method, they click run whisker and wait for the results to be displayed.This
CGI program creates a Web page, allowing them to view the results of their analysis, and click on hyperlinks to various directories on that server.This includes
files (including password files) that can be clicked on for viewing.
FTP Security
Another part of Internet-based security that should be considered is FTP-based
traffic. FTP is an application layer protocol within the TCP/IP protocol suite that
allows transfer of data primarily via ports 20 and 21 and then rolls over past port
1023 to take available ports for needed communication.This being said, FTP is
no different from Telnet where credentials and data are sent in cleartext so that, if
captured via a passive attack such as sniffing, the information could be exploited
to provide unauthorized access.This section explores FTP’s weaknesses and looks
at a FTP-based hack in progress with a sniffer.
The way to secure FTP is with its “secure” version, Secure FTP(S/FTP). S/FTP
is a secure method of using FTP. It is similar to SSH which is a solid replacement
for Telnet. S/FTP applies the same concept: added encryption to remove the
inherent weakness of FTP where everything is sent in cleartext. A Secure FTP
client is available for Windows, Macintosh OS X, and most UNIX platforms. A
current version can be downloaded at
Another consideration when sharing data between partners is the transport
mechanism.Today, many corporations integrate information collected by a third
party into their internal applications or those they provide to their customers on
the Internet. One well-known credit card company partners with application
vendors and client corporations to provide data feeds for employee expense
reporting. A transport method they support is batch data files sent over the
Internet using S/FTP. S/FTP is equivalent to running regular, unencrypted FTP
over SSH. Alternatively, regular FTP might be used over a point-to-point VPN.
Blind FTP/Anonymous
FTP servers that allow anonymous connections do so to allow users who do not
have an account on the server to download files from it.This is a popular way to
make files available to the public over the Internet. However, it also presents a
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security threat. Anonymous connections to servers running the FTP process allow
the attacking station to download a virus, overwrite a file, or abuse trusts that the
FTP server has in the same domain.
FTP attacks are best avoided by preventing anonymous logins, stopping
unused services on the server, and creating router access lists and firewall rules. If
anonymous logons are required, the best course of action is to update the FTP
software to the latest revision and keep an eye on related advisories. It is a good
idea to adopt a general policy of regular checks of advisories for all software that
you are protecting. For further information, visit
FTP Sharing and Vulnerabilities
Another aspect of FTP that opens the system up to security problems is the
third-party mechanism included in the FTP specification known as proxy FTP. It
is used to allow an FTP client to have the server transfer the files to a third computer, which can expedite file transfers over slow connections. However, it also
makes the system vulnerable to something called a “bounce attack.”
This attack is initiated by a hacker who first uploads files to the FTP server.
Then they sends an FTP “PORT” command to the FTP server, using the IP
address and port number of the victim machine, and instruct the server to send
the files to the victim machine.This can be used, for example, to transfer an
upload file containing SMTP commands so as to forge mail on the third-party
machine without making a direct connection. It will be hard to track down the
perpetrator because the file was transferred through an intermediary (the FTP
For more information about the “bounce attack” and how to prevent it, see
RFC 2577.
Packet Sniffing FTP Transmissions
OBJECTIVE As mentioned earlier in this section, FTP traffic is sent in cleartext so that cre-
dentials, when used for an FTP connection, can easily be captured via MITM
attacks, eavesdropping, or sniffing. Exercise 5.03 looks at how easy it is to crack
FTP with a sniffer. Sniffing (covered in Chapter 2) is a type of passive attack that
allows hackers to eavesdrop on the network, capture passwords, and use them for
a possible password cracking attack.
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In this exercise, you will use a protocol analyzer (Sniffer Pro) to capture
FTP traffic on the network. You will look at someone logging into an FTP
site with their credentials, and because the network is being sniffed, you
will be able to capture the credentials to use later to get into the server.
1. First, open your protocol analyzer. Sniffer Pro was used for these
screenshots, but you can use any protocol analyzer you are comfortable with.
2. Build a filter to pick up only FTP-based communications. The filter
shown in Figure 5.17 was built to capture only FTP-based traffic.
Creating your own filter for this exercise is not absolutely necessary, but makes it much easier to look for FTP traffic when that is
the only type of traffic that has been captured.
Figure 5.17 Building a FTP-based Filter for Your Protocol Analyzer
3. Once you have made the profile for the filter, you can specify only
FTP traffic will be allowed through it, as seen in Figure 5.18. This
is important because you do not want to alter the default profile.
Make a new one and then select only FTP under TCP. This will
allow you to capture only FTP-based traffic.
4. Now that you have your filter defined and ready to use, start to
capture traffic and simulate a logon to a FTP server. We chose to
log on to Novell’s FTP site at Below, you can see
everything that we did from logging on to exiting the server.
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Figure 5.18 Setting FTP as the Only Protocol to Capture with the
5. You must make sure that you position your sniffer where it will be
able to capture such data. In this exercise, you can run the sniffer
from your local machine on which you are using FTP.
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\rshimonski>ftp
ftp> open
Connected to
220 NcFTPd Server (licensed copy) ready.
User ( anonymous
331 Guest login ok, send your complete e-mail address as password.
Password: *****************
230-You are user #12 of 400 simultaneous users allowed.
230230-This content is also available via HTTP at
230230-Other FTP mirror sites of are: (United States) (United States) (Australia) (Germany) (Japan) (Netherlands)
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230230-World Wide Web Novell Support sites:
230- (United States)
230- (Australia)
230- (Germany)
230- (Japan)
230230 Logged in anonymously.
ftp> bye
221-Thank you and have a nice day.
C:\Documents and Settings\rshimonski>
6. Next, you can stop your sniffer. Examine the traffic it captured.
Figure 5.19 clearly shows that FTP traffic has been captured and
is being displayed. You should also be aware that you have captured a password with credentials in this capture. Figure 5.20
shows a close up of the captured password. All of this information comes from running the sniffer and capturing your logon.
Figure 5.19 Viewing Captured FTP Data
Figure 5.20 A Closer Look at the Captured Password
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Directory Services and LDAP Security
LDAP is used for a bevy of purposes. LDAP is a protocol that enables clients to
access information within a directory service. LDAP was created after X.500, a
directory service standard protocol, because of the high overhead and subsequent
slow response of heavy X.500 clients, hence the name lightweight.
LDAP services are used to store information of all kinds. LDAP clients must
authenticate to the server before being allowed access to the directory.
Authentication information is sent from the client to the server as part of a
“bind” operation. LDAPv3 also allows for anonymous clients to send LDAP
requests to the server without first performing the bind operation.
X.500 is covered in detail in Chapter 10.
Version 3 is the current version of LDAP at the time of this writing. It supports a number of different security mechanisms. Clients (users, computers, or
applications) connect to the LDAP server using a distinguished name and authentication credentials (usually a password).The distinguished name is a unique hierarchical name used to identify an object in the directory by showing its exact
location in the directory, listing its parent (container) objects. LDAP directories
are organized as tree structures (sometimes called the Directory Information Tree
[DIT]). Segmenting the tree based on organization or division and storing each
branch on separate directory servers increases the security of the LDAP information. By following this structure, even if one directory server is compromised,
only a branch of the tree (rather than the entire tree) is compromised.
The LDAP naming convention is used by directory services that are LDAP
compliant or compatible, such as Microsoft’s Active Directory and Novell’s NDS.
The following is an example of a distinguished name:
CN=DellDude OU=Marketing DC=tacteam DC=net
This distinguished name identifies a computer named DellDude that resides
in an organizational unit called Marketing in the domain.
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LDAP can be used over SSL, which extends security into the Internet. Some
of these types of services integrate as objects, such as PKI certificates, in the
authentication process using smart card technologies, and in the extended properties of account objects so that they can support extra security requirements.To
use SSL with LDAP, the LDAP server must have an X.509 server certificate.
Additionally, SSL must be enabled on the server.
The challenge with using a protocol such as LDAP is that the connectivity
must be facilitated through a script or program.These types of scripts must indicate the location of the objects within the directory service to access them. If the
administrator wants to write a quick, simple script, this means that the name of
the directory service and the names and locations of the objects that are being
accessed must each be placed in the script and known prior to the script being
written. If they need to access a different object, they usually need to rewrite the
script or develop a much more complex program to integrate the directory services. Even so, compare scripting to native access with queries and interactive
responses, and the value of a homogenous network with a single directory service
is revealed. In a homogenous network, there is no need to logically connect two
directory services with a script.This greatly reduces the time and effort involved
in administering the network.
Homogenous networks are unusual at best.With multiple types of network
OSs, desktop OSs, and infrastructure OSs available today, it is likely that there
will be multiple systems around. It follows that they all must be managed in different ways.
LDAP enabled Web servers can handle authentication centrally, using the
LDAP directory.This means users will only need a single login name and password for accessing all resources that use the directory. Users benefit from single
sign-on to allow access to any Web server using the directory, or any passworded
Web page or site that uses the directory.The LDAP server constitutes a security
realm, which is used to authenticate users.
Another advantage of LDAP security for Web-based services is that access
control can be enforced based on rules that are defined in the LDAP directory
instead of the administrator having to individually configure the OS on each
Web server.
There are security programs available, such as PortalXpert Security, which
can be used with LDAP to extend enforcement of the security policies that are
defined by the LDAP directory to Web servers that are not LDAP enabled, and
provide role-based management of access controls.
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LDAP is vulnerable to various security threats, including spoofing of directory services, attacks against the databases that provide the directory services, and
many of the other attack types discussed in this book (for example, viruses, OS
and protocol exploits, excessive use of resources and denial of service, and so
For more detailed information about LDAP security issues, see the white
paper titled “Introduction to Security of LDAP Directory Services” by
Wenling Bao at the SANS Institute Web site at
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Summary of Exam Objectives
This chapter looked at the Security+ exam topics in the area of Web-based security with an emphasis on World Wide Web (WWW) security, FTP-based security
and LDAP-based security.The Security+ technician must know how to configure, manage, and service security on a Web platform. As discussed,Web-based
services are commonly vulnerable to threats and exploitation.
The problems associated with Web-based exploitation can affect a wide array
of users, including end users surfing Web sites, using instant messaging, and shopping online. End users can have many security problems associated with their
Web browsers, as well.This chapter discussed possible vulnerabilities, how to
securely surf the Web, and how to shop online safely.
Another issue the Security+ Technician needs to understand is securing Webbased services and servers. Since Web-based services are usually exposed to the
public Internet, thus increasing risk, Security+ Technicians will need to know
how to deal with issues relating to these services.
This chapter also looked at FTP and LDAP services relating to the Web and
examined security issues related to FTP and how exploitable it really is.The last
section dealt with LDAP, its vulnerabilities, and how it provides security benefits
when properly configured.
Exam Objectives Fast Track
Web Security
; Web servers on the network that you are not aware exist are sometimes
called rogue Web servers. If you find such rogue Web servers, you should
disable the Web-based services to remove these Web servers from the
network if they are not needed.
; The first task you should undertake to lock down your Web server is
applying the latest patches and updates from the vendor. After this task is
accomplished, the network administrator should follow the vendor’s
recommendations for securely configuring Web services.
; Maintaining a secure Web server means ensuring that all scripts and Web
applications deployed on the Web server are free from Trojans, backdoors, or other malicious code.
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; Web browsers are a potential threat to security. Early browser programs
were fairly simple, but today’s browsers are complex; they are capable not
only of displaying text and graphics but of playing sound files and
movies and running executable code.The browser software also usually
stores information about the computer on which it is installed and about
the user (data stored as cookies on the local hard disk), which can be
uploaded to Web servers—either deliberately by the user or in response
to code on a Web site without the user’s knowledge.
; ActiveX controls are Microsoft’s implementation of the COM. Microsoft
designed ActiveX to replace the older OLE model used in earlier
versions of the Windows platform. ActiveX is an improvement on OLE,
in that it adds extensibility to the model and allows for distributed
computing (DCOM) as well as better performance in local applications.
ActiveX controls can be used to run attacks on a machine if created by
malicious programmers.
; A cookie is a kind of token or message that a Web site hands off to a
Web browser to help track a visitor between clicks.The browser stores
the message on the visitor’s local hard disk in a text file.The file contains
information that identifies the user and their preferences or previous
activities at that Web site.
FTP Security
; Another part of Internet-based security one should consider is FTPbased traffic. FTP is an Application Layer protocol within the TCP/IP
protocol suite that allows transfer of data primarily via ports 20 and 21 and
then rolls over past port 1023 to take available ports for needed
; Anonymous connections to servers running the FTP process allow the
attacking station to download a virus, overwrite a file, or abuse trusts
that the FTP server has in the same domain.
; FTP is like Telnet in that the credentials and data are sent in cleartext, so
if captured via a passive attack like sniffing, they can be exploited to
provide unauthorized access.
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LDAP Security
; LDAP services are used to store information of all kinds. LDAP clients
must authenticate to the server before being allowed access to the
directory. Authentication information is sent from the client to the server
as part of a “bind” operation.
; Version 3 is the current version of LDAP at the time of this writing. It
supports a number of different security mechanisms.
; LDAP can be used over SSL, which extends security into the Internet.
; LDAP-enabled Web servers can handle authentication centrally, using the
LDAP directory.This means users will only need a single login name
and password for accessing all resources that use the directory.
; LDAP is vulnerable to various security threats, including spoofing of
directory services, as well as attacks against the databases that provide the
directory services and many of the other attack types that can be
launched against other types of services (for example, viruses, OS and
protocol exploits, excessive use of resources and DoS attacks, and so on).
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Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: Web servers are critical components in our network infrastructure.We want
to make sure that they are as safe as possible form attack since they will be
publicly accessible from the Internet.What is the number one issue regarding
Web services and how to fix them?
A: Service packs, hot fixes, and updates need to be applied to any system or
application, but to Web services in particular. It is very important to do this
because these systems are generally directly accessible from the Internet and
because of this, they are prone to more problems from possible attacks than
other servers on an internal network. Make sure you keep the fixes on these
systems as current as you possibly can.
Q: I am afraid of Web servers learning my identity and using it against me. I
think that if they have access to my cookies, they have access to my system. Is
this true?
A: No, it is not. A cookie is a kind of token or message that a Web site hands off
to a Web browser to help track a visitor between clicks.The browser stores
the message on the visitor’s local hard disk in a text file.The file contains
information that identifies the user and their preferences or previous activities
at that Web site. A Web server can gain valuable information about you, but
although it can read the cookie that does not mean that the Web server can
necessarily read the files on your hard disk.
Q: My Web browser is very old. I believe it may be Internet Explorer version
4.0. Should I be overly concerned about problems with exploits to my
A: Yes, you should be. Earlier versions of popular Web browsers such as Internet
Explorer and Netscape are known to have numerous vulnerabilities, which
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have been fixed in later versions. Upgrading to the current version of
Internet Explorer is easy and costs nothing, so there is no reason to risk your
data and the integrity of your system and network by continuing to run an
outdated version of the browser.
Q: I want to FTP a file to a server.When I logged into the FTP server with my
credentials and started to transfer the file, I remembered hearing that FTP is
sent in cleartext. Have I just exposed myself to an attacker?
A: Yes.When you use FTP you can potentially expose yourself to hackers that
may be eavesdropping on the network. Because of this fact, you should always
consider an alternative if you really want to be secure when using FTP.
S/FTP is one such alternative.
Q: Sniffers are used on my network. Is it possible to FTP something securely?
A: Yes, you can use S/FTP, which is a secure form of FTP. It is very similar to
SSH in that is encrypts the traffic sent so that eavesdropping will not pick up
any usable data.
Q: I have a Web server that uses CGI scripting to work with a backend database.
I have learned that there may be problems with code-based exploits. Should I
be concerned when using CGI?
A: CGI scripts can definitely be exploited, especially if they are poorly written.
CGI scripts can be exploited within the browser itself and may open up
potential holes in your Web server or provide access to the database.
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Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
Web Security
1. When performing a security audit on a company’s Web servers, you note
that the Web service is running under the security context of an account
that is a member of the server’s local Administrators group.What is the best
recommendation to make in your audit results?
A. Use a different account for the Web service that is a member of the
Domain Administrators group rather than the local Administrators
B. Use a different account for the Web service that only has access to those
specific files and directories that will be used by the Web site.
C. Use a different account for the Web service that is not a member of an
Administrators group but has access to all files on the system.
D. Recommend that the company continue with this practice as long as
the account is just a member of the local Administrators group and not
the Domain Administrators group.
2. While performing a routine port scan of your company’s internal network,
you find several systems that are actively listening on port 80.What does this
mean and what should you do?
A. These are rogue FTP servers and should be disabled.
B. These are rogue HTTP servers and should be disabled.
C. These are LDAP servers and should be left alone.
D. These are IRC servers and should be left alone.
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3. You determine that someone has been using Web spoofing attacks to get
your users to give out their passwords to an attacker.The users tell you that
the site at which they have been entering the passwords shows the same
address that normally shows in the status line of the browser.What is the
most likely reason that the users cannot see the URL that they are actually
A. The attacker is using a digital certificate created by a third party CA.
B. The attacker is using HTTP/S to prevent the browser from seeing the
real URL.
C. The attacker is using ActiveX to prevent the Web server from sending
its URL.
D. The attacker is using JavaScript to prevent the browser from displaying
the real URL.
4. You are creating a DMZ for a company and need to allow external users to
access Web servers in the DMZ using HTTP/S as well as allow internal
users to access the same Web servers using standard HTTP.What is the best
way to configure the external and internal firewalls to meet these requirements?
A. Open port 80 on the external firewall and port 443 on the internal
B. Open port 443 on the external firewall and port 80 on the internal
C. Open port 80 on the external firewall and port 110 on the internal
D. Open port 110 on the external firewall and port 80 on the internal
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5. When you use Java, the JVM isolates the Java applet to a sandbox when it
executes.What does this do to provide additional security?
A. This prevents the Java applet from accessing data on the client’s hard
B. This prevents the Java applet from communicating to servers other than
the one from which it was downloaded.
C. This prevents the Java applet from failing in such a way that the Java
applet is unable to execute.
D. This prevents the Java applet from failing in such a way that it affects
another application.
6. You are setting up a test plan for verifying that new code being placed on a
Web server is secure and does not cause any problems with the production
Web server.What is the best way to test the code prior to deploying it to
the production Web server?
A. Test all new code on a development PC prior to transferring it to the
production Web server.
B. Test all new code on an active internal Web server prior to transferring
it to the production Web server.
C. Test all new code on a duplicate Web server prior to transferring it to
the production Web server.
D. Test all new code on another user’s PC prior to transferring it to the
production Web server.
7. Some new code has been developed for your Web site that accesses a
database to present dynamic content to the Web client.What is one of the
most important quality assurance tests that you should perform on this code
from the security perspective?
A. Verify that no user IDs or passwords are in code that could be downloaded by the client.
B. Verify that the code is small enough to be quickly downloaded by the
C. Verify that the code has been tested on the developer’s workstation.
D. Verify that the code is written in the correct scripting language.
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8. A Web site administrator implemented a new Web application on a Web site
in his organization.The site was consequently hacked through a bug in the
application.The administrator defended his use of the application, based on
the fact that it was digitally signed.Why did the use of code signing not prevent this problem?
A. The certificate used by the developer to sign the code must have been
B. Code signing did not prevent this because it does not ensure that the
code is from a verified source.
C. Code signing did not prevent this because the certificate must not have
been issued by an authorized CA.
D. Code signing did not prevent this because it does not ensure that the
code does not have any bugs.
9. You are looking at using several ActiveX controls that have been marked as
“Safe for Scripting” by the third-party developer. Should you still test these
thoroughly prior to using them? Why or why not?
A. No. If they have been marked as “Safe for Scripting,” they have already
been verified as safe and should not cause any problems.
B. No. ActiveX controls are run in a sandbox, so even if there are problems
with the scripts, it will not affect anything else.
C. Yes. Any new scripts should always be thoroughly tested regardless of
how the script is marked.
D. Yes. Scripts marked as “Safe for Scripting” are run in a separate memory
segment and should be tested prior to allowing them to run in that
10. You are designing a security policy for a company and want to ensure that
client systems are as secure as possible. As part of this, you do not want some
specific script types from Web sites to be able to be executed on the workstation.What should you define within the security policy to ensure this?
A. Do not allow graphical browsers to be used.
B. Require that all browsers have the JVM enabled.
C. Require that all browsers deny the unwanted script languages.
D. Require that all browsers require HTTP/S connections.
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11. You are maintaining the Web server for a company when a new security
patch is released for the Web server software.What is the best action to take?
A. Implement the patch immediately to negate the security vulnerability.
B. Test the patch on a user’s workstation to determine if it has any bugs.
C. Test the patch on a duplicate Web server to determine if it has any bugs.
D. Do not implement the patch until you experience the bug that it was
released to fix.
12. You have been tasked with increasing the security of your corporation’s Web
servers. One of the areas you are looking at is the execution of custom CGI
scripts.What is one way to increase the security of these?
A. Ensure that all of the CGI scripts use the latest version of the Java SDK.
B. Use CGI wrappers to test and contain the CGI scripts.
C. Require that all CGI scripts use SSL to communicate with the client.
D. Back up all of the CGI scripts so they can be restored quickly in the
event of an attack.
13. You are tasked with setting up a process to transfer confidential data from an
external site to your internal systems.You are considering using FTP for this
transfer.What advantage does S/FTP provide that would make it a better
A. All data is compressed to prevent it from being captured on the network
in cleartext.
B. All data is encrypted to prevent it from being captured on the network
in cleartext.
C. It uses strong passwords for authentication.
D. It uses anonymous passwords for authentication.
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14. You have performed some scans of your network and identified that there
are several network cards on the LAN running in promiscuous mode.This
indicates that someone is running a network sniffer. How does this affect the
security of a FTP server that is on the network?
A. This could allow systems on the network to capture the files being sent
to and from the FTP server.
B. This could allow systems on the network to capture IDs and passwords
used for the FTP server in cleartext.
C. Both A and B.
D. This does not adversely affect the security of the FTP server.
15. When using LDAP for authentication in an internetworking environment,
what is the best way to ensure that the authentication data is secure from
network sniffing?
A. Use LDAP with Active Directory to keep all passwords encrypted on the
B. Require that the clients use strong passwords so that they cannot be
easily guessed.
C. Use LDAP over HTTP/S to encrypt the authentication data.
D. Use LDAP over SSL to encrypt the authentication data.
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. B
9. C
2. B
10. C
3. A
11. C
4. B
12. B
5. D
13. B
6. C
14. C
7. A
15. D
8. D
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Infrastructure Security
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Chapter 6
Devices and Media
Domain 3.0 Objectives in this Chapter:
Device-based Security
Media-based Security
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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Implementing infrastructure security is one of the biggest parts of being a
Security+ technician. As such, device and media security is covered extensively in
the Security+ exam. Security+ technicians must know all of the components of a
network and all of the potential issues that may occur regarding every piece of
common infrastructure within a network environment.
This chapter covers all of the critical network infrastructure including devices
such as firewalls, routers, switches, servers, workstations, and the cabling that connects them all together. It also looks at how to connect these items with a wireless
connection. It also looks at Intrusion Detection System (IDS) devices and how
they fit in the topology, as well as other types of network monitoring equipment.
Lastly, this chapter looks at how hard disks, smart cards, and other forms of
media are secured. Not only is it important to understand how all of the pieces
fit together, but it is also important to understand how each media form is vulnerable to attack and exploitation and how the Security+ technician needs to
view each one.
According to the CompTIA objectives for the Security+ exam, infrastructure security comprises 20 percent of the Security+ exam. Approximately
one-third of this is related to devices and media. Firewalls, routers, and
IDSs are covered extensively on the Security+ exam.
Device-based Security
A large component of infrastructure security is based on the proper implementation of hardware devices in a network. By implementing and configuring hardware
devices correctly, Security+ technicians can greatly decrease their vulnerability to
attack. For example, properly configuring a firewall can help protect networks from
external attacks.
The Security+ exam focuses on the situations in which firewalls should be
used and the appropriate implementation of the devices. In many security implementations the correct devices are located in the correct places on the network
but are incorrectly configured, therefore leaving the network vulnerable to attack.
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Alternatively, many networks do not have the correct security devices in place
due to a simple lack of planning and are therefore vulnerable.
Knowing what security problems are inherent in a device is critical to
knowing how to implement the device and the necessary security precautions
around that device. For example, knowing the insecure nature of wireless transmissions and their range can help when planning where to physically locate wireless access points.This section looks at a variety of hardware devices found on
most networks, where in the infrastructure they are located, what purposes they
serve, the security they add to the network, and the possible exploits that can be
performed on them. It will also cover some “best practices” on how to configure
these devices and review what their overall impact is on network security.
Understanding how firewalls work and how to properly implement firewall rules is a critical part of the Security+ exam.
A firewall is the most common device used to protect an internal network from
outside intruders.When properly configured, a firewall blocks access to an
internal network from the outside, and blocks users on the internal network from
accessing potentially dangerous external networks or ports.
There are three firewall technologies examined in the Security+ exam:
Packet filtering
Application layer gateways
Stateful inspection
All of these technologies have advantages and disadvantages, but the
Security+ exam specifically focuses on their abilities and the configuration of
their rules. A packet filtering firewall works at the Network layer of the Open
Systems Interconnection (OSI) model and is designed to operate rapidly by
either allowing or denying packets. An application layer gateway operates at the
Application layer of the OSI model, analyzing each packet and verifying that it
contains the correct type of data for the specific application it is attempting to
communicate with. A stateful inspection firewall checks each packet to verify that
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it is an expected response to a current communications session.This type of
firewall operates at the Network layer, but is aware of the Transport, Session,
Presentation, and Application layers and derives its state table based on these
layers of the OSI model.
Packet Filtering Firewalls
A packet filtering firewall can be configured to deny or allow access to specific
ports or Internet Protocol (IP) addresses.The two policies that can be followed
when creating packet filtering firewall rules are “allow by default,” and “deny by
default.” “Allow by default” allows all traffic to pass through the firewall except
traffic that is specifically denied. “Deny by default” blocks all traffic from passing
through the firewall except for traffic that is explicitly allowed.
Deny by default is the best security policy because it follows the general
security concept of restricting all access to the minimum level necessary to support business needs.The best practice is to deny access to all ports except those
that are absolutely necessary. For example, if configuring an externally facing firewall for a DMZ, Security+ technicians may want to deny all ports except port
443 (the SSL port) in order to require all connections coming in to the DMZ to
use Hyper Text Transfer Protocol Secure (HTTPS) to connect to the Web servers.
Although it is not practical to assume that only one port will be needed, the idea
is to keep access to a minimum by following the best practice of denying by
A firewall works in two directions. It can be used to keep intruders at bay,
and it can be used to restrict access to an external network from its internal users.
Why do this? A great example is found in some Trojan horse programs.When
Trojan horse applications are initially installed, they report back to a centralized
location to notify the author or distributor that the program has been activated.
Some Trojan horse applications do this by reporting to an Internet Relay Chat
(IRC) channel or by connecting to a specific port on a remote computer. By
denying access to these external ports in the firewall configuration, Security+
technicians can prevent these malicious programs from compromising their
internal network.
The Security+ exam extensively covers ports and how they should come into
play in a firewall configuration.The first thing to know is that out of 65,535
ports, ports 0 through 1023 are considered well-known ports.These ports are used
for specific network services and should be considered the only ports allowed to
transmit traffic through a firewall. Ports outside the range of 0 through 1023 are
either registered ports or dynamic/private ports.
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User ports range between 1024 through 49,151
Dynamic/private ports range from 49,152 through 65,535
Damage & Defense…
If there are no specialty applications communicating with a network, any
connection attempt to a port outside the well-known ports range should be considered suspect.While there are some network applications that work outside of
this range that may need to go through a firewall, they should be considered the
exception and not the rule.With this in mind, ports 0 through 1023 still should
not be enabled. Many of these ports also offer vulnerabilities, therefore it is best
to continue with the best practice of denying by default and only opening the
ports necessary for specific needs.
For a complete list of assigned ports visit the Internet Assigned Numbers
Authority (IANA) at direct link to their list of ports is at IANA is the centralized organization responsible for assigning IP addresses and ports.They are also the authoritative source for which ports applications are authorized to use for the services the
applications are providing.
Denial of Service Attacks
All firewalls are vulnerable to Denial of Service (DoS) attacks. These
attacks attempt to render a network inaccessible by flooding a device
such as a firewall with packets to the point that it can no longer accept
valid packets. This works by overloading the processor of the firewall by
forcing it to attempt to process a number of packets far past its limitations. By performing a DoS attack directly against a firewall, an attacker
can get the firewall to overload its buffers and start letting all traffic
through without filtering it. This is one method used to access internal
networks protected by firewalls. If a technician is alerted to an attack of
this type, they can block the specific IP address that the attack is coming
from at their router.
An alternative attack that is more difficult to defend against is the
Distributed Denial of Service attack (DDoS). This attack is worse because
it can come from a large number of computers at the same time. This is
accomplished either by the attacker having a large distributed network of
systems all over the world (unlikely) or by infecting normal users’ computers with a Trojan horse applications, which allows the attacker to force
the systems to attack specific targets without the end user’s knowledge.
These end user computers are systems that have been attacked in the past
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and infected with one of these Trojan horses by the attacker. By doing
this, the attacker is able to set up a large number of systems (called zombies) to each perform a DoS attack at the same time. This type of attack
constitutes a DDoS attack. Performing an attack in this manner is more
effective due to the number of packets being sent. In addition, it introduces another layer of systems between the attacker and the target,
making the attacker more difficult to trace.
A port is a connection point into a device. Ports can be physical, such as serial
ports or parallel ports, or they can be logical. Logical ports are ports used by networking protocols to define a network connection point to a device. Using
Transmission Control Protocol/Internet Protocol (TCP/IP), both TCP and User
Datagram Protocol (UDP) logical ports are used as connection points to a network device. Since a network device can have thousands of connections active at
any given time, these ports are used to differentiate between the connections to
the device.
A port is described as well-known for a particular service when it is normal
and common to find that particular software running at that particular port
number. For example,Web servers run on port 80 by default, and File Transfer
Protocol (FTP) file transfers use ports 20 and 21 on the server when it is in active
mode. In passive mode, the server uses a random port for data connection and port
21 for the control connection.
The Security+ exam requires that you understand how the FTP process
works. There are two modes in which FTP operates: active and passive.
Active Mode
1. The FTP client initializes a control connection from a random
port higher than 1024 to the server’s port 21.
2. The FTP client sends a PORT command instructing the server to
connect to a port on the client one higher than the client’s control port. This is the client’s data port.
3. The server sends data to the client from server port 20 to the
client’s data port.
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Passive Mode
1. The FTP client initializes a random port higher than 1023 as the
control port, and initializes the port one higher than the control
port as the data port.
2. The FTP client sends a PASV command instructing the server to
open a random data port.
3. The server sends a PORT command notifying the client of the
data port number that was just initialized.
4. The FTP client then sends data from the data port it initialized to
the data port the server instructed it to use.
To determine what port number to use, technicians need to know what port
number the given software is using.To make that determination easier, there is a
list of common services that run on computers along with their respective wellknown ports.This allows the technician to apply the policy of denying by default
and only open the specific port necessary for the application to work. For
example, if they want to allow the Siebel Customer Relations Management
application to work through a firewall, they would check against a port list (or
the vendor’s documentation) to determine that they need to allow traffic to port
2320 to go through the firewall. A good place to search for port numbers and
their associated services online is at the Snort Intrusion Detection Open Source
Web page ( will notice that even
Trojan horse applications have well-known port numbers. A few of these have
been listed in Table 6.1.
Table 6.1 Well-Known Ports of Trojan Horses
Trojan Horse
Back Orifice
31337 and 31338 (modifiable)
Back Orifice 2000
8787, 54320, and 54321 (modifiable)
10000 and 10005
1243, 1999, 2773, 2774, 6667, 6711, 6712, 6713,
6776, 7000, 7215, 16959, 27374, 27573, and 54283
(depending on version)
999 and 6667
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Unfortunately, for nearly every possible port number, there is a virus or
Trojan horse application that could be running there. For a more comprehensive
list of Trojans listed by the port they use, go to the Blackcode Web site at
The Security+ exam puts a great deal of weight on your knowledge of
specific well-known ports for common network services. The most important ports to remember are:
FTP Active Mode Control Port (see the Security+ exam Warning
on FTP for further information)
FTP Active Mode Data Port (see the Security+ exam Warning
on FTP for further information)
Secure Shell (SSH)
Simple Mail Transfer Protocol (SMTP)
Hypertext Transfer Protocol (HTTP)
Post Office Protocol 3 (POP3)
Network News Transfer Protocol (NNTP)
Internet Message Access Protocol (IMAP)
Secure Sockets Layer (SSL) (HTTPS)
Memorizing these ports and the services that run on them will help
you with firewall or network access questions on the Security+ exam.
Packet filtering has both benefits and drawbacks. One of the benefits is speed.
Since only the header of a packet is examined and a simple table of rules is
checked, this technology is very fast. A second benefit is ease of use.The rules for
this type of firewall are easy to define and ports can be opened or closed quickly.
In addition, packet-filtering firewalls are transparent to network devices. Packets
can pass through a packet-filtering firewall without the sender or receiver of the
packet being aware of the extra step. A major bonus of using a packet-filtering
firewall is that most current routers support packet filtering.
There are two major drawbacks to packet filtering:
A port is either open or closed.With this configuration, there is no way
of simply opening a port in the firewall when a specific application
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needs it and then closing it when the transaction is complete.When a
port is open, there is always a hole in the firewall waiting for someone
to attack.
The second major drawback to pack filtering is that it does not understand the contents of any packet beyond the header.Therefore, if a
packet has a valid header, it can contain any payload.This is a common
failing point that is easily exploited.
To expand on this, since only the header is examined, packets cannot be filtered by user names, only IP addresses.With some network services such as TFTP
or various UNIX “r” commands this can cause a problem. Since the port for
these services is either open or closed for all users, the options are either to
restrict system administrators from using the services, or invite the possibility of
any user connecting and using these services.The operation of this firewall technology is illustrated in Figure 6.1.
Referring to Figure 6.1 the sequence of events is as follows
1. Communication from the client starts by going through the seven layers
of the OSI model.
2. The packet is then transmitted over the physical media to the packetfiltering firewall.
3. The firewall works at the Network layer of the OSI model and examines the header of the packet.
4. If the packet is destined for an allowed port, the packet is sent through
the firewall, over the physical media, and up through the layers of the
OSI model to the destination address and port.
Application Layer Gateways
The second firewall technology is called application filtering or an application layer
gateway.This technology is more advanced than packet filtering as it examines the
entire packet and determines what should be done with the packet based on specific defined rules. For example, with an application layer gateway, if a Telnet
packet is sent through the standard FTP port, the firewall can determine this and
block the packet if a rule is defined disallowing Telnet traffic through the FTP
port. It should be noted that this technology is used by proxy servers to provide
application-layer filtering to clients.
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Figure 6.1 Packet Filtering Technology
OSI Model
OSI Model
Open Port
OSI Model
Data Link
Data Link
Data Link
One of the major benefits of application layer gateway technology is its application layer awareness. Since application layer gateway technology can determine
more information from a packet than a simple packet filter can, application layer
gateway technology uses more complex rules to determine the validity of any
given packet.These rules take advantage of the fact that application layer gateways
can determine whether data in a packet matches what is expected for data going
to a specific port. For example, the application layer gateway can tell if packets
containing controls for a Trojan horse application are being sent to the HTTP
port (80) and thus, can block them.
While application layer gateway technology is much more advanced than
packet filtering technology, it does have its drawbacks. Due to the fact that every
packet is disassembled completely then checked against a complex set of rules,
application layer gateways are much slower than packet filters. In addition, only a
limited set of application rules are predefined and any application not included in
the predefined list must have custom rules defined and loaded into the firewall.
Finally, application layer gateways process the packet at the Application layer of
the OSI model. By doing so, the application layer gateway must then rebuild the
packet from the top down and send it back out.This breaks the concept behind
client/server architecture and slows the firewall down even further.
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The Security+ exam focuses on the use of appropriate firewall technologies in scenario-based questions. You will need to know when to implement a packet filtering firewall, an application layer gateway, a stateful
inspection firewall, or a combination of these technologies. Remember
that it is not always best to use the most sophisticated technology available. For example, if speed is an issue and packet filtering will work,
there is no reason to implement an application layer gateway instead of
a packet-filtering firewall.
Client/server architecture is based on the concept of a client system
requesting the services of a server system.This was developed to increase application performance and cut down on the network traffic created by earlier file
sharing or mainframe architectures.When using an application layer gateway, the
client/server architecture is broken as the packets no longer flow between the
client and the server. Instead, they are deconstructed and reconstructed at the
firewall.The client makes a connection to the firewall at which point the packet
is analyzed, then the firewall creates a connection to the server for the client. By
doing this, the firewall is acting as a proxy between the client and the server.The
operation of this technology is illustrated in Figure 6.2.
Stateful Inspection Firewalls
Stateful inspection is a compromise between these two existing technologies. It
overcomes the drawbacks of both simple packet filtering and application layer
gateways, while enhancing the security provided by the firewall. Stateful inspection technology supplies application layer awareness without actually breaking the
client/server architecture by disassembling and rebuilding the packet. Additionally,
it is much faster than an application layer gateway due to the way packets are
handled. It is also more secure than a packet-filtering firewall, due to application
layer awareness and the introduction of application- and communication-derived
state awareness.
The primary feature of stateful inspection is the monitoring of application
and communication states.This means that the firewall is aware of specific application communication requests and knows what should be expected out of any
given communication session.This information is stored in a dynamically updated
state table and any communication not explicitly allowed by a rule in this table is
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denied.This allows the firewall to dynamically conform to the needs of the applications and open or close ports as needed. Ports are closed when the requested
transactions are completed, which provides another layer of security.
Figure 6.2 Application Layer Gateway Technology
Application Layer Gateway
OSI Model
OSI Model
OSI Model
Data Link
Data Link
Data Link
A great example of how these different technologies work is the FTP process.
With FTP, the client has the option of requesting that the server open a back
connection.With a packet filtering firewall, the only options are either leaving all
ports beyond port 1023 open thus allowing the back connection to be permitted,
or closing them which makes the attempted communication fail.
With an application layer gateway, this type of communication can easily be
permitted, but the performance of the entire session will be degraded due to the
additional sessions created by the application layer gateway itself.With stateful
inspection, the firewall simply examines the packet where the back-connection
is requested, then allows the back-connection to go through the firewall when
the server requests it on the port previously specified by the requesting packet.
When the FTP session is terminated, the firewall closes off all ports that were
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used and removes their entries from the state table. Figure 6.3 shows how this
technology works.
Figure 6.3 Stateful Inspection Technology
Stateful Inspection
OSI Model
OSI Model
Data Link
Data Link
Data Link
Firewalls comprise one of the most important aspects of network security as it relates to connections to the Internet. If you understand the
basic concepts of how the different firewalls work and know the proper
place to implement them, you will do fine on these Security+ exam
questions. You do not have to be a firewall specialist to pass the
Security+ exam; you just have to know what they are, how they work,
what to do with them, and how the different types of firewalls should
be configured.
Keep in mind that while a firewall is important to infrastructure security relating to Internet connections, it is not the only aspect of network
security. All of the subjects discussed in this book should be taken into
consideration as part of your overall security plan.
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Routers are a critical part of all networks and can be both a security aid and a
security vulnerability. A router basically has two or more network interfaces
through which network traffic is forwarded or blocked.They are often used to
segment networks into smaller subnets or to link multiple networks together.The
router decides how and when to forward packets between the networks based on
an internal routing table.This routing table tells the router which packets to forward.The routing table can either be static where each route is explicitly defined
or dynamic where the router learns new routes by the use of routing protocols. In
addition to the routing table, a typical router also supports access control lists
(ACLs) that specify which packets to allow or explicitly block. Every packet
going through a router will be checked against the ACL to see if the packet is
allowed to be forwarded, and also checked against the routing table to determine
where to forward the packet if allowed. It also tells the router which network(s)
exist on which interfaces and enables the router to put the packet on the appropriate interface.
Routers are covered extensively on the Security+ exam. Make sure that
you understand what they are used for and how they are vulnerable to
Most current routers offer security capabilities along with their routing functionality. Segmenting a network using routers limits the amount of data flowing
between segments.Typically, this applies to broadcast traffic. Not propagating
broadcast traffic between segments limits the amount of data that can be obtained
from them using a sniffer.The less information made available to a potential
attacker the better.
Routers also allow technicians to explicitly deny some packets the ability to
be forwarded between segments. For example, using just the internal security features of some routers can prevent users on the internal network from using Telnet
to access external systems.Telnet is always a security risk as the passwords and all
communications are transmitted in cleartext. Because of this, it is best not to create
Telnet sessions between the internal network and an external network.Without a
firewall, a rule can be put in place within the router to drop packets attempting
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to connect to port 23 on any external system. All of this is done by properly configuring the ACLs for the router. An example rule for Cisco routers is as follows:
Head of the Class…
access-list 101 deny any any eq 23
Defining an ACL for a Cisco Router
There are two types of access lists available to filter traffic on Cisco
routers. The simplest is a standard access list. This type of access list
allows technicians to filter traffic from specific addresses or subnet
ranges. Cisco also provides extended access lists, which allow technicians
to filter based on a variety of criteria. The extended access list allows technicians to use source addresses, destination addresses, and specific network services (such as POP3) as the basis of filtering rules.
After an ACL has been defined, it is applied to a specific interface on
the router and designated whether the ACL applies to inbound or outbound traffic. The following command is used to define a standard access
access-list <list_number> <permit/deny> <source_addresss> <mask>
For example, to create an “anti-spoof” set of rules (as discussed in
this section), the following rules can be used:
access-list 1 deny
access-list 2 allow
The first rule is applied to the wide area network (WAN) interface to
deny all traffic coming into that interface from an IP address belonging to
the internal network. The second rule is then applied to the internal interface to allow all traffic coming into that interface from the internal network addresses to pass through.
Another useful security feature of routers is their ability to block spoofed
packets. Spoofed packets are packets that contain an IP address in the header that
is not the actual IP address of the originating computer.This technique is often
used by hackers to fool systems into thinking that the packet came from an
authorized system, when it actually originated at the hacker’s system. Routers
combat this by giving technicians the ability to drop packets coming through an
interface from the wrong subnet. For example, if a packet comes in from the
router’s external interface using an IP address from the network on the router’s
internal interface, the router can be instructed to drop the packet and not forward it. It should be noted that this ability has not always been a feature of
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routers and some older routers or routers using old firmware or operating systems (OSs) may not provide this function.This is another reason to keep the
router’s firmware and OS up-to-date.To keep routing tables up-to-date between
multiple routers on a network, the routers can communicate changes to the
routing tables via routing protocols.These protocols are designed to let routers send
data to each other with the specific purpose of keeping the routing tables current
across all routers.There are several different routing protocols with each having
specific capabilities and packet formats.These routing protocols are primarily
broken up into two types: link-state and distance-vector. An example of a distancevector routing protocol is Routing Information Protocol (RIP), and an example
of a distance-vector routing protocol is Open Shortest Path First (OSPF).
These routing protocols are great for keeping routing tables up-to-date and
make the administration of routing within a network much easier.They do come
with a downside, however. Attackers can sometimes add their own entries into
routing tables using these protocols and can effectively take control of a network.
This type of attack is performed by spoofing the address of another router within
a communication to the target router, and putting the new routing information
into the packet.This attack is not easy, as most routers provide some level of password security within the routing protocols. However, it is important to be aware
of this potential vulnerability and to make sure that the most secure routing protocols are being used.
A method of avoiding this problem is to use static routes instead of relying on
routing protocols. Static routes are predefined routes that are manually set in the
routing table. Using static routes eliminates the possibility of a routing table being
modified by attacks exploiting routing protocols.
When taking the Security+ exam, make sure that you understand the
difference between firewalls, routers, and switches. You may be asked
questions that make you choose the best device to use in a particular
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Switches are a type of networking device similar to hubs, which connect network
equipment together. Switches differ from routers primarily in that routers are
used to join network segments and Layer 2 switches are used to create that network segment. Layer 2 switches operate at the data link layer of the OSI model
and use the Media Access Control (MAC) addresses of network cards to route
packets to the correct port. Layer 3 switches are closer in function to routers and
operate at the network layer of the OSI model.These switches route packets
based on the network address, rather than using the MAC address.They both
offer a great advantage over hubs in that they eliminate packet collisions by giving
each system a direct connection with its destination system. A packet collision
occurs when two or more packets are sent across the physical network at the
same time.When many systems are on a network attempting to communicate, a
large number of collisions can occur and slow down the overall network unless
they are curbed by the use of a switch.
Switches offer greater network security by controlling the amount of data
that can be gathered by sniffing on the network.With a hub, all data going across
the network is sent to all ports on the hub.This means that any system connected
into the hub is able to run a sniffer and collect all of the data going to all of the
systems connected to the hub.This can give an attacker access to passwords, confidential data, and further insight into the network configuration.With a switch,
each connection is given a direct path to its destination.This has the side effect of
blocking communications data from systems passively sniffing on the network.
Since they can only see data coming from and going to their system, they are not
able to gather much unauthorized data.When a switch first boots up without any
information as to which systems are connected to which port, it broadcasts the
traffic for individual systems until their location is determined. After the switch
knows which port each system is connected to, it routes packets directly out that
port rather than broadcasting.
However, if an intruder gains administrative access to a switch, they can overcome this safety feature by using the switched port analyzer (SPAN) or mirroring
feature.To use a SPAN, the switch is configured to route a copy of all packets
going to or from one or more ports to a specific port. A sniffer is then placed on
the port that the copy is being routed to and reads all of the packets going
through the switch.The SPAN feature is often used by network administrators to
perform troubleshooting on their networks; however, this can also be exploited
by an intruder.
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Switches also have the ability to segment networks using virtual local area
networks (VLANs).This gives the added capability of segmenting out the network and making the overall network more manageable. In addition,VLANs can
add security to a network. By segmenting a network, administrators can isolate
the traffic going across each VLAN.This keeps the data flowing across one VLAN
from being visible to the other. Another vulnerability of switches is that there is a
chance for an attacker to override the security features provided by the switch.
For example, a DoS attack can be performed against some older switches similar
to the type that can be performed against a router.This can result in overloading
of the buffers in the switch, making it act like a hub and sending all data going
through the switch to all ports.This would then allow an attacker to sniff out
data as if they were connected to a hub rather than a switch. Keep in mind, this
vulnerability only affects older switches and should not be a problem with newer
In addition, packets can be sent to a switch that can make it think an
attacking system is a different system on the network and cause it to route
packets intended for the target over to the attacker instead.This is called ARP
spoofing and is done by sending an Address Resolution Protocol (ARP) packet to
the switch containing the machine name of the target and the MAC address of
the attacker. By doing an ARP spoof, intruders can hijack sessions that a client
was previously using.
This can also be used as a man-in-the-middle (MITM) attack between two
network devices. Figure 6.4 shows an example network of how this works
between two clients.
To perform an attack using ARP spoofing, the intruder would follow this
1. The intruder (I) sends an ARP packet to a client (C1) using the IP
address of another client (C2), but the MAC address for the intruder (I).
2. The intruder (I) sends an ARP packet to a client (C2) using the IP
address of another client (C1), but the MAC address for the intruder (I).
3. Now both clients have ARP cache entries for each other’s IP address,
but the MAC address for these entries point to the intruder.The
intruder routes packets between C1 and C2 so that communications are
not interrupted.
4. The intruder sniffs all packets it is routing and is able to see all communications between the clients.
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Figure 6.4 Sample Network for ARP Spoofing
Normal Communications
Man in the Middle Attack
This process allows intruders to view all traffic between two clients, but ARP
spoofing can potentially be more damaging. By performing a MITM attack
between a router and the switch, an intruder can see all data coming through the
router. Additionally, if an intruder replies to every ARP request sent out by the
switch, it can intercept traffic going to all clients.This gives the intruder the
option of performing a DoS attack by not allowing any client to communicate
with the switch, not routing traffic to the intended client, and sniffing the data
being communicated via the MITM attack.
Another vulnerability of most switches is that they can be configured by a
standard Telnet session. If the network from which the Telnet session originated is
sniffed, passwords for the switch can be easily obtained, because they are sent in
cleartext. Some newer switches allow a secure session to be made for configuring
the switch.This secure session is made by using SSH instead of Telnet to connect
to the router. All communication between the client and the router is encrypted
when using SSH. Also, with both older and newer switches, configuration can be
performed via a console connection to the switch so that no configuration data
goes across the network.This is the most secure method of configuring switches,
but most network administrators find it inconvenient. SSH provides both security
and convenience on switches.
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The Security+ exam requires you to understand what a switch does, how
it works, and how it differs from other network devices such as firewalls,
hubs, and routers. Make sure that you have a clear understanding of this
and know the vulnerabilities of switches that can be exploited.
Wireless technology is discussed in detail in Chapter 4 of this guide; however,
based on the Security+ exam objectives, devices related to wireless technology
are also covered in this section.Wireless technology provides a convenient
method of accessing a network by eliminating the cables that are generally associated with network connectivity.While this can be a great convenience to laptop
users, it introduces a whole new world of security vulnerabilities to a network.
The devices associated with wireless networking are wireless access points and
the wireless network cards used to communicate with the access points.Wireless
network cards are not generally designed to communicate with other wireless
network cards, but rather to a wireless access point.This cuts down on the security vulnerabilities associated with network cards, but makes access points even
more critical to network security.
A new attack technique that has risen in the popularity of wireless networks
is war driving.This involves a hacker driving around with a laptop equipped with
a wireless network card looking for wireless cells to connect to. Usually they will
have a high-powered antenna to increase the effective range of their scans. In
recent news, war drivers have been able to easily connect to corporate and government networks using this technique.The vulnerabilities that were exploited
on these networks could have been negated if the implementation of the wireless
network had included adequate security measures.
Wireless access points have a limited range (this differs by model) within
which they can effectively communicate with client systems. Keeping this range
in mind when planning a wireless implementation significantly improves the corresponding security implementation. Planning the placement of the wireless
access points so that the outer range of their transmission distance corresponds
with the walls of the building, prevents external access to a wireless network.
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In addition, both incoming and outgoing wireless transmissions can also be
stopped by the walls of a building.When planning a wireless implementation
within a new construction, it is important to work with the designers to make
sure that the external walls contain metal studs that are grounded. Using thin
layers of aluminum under the drywall creates what is effectively a wireless shield.
This will block most radio transmissions into and out of the building.This will
also interfere with pager and cellular phone usage.
Proper placement of wireless access points and appropriate shielding within
the building where possible, will substantially decrease the vulnerability of a wireless network. Applying secure transmission protocols and configuring the wireless
access point to only accept authorized connections will also help in securing a
When taking the Security+ exam and working a wireless-related question, keep in mind that wireless technology by itself is insecure. The
Security+ exam expects you to know what can and should be done to
secure wireless connections. Pay close attention to Chapter 4 where wireless security is discussed in detail.
With the popularity of broadband access, modems are becoming less necessary
for the average computer user; however, most systems still have modems installed
and many corporate systems still have modems in place for remote access.These
devices often provide a simple and unexpected method for an intruder to access
Typically, remote access service (RAS) servers and fax servers are common
places for modems to be located within a corporate network. Properly configured
modems are fairly secure; however, the users of a corporate network may have
modems in their PCs that they configure so they can dial in to remotely access
their systems.This is done when no other remote access solution has been provided or if they feel that the existing remote access solution is inconvenient.
These types of situations can provide an intruder with the perfect entry point to
a network.The best solution to this problem is to implement a security policy to
control the installation of modems on corporate systems, and to verify that those
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systems that need modems are properly secure. (Security policies are covered in
detail in Chapter 12, “Operational and Organizational Security: Policies and
Disaster Recovery.”) It is also a good idea to audit this by using a war-dialing
application (Exercise 6.01) to scan corporate phone numbers to verify that no
unexpected modems answer. A walkthrough audit of the corporate systems
should also be done to verify that no unauthorized modems have been installed.
For this exercise, you will be using a free, publicly available war dialer to
test a fictitious range of phone numbers. You will be using The Dialing
Demon v1.05 which can be downloaded from
1. After extracting the files, run DEMON105.exe from within a DOS
window. After starting the executable, you will be presented with
the screen shown in Figure 6.5.
Figure 6.5 The Dialing Demon Splash Screen
2. Pressing Enter at this screen walks you through a series of configuration questions to determine the com port that your modem is
on, its speed, and a few other options. A basic configuration is
shown in Figure 6.6. The values used in this configuration will
vary depending on your system’s modem configuration and personal preferences.
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Figure 6.6 The Dialing Demon Configuration Screen
3. After the application has your basic configuration information,
you will be prompted for the dialing configuration you wish to
use. This includes the dialing prefix and range of numbers you
wish to dial. The range you use here should correlate with the
phone numbers you wish to scan. Figure 6.7 shows an example
Figure 6.7 The Dialing Demon Number Range Configuration Screen
4. As seen in Figure 6.7, dialing a large range like this can take a
very long time. Normally it is best to do only a small range at a
time and span it over a number of days. After answering Y to the
“Begin dialing sequence” question, the dialer begins dialing every
number in the range and creates a report showing which numbers have modems connected.
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Remote Access Service (RAS) is a common method of allowing users of a corporate network to access network resources either from home or on the road.
This is another network feature that provides additional functionality while
increasing the risk of security breaches of the network. A security professional’s
job is to minimize this risk and still provide the necessary services that users need
to perform their duties.
RAS servers typically have an array of modems and dial-in lines available for
users to connect through.They provide some form of authentication and then
connect the user to the corporate network as if their system was physically
located on the local area network (LAN).The authentication for RAS servers is
typically done with Challenge Handshake Authentication Protocol (CHAP),
Microsoft Challenge Handshake Authentication Protocol (MS-CHAP), Password
Authentication Protocol (PAP), Secure Password Authentication Protocol (SPAP),
or Extensible Authentication Protocol (EAP). CHAP and MS-CHAP are more
secure than PAP or SPAP as they do not send an actual password to the RAS
server. EAP offers additional features in that it can be configured to accept a
plethora of third-party authentication methods.This could include smart cards,
Kerberos, or biometric authentication. (Additional information on CHAP can be
found in Chapter 3.)
Most RAS servers offer additional security features such as mandatory callback.
This feature requires users to connect from a number the administrator has
entered into the system. After initial connection and authentication, the server
disconnects and dials the user’s callback number.The user’s system is then
required to answer this call to complete the connection process. Some RAS
servers use caller ID to identify the number the user is connecting from and
then to either authorize the connection based on the number or log it.
RAS servers also allow technicians to implement security features that
control the protocols available to communicate with their corporate network.
For example, they can block protocols not in use within the network such as
Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) or
Network Basic Input/Output System (NetBIOS).
When securing a RAS server, it is critical to use the best authentication
method possible for the environment. Implementing callback verification is also a
good idea. For example, if remote users always call from home, then callback verification would work well and add another layer of security. However, if dealing
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with a mobile sales force calling in from anywhere, callback verification as a security mechanism is severely limited.
Knowing that specific protocols can be filtered through a RAS is very
important. This feature allows you to implement an additional layer of
security by keeping unauthorized protocols from being used on your network. The Security+ exam expects you to have knowledge of this security feature and to understand how it can help protect your network.
If an intruder detects dial-in numbers either through war dialing or some
other means, they will try everything possible to access the network through the
RAS server. Using strong password security for user accounts is critical to making
it more difficult for intruders to access the network. It is also a good idea to use
user IDs for the user’s RAS account that differ from their e-mail or standard
LAN access IDs.This makes it more difficult for intruders to access an internal
network should they manage to get through the RAS security, as they would still
need to determine the user’s normal LAN ID and password to access any network resources.
Overall, RAS is an important service to provide when remote access is
needed via dial-up; however, it presents several security vulnerabilities that must
be addressed. Proper implementation of this service allows administrators to provide for the remote access needs of their users while keeping their network as
secure as possible. Following is a list of industry best practices for keeping a RAS
implementation secure:
Use the most secure authentication method supported by the clients
and servers.
Encrypt communications between the client and server, where possible.
Implement mandatory callback verification, if possible.
Block unnecessary network protocols from being used across the RAS
Use user IDs for the RAS server, which differ from the users’ IDs for
other servers on the LAN.
Enforce strong passwords for user IDs.
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One area that is often overlooked in the IT security field is telecommunications. A
company’s business can be just as easily disrupted by having its telecommunications disabled as it can by having its computer network disabled.That makes this
an important area to be aware of when developing an overall security plan.
Typically, most small companies use a small number of dedicated telephone
lines for both incoming and outgoing calls, which keeps the responsibility of providing telephone service on the service provider. In larger companies, however,
having dedicated lines for hundreds or thousands of employees is both inefficient
and expensive.
The solution to this problem is to install a Private Branch eXchange (PBX). A
PBX is a device that handles routing of internal and external telephone lines.This
allows a company to have a limited number of external lines and an unlimited
(depending on the resources of the PBX) number of internal lines. By limiting the
number of external lines, a company is able to control the cost of telephone service while still providing for the communications needs of its employees. For
example, a company may have 200 internal lines or extensions but only 20 external
lines.When an employee needs to communicate outside of the company, one of
the external lines is used, but when two employees communicate via the telephone system the routing is done completely by the PBX and no external lines
are used.
PBX systems offer a great cost benefit to large companies, but they also have
their own vulnerabilities. Many PBXs are designed to be maintained by an offsite vendor and therefore have some method of remote access available.This can
be in the form of a modem or, on newer models, a connection to a LAN.The
best practice is to disable these remote access methods until the vendor has been
notified that they need to perform maintenance or prepare an update.This limits
the susceptibility to direct remote access attacks.
PBXs are also vulnerable to DoS attacks against their external phone lines.
There is also the possibility of them being taken over remotely and used to make
unauthorized phone calls via the company’s outgoing lines.Voicemail capability
can also be abused. Hackers who specialize in telephone systems, called phreakers,
like to take control over voicemail boxes which use simple passwords, and change
the passwords or the outgoing messages.
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Virtual Private Network
The most common alternative to running RAS servers for remote access is to
provide remote access via a virtual private network (VPN). A VPN allows end
users to create a secure tunnel through an unsecured network to connect to their
corporate network.Typically, users simply dial into their Internet Service Provider
(ISP) and then use a software client to create the VPN connection to their corporate network. At that point, the user’s system functions as if it were located on
their LAN.
In large environments,VPNs are generally less expensive to implement and
maintain than RAS servers, because there is no incoming telephone line or
modem overhead. In addition, a higher level of security can be implemented as
communications are encrypted to create a secure tunnel.VPNs can also be used
to link multiple networks securely.This gives administrators the ability to use
existing connections to the Internet to build their WAN rather than creating new
links between networks with additional leased lines.
VPNs use a variety of protocols to support this encrypted communication
including Secure Internet Protocol (IPSec), Layer 2 Tunneling Protocol (L2TP),
Point-to-Point Tunneling Protocol (PPTP), and SSH. IPSec is the most popular
protocol used for dedicated VPN devices followed by L2TP and PPTP. SSH is
available for VPNs running under the Windows platform, but it is typically used
more frequently in UNIX-based VPNs.
The tunneling protocols used in VPNs are covered in great detail in
Chapter 3. Please refer to this chapter for additional information.
VPNs can be created using either Windows- or UNIX-based servers, or they
can be implemented using dedicated hardware.There are several firewalls and
routers on the market that support VPNs, and there are also dedicated VPN solutions that are not designed to be run as firewalls or routers.
These devices allow administrators to easily create a VPN utilizing dedicated
hardware.This typically gives a large performance increase over a server-based
solution. Remember that encryption always creates a great deal of overhead on
servers due to the additional processing required to encrypt the data.
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There are three types of VPNs that can be set up for an organization.The
business purpose of the VPN defines what type of VPN should be used.These
three types are:
Remote access VPN
Site-to-site intranet-based VPN
Site-to-site extranet-based VPN
A remote access VPN is used when end users require remote access to the
corporate network.This type of VPN connects multiple remote clients to the
corporate LAN. A site-to-site intranet-based VPN is used to connect two or
more remote corporate sites to a centralized network using demand-dial routing to
cut down on cost. Rather than using a full leased line for sending small amounts
of data, demand-dial routing allows an organization to connect remote sites to
the centralized site only when needed. A site-to-site extranet-based VPN allows
two separate corporations to connect to each other to perform secure data transfers. Figure 6.8 shows an example of a remote access VPN, while Figures 6.9 and
6.10 show site-to-site intranet- and extranet-based VPNs.
Figure 6.8 Remote Access VPN
Corporate Network
VPN Device
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Figure 6.9 Site-to-Site Intranet-based VPN
Central Office
VPN Device
VPN Device
Branch Office
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Figure 6.10 Site-to-Site Extranet-based VPN
Company ABC
VPN Device
VPN Device
Company ABC
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Whether implementing a server-based or dedicated hardware-based VPN
solution, it is important to make sure that the VPN servers or devices are as
secure as possible.This should always include changing the default passwords to
strong passwords, ensuring that the best encryption methods available for the
implementation are being used, and making sure that the software and devices are
up-to-date with the latest updates from the vendor.
Understanding some basic concepts about VPNs will help you a great
deal with the Security+ exam. If you keep in mind that a VPN is not a
real network, but a virtual network based on tunneling packets through
an insecure network, you should not have too much trouble with this
part of the Security+ exam. Think of an actual tunnel going through a
mountain. Trying to go through a mountain without the supports in a
tunnel would be foolish, the use of the supported or secure tunnel
makes this a secure and safe path to take. Applying the same type of
symbolism to any difficult concept you wish to understand will make the
Security+ exam a stress-free and rewarding experience.
An Intrusion Detection System (IDS) is the high-tech equivalent of a burglar
alarm configured to monitor access points, hostile activities, and known intruders.
These systems typically trigger on events by referencing network activity against
an attack signature database. If a match is made, an alert takes place and the event
is logged for future reference. Creating and maintaining the attack signature
database is the most difficult part of working with IDS technology. It is important
to always keep the IDS up-to-date with the latest signature database provided by
the vendor as well as updating the database with the signatures found in testing.
The Security+ exam expects you to understand the different types of IDSs,
what they are used for, and how they can help protect your network.
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Attack signatures consist of several components used to uniquely describe an
attack. An ideal signature is one that is specific to the attack while being as simple
as possible to match with the input data stream (large complex signatures may
pose a serious processing burden). Just as there are varying types of attacks, there
must be varying types of signatures. Some signatures define the characteristics of a
single IP option, such as a nmap portscan, while others are derived from the
actual payload of an attack. Most signatures are constructed by running a known
exploit several times, monitoring the data as it appears on the network, and
looking for a unique pattern that is repeated on every execution.This method
works well at ensuring that the signature consistently matches an attempt by that
particular exploit. Remember that the idea is for the unique identification of
attacks, not merely the detection of attacks.
Notes From the Underground…
Baiting with Honeynets
Recently, there has been an upsurge in the use of honeynets or honeypots
as a defensive tool. A honeynet is a system that is deployed with the
intended purpose of being compromised. This is an excellent tool for distracting intruders from the important systems on your network by luring
them to a group of systems where they can be detected. This is done by
making the honeynet look more attractive than the real servers in your
network. A hacker will attack a server that appears vulnerable and looks
like it contains important data rather than attempt to break into a system
that seems well protected.
The current best-known configuration type for these tools is where
two systems are deployed, one as bait and the other configured to log all
traffic. The logging host should be configured as a bridge (invisible to any
remote attacker) with sufficient disk space to record all network traffic for
later analysis. The system behind the logging host can be configured in
any fashion. Most systems are bait, meaning they are designed to be the
most attractive targets on a network segment. The defender hopes that
all attackers will see this easy point of presence and target their attacks in
that direction.
No system is foolproof. Attackers are able to discern that they are
behind a bridge by the lack of Layer 2 traffic and the discrepancy in MAC
addresses in the bait system’s ARP cache. See
for more details.
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There are two types of IDSs that can be used to secure a network: system
IDSs or network IDSs. A system IDS (referred to as an IDS) runs on each individual server on which the administrator wants to perform intrusion detection. A
network IDS (NIDS) does intrusion detection across the network. System IDSs
are great for ensuring that the server on which it is installed is capable of
detecting attacks.They are also more efficient than NIDS because they only analyze the data from one system rather than the entire network. NIDS, however, has
the ability to detect attacks that may be occurring on multiple systems at the
same time or to catch someone doing a portscan of an entire network.
One of the major benefits of IDSs is that they do not necessarily have to
passively monitor a network. Most IDSs can also perform corrective action when
an attack is identified.This can range from paging the administrator to working
with the firewall to block specific IPs from accessing the network.This is very
useful in blocking attacks and also gathering information about the attackers
within the logs.
One of the vulnerabilities of NIDSs is that they can be overloaded. Since
they analyze every packet on the network (or specific subnets), if the network is
overwhelmed with packets the NIDS may not be able to analyze every packet
that goes across. By overloading the NIDS, intruders sometimes avoid detection.
As with any security-related device or application, IDSs should be kept up-todate with the most recent updates and signature files from the vendor.
Whereas a system IDS is installed on a single computer within the network
to secure that specific system, a NIDS is installed within the network infrastructure so that all systems on the network can be protected.The architecture for this
is shown in Figure 6.11.
When being installed, a NIDS is typically configured with a base set of rules
and known attack signatures, which can be expanded on with custom signatures.
Some NIDSs also support a learning mode where the NIDS examines traffic on
the network and learns trends and typical usage of the network. Based on what
the NIDS learns, it can continue monitoring and determine when unusual traffic
patterns are detected so that an administrator can be notified.
There are a few best practices to follow when setting up a NIDS:
1. Ensure that the NIDS used is designed to support the network size it
will be working with. If it cannot support the size of the network, either
use a different NIDS or segment the network and use multiple NIDS.
2. When working with a NIDS, if accessing and controlling the NIDS
remotely it is best to place the controlling system on another subnet.
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3. It is best to set up the NIDS so that all logs are stored on a remote
system on a different subnet.These practices help increase the security of
the NIDS.
Figure 6.11 Network Intrusion Detection System
For further information on a device-based NIDS, look at the Cisco Secure
Intrusion Detection System at
ps976/products_qanda_item09186a00800887c2.shtml. Also, an excellent and
highly regarded software solution can be found at are
many different NIDSs available, each with their own benefits.
Network Monitoring/Diagnostic
1.1.10 Many large networks employ some form of ongoing monitoring or diagnostic
routine to continually keep administrators aware of the status of the network and
allow for proactive corrective actions to potential problems.This can be done
with monitoring software or with dedicated devices located on the network.
In large network configurations, some network administrators may leave a
remotely accessible sniffer attached to a switch.This allows the administrator to
span the ports on the switch and remotely sniff the network traffic.This is a great
tool for network administrators, but if an intruder were to access this system, they
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could potentially gather data from anywhere in the network. If a device like this
is left accessible on the network, it is best to use a strong password to access the
device. In addition, using an encrypted session to communicate with the device
will prevent eavesdropping on the sniffing session.
Another common device generally left attached to networks is some form of
diagnostic equipment.This can range from a simple meter for checking cable
lengths to more advanced equipment capable of diagnosing network problems.
Some of the better diagnostic equipment can be remotely accessed and controlled
via TCP/IP. Again, this is an extremely useful tool for network administrators but
the data available from this tool can be very dangerous in the hands of an
intruder.The same security best practices apply to these devices. Strong passwords
and encrypted sessions should always be the default strategy when dealing with
network monitoring or diagnostic equipment that is remotely accessible.
The vulnerabilities associated with these devices are generally limited to the
ability of intruders to gather data.With the data that can be gathered from these
devices, an intruder can get enough information to cause unlimited damage to a
network or gather a great deal of confidential information.What is the single best
security policy for these devices? If possible, do not connect them until they are
Remember that sniffing a network is a passive attack.
1.1.11 The term workstation basically refers to any computer system that the end users of
a network work on, assuming that the end users do not use servers for their
normal day-to-day work.Workstations are typically one of the most vulnerable
devices attached to a network. Flaws or bugs in all workstation OSs provide
ample opportunity for attackers to gain remote access to systems, to copy data
from the workstations, or to monitor the traffic and gather passwords for access to
more systems. In addition, workstations are more vulnerable simply because there
are typically more workstations on a network than any other network device.The
sheer quantity of workstations makes it more difficult to ensure that they are all
as secure as possible.
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The protocols used by workstations present another possible vulnerability.
Since most networks today operate using TCP/IP as the primary protocol, the
TCP/IP stack of the workstations is a vulnerability.There are many exploits available that cause stack overflows or cause a workstation to be unable to communicate effectively on the network. A DoS attack using malformed TCP/IP packets
can cause a workstation to be unable to communicate and can also overload the
system to the point that it becomes non-functional. For example, the Nuke
exploit under Windows NT will cause the system to display a “blue screen of
death” (a stop error).This exploit operates by making a connection to port 139
of the target system and sending a large packet of random data to the port.This is
known as an out of bounds attack.When the target system receives the packet, the
networking stack is unable to handle the packet and causes the system to crash.
For this exercise, you will be using one of the many freely available Nuke
programs to perform an attack. One such program is DiViNE Intervention
available at
1. After downloading the application, extract the files and run
DIVINT3.exe. You will see the screen shown in Figure 6.12.
Figure 6.12 DiViNE Intervention Main Screen
2. Click the RETRiBUTiON icon. You will see the screen in Figure
3. Click the Fyre icon to bring up the Nuke options screen shown in
Figure 6.14.
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Figure 6.13 DiViNE Intervention RETRiBUTiON Menu
Figure 6.14 DiViNE Intervention FyRE Screen
4. At this screen, type the IP address of your target, the port to send
the OOB packet to (by default, 139), and any message you want
included in the packet. When you have filled this in with the
required information, click Nuke ‘em! to begin the attack. At this
point, the application will show that it is attempting to connect
to the target, and once connected, begins sending OOB packets
to the target. This is shown in Figure 6.15.
Figure 6.15 DiViNE Intervention Attack Screen
In addition, workstations using the Windows OS usually have additional ports
open for using NetBIOS.This introduces vulnerabilities that can allow attackers
to remotely access files on the workstation.This is more secure under Windows
NT or Windows 2000/XP Pro using the New Technology File System (NTFS),
but can present a real problem under Windows 95/98/ME. Even if the shares on
a system are password protected, they can be easily hacked. Administrators should
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always be careful of open shares on the system.Workstations are also vulnerable to
MITM attacks or hijacked sessions.These attacks allow an attacker to monitor or
control communications between the workstation and another system.
The largest security concern in relation to workstations is the end user. End
users always have local access (the ability to work at the local console) to their
workstation, which can cause some big security problems, ranging from changing a
password to something a hacker can easily guess to inadvertently opening e-mails
with viruses or Trojan horse applications running. Java viruses exploit weaknesses
inherent to the way that Web browsers and Java Virtual Machines (JVMs) allow Java
code to perform low level functions on a system with very little security.
There will never be a foolproof solution to this security problem.The best
way to help deter issues like this is to train the end user. Having a formal security
policy (Chapter 12) in place specifying exactly what users can and cannot do
with the company’s workstation is also very important.
Locking down a user’s access to their workstation also helps.Windows workstations can have security policies applied that limit the user’s access to critical
system files.They also have the ability to install or run unauthorized software.
Using a well written and up-to-date virus protection application will help
combat the ability of an end user to overload a mail server or infect every system
in the company with a virus.
Another very important aspect of workstation security is to make sure that
the OSs or software applications always have the latest security patches in place.
Often a vendor will release security patches that address individual vulnerabilities
so technicians will be able to apply them faster, rather than having to wait for a
full service pack.
It is important to understand the differences between workstations and
servers. You should know that workstations are typically used by a single
local user and are designed to support fast front-end processing. Servers
are designed to support a large number of remote users and provide fast
back-end processing and file sharing.
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1.1.12 Large, high-end computer systems with the capability of servicing requests from
multiple users simultaneously are called servers.These systems are the primary
sources on a network to which end users connect to receive or send e-mail, store
files, or access network applications. As such, they are considered one of the most
critical aspects of the network infrastructure and it is critical that they be as
secure as possible.
Typically, people attacking a network use the information gathered from network devices, workstations, or data flowing across the LAN to compromise the
security of the servers.There are other reasons for breaking into a network, such
as setting up additional sites for performing a DDoS attack, but accessing the
servers is usually the goal.
Since this is the primary storage location for data on a network, this is where
attackers will be able to obtain the most data or cause the most damage. It can be
said that these systems are the final goal of most attacks upon a network.
Most servers in a properly secured network are behind one or more firewalls
and have several layers of protection between them and the outside world.
Protecting these systems also includes physical security.There can be all the network security in the world, but it will not help when an attacker walks into a
building and starts typing at the server’s local console. Some systems, such as Web
servers, will always be more vulnerable due to their accessibility from the outside.
Systems in a DMZ are less protected than those on a normal LAN.
Some of the same vulnerabilities that apply to workstations also apply to
servers. OSs or application software may contain bugs or security vulnerabilities
that allow the system to be compromised. In addition, some viruses are able to
infect remote file shares; therefore it is important to make sure that virus scanning
is implemented on all of the servers.This especially applies to e-mail servers
where an e-mail virus can be removed before it makes it to the end user’s e-mail
box. Keeping OSs and application software up-to-date with security patches is
critical to minimizing the vulnerability of servers. Security professionals should
always keep abreast of new bugs or vulnerabilities in the applications running on
their network and be ready to implement workarounds or fixes as soon as they
are available.
It is always a good idea to make sure that the servers are as secure as possible
from outside attack, but it is not wise to forget the possibility of attack from the
inside.There are many cases where confidential data has been leaked from companies due to poor security on their servers or an irate employee. It is important
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to make sure that the most restrictive access control possible is applied to the
user’s accounts. Users should always have access to the data or services necessary
to perform their job functions, but no more than that.This goes back to the fundamental security concept of deny by default. It is always easier to grant a user
access to data than it is to clean up the mess when a user has access to something
that they should not have.
If the data on servers is especially confidential, such as file stores with financial or litigation data, it may be necessary to encrypt communications from the
server as well as the data stored on the server itself.This additional layer of protection helps preserve the confidentiality of the data stored on the system as well
as making it more difficult to break into. At a minimum, it will keep the data
from being read by someone casually sniffing on the network. Again, keep in
mind that security threats come not only from the outside, but also from
employees of the company itself.
Mobile Devices
1.1.13 With mobile devices becoming more powerful and functional, they are quickly
becoming the norm for working on the road rather than a full-size laptop. Since
mobile phones and personal digital assistants (PDAs) are now capable of sending
and receiving e-mail, connecting to remote network applications, and browsing
the Web, their use in the corporate world has exploded.They also have the ability
to store limited amounts of data (with the capacity growing all the time) and
some mobile devices even have word processor and spreadsheet applications.
This gives their users the ability to be completely untethered from a full-size
workstation or laptop.
With these mobile devices comes more work for the security professional.
Workstations are somewhat vulnerable, but at least they are restricted to being
located at a particular site and can be turned off by an administrator if necessary.
Laptops, while mobile, are slightly more secure than handheld mobile devices,
because they are somewhat inconvenient for end users to carry everywhere or
accidentally leave.The areas of vulnerability to focus on with the ultra-compact
mobile devices are those of communications and local data security.
Since many of these devices are able to connect to the Internet, they are
remotely accessible to potential attackers. In addition, as previously mentioned,
network applications can be designed to work with mobile devices over the
Internet.The security of these network applications should be ensured by
requiring that communications with mobile devices be encrypted.
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The data stored locally on mobile devices can contain confidential corporate
information or other information that is best kept out of the hands of attackers.
With this in mind, it is always a good idea to encrypt data stored locally on these
mobile devices. Some newer devices have this ability built into their OSs, but for
those that do not, there may be third-party software available that adds this functionality.
Any time a hacker is able to access a device locally, there is the chance that
with time the hacker can break through any security measure.Therefore, it is a
good idea to keep hackers away from the device.With the small size and convenience of handheld mobile devices, this is especially difficult.The sheer number
of mobile phones and PDAs left at tables in restaurants, in airports, or in public
restrooms is staggering. If a company supplies mobile devices to its users, it is
critical that they be instructed on proper care for the devices, which includes not
leaving them behind.The only real defenses to this are the passwords protecting
the device and encrypting the local data, both of which can be bypassed with
time and perseverance.
Media-based Security
Any system is the sum of all of its parts, and the art and practice of security
administration is no exception.While network devices may be secure and a network may be blocked off from the outside world, it is still important to be concerned with the security of the media that interacts with the network or systems.
This section covers a plethora of different media types ranging from cable
types to removable media.The Security+ exam puts an emphasis on media and
its vulnerabilities.While trying to access a network and its resources remotely is
certainly convenient to the attacker, sometimes a more reliable method is
accessing the data directly through the media used on or with the network.
First we will discuss the physical media used for transmitting data to and from
network devices.To form a network, the devices have to be able to move data
bits to each other. Network cabling is the media used for this purpose.We will go
over several different types of networking media and their respective advantages
and disadvantages. Next, we will cover the physical media used for transporting
data.This is called removable media and comprises everything from floppy disks
to smart cards. Finally, we will go over many of the popular removable media and
discuss their security differences.
Keep in mind that the media being discussed here is physical media used
for transmitting data.There are many other types of media in use within the
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computer industry such as streaming media or media players.These deal with
content rather than data transmissions.This section focuses on the transmission of
data and how to properly secure these transmissions.
Coax Cable
Coaxial (or coax) cable is an older type of cabling that has several different varieties.These cables are used for cabling televisions, radio sets, and computer networks.The cable is referred to as coaxial because both the center wire and the
braided metal shield share a common axis, or centerline.There are a large number
of different types of coax cable in use today, each designed with a specific purpose in mind.This said, many types of coax designed for a specific purpose
cannot be used for something else.
Coax cabling, which can be either thinnet or thicknet, is one of the most vulnerable cabling methods in use. Due to its design, it is very unstable, and has no fault
tolerance.We will examine why each of these coax cable types are so vulnerable.
Thin Coax
Thinnet (thin coax) looks similar to the cabling used for a television’s CATV
connection.Thinnet coax cabling that meets the specifications for computer networking is of a higher quality than that used for television connections, so they
are not interchangeable.The cable type used for thinnet is RG-58 and is specifically designed for networking use. RG-58 has a 50-ohm resistance, whereas television cables are of type RG-59 and have a 75-ohm resistance. Due to the way
thinnet transceivers work (as a current source rather than a voltage source), the
signal going across RG-59 cable is completely different from a signal going across
an RG-58 cable.
Connections between cable segments or to computer systems are accomplished using a T-connector on each network interface card (NIC), which allows
technicians to add an extra cable to the segment. In addition to having T-connectors, both ends of a thinnet cable segment must have a terminator and one end of
the segment must be grounded.These connections are shown in Figure 6.16.
A terminator is basically a 50-ohm resistor with a Bayonet Neill Concelman
(BNC) connector. BNC connectors are the style of connectors used on the end
of thinnet cables.These connectors allow the cables to be easily connected to
T-connectors or barrel connectors.T-connectors are used to add a cable to an
existing segment and connect a device to the segment, whereas barrel connectors
are used to connect two coax cables together to form one cable.
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Figure 6.16 Sample Coax Segment
w/ Ground
Thick Coax
Thicknet (thick coax) cabling is about twice as thick in diameter as thinnet and is
much stiffer and more difficult to work with.This is an older style of cabling (type
RG-8) that is generally used with IBM hardware. Attaching computers to thicknet
cable segments is done by using a vampire tap to cut through the plastic sheath and
make contact with the wires within. A transceiver with a 15-pin adapter unit interface (AUI) is connected to the vampire tap and the NIC is attached to the
transceiver with a transceiver cable.Thicknet cables are similar to thinnet cables in
that they require a 50-ohm terminator on both ends of the segment with one end
grounded. Figure 6.17 shows a sample network using thicknet.
Figure 6.17 Example Thick Coax Network Diagram
Vampire Tap
15-Pin AUI
w/ Ground
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Vulnerabilities of Coax Cabling
Both types of coax cabling share some of the same vulnerabilities. Unfortunately,
it is relatively easy to perform a DoS attack on this type of network by cutting
the cable or disconnecting a device. If communication is not able to flow completely up and down a coax network, the entire network is brought down. In
addition, since connections to the network really cannot be controlled with a
switch or hub, there is no way to prevent unauthorized connections. All an
intruder has to do is tap into the network with either a T-connector or vampire
tap for thinnet or thicknet, respectively.
These vulnerabilities are due to the topology of coax networks. A coax network uses a Bus topology, which basically means that all of the network devices
are connected in a linear fashion. Each device on the network completes the circuit for the network as a whole. Due to this, if any device is removed from the
network or if there is a break anywhere in the cable, the circuit is broken and the
entire network is brought down.
The main advantages to coax networks are the price and the ease of implementation. Since no expensive hubs or switches are required, cost is kept low.
Since all that is required to set up the network is to run a coax cable from one
computer to the next and connect them with T-connectors, this is one of the
easiest networks to implement.
Most coax networks have been or are being replaced with unshielded twisted
pair/shielded twisted pair (UTP/STP) or fiber-optic cabling.Though you may
never work with a coax network, it is important know how vulnerable it is to
disruption of service or intrusion.
While coax is not as commonly used as it used to be, the Security+ exam
expects you to understand how it works and when it should and should
not be used. Understanding the issues that can arise with the use of
coax, such as bringing an entire network down by removing a network
device, will help you answer these questions correctly.
UTP or STP is the next step up from coax. UTP and STP cables are basically
twisted pairs of insulated wires bundled together within a plastic sheath. STP
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includes a layer of shielding material between the wires and the sheath.This type
of cable is sometimes referred to by a category number that designates how many
pairs of wires are in the sheath and what the quality and rating of the cable is.
CAT-3 is similar to telephone wire and has two pairs of wires, but it is still rated
for data communications. CAT-1 and CAT-2 cable also exist, but CAT-1 is only
used for voice communication and CAT-2 has a maximum rated data limit of 4
Mbps.Table 6.2 shows the categories of UPT/STP cable and their description.
Table 6.2 Categories and Descriptions of UPT/STP Cables
Category 1
Used for voice transmission; not suitable for data
Category 2
Low performance cable; used for voice and low-speed
data transmission; has capacity of up to 4 Mbps.
Category 3
Used for data and voice transmission; rated at 10 MHz;
voice-grade; can be used for Ethernet, Fast Ethernet,
and Token Ring.
Category 4
Used for data and voice transmission; rated at 20 MHz;
can be used for Ethernet, Fast Ethernet, and Token Ring.
Category 5
Used for data and voice transmission; rated at 100 MHz;
suitable for Ethernet, Fast Ethernet, Gigabit Ethernet,
Token Ring, and 155 Mbps ATM.
Category 5e
Same as Category 5 but manufacturing process is
refined; higher grade cable than Category 5; rated at
200 MHz; suitable for Ethernet, Fast Ethernet, Gigabit
Ethernet, Token Ring, and 155 Mbps ATM.
Category 6
Rated at 250 MHz; suitable for Ethernet, Fast Ethernet,
Gigabit Ethernet, Token Ring, and 155 Mbps ATM.
Category 6 (Class E) Similar to Category 6 but is a proposed international
standard to be included in ISO/IEC 11801.
Category 6 (STP)
STP cable; rated at 600 MHz; used for data transmission; suitable for Ethernet, Fast Ethernet, Gigabit
Ethernet, Token Ring, and 155 Mbps ATM.
Category 7
Rated at 600 MHz; suitable for Ethernet, Fast Ethernet,
Gigabit Ethernet, Token Ring, and 155 Mbps ATM.
Category 7 (Class F) Similar to Category 7 but is a proposed international
standard to be included in ISO/IEC 11801.
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This type of cable typically uses a RJ-11 connector (like a telephone) to connect to devices on the network, but can also use a RJ-45 connector. CAT-5 cable
contains four pairs of wires and uses RJ-45 connectors for its connections.This
type of cabling is typically used for newer token ring networks and Ethernet networks. Compared to coax, it is easier to run this type of cable and it takes up less
space in the cable runs. In addition, it allows for centralized connectivity points
such as hubs and switches. It is important to make sure that the hubs and
switches are physically secure so that unauthorized connections cannot be made
by simply plugging in a new cable.
Due to the ability to use hubs and switches with UTP/STP cable, it is possible to support Bus topology, Star topology, and Token Ring topology. Bus topology is
supported with hubs, but even the support of a Bus topology in a network using
UTP/STP has an advantage over a coax bus network. If a network device is
removed or a cable breaks, the hub detects the break and routes the circuit
around it.This keeps the network up even if these problems occur.
Star topology looks the same as Bus topology using a hub on a network diagram, but differs in the way the hub routes the circuit internally. A diagram illustrating the Star topology is shown in Figure 6.18. In a hub using a Star topology,
data is communicated to all ports simultaneously rather than flowing from one to
the next.
Figure 6.18 Star Topology
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In addition, some hubs and switches allow administrators to disable ports that
are not in use. Using this capability is also a very good idea.
One downside to UTP cable is that it is vulnerable to electromagnetic interference (EMI) and radio frequency interference (RFI).These types of interference
are caused by everything from microwaves to power cables.This is one reason
that UTP cable should never be run in the same area as electrical wiring. STP
cable is shielded to protect it from these forms of interference, but is more
expensive and not as easy to work with. In addition, both coax cabling and
UTP/STP are vulnerable to eavesdropping.The simple act of sending electricity
down the wires in the cables creates a pulse that can be monitored and translated
into the actual data using specialized devices.
The Security+ exam expects you to be aware of EMI and RFI. While it
is highly unlikely that anyone with equipment at this level of sophistication will want to monitor your network, it is certainly something to be
aware of.
Fiber Optic Cable
Fiber optic cable (referred to as fiber) is the latest and greatest in network cabling.
Fiber is basically a very thin piece of glass or plastic that has been stretched out and
encased in a sheath. It is used as a transport media, not for electrons like the copper
cable used in coax or UTP/STP, but for protons. In other words, fiber optic cables
transport light. An optical transmitter is located at one end of the cable with a
receiver at the other end. With this in mind, it takes a pair of fiber optic lines to
create a two-way communications channel.
Fiber has many advantages over coax and UTP/STP. It can transfer data over
longer distances at higher speeds. In addition, it is not vulnerable to EMI/RFI
interference because there is nothing metallic in the fiber optic cable to conduct
current, which also protects it from lightning strikes. Unlike coax and UTP/STP,
fiber optics cannot succumb to typical eavesdroppers without actually cutting the
line and tapping in with a highly complex form of optical T-connector, and
when attempted creating a noticeable outage.
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The complexity of making connections using fiber is one of its two major
drawbacks. Remember that these cables carry light that makes them rather unforgiving.The connection has to be optically perfect or performance will be downgraded or the cable may not work at all.The other major drawback is cost. Fiber
is much more expensive than coax or UTP/STP, not only for the cable, but also
for the communications equipment.When dealing with optical equipment, costs
usually at least double or triple.
The Security+ exam expects you to know about the advantages and disadvantages of this type of network media.You will also need to know how fiber
compares and contrasts with coax and UTP/STP. Generally, fiber is used in data
centers or for runs between buildings, and UTP cabling is used for connections
to users’ workstations.
Choosing the right network media to use in a given situation is part of
the Security+ exam. There are always situations when one type of cable
is more appropriate than another type. For example, if you are putting
cabling into a location with a lot of EMI, you will want to use STP or
fiber to ensure that the network connection is reliable.
It is also important to keep safety in mind when installing cabling.
When the plastic sheath of some cabling catches on fire it releases toxic
fumes. There is a special type of sheathing material used to prevent this
called plenum. Plenum cabling is flame retardant and does not release
any toxic fumes. It is actually required by some building codes to be used
in overhead ceilings and in buildings over a certain height. Make sure
that you check the local building codes to see if this is a requirement in
any buildings you are wiring.
Removable Media
Dealing with security while data is stored or being communicated on a physical
network is only one aspect of information security. Another part of security concerns what happens to the data when it has been removed from the network and
placed on another media.This media is called removable media and is another area
that the Security+ exam focuses on.
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In the past, the transmission of data via removable media was called sneakernet,
referencing the fact that the underlying protocol involved people physically carrying the media from place to place to transfer it from one computer to another.
This section covers the following removable media types:
Recordable compact disks (CDRs)
Hard drives
Smart cards
Magnetic Tape Magnetic tape is one of the most commonly used types of removable media for
backing up data on a network. In the past, this was accomplished with the use of
large reel-to-reel tape systems.Today, a small cassette tape offers more capacity
and takes up less space.Typical magnetic tapes hold several gigabytes of data and
offer a quick and mostly reliable method of backing up critical data.
Unfortunately, the primary drawback and vulnerability of removable media is
the fact that it is portable.When not properly secured, a magnetic tape can be
removed from a site and restored to any system with a similar tape drive.When
this data is restored, any permissions previously defined on the data from the OS
is rendered ineffective.This could allow an intruder to gain access to secure data
with a minimum of effort.
There are two major ways to secure this vulnerability:
First, most backup programs offer the ability to encrypt the data being
backed up.This increases the amount of time necessary to run the
backup, but from a security perspective, is a very good idea. In addition,
an OS or third party software may offer the ability to encrypt the data
while it is still in use on the drive.This, too, is an excellent idea.
Encrypting the data makes it more difficult for an intruder to access it.
The second way of securing data is to protect it from being obtained by
an intruder. If an intruder cannot take the media out of the secure area,
they will not be able to restore it on a remote system. Some data centers
have large electromagnets around the doorway to prevent this. If a piece
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of magnetic media such as a disk or a tape is brought through the electromagnet, it is rendered useless by the magnetic field.
Aside from securing backup tapes from intruders, they also need to be
secured from nature. Having the best backup system available will not help if the
tapes are in the building when a tornado rips through. Using off-site storage is a
great solution for this problem. Storing the backup tapes in a separate location
ensures that even if the site is destroyed, the data will be safe.
CDR Recordable compact disks (CDRs) are becoming more commonly used within
organizations.Their low cost and relatively high capacity make them a perfect
solution for physically moving data from place to place.There are several different
types of CDRs, which have longer or shorter life spans or data capacity.Whatever
the need, there is a CDR media to support them.
CDRs are not vulnerable to magnets, which makes them more reliable than
magnetic tape when working in an industrial or manufacturing environment.
Their capacity is large enough that small systems can be backed up on them and
data can be saved to them for transfer to another location.
CDRs are, however, very vulnerable to being scratched. If the plastic disk that
makes up the media is scratched too much, the laser that is supposed to reflect
through the plastic will be unable to do so and the data will not be readable. In
addition, CDRs look just like commercially pressed CDs and can therefore be
easily carried out of a building without arousing suspicion.
Hard Drives Hard drives are basically a form of magnetic media that consist of platters within
a metal casing containing a built-in read/write mechanism.The platters contain
the data and are written to and read from using the read/write mechanism.They
typically store much more data than tapes and CDRs.While they are not usually
considered removable media, many newer server systems sport a hot-swap chassis
that allows for drives to be quickly and easily removed when they need to be
replaced. It is in this sense, that the Security+ exam considers hard drives to be
removable media.
The security of hard drives in the context of removable media involves two
main aspects: encryption and physical security. Encrypting the contents of a hard
drive ensures that anyone who manages to get a drive off of the premises will
have a very hard time accessing the data on the drive. Remember that with
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Head of the Class…
enough time and resources, any encryption algorithm can be broken, but most
intruders will not put that level of effort into obtaining data frivolously.
Physical security is covered extensively in Chapter 12. As it relates to hard
drives, the servers containing the drives should always be in a secure location.
Many servers with hot-swap chassis have locks on the chassis to secure the drives,
which, though inconvenient, is also a good security measure. In addition, any
servers mounted in a rack with a lockable door should be secured as well. Every
bit of precaution that slows down or stops an intruder helps.
File Systems
File systems are methods that dictate how a computer stores and retrieves
files, how files are named, and whether some files can be stored more
securely than others. Numerous types of file systems are available for different OSs, including DOS, Windows, Macintosh, OS/2, and UNIX. You
decide on the type of file system your computer will use when you format
the hard disk.
The most secure file system for computers running Windows NT and
Windows 2000 is NTFS, which supports long filenames and compression,
and allows you to determine who has access to a particular file.
Since hard drives are magnetic media, the same security measure that applies
to tapes also applies here. If possible in the overall security design and budget,
adding electromagnets around the entrances and exits of a data center can help
prevent confidential data from leaving the premises. Applying appropriate encryption and physical security can make it very difficult for intruders to obtain data
from the hard drives.
Diskettes Diskettes (also called floppy disks) are another form of magnetic media developed
to transfer data. Prior to CDRs, diskettes were the most common method of
physically transferring data between systems. Older diskettes hold anywhere from
256K on old eight-inch floppy diskettes to 2GB on Iomega’s Jaz drive technology.They consist of a magnet-sensitive disk or platter encased in some form of
plastic housing.
The same security policies that apply to magnetic tape and CDRs should
apply to diskettes. If possible, users should be kept from removing floppy disks
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from the premises. In addition, it is a good idea to keep users from bringing in
diskettes, as they could contain viruses or other malicious programs.
An additional security measure that can be applied to diskettes is simply
removing the floppy disk drive from users’ computers to prevent them from
bringing in or removing data. As most new systems support booting from a CDROM or the network, a floppy drive is usually an unnecessary piece of hardware
in the corporate environment.
Flashcards Flashcards are a chip-based solution to portable data storage.They range tremen-
dously in capacity, but offer certain advantages over magnetic-based technologies.
They are not susceptible to damage from magnetic fields, and they are less prone
to wear out over time. As they use integrated circuit technology to store the data,
they are more stable than their magnetic counterparts. Following is a list of some
types of flashcards:
CompactFlash (most often found in digital cameras)
SmartMedia (most often found in digital cameras)
Memory Stick (most often found in digital cameras)
PCMCIA Type I and Type II memory cards (used as solid-state disks in
Memory cards for video game consoles
Flashcards have a large variety of uses ranging from a simple data storage
solution for PC card ports in laptops to holding backup configuration or boot
information for routers. Since they are small and portable, they are a good solution for storing limited amounts of data when portability or reliability are key
While magnets will not cause damage to flashcards, in some cases they can
be damaged by static electricity. It is important to take the standard precautions
needed around most electronic equipment with flashcards. Avoid holding a flashcard while walking across plush carpet. Flashcards are also easily damaged when
Protecting the data stored on a flashcard is another area on which the
Security+ exam focuses. Most early flashcards offered no data protection capabilities whatsoever and therefore pose a security risk. Some new flashcards offer
built-in security mechanisms such as encryption and authentication services.
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These require that the user authenticate against the card in order to decrypt the
data on the card. Using these newer cards is recommended, due to the additional
security features. Additionally, it never hurts to encrypt data before placing it on
the card.
Smart Cards Smart cards refer to a broad range of devices that either allow you to store a small
amount of data, or run some processing routines, or both. smart cards are typically
the size of a standard credit card and contain one or more chips embedded in the
plastic.They are used primarily as a form of identification for devices with the
capability of reading them. In addition, they can store data related to the owner
of the card when being used for identification or simply as a small, very portable
data store.
Smart cards are designed to be tamper-proof and most of the designers do a
good job of this. Some cards are even rendered useless if the card is modified in
any way.The reason behind this design is not only to keep the owner’s data private, but also to prevent the data from being changed.
When using a smart card for identification or authentication purposes, the
goal is to prevent the identification information from being altered. Smart card
designers go a long way towards accomplishing this goal by making them difficult
to tamper with. In addition, some smart cards also encrypt the data on the card in
order to prevent it from being read by unauthorized entities.
Due to their physical design (embedded in a piece of plastic), smart cards have
a great deal of defense against normal removable media vulnerabilities.They are
immune to magnetic fields and static shock, and resistant to physical abuse.
Bending or cutting a card will, of course, damage it, but carrying it around on a
key chain or badge holder is usually safe. It is recommended that they not be
placed in wallets so they will not get bent, but overall, they provide a great deal
of resistance to physical damage.
Smart card technology is becoming more and more common.They are used
within digital satellite systems, health program identification programs, and some
credit card programs.They are also used for user authentication on high security
Smart cards are covered in Chapter 10, “Public Key Infrastructure.”
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Summary of Exam Objectives
For the Security+ exam, it is important to know and understand many different
aspects of devices and media. In the area of devices, it is necessary to understand
the three major types of firewalls and how they function.
Packet filtering firewalls block packets based on the IP address and port.
Application layer gateways allow a greater level of security by examining
each packet to verify that it has the correct content of the communication session that it is attempting to use.
Stateful inspection firewalls are a compromise between these two technologies.They have speed close to that of packet filtering, with a higher
security level.They verify that each packet going through the firewall
belongs to a valid communications session.
Routers basically shuttle packets between their interfaces, each of which is
attached to a different subnet. A router examines the destination of the packet
and sends the packet out the appropriate interface belonging to the packet’s destination network.
A switch is a device that allows for fast, reliable communication within a
subnet.They can also support packet switching over multiple subnets by using
VLANs. A switch makes a direct connection between devices communicating to
each other through its ports.This eliminates collisions that are common with
hubs and also limits the amount of data that can be obtained by packet sniffing
on one of the switch’s ports.
Wireless technology allows network communication to take place without any
wires connecting it to the network.This technology is useful but brings security
risks with it. Securing a wireless access point is critical to making sure that the
wireless network is secure.This device also allows administrators to implement
encryption over their wireless network that will help a great deal with security.
Modems allow a backdoor into many otherwise secure networks. In many
environments, either servers or users’ systems have modems in them that can
allow intruders to dial into a computer that is also located on the network.
Through this medium, they can gain remote access to the network while completely bypassing the firewalls.
RAS is a method of providing remote access to corporate network users who
travel or who need to access the network from home.Typically, a bank of
modems is connected to the RAS system into which users can dial and provide
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authentication credentials . After the credentials are verified, users are granted
access and their computers act as if they are physically located on the corporate
network. Since this is an intentional remote access point to a network, it is wise
to secure it as much as possible.This includes good password security, encryption,
and possibly callback verification.
Since most businesses require telecommunications to work with their customers, telecom and PBXs are critical to business functions. Since many of these
systems allow for remote access, securing that remote access is one way of preventing attacks on the telecommunications infrastructure.
VPNs allow you to create a secure tunnel over an unsecured network such as
the Internet between either a computer and a network or two networks.This
allows users to connect to the corporate network from their normal ISPs, saving
a great deal of cost. Using strong encryption for this link is critical to maintaining
a secure network. In addition, using good authentication will help keep intruders
from using the VPN against you.
IDS, whether implemented passively or actively, goes a long way towards
helping keep a network secure. If you do not know that an attack is occurring,
there is not much you can do to stop it. IDS helps solve this problem by making
technicians aware of a situation before it escalates to a point where it can no
longer be contained. If your IDS is designed as an active IDS, it can help stop an
attack as soon as it happens without relying on an administrator to be immediately available.
Network monitoring and diagnostic equipment should be kept off the network whenever possible. Due to the need to monitor and analyze the network,
this may not always be possible. In this case, it is best to keep these devices as
secure as possible by encrypting communication between the device and its user,
and always making sure that the devices do not use default passwords. Good password security is critical to keeping these devices safe from intruders.
Workstations are one of the most insecure devices on a network because they
are constantly used locally by users with a huge range of skills and needs. Since
users have direct local access to the system, it is impossible to keep the system
completely secure. Use password policies to force users to change their passwords
Servers are one place where administrators should focus a great deal of time
implementing good security practices. One of the most important security policies to implement with servers is to make sure that they always have the latest OS
and application security patches. In addition, it is important to always monitor
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security-related newsgroups and listservs to keep abreast of the latest vulnerabilities in the software on the network.
Mobile devices provide a security leak simply because they allow confidential
corporate information to be easily transported anywhere. In addition, many
mobile devices provide methods to allow users to connect to a remote network.
If these devices are not adequately secured, they can allow anyone who gains possession of the device to access the network. Securing communications going in
and out of mobile devices is one method of combating this and encrypting data
stored on the device itself is another.
Coax cabling is an older style of network media that still has many limitations, which includes the fact that it is difficult to work with, is only good for
short distances, is limited to slower speeds, and is very vulnerable to breakdown.
In most network designs using coax, a single break in the line can bring down
the entire network.
UTP and STP cable are a step up, using multiple pairs of wires to provide
network communication.This allows for greater distance, speed, and ease of use.
In addition, most network designs using UTP or STP can work around a break
in the cabling. A major vulnerability of both coax and UTP/STP cabling is that
with the correct equipment, the network can be eavesdropped upon without
having to connect to it.
Fiber-optic cable eliminates all of these vulnerabilities by using optical technology rather than normal electronic technology. All communication takes place
on a wave of light, which provides high speed, reliable communication. In addition, it is not as vulnerable to eavesdropping and not at all vulnerable to EMI and
RFI.The downside of using fiber-optic cable is that it is very expensive.
As far as removable media is concerned, magnetic tape was one of the earliest
and most commonly used forms of data storage. It is still used regularly in backup
systems and provides a low-cost solution to storing large amounts of data.
Encrypting the data stored on the tapes and keeping the tapes secure are two
good security practices. It is important to remember that magnetic tape is vulnerable to magnetic fields and can easily be erased with a simple magnet.
CDRs allow administrators to store a small amount of data on a sturdy plastic
disk.They are not vulnerable to magnetic fields and are very portable.This leads
to the possibility of a security leak of confidential corporate data. It is always wise
to prevent CDRs from being brought in to or taken out of a site.
Hard drives are considered removable media in that many servers have hotswappable hard drives which allow a drive to be removed without having to
open up the system.This could conceivably allow an intruder to simply walk out
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with data.This should be prevented with physical security for the data center
itself and by locking the drive chassis on the server.
Diskettes are also magnetic-based and allow you to store data in another
portable format. Most systems have no need for floppy disk drives with the popularity of CD-ROMs, so it is not a bad idea to remove these drives from users’
workstations.This helps in preventing viruses from being introduced to the network from users bringing in infected diskettes.
Flashcards are based on memory chips and are very reliable.They never wear
out if well taken care of. Many routers use flashcards for storing configuration
information, and they are also commonly used for storing pictures from digital
cameras. Encrypting the data on flashcards is a good idea and allows you to keep
your data secure.
Smart cards are credit card-sized devices that allow administrators to store
limited amounts of data.They are often used for identification or as a small data
store due to their size and low cost. Many also offer authentication capabilities by
using a built-in processor.This helps keep the personal and confidential information stored on these cards secure.
Exam Objectives Fast Track
Device-based Security
; Firewalls, routers, IDSs, and switches are devices that can all help secure a
network as long as they are properly configured.
; Wireless, modems, RAS, PBXs, and VPNs all allow remote access to a
computer or telecommunications network and should be made as secure
as possible to prevent intrusion or attacks.
; Network monitoring or diagnostic equipment, workstations, servers, and
mobile devices are all capable of being abused by intruders when
attached to a network and should therefore have their communications
encrypted when possible, and be protected with strong passwords.
Media-based Security
; Coax, UPT, STP, and fiber are all media used to physically connect
devices to a network and each has its own benefits and vulnerabilities.
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; Magnetic tape, hard drives, and diskettes are all magnetic-based
removable media that offer different storage capabilities while still being
vulnerable to magnetic fields.
; CDRs, flashcards, and smart cards are not based on magnetic technology
and allow for a less vulnerable method of storing data on removable
Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: Since application layer gateways are the most secure firewalls, is this the kind I
should always recommend and use?
A: Not necessarily. Application layer gateways provide the most intensive security, but due to the amount of processing they have to do, their speed it limited. A better solution is to analyze the security needs of the network and use
the best firewall based on these needs.
Q: What is the best remote access option for a typical network?
A: It depends on the needs of the business and the cost the company is willing
to absorb. Both RAS and VPN have their advantages. RAS is typically more
expensive to maintain in a large environment with many users, due to the
modem pool that has to be made available.VPNs can also be expensive if a
business opts to pay for the remote user’s ISP.
Q: Should I avoid implementing wireless because of its vulnerabilities?
A: By using encryption and configuring your wireless access point and network
cards properly, you can make a wireless network almost as secure as a wired
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Q: Is fiber the best networking media to implement in a standard office
A: Normally, due to cost limitations, offices are wired with UTP or STP and the
data center is wired with fiber. Fiber is also often used as a backbone to connect one building to another.This is typically the most cost-efficient manner
of providing high-speed networking for your servers and providing acceptable
access speeds to your users.
Q: What is the best removable media to use for backing up my servers?
A: Magnetic tape is used for backups, due to its high capacity and low cost.
Q: Should I implement an IDS on my network?
A: Think of it like this:Would you rather know when you are being attacked, or
find out when the attack is done?
Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
Device-based Security Questions
1. You are implementing a firewall for a small company that wishes to establish
an Internet presence.The company wants to use its dedicated Internet connection to allow employees to access the Internet as well as host a Web server.
What is the best type of firewall to use in this situation?
A. A packet filtering firewall
B. A stateful inspection firewall
C. An application layer gateway
D. No firewall is necessary
2. A company has contracted you to audit their security practices in day-to-day
IT operations.You are working with the team responsible for configuring the
company’s routers and notice that the technician is using a normal Telnet
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session to log in to all of the routers he is working with.What recommendation would you make in your report?
A. Telnet is an unsafe method of communicating with the company’s
routers and the technician should use the router’s Web interface instead.
B. Telnet is an unsafe method of communicating with the company’s
routers and the technician should use the router’s SSH interface instead.
C. Telnet is an unsafe method of communicating with the company’s
routers and the technician should use the router’s console port instead.
D. Telnet is a safe method of communicating with the company’s routers
and you have no recommendation.
3. Your company is considering implementing wireless networking in various
conference rooms so that visiting executives can access the Internet from
their wireless-equipped laptops or PDAs.The conference rooms are on the
second floor of the building and all of them have windows looking out on
parking areas.Why would you recommend against implementing this?
A. The wireless communications would interfere with normal communications on the LAN.
B. This is a security risk as someone with a laptop, a wireless network card,
and an antenna could sit in the parking lot and access the wireless cell.
C. Wireless would not work in the conference rooms because the signals
would resonate off the windows.
D. There is nothing wrong with this idea and no reason to recommend
against it.
4. You have been asked to implement RAS for your company.The users who
will be dialing into the system will always be connecting from their homes
and will not be authorized to use the system from other locations.What RAS
security feature should be implemented to enforce this policy?
A. Call-back verification
B. RADIUS authentication
C. Unlisted telephone numbers
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5. To allow its employees remote access to the corporate network, a company
has implemented a hardware VPN solution.Why is this considered a secure
remote access solution?
A. Because only the company’s employees will know the address to connect
to in order to use the VPN.
B. Because VPNs use the Internet to transfer data.
C. Because a VPN uses compression to make its data secure.
D. Because a VPN uses encryption to make its data secure.
6. The network team at your company has placed a sniffer on the network to
analyze an ongoing network-related problem.The team connects to the
sniffer using Telnet to view the data going across the network.What would
you recommend to increase the security of this connection without making it
significantly more difficult for the network team members to do their jobs?
A. Require the network team to remove the sniffer immediately.
B. Require the network team to view the data from the local console of
the sniffer.
C. Encrypt the connection to the sniffer using PAP.
D. Use SSH to make the connection to the sniffer rather than Telnet.
7. Some new servers are being installed on your company’s network and you
have been asked to work with the installer to ensure that they are as secure as
possible from hack attempts.What is the most important step you should take
to ensure that the servers’ OSs are secure?
A. Make sure that the installer is certified.
B. Make sure that the latest OS service pack is installed.
C. Make sure that the latest OS service pack and all security patches
are installed.
D. Make sure that the servers have locks on the hot-swap drive chassis.
Media-based Security Questions
8. Your company uses UTP cable for all of its network connections including
workstations and servers.The users have reported problems connecting to one
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of the most important servers on the network and you have been called in to
look at it, due to a possible physical security breach by a former employee.
While examining the server, you find that a small battery-powered motor has
been placed and is running next to the server’s network connection.What is
causing the network problem?
A. Electromagnetic interference
B. Static electricity
C. Unknown problems with the user’s workstations
D. Unknown, but the motor is probably unrelated
9. You have been asked to implement a secure network infrastructure for a farm
of servers.Your company has asked you to use the most secure cable available
for this.Why would you choose fiber?
A. Fiber has shielding so that it cannot be cut through.
B. Fiber is impervious to EMI and is therefore more secure.
C. Fiber uses light rather than electricity for communications, making it less
likely to be hacked into remotely.
D. Fiber is unable to be easily tapped into.
10. Your site is having a problem with users burning corporate data to CDRs
and removing them from the site.What is the first thing that should be done
to combat this?
A. Have the site’s physical security team restrict the removal of any CDRs
from the building.
B. Have the company’s management sign off on a security policy restricting
the burning of CDRs at the site and distribute this to all of the
C. Remove CDR burners from all of the company’s computers.
D. Send an e-mail to all of the users telling them not to burn CDRs.
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11. What should you do to data stored on a hard drive in order to make it as
secure as possible if the drive is removed from your site?
A. Encrypt it.
B. Compress it.
C. Archive it.
D. Make sure that a password is required to log into all computers at
your site.
12. Your company has had a problem in the past with virus infections occurring
on the corporate network.These problems have been traced to users bringing
in infected floppy disks and infecting their office computers.What is the best
solution to this problem?
A. Send an e-mail to all of the users telling them not to use infected disks.
B. Ensure that every office computer has up-to-date virus protection software loaded and active.
C. Make the users use CDs for data transfer.
D. Ensure that the users are supplied with a batch of new, virus-free disks.
13. The traveling salespeople in your company use flashcards to store customer
data for use in their laptops.This is done to ensure that if someone steals the
laptop, the data will be safe on the flashcard, which is stored separately.What
else should be done to ensure that the customer’s information remains confidential?
A. Require that the salespeople encrypt the contents of the flashcard.
B. Require that the salespeople keep their flashcard at the office.
C. Require that the salespeople keep their flashcard in their laptop.
D. Require that old customer data be regularly erased from the flashcard.
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14. You are working with a technology firm to ensure that their latest development meets with strict security requirements. Part of the technology being
developed includes the need for some form of client authentication. Due to
the security requirements for the technology, a 128-bit key must be used to
authenticate the user.What media would you recommend the company use
for storing this 128-bit key for each user?
A. Floppy disk
C. Flashcard
D. Smart card
15. While performing a security audit for a company, you determine that many
employees are using removable media to store all of their data rather than the
network drive space that they have been allocated.They say this is due to the
fact that they “do not trust the network.”What policy do you recommend
the company implement?
A. The company should implement a policy requiring that the employees
use the network drives rather than removable media due to the security
risk of having corporate data on removable media.
B. The company should implement a policy requiring that the employees
only use removable media for important files.
C. The company should implement a policy requiring that the employees
use the network drives rather than removable media, due to the cost of
removable media.
D. The company should implement a policy requiring that the employees
use only company-provided removable media.
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. A
9. D
2. B
10. B
3. B
11. A
4. A
12. B
5. D
13. A
6. D
14. D
7. C
15. A
8. A
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Chapter 7
Topologies and IDS
Domain 3.0 Objectives in this Chapter:
Security Topologies
Intrusion Detection
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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In today’s network infrastructures, it is critical to know the fundamentals of basic
security infrastructure. In fact, there are portions of today’s networks that directly
relate to security that you may not even be aware of. For example, if you are
working with Cisco technologies (or other switch vendors), you might be
familiar with virtual local area network (VLAN) technology.VLANs are responsible for securing a broadcast domain to a group of switch ports.This relates
directly to security because different Internet Protocol (IP) subnets can be put on
different port groupings and separated, either by routing or by applying an access
control list (ACL). For example, the Executive group can be isolated from the
general user population on a network. Use of VLANs directly relates to security
and basic network topologies. Other items discussed in this chapter include:
The definition and use of demilitarized zones (DMZ)
Network Address Translation (NAT)
An ACL is a list of users that have permission to access a resource or
modify a file. ACLs are used in nearly all modern-day operating systems
(OSs) to determine what permissions a user has on a particular resource
or file.
The second half of this chapter covers intrusion detection. It is important to
understand not only the concepts of intrusion detection, but also the use and
placement of intrusion detection systems (IDSs) within a network infrastructure.
Placement of an IDS is critical to deployment success.This section also covers
IDS signatures, monitoring, honeypots, and incident response.
You do not need to know how to configure an actual IDS system to pass
the Security+ exam, although it can benefit your security career. You only
need to master the concepts of IDS and the types of IDS systems available.
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Security Topologies
Not all networks are created the same; thus, not all networks should be physically
laid out in the same fashion.The judicious usage of differing security topologies
in a network can offer enhanced protection and performance. For example, suppose you have an e-commerce application that uses IIS servers running a custom
Active Server Page (ASP) application, which calls on a second set of servers
hosting custom COM+ components, which in turn interact with a third set of
servers that house an SQL 2000 database. Figure 7.1 provides an example of this
Figure 7.1 The Complex N-Tier Arrangement
IIS Servers
COM+ Servers
SQL Servers
This is a fairly complex example, but helps illustrate the need for differing
security topologies on the same network. Under no circumstances should
COM+ servers or SQL 2000 servers be exposed to the Internet directly—they
should be protected by placing them behind a strong security solution. At the
same time, you do not want to leave Internet Information Servers (IIS) exposed
to every hacker and script kiddie out there, so they should be placed in a DMZ
or behind the first firewall or router.
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Head of the Class…
What Is A Firewall?
According to the Microsoft Computer Dictionary (Fifth Edition), a firewall
is a security system that is intended to protect an organization’s network
against external threats, such as hackers, coming from another network,
such as the Internet.
Simply put, a firewall is a hardware or software device used to keep
undesirables electronically out of a network the same way that locked
doors and server racks keep undesirables physically away from a network.
A firewall filters traffic crossing it (both inbound and outbound) based on
rules established by the firewall administrator. In this way, it acts as a sort
of digital traffic cop, allowing some (or all) of the systems on the internal
network to communicate with some of the systems on the Internet, but
only if the communications comply with the defined rule set.
While differing topologies can be effectively used together, in some instances
they need to be used completely separately from each other.The next sections
examine the concept of security zones, how to employ them on a network, how
they work, and what they can provide in regards to increased security.
Make sure you know the definitions of and the differences between a
firewall, a DMZ, and an IDS.
Security Zones
The easiest way to think of security zones is to imagine them as discrete network
segments holding systems that share common requirements.These common
requirements can be:
The types of information they handle
Who uses them
What levels of security they require to protect their data
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A security zone is defined as any portion of a network that has specific
security concerns or requirements. Intranets, extranets, DMZs, and VLANs
are all security zones.
It is possible to have systems in a zone running different OSs, such as
Windows 2000 and NetWare 6.The type of computer, whether a PC, server, or
mainframe, is not as important as the security needs of the computer. For
example, there is a network that uses Windows 2000 Server computers as domain
controllers, Domain Name System (DNS) servers, and dynamic host control protocol (DHCP) servers.There are also Windows 2000 Professional clients and
NetWare 6 file servers on the network. Some users may be using Macintosh
computers running OS X or OS 9, while others may be running one or more
types of Linux or UNIX.This is an extremely varied network, but it may still
only have one or two security zones. As stated earlier, the type (or OS) of a computer is not as important with regards to security zones and its role.
In the early days of business Internet connectivity, the concept of security
zones was developed to separate systems available to the public Internet from private systems available for internal use by an organization. A device that acted as a
firewall separated the zones. Figure 7.2 shows a visual representation of the basic
firewall concept.
Figure 7.2 A Basic Firewall Installation
(External Network)
Web Server
The firewall uses its configured
ruleset to allow or disallow traffic
to cross it, thus providing security
for resources inside the firewall.
Mail Server
Internal Network Computers
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Modern firewalls are feature-rich and complex devices, but as a minimum
most provide the ability to:
Block traffic based on certain rules.The rules can block unwanted, unsolicited, spurious, or malicious traffic. (See Figure 7.3.)
Figure 7.3 A Sample Firewall Rule Set
Mask the presence of networks or hosts to the outside world. Firewalls
can also ensure that unnecessary information about the makeup of the
internal network is not available to the outside world.
Log and maintain audit trails of incoming and outgoing traffic.
Provide additional authentication methods.
Some newer firewalls include more advanced features, such as integrated virtual private networking (VPN) applications that allow remote users to access local
systems through a secure, encrypted tunnel. Some firewalls have integrated IDSs
in their product and can make firewall rule changes based on the detection of
suspicious events happening at the network gateway. (IDS products and their use
are covered later in this chapter.) These new technologies have much promise and
make great choices for creating a defense in depth strategy, but remember that the
more work the firewall is doing to support these other functions, the more
chance there is that these additional tools may impact the throughput of the firewall device.
In addition, when a number of these features are implemented on any single
device (especially a firewall), it creates a wide opportunity for a successful attacker
if that device is ever compromised. If one of these new hybrid information security devices are chosen, it is important to stay extra vigilant about applying
patches and to include in the risk mitigation planning how to deal with a situation in which this device falls under the control of an attacker.
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Using a Defense in Depth Strategy
The defense in depth strategy is one that specifies the use of multiple
layers of network security. In this way, you avoid depending on one single
protective measure deployed on your network. In other words, to eliminate the false feeling of security because you implemented a firewall on
your Internet connection, you should implement other security measures
such as an IDS, auditing, and biometrics for access control. You need
many levels of security (hence, defense in depth) to be able to feel safe
from potential threats. A possible defense in depth matrix with auditing
included could look like the graphic in Figure 7.4.
Figure 7.4 A Graphical Representation of Defense in Depth
Security Policy
Auditing and Access Control
IDS System
Risk mitigation, according to the Project Management Institute (PMI),
seeks to reduce the probability and/or impact of a specific risk below an
acceptable threshold. For more information on risk and project management topic, visit the PMI online at
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Although the installation of a firewall or hybrid device protects the internal
systems of an organization, it does nothing to protect the systems that are made
available to the public Internet. A different type of implementation is needed to
add basic protection for those systems that are offered for public use.Thus enters
the concept of the DMZ.
A DMZ is a special section of the network, usually closest to the Internet,
which uses switches, routers, and firewalls to allow access to public
resources without allowing this traffic to reach the resources and computers in the private network.
Introducing the Demilitarized Zone “DMZ” is a military term used to signify a recognized “safe” or buffer area
between two countries where, by mutual agreement, no troops or war-making
activities are allowed.There are usually strict rules regarding what is allowed
within the zone. In computer security, the DMZ is a “neutral” network segment
where systems accessible to the public Internet are housed, which offers some
basic levels of protection against attacks.
The creation of these DMZ segments is usually done in one of two ways:
Layered DMZ implementation
Multiple interface firewall implementation
In the first method, the systems are placed between two firewall devices with
different rule sets, which allows systems on the Internet to connect to the offered
services on the DMZ systems but prevents them from connecting to the computers on the internal segments of the organization’s network (often called the
protected network). Figure 7.5 shows a common installation using this layered
The second method is to add a third interface to the firewall and place the
DMZ systems on that network segment. (See Figure 7.6.) This allows the same
firewall to manage the traffic between the Internet, the DMZ, and the protected
network. Using one firewall instead of two lowers the costs of the hardware and
centralizes the rule sets for the network, making it easier to manage and
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shoot problems. Currently, this multiple interface design is the preferred method
for creating a DMZ segment.
Figure 7.5 A Layered DMZ Implementation
(External Network)
Mail Server
Web Server
Internal Network
Figure 7.6 A Multiple Interface Firewall DMZ Implementation
Mail Server
(External Network)
Web Server
Internal Network
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In either case, the DMZ systems are offered some level of protection from the
public Internet while they remain accessible for the specific services they provide
to external users. In addition, the internal network is protected by a firewall from
both the external network and the systems in the DMZ. Because the DMZ systems still offer public access, they are more prone to compromise and thus they
are not trusted by the systems in the protected network.This scenario allows for
public services while still maintaining a degree of protection against attack.
Hosts located in a DMZ are generally accessed from both internal network clients and public (external) Internet clients. Examples of DMZ bastion hosts are DNS servers, Web servers, and File Transfer Protocol (FTP)
servers. A bastion host is a system on the public side of the firewall,
which is exposed to attack. The word bastion comes from sixteenth century French word, meaning the projecting part of a fortress wall that
faces the outside and is exposed to attackers.
The role of the firewall in all of these scenarios is to manage the traffic
between the network segments.The basic idea is that other systems on the
Internet are allowed to access only the services of the DMZ systems that have
been made public. If an Internet system attempts to connect to a service not
made public, the firewall drops the traffic and logs the information about the
attempt (if configured to do so). Systems on a protected network are allowed to
access the Internet as they require, and they may also access the DMZ systems for
managing the computers, gathering data, or updating content. In this way, systems
are exposed only to attacks against the services that they offer and not to underlying processes that may be running on them.
The systems in the DMZ can host any or all of the following services:
Internet Web Site Access IIS or Apache servers, for example, that
provide Web sites for public and private usage. Examples would be or Both of these Web
sites have both publicly and privately available contents.
FTP Services FTP file servers that provide public and private downloading and uploading of files. Examples would be the FTP servers
used by popular download providers at or
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Topologies and IDS • Chapter 7 FTP is designed for faster file transfer with less overhead, but does not have all of the special features that are available in
Hypertext Transfer Protocol (HTTP), the protocol used for Web page
E-mail Relaying A special e-mail server that acts as a middleman of
sorts. Instead of e-mail passing directly from the source server to the destination server (or the next hop in the path), it passes through an e-mail
relay that then forwards it. E-mail relays are a double-edged sword and
most security professionals prefer to have this function disabled on all
publicly accessible e-mail servers. On the other hand, some companies
have started offering e-mail relaying services to organizations as a means
of providing e-mail security.
DNS Services A DNS server might be placed in the DMZ in order to
point incoming access requests to the appropriate server with the DMZ.
This can alternatively be provided by the Internet Service Provider
(ISP), usually for a nominal extra service charge. If DNS servers are
placed in the DMZ, it is important to be careful and ensure that they
cannot be made to conduct a zone transfer (a complete transfer of all
DNS zone information from one server to another) to any server.This is
a common security hole found in many publicly accessible DNS servers.
Intrusion Detection The placement of an IDS system (discussed later
in this chapter) in the DMZ is difficult and depends on the network
requirements. IDSs placed in the DMZ will tend to give more false positive results than those inside the private internal network, due to the
nature of Internet traffic and the large number of script kiddies out
there. Still, placing an IDS on the DMZ can give administrators early
warning of attacks taking place on their network resources.
Demand for business applications has swelled, and these basic implementations have gotten more complex.With the advent of e-commerce, more attention
must be paid to securing transaction information that flows between consumers
and the sites they use, as well as between e-commerce businesses themselves.
Customer names, addresses, order information, and especially financial data need
greater care and handling to prevent unauthorized access.This greater care is
accomplished through the creation of the specialized segments mentioned earlier
(which are similar to the DMZ) called security zones.
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Multiple Needs Equals Multiple Zones
Security requirements for storing customer information and financial data are different from the requirements for storing routine, less sensitive information that
businesses handle. Because this data requires processing and much of the processing is done over the Internet, more complicated network structures must be
created. Many organizations choose to implement a multiple segment structure to
better manage and secure their different types of business information.
This multi-segment approach allows flexibility, because new segments with
specific purposes and security requirements can be easily added to the model. In
general, the two segments that are widely accepted are:
A segment dedicated to information storage
A segment specifically for the processing of business information
Each of these two new segments has special security and operability concerns
above and beyond those of the rest of the organizational intranet. In reality,
everything comes down to dollars—what is it going to cost to implement a security solution versus what will it cost if the system is breached by attackers.Thus
the value of raw data is different than the value of the financial processing system.
Each possible solution has its pluses and minuses, but in the end a balance is
struck between cost versus expected results.Thus, the creation of different zones
(segments) for different purposes. Note that the Web and e-mail servers would
likely receive the least amount of spending and security measures, which is not to
say that they will be completely ignored, they just would not receive as much as
the financial servers might.
Creation of multiple segments changes a network structure to look like the
drawing in Figure 7.7.
The diagram shown in Figure 7.7 includes the following two new zones:
The data storage network
The financial processing network
The data storage zone is used to hold information that the e-commerce application requires, such as inventory databases, pricing information, ordering details,
and other non-financial data.The Web servers in the DMZ segment serve as the
interface to the customers; they access the servers in the other two segments to
gather the required information and to process the users’ requests.
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Figure 7.7 A Modern E-Commerce Implementation
DMZ Segements
Web & Mail Servers
Data Storage Servers
(External Network)
Internal Network
Financial Processing
When an order is placed, the business information in these databases is
updated to reflect the real time sales and orders of the public.These businesssensitive database systems are protected from the Internet by the firewall, and they
are restricted from general access by most of the systems in the protected network.This helps protect the database information from unauthorized access by an
insider or from accidental modification by an inexperienced user.
You will not need to know how an e-commerce DMZ is set up to pass
the Security+ exam; however, it is important to know this information
for real-world security work.
The financial information from an order is transferred to the financial processing segment. Here the systems validate the customer’s information and then
process the payment requests to a credit card company, a bank, or a transaction
clearinghouse. After the information has been processed, it is stored in the
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database for batch transfer into the protected network, or it is transferred in real
time, depending on the setup.The financial segment is also protected from the
Internet by the firewall, as well as from all other segments in the setup.This
system of processing the data in a location separate from the user interface creates
another layer that an attacker must penetrate to gather financial information
about customers. In addition, the firewall protects the financial systems from
access by all but specifically authorized users inside a company.
Access controls also regulate the way network communications are initiated.
For example, if a financial network system can process credit information in a
store-and-forward mode, it can batch those details for retrieval by a system from
the protected network.To manage this situation, the firewall permits only systems
from the protected network to initiate connections with the financial segment.
This prevents an attacker from being able to directly access the protected network
in the event of a compromise. On the other hand, if the financial system must use
real-time transmissions or data from the computers on the protected network, the
financial systems have to be able to initiate those communications. In this event,
if a compromise occurs, the attacker can use the financial systems to attack the
protected network through those same channels. It is always preferable that DMZ
systems not initiate connections into more secure areas, but that systems with
higher security requirements initiate those network connections. Keep this in
mind as you design your network segments and the processes that drive your site.
The phrase store-and-forward refers to a method of delivering transmissions in which the messages are temporarily held by an intermediary
before being sent on to their final destination. Some switches and many
e-mail servers use the store-and-forward method for data transfer.
In large installations, these segments may vary in placement, number, and/or
implementation, but this serves to generally illustrate the ideas behind the process. An actual implementation may vary from this design. For example, an
administrator may wish to place all the financial processing systems on the protected network.This is acceptable as long as the requisite security tools are in
place to adequately secure the information.We have also seen implementation of
the business information off an extension of the DMZ, as well as discrete DMZ
segments for development and testing. Specific technical requirements will impact
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actual deployment, so administrators may find that what they currently have in
place on a network (or the need for a future solution) may deviate from the diagrams shown earlier.The bottom line is to ensure that systems are protected.
DMZ design is covered on the Security+ exam. You must know the basics
of DMZ placement and what components the DMZ divides.
Problems with Multi-zone Networks
Some common problems do exist with multiple-zone networks. By their very
nature they are complex to implement, protect, and manage. Firewall rule sets are
often large, dynamic, and confusing, and the implementation can be arduous and
resource intensive.
Creating and managing security controls such as firewall rules, IDS signatures,
and user access regulations is a large task.These processes should be kept as
simple as possible without compromising security or usability. It is best to start
with deny-all strategies and permit only the services and network transactions
required to make the site function, and then carefully manage the site’s performance making small changes to the access controls to more easily manage the
rule sets. Using these guidelines, administrators should be able to quickly get the
site up and running without creating obvious security holes in the systems.
As a site grows and offers new features, new zones may have to be created.
The above process should be repeated for creating the rule sets governing these
new segments. As always, it is important to audit and inspect any changes and
keep backups of the old rule sets in case they are needed again.
Intranet Thus far, this chapter has only discussed the systems that reside outside of the
protected internal network.These servers are the ones that are located in the
DMZ.The rest of the internal network is called the intranet, which means a private internal network.The intranet, therefore, is every part of a network that lies
on the inside of the last firewall from the Internet. Figure 7.8 gives an example of
an intranet.
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Figure 7.8 A Simple Intranet Example
The Internet
and DMZs
Last Firewall from
the Internet
The terminology can be confusing to beginners. One might think the
internal network would be the Internet, but this is not the case. An
Internet (including the global Internet) refers to communications
between different networks, while the intranet refers to communications
within a network. It may help to use a comparison: interstate commerce
refers to business transacted across state lines (between different states),
while intrastate commerce refers to business transacted within one state.
It is expected that all traffic on the intranet will be secure and safe from the
prying eyes on the Internet. It is the network security professional’s job to make
sure that this happens.While a security breach of a DMZ system can be costly to
a company, a breach that occurs inside an intranet could be extraordinarily costly
and damaging. If this happens, customers and business partners might lose faith in
the company’s ability to safeguard sensitive information, and other attackers will
likely make the network a favorite target for future attacks.
To ensure that all traffic on the intranet is secure, the following issues should
be addressed:
Make sure that the firewall is configured properly to stop attack attempts
at the firewall.There are many different opinions on how to do this, but
the majority of security professionals agree that you should start with a
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“block everything” mentality and then open the firewall on a case-bycase basis, thereby only allowing specific types of traffic to cross it
(regardless of which direction the traffic is flowing).
Additionally, make sure that the firewall is configured properly to prevent unauthorized network traffic, such as file sharing programs (for
example, Gnutella or Morpheus) from being used on the internal network.These types of programs can sometimes be difficult to block, but it
can be done.
Make sure the firewall will watch traffic that leaves the network from
trusted hosts, and ensure that it is not intercepted and altered in route;
steps should also be taken to try to eliminate spoofing from attackers.
Make sure that the antivirus software is in use and up to date. Consider
implementing an enterprise-level solution, consisting of a central server
responsible for coordinating and controlling the identification and collection of viruses on your network.
Educate users on the necessity of keeping their computers logged out
when not in use.
Implement Secure Internet Protocol (IPSec) on the intranet between all
clients and servers to prevent eavesdropping; note that more often than
not, the greatest enemy lies on the inside of the firewall.
Conduct regular, but unannounced, security audits and inspections. Be
sure to closely monitor all logs that are applicable.
Do not allow the installation of modems in any intranet computers. Do
not allow any connection to the Internet except through the firewall
and proxy servers, as applicable.
A proxy server is a server that sits between an intranet and its Internet
connection. Proxy servers provide features such as document caching (for
faster browser retrieval) and access control. Proxy servers can provide security for a network by filtering and discarding requests that are deemed
inappropriate by an administrator. Proxy servers also protect the internal
network by masking all internal IP addresses—all connections to Internet
servers appear to be coming from the IP address of the proxy servers.
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Of course, there are literally hundreds of other issues that may need to be
addressed but these are some of the easiest ones to take care of and the most
commonly exploited ones.
All of the Internet security measures listed here should be used at your
discretion, based on what is available and what meets the business
needs of your company. You can use any one of these, all of these, or
continue with an almost infinite list of applied security measures that are
covered in this book.
Extranet Extranets are a special implementation of the intranet topology. Creating an
extranet allows for access to a network (more likely, certain parts of a network)
by trusted customers, partners, or other users.These users, who are external to
the network—they are on the Internet side of the firewalls and other security
mechanisms—can then be allowed to access private information stored on the
internal network that they would not want to place on the DMZ for general
public access.The amount of access that each user or group of users is allowed to
have to the intranet can be easily customized to ensure that each user or group
gets what they need and nothing more. Additionally, some organizations create
extranets to allow their own employees to have access to certain internal data
while away from the private network.
The following is an example of how two companies might each choose to
implement an extranet solution for their mutual betterment. Company A makes
door stoppers and has recently entered into a joint agreement with Company B.
Company B makes cardboard boxes. By partnering together, both companies are
hoping to achieve some form of financial gain. Company A is now able to get
cardboard boxes (which it needs to ship its product) made faster, cheaper, and to
exact specification; Company B benefits from newfound revenue from Company
A. Everybody wins and both companies are very happy. After some time, both
companies realize that they could streamline this process even more if they each
had access to certain pieces of data about the other company. For example,
Company A wants to keep track of when its cardboard boxes will be arriving.
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Company B, on the other hand, wants to be able to control box production by
looking at how many orders for door stoppers Company A has.What these two
companies need is an extranet. By implementing an extranet solution, both companies will be able to get the specific data they need to make their relationship
even more profitable, without either company having to grant full, unrestricted
access to its private internal network. Figure 7.9 graphically depicts this extranet
Figure 7.9 A Simple Extranet Example
By implementing an extranet solution, users outside of the internal
network can access certain information across the Internet without
the need for a dedicated line.
Company A
Company B
You must have a functional intranet setup before attempting to create
an extranet.
Users attempting to gain access to an extranet require some form of authentication before they are allowed access to resources.The type of access control
implemented can vary, but some of the more common include usernames/passwords and digital certificates. Once an extranet user has been successfully authenticated, they can gain access to the resources that are allowed for their access
level. In the previous example, a user from Company B’s production department
might need to see information about the number of door stoppers being ordered,
while a user from Company A’s shipping department might need to see information detailing when the next shipment of boxes is expected.
Be able to readily define an extranet. You must know the difference
between the Internet, intranet, and extranet.
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A VLAN can be thought of as the equivalent to a broadcast domain.
A broadcast domain consists of a group of nodes (computers) that
receive Layer 2 broadcasts sent by other members of the same group.
Typically, broadcast domains are separated by creating additional network segments or by adding a router.
Do not confuse broadcast domains with collision domains. Collision
domains refer specifically to Ethernet networks. The area of network
cabling between Layer 2 devices is known as a collision domain. Layer 2
devices typically include switches that rely on the physical address (Media
Access Control [MAC] address) of computers to route traffic.
VLANs are a way to segment a network, as discussed above.When thinking
of a VLAN, think of taking a switch and physically cutting it into two or more
pieces with an axe. Special software features found in newer, more expensive
switches, allow administrators to physically split one physical switch into multiple
logical switches, thus creating multiple network segments that are completely separate from one another.
The VLAN is thus a logical local area network that uses a basis other than a
physical location to map the computers that belong to each separate VLAN. (For
example, each department within a company could comprise a separate VLAN,
regardless of whether or not the department’s users are located in physical proximity.) This allows administrators to manage these virtual networks individually
for security and ease of configuration.
Let’s look at an example of using VLANs.There is an Engineering section
consisting of 14 computers and a Research section consisting of eight computers,
all on the same physical subnet. Users typically communicate only with other systems within their respective sections. Both sections share the use of one Cisco
Catalyst 2924XL switch.To diminish the size of the necessary broadcast domain
for each section, the administrator can create two VLANs, one for the
Engineering section and one for the Research section. After creating the two
VLANs, all broadcast traffic for each section will be isolated to its respective
VLAN. But what happens when a node in the Engineering section needs to
communicate with a node in the Research section? Do the two systems connect
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from within the Catalyst 2924XL switch? No; this cannot occur since the two
sections have been set up on two different VLANs. For traffic to be passed
between VLANs (even when they are on the same switch) a router must be used.
Figure 7.10 graphically depicts the previous example of splitting one switch
into two VLANs. Note that two switches can also be split into two VLANs or
more, depending on the need.The following example shows how to split two
switches into multiple VLANs with each VLAN acting as its own physically separated network segment. In reality, many more VLANs can be created; they are
only limited by port density (the number of ports on a switch) and the feature set
of the switch’s software.
Figure 7.10 Using VLANs to Segment Network Traffic
Other Network
Each VLAN functions like a separate switch due to the combination of hardware and software features built into the switch itself.Thus, the switch must be
capable of supporting VLANs in order to use them.The following are typical
characteristics of VLANs when implemented on a network:
Each VLAN is the equivalent of a physically separate switch as far as network traffic is concerned.
A VLAN can span multiple switches, limited only by imagination and
the capabilities of the switches being used.
Trunks carry the traffic between each switch that is part of a VLAN. A
trunk is defined as a point-to-point link from one switch to another
switch.The purpose of a trunk is to carry the traffic of multiple VLANs
over a single link.
Cisco switches, for example, use the Cisco proprietary Inter-Switch Link
(ISL) and IEEE 802.1Q protocol as their trunking protocols.
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Know that VLANs implement security at the switch level. If you are not
on the same VLAN as another user on your network and access is not
allowed, you can secure communications from such hosts.
A complete description of VLANs beyond the scope of the Security+ exam,
can be found at
family_home.html.The IEEE 802.1Qstandard can be downloaded at
Network Address Translation
Network address translation (NAT) is a feature of many firewalls, proxies, and
routing-capable systems. NAT has several benefits, one of which is its ability to
hide the IP address and network design of the internal network.The ability to
hide the internal network from the Internet reduces the risk of intruders
gleaning information about the network and exploiting that information to gain
access. If an intruder does not know the structure of a network, the network
layout, the names and IP address of systems, and so on, it is very difficult to gain
access to that network.
NAT enables internal clients to use nonroutable IP addresses, such as the private IP addresses defined in RFC 1918, but still enables them to access Internet
resources. NAT restricts traffic flow so that only traffic requested or initiated by
an internal client can cross the NAT system from external networks.
If only a single system is linked to the Internet with a broadband connection,
NAT is of little use. However, for local networks that share a broadband connection, NAT’s benefits can be utilized for security purposes.When using NAT, the
internal addresses are reassigned to private IP addresses and the internal network
is identified on the NAT host system. Once NAT is configured, external malicious users are only able to access the IP address of the NAT host that is directly
connected to the Internet, but they are not able to “see” any of the internal computers that go through the NAT host to access the Internet.
When NAT is used to hide internal IP addresses (see Figure 7.11), it is sometimes called a NAT firewall; however, do not let the word firewall give you a false
sense of security. NAT by itself solves only one piece of the security perimeter
puzzle. A true firewall does much more than link private IP addresses to public
ones, and vice versa.
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Figure 7.11 NAT Hides the Internal Addresses
The NAT router has a routing table that keeps track of all connection
requests that originate from the internal network. The NAT router
modifies all outgoing packets, by replacing the internal client’s
IP address with its own IP address, and then forwards them to
their destination (or next hop). Returning packets are then
routed back to the correct internal client by using the routing table.
Requests that originate from the Internet can be routed to the
correct internal client as long as a static mapping has been
created in the NAT router’s table.
NAT Router
Damage & Defense…
Deploying a NAT Solution
NAT is relatively easy to implement, and there are several ways to do so.
Many broadband hardware devices (cable and DSL modems) are called
cable/DSL “routers” because they allow you to connect multiple computers. However, they are actually combination modem/NAT devices
rather than routers because they require only one external (public) IP
address. You can also buy NAT devices that attach your basic cable or DSL
modem to the internal network. Alternatively, the computer that is
directly connected to a broadband modem can use NAT software to act
as the NAT device itself. This can be an add-on software program such as
Sygate ( or the NAT software that is built into some
OSs. For example, Windows 2000 Server includes a fully configurable NAT
as part of its Routing and Remote Access services. Windows 98SE, 2000
Professional, ME, and XP include a “lite” version of NAT called Internet
Connection Sharing (ICS).
For a quick, illustrated explanation of how NAT works with a broadband connection, see the HomeNetHelp article at
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Exercise 7.01 walks through the steps of configuring ICS on a Windows XP
Professional computer. ICS is a simple form of NAT, allowing one host computer
to share its internet connection with the rest of the computers in the network.
ICS is best implemented in very small offices or homes where the total number
of computers is very small, roughly four or less. ICS requires two network connections in the host computer, one of which must be a local area network (LAN)
connection. All client computers should be configured for DHCP.
1. Open the Network Connections folder by clicking Start | Settings
| Control Panel | Network Connections.
2. Open the Properties page for your LAN connection by rightclicking on it and selecting Properties from the context menu.
3. Switch to the Advanced tab. You should see the page shown in
Figure 7.12.
Figure 7.12 Network Adapter Advanced Properties
4. Place a check in the Allow other network users to connect
through this computer’s Internet connection box.
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5. If you want to allow other users to control or disable the shared
connection, place a check in the Allow other network users to
control or disable the shared Internet connection box.
Head of the Class…
6. Click OK to close the network adapter Properties page.
Public and Private Addressing
Certain IP address ranges are classified as Private IP addresses, meaning
they are not to be routed on the Internet. These addresses are intended
only for use on private internal networks. There are three groups of private IP addresses under the IPv4 standard as outlined here: - (10/8 prefix) - (172.16/12 prefix) - (192.168/16 prefix)
The network segment shown in Figure 7.11 uses private IP addresses
on the internal network from the 192.168.5.x subnet. The allowable
addresses in this subnet would then be through The address is considered to be a broadcast address—one that would be used if a computer needed to send a
transmission to all other computers on that subnet. Typically the gateway
or router will occupy the first address in a given range, as is the case in
Figure 7.11 where the router has been assigned the address of on its LAN interface.
Note that in Exercise 7.01, the ICS host computer is statically
assigned the IP address and all ICS clients will automatically
be assigned IP addresses in the 192.168.0.x range so that they can communicate directly with the ICS host without needing a router.
For a complete discussion on private IP addresses, see RFC 1918 at The Internet Assigned
Numbers Authority (IANA) maintains a current listing of all IPv4 IP address
range assignments at You
can also examine all of the special IPv4 IP address assignments at
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Tunneling is used to create a virtual tunnel (a virtual point-to-point link)
between you and your destination using an untrusted public network as the
medium. In most cases, this would be the Internet.When establishing a tunnel,
commonly called a VPN, a safe connection is being created between two points
that cannot be examined by outsiders. In other words, all traffic that is traveling
through this tunnel can be seen but cannot be understood by those on the outside. All packets are encrypted and carry information designed to provide authentication and integrity.This ensures that they are tamperproof and thus can
withstand common IP attacks, such as the Man-in-the-Middle (MITM) and
packet replay.When a VPN is created, traffic is private and safe from prying eyes.
Tunneling is used in conjunction with encryption to provide total end-toend data protection across an untrustworthy network, such as the
Internet. Point-to-Point Tunneling Protocol (PPTP) and Layer 2 Tunneling
Protocol (L2TP) are popular VPN tunneling protocols, while Microsoft
Point-to-Point Encryption (MPPE) and IPSec are their encryption counterparts. Do not confuse tunneling with encryption.
VPN tunneling provides confidentiality of data, in that the traffic is encrypted,
typically using MPPE or IPSec.VPNs created using the L2TP use IPSec for
encryption, whereas tunnels created with the PPTP use MPPE.Windows 2000 and
newer Microsoft OSs can use IPSec; all older versions must use MPPE.
Most other new OSs also provide support for L2TP and IPSec.Tunnels can
also be created using IPSec alone (without L2TP) or using Secure Shell (SSH) or
Crypto Internet Protocol Encapsulation (CIPE) in Linux/UNIX environments.
It is important to understand that tunneling and encryption are two separate processes, both of which are necessary to create a VPN.
For more information about VPN technologies, see
public/cc/so/cuso/epso/sqfr/safev_wp.htm from Cisco systems.Tunneling is
often used when configuring and implementing an extranet solution, but is not
limited to usage only in that situation. Consider Figure 7.13, where we have created a VPN tunnel from your network to the network of a business partner.
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Figure 7.13 Setting Up a Business-to-Business VPN
VPN tunnel through the Internet from one
intranet to another intranet provides for secure
and authentic communications.
Partner Network
Your Network
VPN Server
VPN Server
You can also establish a VPN from your home computer to the corporate
network by making use of your ISP connection, as shown in Figure 7.14.
Figure 7.14 Establishing a VPN Tunnel to Access the Corporate Network
from Home
Your Network
ISP Network
Dial-up Connection to
your ISP
VPN Server
VPN tunnel through the Internet from
your home computer to the corporate
intranet. All communications are
secure and authentic.
Your Home Computer
RAS Server
Exercise 7.02 outlines the basic process to create a VPN connection from a
Windows XP Professional computer—very useful when traveling away from the
corporate network.
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1. Open the Network Connections folder by clicking Start | Settings
| Control Panel | Network Connections.
2. Click File | New Connection to start the New Connection Wizard.
3. Click Next to dismiss the opening page of the Wizard.
4. Select Connect to the network at my workplace and click Next.
5. Select Virtual Private Network connection and click Next.
6. Enter the name of the connection, such as the company or network name, and click Next.
7. Select to have Windows automatically connect or not to automatically connect to the Internet (as desired) and click Next.
8. Enter the destination IP address and click Next. This should be the
IP address of the VPN server you are attempting to connect to.
9. Click Finish when you are done with the Wizard.
10. You can perform further (more advanced) configuration of the
VPN connection by opening the new connection and then clicking
Intrusion Detection
Firewalls and other simple boundary devices lack some degree of intelligence
when it comes to observing, recognizing, and identifying attack signatures that
may be present in the traffic they monitor and the log files they collect.Without
sounding critical of other systems’ capabilities, this deficiency explains why IDSs
are becoming increasingly important in helping to maintain proper network
security.Whereas other boundary devices may collect all the information necessary to detect (and often, to foil) attacks that may be getting started or are already
underway, they have not been programmed to inspect for and detect the kinds of
traffic or network behavior patterns that match known attack signatures or that
suggest potential unrecognized attacks may be incipient or in progress.
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In a nutshell, the simplest way to define an IDS is to describe it as a specialized tool that knows how to read and interpret the contents of log files from
routers, firewalls, servers, and other network devices. Furthermore, an IDS often
stores a database of known attack signatures and can compare patterns of activity,
traffic, or behavior it sees in the logs it is monitoring against those signatures to
recognize when a close match between a signature and current or recent
behavior occurs. At that point, the IDS can issue alarms or alerts, take various
kinds of automatic action ranging from shutting down Internet links or specific
servers to launching backtraces, and make other active attempts to identify
attackers and actively collect evidence of their nefarious activities.
By analogy, an IDS does for a network what an antivirus software package
does for files that enter a system: It inspects the contents of network traffic to
look for and deflect possible attacks, just as an antivirus software package inspects
the contents of incoming files, e-mail attachments, active Web content, and so
forth to look for virus signatures (patterns that match known malware) or for
possible malicious actions (patterns of behavior that are at least suspicious, if not
downright unacceptable).
To eliminate confusion on the Security+ exam, the simplest definition of
IDS is: A device that monitors and inspects all inbound and outbound
network traffic and identifies patterns that may indicate suspicious activities or attacks. Do not confuse this with a firewall, which is a device that
inspects all inbound and outbound network traffic looking for disallowed
types of connections.
To be more specific, intrusion detection means detecting unauthorized use of
or attacks on a system or network. An IDS is designed and used to detect and
then to deflect or deter (if possible) such attacks or unauthorized use of systems,
networks, and related resources. Like firewalls, IDSs may be software-based or
may combine hardware and software (in the form of preinstalled and preconfigured standalone IDS devices). Often, IDS software runs on the same devices or
servers where firewalls, proxies, or other boundary services operate; an IDS not
running on the same device or server where the firewall or other services are
installed will monitor those devices closely and carefully. Although such devices
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tend to operate at network peripheries, IDS systems can detect and deal with
insider attacks as well as external attacks.
Network- and Host-Based IDSs
IDS systems vary according to a number of criteria. By explaining those criteria,
we can explain what kinds of IDSs you are likely to encounter and how they do
their jobs. First and foremost, it is possible to distinguish IDSs on the basis of the
kinds of activities, traffic, transactions, or systems they monitor. In this case, IDSs
may be divided into network-based, host-based, and application-based types. IDSs
that monitor network backbones and look for attack signatures are called networkbased IDSs, whereas those that operate on hosts defend and monitor the operating
and file systems for signs of intrusion and are called host-based IDSs. Some IDSs
monitor only specific applications and are called application-based IDSs. (This type
of treatment is usually reserved for important applications such as database management systems, content management systems, accounting systems, and so forth.)
Read on to learn more about these various types of IDS monitoring approaches:
Network-based IDS Characteristics
Pros: Network-based IDSs can monitor an entire large network with
only a few well-situated nodes or devices and impose little overhead
on a network. Network-based IDSs are mostly passive devices that
monitor ongoing network activity without adding significant overhead or interfering with network operation.They are easy to secure
against attack and may even be undetectable to attackers; they also
require little effort to install and use on existing networks.
Cons: Network-based IDSs may not be able to monitor and analyze
all traffic on large, busy networks and may therefore overlook attacks
launched during peak traffic periods. Network-based IDSs may not
be able to monitor switch-based (high-speed) networks effectively,
either.Typically, network-based IDSs cannot analyze encrypted data,
nor do they report whether or not attempted attacks succeed or fail.
Thus, network-based IDSs require a certain amount of active, manual
involvement from network administrators to gauge the effects of
reported attacks.
Host-based IDS Characteristics
Pros: A host-based IDS can analyze activities on the host it monitors
at a high level of detail; it can often determine which processes
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and/or users are involved in malicious activities.Though they may
each focus on a single host, many host-based IDS systems use an
agent-console model where agents run on (and monitor) individual
hosts but report to a single centralized console (so that a single console can configure, manage, and consolidate data from numerous
hosts). Host-based IDSs can detect attacks undetectable to the network-based IDS and can gauge attack effects quite accurately. Hostbased IDSs can use host-based encryption services to examine
encrypted traffic, data, storage, and activity. Host-based IDSs have no
difficulties operating on switch-based networks, either.
Cons: Data collection occurs on a per-host basis; writing to logs or
reporting activity requires network traffic and can decrease network
performance. Clever attackers who compromise a host can also
attack and disable host-based IDSs. Host-based IDSs can be foiled by
Denial of Service (DoS) attacks (since they may prevent any traffic
from reaching the host where they are running or prevent reporting
on such attacks to a console elsewhere on a network). Most significantly, a host-based IDS consumes processing time, storage, memory,
and other resources on the hosts where such systems operate.
Application-based IDS Characteristics
Pros: Application-based IDSs concentrate on events occurring within
some specific application.They often detect attacks through analysis
of application log files and can usually identify many types of attacks
or suspicious activity. Sometimes an application-based IDS can track
unauthorized activity from individual users.They can also work
with encrypted data, using application-based encryption/decryption
Cons: Application-based IDSs are sometimes more vulnerable to
attack than the host-based IDS.They can also consume significant
application (and host) resources.
In practice, most commercial environments use some combination of network-, host-, and/or application-based IDS systems to observe what is happening
on the network while also monitoring key hosts and applications more closely.
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You must be able to clearly describe the differences between the three
types of IDS systems. Go back over them until you know them very well.
IDSs may also be distinguished by their differing approaches to event analysis.
Some IDSs primarily use a technique called signature detection.This resembles the
way many antivirus programs use virus signatures to recognize and block infected
files, programs, or active Web content from entering a computer system, except
that it uses a database of traffic or activity patterns related to known attacks, called
attack signatures. Indeed, signature detection is the most widely used approach in
commercial IDS technology today. Another approach is called anomaly detection. It
uses rules or predefined concepts about “normal” and “abnormal” system activity
(called heuristics) to distinguish anomalies from normal system behavior and to
monitor, report on, or block anomalies as they occur. Some IDSs support limited
types of anomaly detection; most experts believe this kind of capability will
become part of how more IDSs operate in the future. Read on for more information about these two kinds of event analysis techniques:
Signature-based IDS characteristics
Pros: A signature-based IDS examines ongoing traffic, activity, transactions, or behavior for matches with known patterns of events specific to known attacks. As with antivirus software, a signature-based
IDS requires access to a current database of attack signatures and
some way to actively compare and match current behavior against a
large collection of signatures. Except when entirely new, uncataloged
attacks occur, this technique works extremely well.
Cons: Signature databases must be constantly updated, and IDSs must
be able to compare and match activities against large collections of
attack signatures. If signature definitions are too specific, a signaturebased IDS may miss variations on known attacks. (A common technique for creating new attacks is to change existing known attacks
rather than to create entirely new ones from scratch.) Signaturebased IDSs can also impose noticeable performance drags on systems
when current behavior matches multiple (or numerous) attack signatures, either in whole or in part.
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Anomaly-based IDS characteristics
Pros: An anomaly-based IDS examines ongoing traffic, activity, transactions, or behavior for anomalies on networks or systems that may
indicate attack.The underlying principle is the notion that “attack
behavior” differs enough from “normal user behavior” that it can be
detected by cataloging and identifying the differences involved. By
creating baselines of normal behavior, anomaly-based IDS systems
can observe when current behavior deviates statistically from the
norm.This capability theoretically gives anomaly-based IDSs abilities
to detect new attacks that are neither known nor for which signatures have been created.
Cons: Because normal behavior can change easily and readily,
anomaly-based IDS systems are prone to false positives where attacks
may be reported based on changes to the norm that are “normal,”
rather than representing real attacks.Their intensely analytical
behavior can also impose heavy processing overheads on systems
they are running. Furthermore, anomaly based systems take a while
to create statistically significant baselines (to separate normal
behavior from anomalies); they are relatively open to attack during
this period.
Today, many antivirus packages include both signature-based and anomalybased detection characteristics, but only a few IDSs incorporate both approaches.
Most experts expect anomaly based detection to become more widespread in
IDSs, but research and programming breakthroughs will be necessary to deliver
the kind of capability that anomaly based detection should be, but is currently
not, able to deliver.
Finally, some IDSs are capable of responding to attacks when they occur.This
behavior is desirable from two points of view. For one thing, a computer system
can track behavior and activity in near-real time and respond much more quickly
and decisively during the early stages of an attack. Since automation helps hackers
mount attacks, it stands to reason that it should also help security professionals
fend them off as they occur. For another thing, IDSs run 24 hour per day/7 days
per week, but network administrators may not be able to respond as quickly
during off hours as they can during peak hours (even if the IDS can page them
with an alarm that an attack has begun). By automating a response to block
incoming traffic from one or more addresses from which an attack originates, the
IDS can halt an attack in process and block future attacks from the same address.
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Head of the Class…
Getting More Information on IDS
For quick access to a great set of articles and resources on IDS technology,
visit and search for intrusion detection.
There are several good articles to be found on this topic including, but not
limited to:
“Intrusion Detection: A Guide to the Options” at
“Intrusion-detection Systems Sniff Out Security Breaches”
“Recommendations for Deploying an Intrusion-detection
System” at
By implementing the following techniques, IDSs can fend off expert and
novice hackers alike. Although experts are more difficult to block entirely, these
techniques can slow them down considerably:
Breaking TCP connections by injecting reset packets into attacker connections causes attacks to fall apart.
Deploying automated packet filters to block routers or firewalls from
forwarding attack packets to servers or hosts under attack stops most
attacks cold—even DoS or Distributed Denial of Service (DDoS)
attacks.This works for attacker addresses and for protocols or services
under attack (by blocking traffic at different layers of the ARPA networking model, so to speak).
Deploying automated disconnects for routers, firewalls, or servers can
halt all activity when other measures fail to stop attackers (as in extreme
DDoS attack situations, where filtering would only work effectively on
the ISP side of an Internet link, if not higher up the ISP chain as close
to Internet backbones as possible).
Actively pursuing reverse DNS lookups or other ways of attempting to
establish hacker identity is a technique used by some IDSs, generating
reports of malicious activity to all ISPs in the routes used between the
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attacker and the attackee. Because such responses may themselves raise
legal issues, experts recommend obtaining legal advice before repaying
hackers in kind.
Signature-Based IDSs and Detection Evasion
An IDS is, quite simply, the high-tech equivalent of a burglar alarm configured to
monitor access points, hostile activities, and known intruders.These systems typically trigger on events by referencing network activity against an attack signature
database. If a match is made, an alert takes place and is logged for future reference. It
is the makeup of this signature database that is the Achilles heel of these systems.
Attack signatures consist of several components used to uniquely describe an
attack.The signature is a kind of detailed profile that is compiled by doing an
analysis of previous successful attacks. An ideal signature would be one that is specific to the attack, while being as simple as possible to match with the input data
stream (large complex signatures may pose a serious processing burden). Just as
there are varying types of attacks, there must be varying types of signatures. Some
signatures define the characteristics of a single IP option, perhaps that of an nmap
portscan, while others are derived from the actual payload of an attack.
Most signatures are constructed by running a known exploit several times,
monitoring the data as it appears on the network and looking for a unique pattern that is repeated on every execution.This method works fairly well at
ensuring that the signature will consistently match an attempt by that particular
exploit. Remember, the idea is for the unique identification of an attack, not
merely the detection of attacks.
Signatures are defined as a set of actions or events that constitute an
attack pattern. They are used for comparison in real time against actual
network events and conditions to determine if an active attack is taking
place against the network. The drawback of using attack signatures for
detection is that only those attacks for which there is a released signature will be detected. It is vitally important that the signature database
be kept up to date.
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A computing system, in its most basic abstraction, can be defined as a finite
state machine, which literally means that there are only a specific predefined
number of states that a system may attain.This limitation hinders the IDS, in that
it can be well armed at only a single point in time (in other words, as well armed
as the size of its database).This poses several problems:
First, how can one have foreknowledge of the internal characteristics
that make up an intrusion attempt that has not yet occurred? You cannot
alert on attacks you have never seen.
Second, there can be only educated guesses that what has happened in
the past may again transpire in the future.You can create a signature for a
past attack after the fact, but that is no guarantee you will ever see that
attack again.
Third, an IDS may be incapable of discerning a new attack from the
background white noise of any network.The network utilization may be
too high, or many false positives cause rules to be disabled.
And finally, the IDS may be incapacitated by even the slightest modification to a known attack. A weakness in the signature matching process, or
more fundamentally, a weakness in the packet analysis engine (packet
sniffing/reconstruction) will thwart any detection capability.
The goals of an attacker in relation to IDS evasion are twofold:
To evade detection completely
To use techniques and methods that increase the processing load of the
IDS sensor significantly
As more methods are employed by attackers on a wide scale, more vendors
will be forced to implement more complex signature matching and packet analysis engines.These complex systems will undoubtedly have lower operating
throughputs and will present more opportunities for evasion.The paradox is that
the more complex a system becomes, the more opportunities there are for vulnerabilities. Some say the ratio for bugs to code may be as high as 1:1,000, and
even conservatives say a ratio of 1:10,000 may exist.With these sorts of figures in
mind, a system of increasing complexity will undoubtedly lead to new levels of
increased insecurity.
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Popular Commercial IDS Systems
Literally hundreds of vendors offer various forms of commercial IDS implementations.The most effective solutions combine network- and host-based IDS
implementations. Likewise, most such implementations are primarily signaturebased, with only limited anomaly based detection capabilities present in certain
specific products or solutions. Finally, most modern IDSs include some limited
automatic response capabilities, but these usually concentrate on automated traffic
filtering, blocking, or disconnects as a last resort. Although some systems claim to
be able to launch counterstrikes against attacks, best practices indicate that automated identification and backtrace facilities are the most useful aspects that such
facilities provide and are therefore those most likely to be used.
A huge number of potential vendors can provide IDS products to companies
and organizations.Without specifically endorsing any particular vendor, the following products offer some of the most widely used and best-known solutions in
this product space:
Cisco Systems is best known for its switches and routers, but
offers significant firewall and intrusion detection products as well
GFI LANguard is a family of monitoring, scanning, and file integrity
check products that offer broad intrusion detection and response capabilities (
Internet Security Systems (ISS) offers a family of enterprise-class
security products called RealSecure that includes comprehensive intrusion detection and response capabilities (
Network-1 Security Solutions offers various families of desktop and
server (host-based) intrusion detection products, along with centralized
security management facilities and firewalls (
Tripwire is the best known vendor of file integrity and signaturechecking utilities (also known as Tripwire). But Tripwire also offers
integrity check products for routers, switches, and servers, along with
a centralized management console for its various products
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Head of the Class…
Weighing IDS Options
In addition to the various IDS vendors mentioned in the preceding list,
judicious use of a good Internet search engine can help network administrators identify more potential IDS suppliers than they would ever have
the time or inclination to investigate in detail. That is why we also urge
administrators to consider an alternative: deferring some or all of the
organization’s network security technology decisions to a special type of
outsourcing company. Known as managed security services providers
(MSSPs), these organizations help their customers select, install, and
maintain state-of-the-art security policies and technical infrastructures to
match. For example, Guardent is an MSSP that includes comprehensive
firewall and IDSs among its various customer services; visit for a description of the company’s various service
programs and offerings.
A clearinghouse for ISPs known as ISP-Planet offers all kinds of interesting
information online about MSSPs, plus related firewall,VPN, intrusion detection,
security monitoring, antivirus, and other security services. For more information,
visit any or all of the following URLs:
ISP-Planet Survey: Managed Security Service Providers, participating
provider’s chart:
Managed firewall services chart:
Managed virtual private networking chart:
Managed intrusion detection and security monitoring:
Managed antivirus and content filtering, and URL blocking:
Managed vulnerability assessment, emergency response, and forensics:
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Honeypots and Honeynets
A honeypot is a computer system that is deliberately exposed to public access—
usually on the Internet—for the express purpose of attracting and distracting
attackers. Likewise, a honeynet is a network set up for the same purpose, where
attackers not only find vulnerable services or servers but also find vulnerable
routers, firewalls, and other network boundary devices, security applications, and
so forth. In other words, these are the technical equivalent of the familiar police
“sting” operation. Although the strategy involved in luring hackers to spend time
investigating attractive network devices or servers can cause its own problems,
finding ways to lure intruders into a system or network improves the odds of
being able to identify those intruders and pursue them more effectively. Figure
7.15 shows a graphical representation of the honeypot concept in action.
Figure 7.15 A Honeypot in Use to Keep Attackers from Affecting Critical
Production Servers
Attacker spends all of their time attacking the honeypot because it looks
like a poorly configured and insecure production server.
The Internet
and DMZs
Production Server
Production Server
The honeypot provides
alerts to the network
administrator so they can
take defensive measures as
desired to stop or monitor
the attack.
The production servers continue operating without being
affected by the attempted attack.
The honeypot only appears to be a critical production server. However, it is running a special IDS package
that can intelligently respond to the attacker, track the attackers actions, and keep the attacker engaged while
important attack information is being collected. The attack signature that is collected can be used later to prevent
attacks of the same sort from actually succeeding against real servers. In most cases, the attacker never knows
the difference between the honeypot and a real server and thus makes no lasting damage to the network itself.
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Notes from the Underground…
Walking the Line Between
Opportunity and Entrapment
Most law enforcement officers are aware of the fine line they must walk
when setting up a “sting”—an operation in which police officers pretend
to be victims or participants in crime with the goal of getting criminal suspects to commit an illegal act in their presence. Most states have laws
that prohibit entrapment; that is, law enforcement officers are not
allowed to cause a person to commit a crime and then arrest him or her
for doing it. Entrapment is a defense to prosecution; if the accused
person can show at trial that he or she was entrapped, the result must be
an acquittal.
Courts have traditionally held, however, that providing a mere
opportunity for a criminal to commit a crime does not constitute entrapment. To entrap involves using persuasion, duress, or other undue pressure to force someone to commit a crime that the person would not
otherwise have committed. Under this holding, setting up a honeypot or
honeynet would be like the (perfectly legitimate) police tactic of placing
an abandoned automobile by the side of the road and watching it to see
if anyone attempts to burglarize, vandalize, or steal it. It should also be
noted that entrapment only applies to the actions of law enforcement or
government personnel. A civilian cannot entrap, regardless of how much
pressure is exerted on the target to commit the crime. (However, a civilian
could be subject to other charges, such as criminal solicitation or criminal
conspiracy, for causing someone else to commit a crime.)
The following characteristics are typical of honeypots or honeynets:
Systems or devices used as lures are set up with only “out of the box”
default installations so that they are deliberately made subject to all
known vulnerabilities, exploits, and attacks.
The systems or devices used as lures do not include sensitive information
(for example, passwords, data, applications, or services an organization
depends on or must absolutely protect), so these lures can be compromised, or even destroyed, without causing damage, loss, or harm to the
organization that presents them to be attacked.
Systems or devices used as lures often also contain deliberately tantalizing objects or resources, such as files named password.db, folders named
Top Secret, and so forth—often consisting only of encrypted garbage data
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or log files of no real significance or value—to attract and hold an
attacker’s interest long enough to give a backtrace a chance of identifying the attack’s point of origin.
Systems or devices used as lures also include or are monitored by passive
applications that can detect and report on attacks or intrusions as soon as
they start, so the process of backtracing and identification can begin as
soon as possible.
Although this technique can help identify the unwary or unsophisticated
attacker, it also runs the risk of attracting additional attention from savvier
attackers. Honeypots or honeynets, once identified, are often publicized on
hacker message boards or mailing lists and thus become more subject to attacks
and hacker activity than they otherwise might be. Likewise, if the organization
that sets up a honeypot or honeynet is itself identified, its production systems and
networks may also be subjected to more attacks than might otherwise occur.
A honeypot is a computer system that is deliberately exposed to public
access—usually on the Internet—for the express purpose of attracting
and distracting attackers. Likewise, a honeynet is a network set up for
the same purpose, where attackers not only find vulnerable services or
servers but also find vulnerable routers, firewalls, and other network
boundary devices, security applications, and so forth. You must know
these for the Security+ exam.
The honeypot technique is best reserved for use when a company or organization employs full-time IT security professionals who can monitor and deal with
these lures on a regular basis, or when law enforcement operations seek to target
specific suspects in a “virtual sting” operation. In such situations, the risks are sure
to be well understood, and proper security precautions, processes, and procedures
are far more likely to already be in place (and properly practiced). Nevertheless,
for organizations that seek to identify and pursue attackers more proactively, honeypots and honeynets can provide valuable tools to aid in such activities.
Although numerous quality resources on honeypots and honeynets are available (try searching on either term at, the following resources are particularly valuable for people seeking additional
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information on the topic. John McMullen’s article “Enhance Intrusion Detection
with a Honeypot” at
r00220010412mul01.htm&fromtm=e036 sheds additional light on this topic.The
Honeynet Project at is probably the best overall resource on
the topic online; it not only provides copious information on the project’s work
to define and document standard honeypots and honeynets, it also does a great
job of exploring hacker mindsets, motivations, tools, and attack techniques.
Judging False Positives and Negatives
To be an effective tool, an IDS must be able to digest and report information
efficiently. A false positive is a triggered event that did not actually occur, and may
be as innocuous as the download of a signature database (downloading of an IDS
signature database may trigger every alarm in the book) or some unusual traffic
generated by a networked game.This, although annoying, is usually not of much
consequence, but can easily happen and is usually tuned down by an initial configuration and burn-in of a network IDS (NIDS) configuration. More dangerous,
however, is the possibility for a false negative, which is the failure to be alerted to
an actual event.This would occur in a failure of one of the key functional units
of a NIDS. False negatives are the product of a situation in which an attacker
modifies the attack payload in order to subvert the detection engine.
False positives have a significant impact on the effectiveness of an IDS sensor.
If there are a reasonable number of false positives being detected, the perceived
urgency of an alert may be diminished by the fact that there are numerous events
being triggered on a daily basis that turn into wild goose chases. In the end, all
the power of IDS is ultimately controlled by a single judgment call on whether
or not to take action.
A false positive is defined as a positive detection result that is false or
untrue. This can be dangerous because you may spend wasted time
trying to put together the facts of the case and look for a weakness in
your system. A false negative, on the other hand, is a negative detection
event that is actually positive or true. False negatives are much more
costly than false positives, as a false negative gives you the feeling that
everything is OK, all the while an attacker has comprised your systems
and is helping themselves to your sensitive and valuable data.
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Incident Response
The first thing that must be done after receiving notification of an attack is to
respond to the attack. In some cases the administrator may want to allow the
attack to continue for a short period of time so that they can collect further data
and other evidence about the attack, its origin, and its methods. After terminating
the attack, or upon discovering the evidence of the attack, they must take all
available steps to ensure that the chain of evidence will not be lost.They must
save and export log and audit files and close open ports that have been exploited
and secure services that should not have been running in the first place. In short,
take every available step to ensure that the same type of attack will not occur
again some time in the future.
For more detailed information about the practical and legal aspects of
incident response, see Scene of the Cybercrime: Computer Forensics
Handbook (ISBN: 1-928994-29-6), published by Syngress.
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Summary of Exam Objectives
In today’s networking world, networks no longer have to be designed the same
way.There are many options available as to how to physically and logically design
a network. All of these options can be used to increase the security of the
internal network by keeping untrusted and unauthorized users out.The usage of
DMZs to segment Web and e-mail traffic to a protected zone between external
and internal firewalls helps prevent attacks that may deface the Web server from
having any effect on the critical database servers. Just the same, an attack on your
Web server will have little lasting damage.
A NAT device can be used to hide the private intranet from the public
Internet. NAT devices work by translating all private IP addresses into one or more
public IP addresses, therefore making it look as if all traffic from the internal network is coming from one computer (or a small group of computers).The NAT
device maintains a routing table of all connection requests and therefore is able to
ensure that all returning packets get directed to the correct originating host.
Extranets can be establishing using VPN tunnels to provide secure access to intranet
resources from different geographic locations.VPNs are also used to allow remote
network users to securely connect back to the corporate network.
IDSs are used to identify and respond to attacks on the network. Several types
of IDSs exist, each with its own unique pros and cons.Which type you choose
depends on your needs, and ultimately on your budget. Honeypots are very
advanced IDSs that can intelligently respond to attacks, actually enticing the
attacker to select them over other real targets on the network. Honeypots can be
used to distract attackers from real servers and keep them occupied while you
collect information on the attack and the source of the attack.
After an attack has occurred, the most important thing to do is to collect all
of the evidence of the attack and its methods.You will also want to take steps to
ensure that the same type of attack cannot be successfully performed on the network in the future.
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Exam Objectives Fast Track
Security Topologies
; A DMZ is a network segment where systems accessible to the public
Internet are housed and which offers some basic levels of protection
against attacks.
; The creation of DMZ segments is usually done by placing systems
between two firewall devices that have different rule sets.This allows
systems on the Internet to connect to the offered services on the DMZ
systems but not to the computers on the internal segments of the
organization (often called the protected network).
; A private internal network is called the intranet, as opposed to the
Internet (which is the large publicly accessible network). It is expected
that all traffic on an intranet will be secure from outside attack or
; An extranet is a special topology that is implemented in certain cases
where there is a need to allow access to some of the internal network
data and resources by users outside of the internal network.
; Using special features found in newer, more expensive switches and
special software in the switch, you can physically split one switch into
two, thus creating two network segments that are completely separate
from one another and creating a VLAN.
; NAT is a feature of many firewalls, proxies, and routing-capable systems.
NAT has several benefits, one of which is its ability to hide the IP
addresses and network design of the internal network.The ability to hide
the internal network from the Internet reduces the risk of intruders
gleaning information about the network and exploiting that information
to gain access. If an intruder does not know the structure of a network,
the network layout, the names and IP address of systems, and so on, it is
very difficult to gain access to that network.
; Tunneling is used to create a virtual point-to-point connection between
you and your destination using an untrusted public network as the
medium. In most cases, this would be the Internet.When you establish
a secure tunnel, commonly called a VPN, you are creating a safe
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connection between two points that cannot be examined by outsiders.
All packets are encrypted and carry information that ensure they are
tamperproof and thus can withstand common IP attacks, such as the
MITM and packet replay.When a VPN is created, you can be reasonably
secure that the traffic is private and safe from prying eyes.
Intrusion Detection
; An IDS is a specialized tool that knows how to read and interpret the
contents of log files from routers, firewalls, servers, and other network
devices. Furthermore, an IDS often stores a database of known attack
signatures and can compare patterns of activity, traffic, or behavior it sees
in the logs it is monitoring against those signatures to recognize when a
close match between a signature and current or recent behavior occurs.
At that point, the IDS can issue alarms or alerts, take various kinds of
automatic action ranging from shutting down Internet links or specific
servers to launching backtraces, and make other active attempts to
identify attackers and actively collect evidence of their nefarious activities.
; IDSs that monitor network backbones and look for attack signatures are
called network-based IDSs, whereas those that operate on hosts defend
and monitor the operating and file systems for signs of intrusion and are
called host-based IDSs. Some IDSs monitor only specific applications
and are called application-based IDSs. (This type of treatment is usually
reserved for important applications such as database management
systems, content management systems, accounting systems, and so forth.)
; IDSs may also be distinguished by their differing approaches to event
analysis. Some IDSs primarily use a technique called signature detection.
This resembles the way many antivirus programs use virus signatures to
recognize and block infected files, programs, or active Web content from
entering a computer system, except that it uses a database of traffic or
activity patterns related to known attacks, called attack signatures.
Signature detection is the most widely used approach in commercial
IDS technology today. Another approach is called anomaly detection. It
uses rules or predefined concepts about “normal” and “abnormal” system
activity (called heuristics) to distinguish anomalies from normal system
behavior and to monitor, report on, or block anomalies as they occur.
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; A honeypot is a computer system that is deliberately exposed to public
access—usually on the Internet—for the express purpose of attracting
and distracting attackers. Likewise, a honeynet is a network set up for the
same purpose, where attackers find vulnerable services or servers and
also find vulnerable routers, firewalls, and other network boundary
devices, security applications, and so forth.
Exam Objectives
Frequently Asked Questions
The following Frequently Asked Questions, answered by the authors of this book,
are designed to both measure your understanding of the Exam Objectives
presented in this chapter, and to assist you with real-life implementation of
these concepts.
Q: Why do I need to create a DMZ for my Web and e-mail servers? Can’t I just
put all of my computers behind my firewall on my intranet?
A: You can, but by doing so you open yourself up to all sorts of attacks that you
would otherwise be protected from if you allow outside users to access any of
those resources.You need a DMZ if you want to make certain resources available to outside users over the Internet (for example, if you want to host a
Web server). By placing certain computers, such as Web servers and front-end
e-mail servers, on a DMZ, you can keep these often abused ports controlled
on your internal firewall (by controlling access by IP address), thus lessening
the chance of a successful attack on your intranet.
Q: What advantage does a honeypot offer me over a traditional IDS system?
A: A honeypot is a very intelligent IDS that not only monitors an attacker, but
also interacts with attackers, keeping them interested in the honeypot and
away from the real production servers on your network.While the attacker is
distracted and examining the non-critical data they find in the honeypot, you
have more time to track the attacker’s identity.
Q: What is the difference between an Internet, intranet, and extranet? Aren’t
they all terms for the same thing?
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A: An internet (with a lowercase “i”) is simply a network of networks that are
connected together.When denoted with a capital “I,” the word refers to the
global Internet, the biggest public network in existence, which grew out of
the ARPANet project. An intranet is a private internal network available to
users within the organization, whereas an extranet is a special topology that is
implemented in certain cases where you have a need to allow access to some
of your internal network data and resources by users outside of your internal
Q: What type of IDS should I choose?
A: The type of IDS you choose to employ on your network will depend on
what type of network you have and what types of applications you are running. Host-based IDSs can effectively monitor one specific computer, but not
the entire network. Network-based IDSs can monitor the entire network
from a high-level view, but may miss some type of attacks. Application-based
IDSs are specific to one application, such as a database application, and will
monitor attacks only on that application.
Q: Why would I want to use a VLAN?
A: VLANs can be used to segment network traffic into different broadcast
domains.This adds another layer of security for your network by keeping certain traffic segmented from the rest of your network traffic—all inside of your
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Self Test
A Quick Answer Key follows the Self Test questions. For complete questions,
answers, and epxlanations to the Self Test questions in this chapter as well as
the other chapters in this book, see the Self Test Appendix.
Security Topologies Questions
1. Rob has two Web servers he needs to protect from attacks. He also needs to
protect the rest of his intranet from all sorts of attacks.What type of network
topology could he implement to protect his Web servers, allowing access to
them, but also providing protection for his intranet?
A. Rob needs to implement WEP128 on his Web servers to require strong
B. Rob should create a DMZ and place his Web servers in it. He should
place his intranet behind the internal firewall.
C. Rob should place a honeypot on his network.
D. Rob should replace his copper-based CAT 5 cabling with fiber optic
2. Hannah wants to configure a VLAN on her network.What advantage can
Hannah expect to get out of a VLAN?
A. It will segment traffic on the internal network for increased security.
B. It will create a DMZ to protect her Web servers from attacks.
C. It will hide her internal network IP addresses from being seen on
the Internet.
D. It will provide a secure tunnel from her intranet to the intranet of a
partner company.
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3. What is the area of the network that typically contains public DNS servers
and Web servers?
A. Firewall
4. Rick is a security auditor for your company. He is in the process of
attempting to attack one of your servers but when you check all of your
production servers, you detect no attacks happening.Why is this so?
A. Rick is actually attacking a server in someone else’s network.
B. Rick is actually attacking a honeypot, not a production server.
C. Rick is being stopped at the firewall.
D. Rick is using the wrong account with which to launch the attack.
5. What types of computers might you expect to find located on an intranet?
(Choose all that apply)
A. Publicly accessible DNS servers
B. Public Web servers
C. SQL 2000 servers
D. User workstations
6. Which of the following protocols can be used to secure a VPN connection?
D. AppleTalk
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7. You need to be able to connect your intranet with the intranet of a business
partner. As far as your network is concerned, what is the correct name for
the partner’s network?
A. Internet
C. Extranet
D. Sneakernet
8. What network topology area will most likely contain critical servers, such as
SQL servers, private Web servers, or domain controllers?
B. Internet
C. Extranet
D. Intranet
Intrusion Detection Questions
9. Jon wants to configure a honeypot on his network to protect his production
servers from damage caused by Internet-based attackers. Can a honeypot be
used to accomplish this goal and why?
A. No, a honeypot does not provide protective measures for the network.
B. Yes, a honeypot can be used to keep an attacker away from real production servers.
C. Yes, a honeypot will prevent an attacker from seeing real production
D. No, a honeypot only provides protection from attacks that originate
from inside his network.
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10. You are interviewing a candidate for the position of assistant security
administrator for your organization.You ask the individual to tell you what a
honeypot is.Which of the following answers is correct?
A. A network depository that can be used to safeguard and store passwords.
B. A safe place to store backup media that provides environmental
C. A fake system put in place on the network to attract attackers and keep
them attacking your real computers.
D. A special firewall device that is often installed with a T1 line to prevent
backtracing of packets to the Network Operations Center.
11. You have installed an Active IDS system onto your network.When an attack
occurs and is detected by your new IDS, what might you expect it to do?
(Choose all that apply)
A. Inform the attacker that his or her actions may be monitored as part of
the network AUP.
B. Disable a service or services.
C. Terminate the connection after a predefined amount of time.
D. Shut down a server or servers.
12. You have an IDS system running only on one computer in your network.
What type of IDS system is this?
A. Active
B. Host
C. Network
D. Anomaly
13. You have detected an attack against your network.Which of the following
are things that you should do as soon as possible? (Choose all that apply)
A. Call the police.
B. Preserve all evidence
C. Convert to Linux
D. Call Microsoft Product Support Services
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14. You have detected an attack against your network.Your server log shows the
originating IP address, but you need to determine what domain it came
from. How can you do this?
A. Perform a reverse DNS lookup.
B. Ping the root server.
C. Examine your DNS server’s A records.
D. Call your ISP to have them locate the required information for you.
15. After analyzing a suspected attack, you incorrectly determine that an attack
has occurred, when in fact one has not occurred.What is this called?
A. False positive
B. False negative
C. Honeypot
D. Signature based IDS
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Self Test Quick Answer Key
For complete questions, answers, and epxlanations to the Self Test questions
in this chapter as well as the other chapters in this book, see the Self Test
1. B
9. B
2. A
10. C
3. B
11. B, C, and D
4. B
12. B
5. C and D
13. A and B
6. C
14. A
7. C
15. A
8. D
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Chapter 8
System Hardening
Domain 3.0 Objectives in this Chapter:
Concepts and Processes of OS and NOS
Network Hardening
Application Hardening
Exam Objectives Review:
Summary of Exam Objectives
Exam Objectives Fast Track
Exam Objectives Frequently Asked Questions
Self Test
Self Test Quick Answer Key
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Security+ technicians need to fully understand the fundamentals of system hardening (also described as “locking down” the system).This knowledge is needed
not only to pass the Security+ exam, but also to work in the field of information
security.You will learn that the skills needed to detect breeches and exploits are
an essential part of the security technician’s repertoire.
The Security+ exam covers the general fundamentals of hardening.This
chapter covers the hardening methods and techniques that can be applied on various systems in the following broad categories:
Operating system-based hardening, which includes information about
securing and hardening various operating systems (client and server), as
well as methods to secure file systems.
Network-based hardening, which examines the procedures and methods
of hardening network devices, services, and protocols.
Application-based hardening, which explores the many things that must
be done to harden and secure application servers, including e-mail and
Web servers.
The first topic covered is operating system (OS) hardening, which covers
important concepts such as locking down file systems and methods for configuring file systems properly to limit access and reduce the possibility of breech.
Many OS default configurations do not provide an optimum level of security
because priority is given to those who need access to data. Even so-called
“secure” OSs may have been configured incorrectly to allow full access.Thus, it is
important to modify OS settings to harden the system for access control. Other
topics covered in the area of OS hardening are how to receive, test, and apply service packs and hotfixes to secure potential vulnerabilities in systems.
Network-based hardening is another important topic that Security+ technicians need to understand. Many network-based devices, such as routers and
switches, must be secured to stop unauthorized individuals from updating the
firmware installed on them, or modifying or installing configurations such as
access control lists (ACLs).This chapter also looks at disabling unneeded services
and protocols on a network. It is important that Security+ technicians know
what services they need and how to disable those they do not need.This can
eliminate headaches and make the network more secure.
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Application-based hardening explores the fundamentals of securing Domain
Name Servers (DNS), Dynamic Host Control Protocol (DHCP), databases, and
other applications, systems, and services on a network.
Concepts and Processes
of OS and NOS Hardening
System security and hardening is the process of building a barrier between the
network and those who would do it harm.The key is to make the barrier more
difficult to cross than anyone else’s. In other words, IT security involves creating a
deterrent to convince a would-be-attacker that a system is more difficult to
breach than some other system.
Let’s start with hardening the OS and network operating system (NOS) environments.This area includes concepts previously studied such as access control,
authentication, and auditing (AAA), media access control (MAC), discretionary
access control (DAC), role-based access control (RBAC), and auditing (discussed
in Chapter 1), as well as a number of sublevels including:
File security
Service packs
When looking at ways to provide file and directory security, you must first
look at how file security can be structured.
Start with everything accessible and lock down the things you want to
Start with everything locked down and open up the things you want to
allow access to
File security is established following the rule of least privilege. Least privilege is
when you start with the most secure environment and then loosen the controls as
needed. Using this method works to be as restrictive as possible with the authorizations provided to users, processes, or applications that access these resources.
Accessibility and security are at opposite ends of the spectrum; the more convenient it is for users to access data, the less secure the network.While looking at
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hardening security through permissions (e.g., AAA), administrators should also
consider updating the methods used to access the resources. It is important to
look at the use and appropriateness of MAC, DAC, and RBAC in controlling
access appropriately, and to coordinate this effort with the establishment of file
system controls.
Head of the Class…
Wide Open or Locked Down? Why Is It Important?
It is important to understand the difference in philosophy from different
manufacturers and within the network security profession. For example,
some vendors use the “allow all unless explicitly denied” method, while
others use the “deny all unless explicitly allowed” method. Each of these
methods has advantages and disadvantages that affect how to prepare
for and implement the hardening process. The “allow all unless explicitly
denied” method allows the security professional to define what they
want to restrict. However, this method may also be more difficult, as
something may be missed that should be restricted. The “deny all unless
explicitly allowed” method restricts everything from the start. While more
secure, this method requires significant administrative effort to analyze
and track the conditions that may need to be loosened, and to implement
those changes.
Other tasks within the OS and NOS hardening area include keeping track of
updates, hotfixes, service packs, and patches.This can be overwhelming, because
these items are delivered at an incredibly rapid rate. Not only are there a lot of
them, but many of the vulnerabilities they address may not apply to a particular
system. Administrators need to make a huge effort to evaluate the need for each
fix or patch. It is very important to fully test the upgrades, patches, service packs,
and hotfixes on test equipment that parallels the live environment. It is never recommended or prudent to apply these “fixes” to production systems without
testing, as sometimes the “fix” ends up breaking critical services or applications.
The following sections discuss and explore methods used to stiffen defenses
and reduce vulnerabilities that exist in systems. Following are some of the ways
that physical systems can be protected:
Protecting files and resources
Applying and maintaining patches
Working with product updates
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File System Controlling access is an important element in maintaining system security.The
Head of the Class…
most secure environments follow the “least privileged” principle, as mentioned
earlier.This principle states that users are granted the least amount of access possible that still enables them to complete their required work tasks. Expansions to
that access are carefully considered before being implemented. Law enforcement
officers and those in government agencies are familiar with this principle
regarding non-computerized information, where the concept is usually termed
need to know. Generally, following this principle means that network administrators receive more complaints from users unable to access resources. However,
receiving complaints from unauthorized users is better than suffering access violations that damage an organization’s profitability or capability to conduct business.
(For more detailed explanations of these principles, refer to Chapter 11.)
In practice, maintaining the least privileged principle directly affects the level
of administrative, management, and auditing overhead, increasing the levels
required to implement and maintain the environment. One alternative, the use of
user groups, is a great time saver. Instead of assigning individual access controls,
groups of similar users are assigned the same access. In cases where all users in a
group have exactly the same access needs, this method works. However, in many
cases, individual users need more or less access than other group members.When
security is important, the extra effort to fine-tune individual user access provides
greater control over what each user can and cannot access.
How Should We Work with File System Access?
Despite the emphasis on group-based access permissions, a much higher
level of security can be attained in all operating platforms by individually
assigning access permissions. Administratively, however, it is difficult to
justify the expense and time involved in tracking, creating, and verifying
individual access permissions for thousands of users trying to access thousands of individual resources. RBAC is a method used to accomplish the
goal of achieving the status of least privileged access. It requires more
design and effort to start the implementation, but develops a much
higher level of control than does the use of groups.
Good practice indicates that the default permissions allowed in most
OS environments are designed for convenience, not security. For this
reason, it is important to be diligent in removing and restructuring these
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Keeping individual user access as specific as possible limits some threats, such
as the possibility that a single compromised user account could grant a hacker
unrestricted access. It does not, however, prevent the compromise of more privileged accounts, such as those of administrators or specific service operators. It
does force intruders to focus their efforts on the privileged accounts, where
stronger passwords are enforced and more auditing and monitoring of account
use occurs. Figure 8.1 displays a possible path for consideration and creation of
file system access.
Figure 8.1 File Security Steps
Evaluate the
Decision on
Updates Updates for OSs and NOSs are provided by the manufacturer of the specific
component. Updates contain improvements to the OS, and new or improved
components the manufacturer believes will make the product more stable, usable,
secure, or otherwise attractive to end users. For example, Microsoft updates are
often specifically labeled Security Updates.These updates address security concerns
recognized by Microsoft, and should be evaluated and installed as needed. In
addition, updates may enhance the capability of a function within the system that
was underdeveloped at the time the system or application was released. Updates
should be thoroughly tested in non-production environments before implementation. It is possible that a “new and improved” function (especially one that
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Damage & Defense…
enhances user convenience) may actually allow more potential for security breach
than the original component. Complete testing is a must.
Updates, Hotfixes, Patches, and….
Affected by the Nimda worm? Problems with Code Red? Most of those
infections and much of the down time could have been avoided if security and network professionals had taken the time to download, evaluate,
and install patches for vulnerabilities known to exist. Although these two
conditions were curable with the use of antivirus solutions, the proliferation of these problems would not have been as intense had administrators and security professionals worked more diligently to protect their
systems. As the emphasis over the past couple of years has switched to
security and integrity, more problems have been recognized in all platforms. Be aware that although you will rarely get recognition for not
being hacked, you will most certainly be recognized (and perhaps no
longer employed) if your systems are hacked and negligence is shown on
your part. Always be sure to test recommended updates and patches in a
non-production environment first, to ensure full compatibility with your
Hotfixes are repair components designed to repair problems occurring on relatively small numbers of workstations or servers. Hotfixes are generally created by
the vendor when a number of clients indicate that there is a compatibility or
functional problem with a manufacturer’s products used on particular hardware
platforms.These are mainly fixes for known or reported problems that may be
limited in scope. As with the implementation of updates, these should be thoroughly tested in a non-production environment for compatibility and functionality before being used in a production environment. Because these are generally
limited in function, it is not a good practice to install them on every machine.
Rather, they should only be installed as needed to correct a specific problem.
To enhance your understanding of the hotfix deployment process, refer to
the Microsoft Windows 2000 Hotfix Installation and Deployment Guide.You can find
this document at
sp3/HFDeploy.htm.This document explains some of the reasoning discussed
about the deployment process, as well as methods of removal should it be
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Service Packs
Service packs are accumulated sets of updates or hotfixes. Service packs are usually tested over a wide range of hardware and applications in an attempt to assure
compatibility with existing patches and updates, and to initiate much broader
coverage than just hotfixes.The recommendations discussed previously apply to
service pack installation as well. Service packs must be fully tested and verified
before being installed on live systems. Although most vendors of OS software
attempt to test all of the components of a service pack before distribution, it is
impossible for them to test every possible system configuration that may be
encountered in the field, so it is up to the administrator to test their own.The
purpose is to slow or deter compromise, provide security for resources, and assure
Damage & Defense…
What Should I Do to Try to Minimize Problems With
Updates, Service Packs, Patches, and Hotfixes?
1. Read the instructions! Most repair procedures include information about their applicability to systems, system requirements,
removal of previous repairs, or other conditions.
2. Install and test in a non-production environment, not on live
3. If offered, use the option to backup the existing components
for repair if the update fails.
4. Verify that the condition that is supposed to be updated or
repaired is actually repaired.
5. Document the repair.
Patches for OSs and NOSs are available from the vendor supplying the product.
These are available by way of the vendor’s Web site or from mirror sites around
the world.They are often security related, and may be grouped together into a
cumulative patch, to repair many problems at once. Since patches are issued at
unpredictable intervals, it is important to stay on top of their availability and
install them after they have been tested and evaluated in a non-production environment.The exception to this is when preparing a new, clean install. In this case,
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it is wise to download and install all known patches prior to introducing the
machines to the network.
Where can you get updates, service packs, hotfixes, and patches? Most
vendors of OSs and NOSs have Web-based download sites that offer this
information. In this exercise, you may use any Internet browser you have
available, and explore the sites of the various vendors that can provide
these items.
Begin by visiting the following sites. Please take a moment to record
where you found the resources as you proceed through the list.
Service Packs
Red Hat
The answer is “yes” in the case of Novell, Microsoft, Mandrake, and
Apple. The answer is “maybe” in the case of Red Hat, as they now
operate an automatic updating service on the desktop, and so do not
always provide the repairs separately. Some vendors require users to purchase a service subscription before downloading the software or
firmware updates, patches, and fixes.
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The Security+ exam requires good knowledge of the hardening processes. It includes questions relating to hardening that you may not have
thought about. For example, hardening can include concepts present in
other security areas, such as locking doors, restricting physical access,
and protecting the system from natural or unnatural disasters.
Network Hardening
When discussing network hardening, there are a number of concerns that are separate from those realized while evaluating and hardening OSs and NOSs.The
appropriate firmware and OS updates implemented on hardware must be evaluated, tested, and implemented. In addition, network configurations must be as
tight as possible.This includes developing appropriate rule sets and not allowing
unnecessary protocol or service access to other areas of the network.To keep
access as restrictive as possible, administrators should follow the principle of least
privilege, and not allow any services, protocols, or transports to operate that are
not defined as critical or necessary to the operation of the networks. It may be
appropriate to implement new technologies while in the network hardening process. Evaluation of Intrusion Detection Systems (IDS), firewall products, and antivirus solutions are also appropriate to hardening networks. Monitoring systems
must be checked and adjusted to verify that the network portion of the system is
secure. Administrators must remain vigilant and proactive in maintaining these
entryways into their environments to ensure that they have done everything possible to eliminate a breach or attack.
This section looks at the types of actions security professionals must take to
limit or reduce attacks, accidental damage, or destruction through their networks.
It also discusses recommendations for the appropriate application, timing, and
installation of updates to the firmware being used and to the OS in the network
device. Additionally, recommendations and best practices for the configuration of
network devices and whether there is a need to disable or enable services and
protocols within a network scope are explored. Finally, recommendations and
procedures for establishing appropriate access control levels for devices and systems within a network are discussed.
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Updates (Firmware) Firmware updates, like software updates, are provided by the manufacturer of the
hardware device being used.These updates generally fix incompatibility issues or
device operation problems, and should be applied if the update involves a repair
for an existing condition, or if it will make the equipment more secure, more
functional, or extends its operational life. It is always necessary to install and test
firmware updates in a non-production environment, to verify that the update
contains the necessary repairs and benefits that are needed. After sufficient testing
of the update and its functionality, it can be installed on other devices of the same
type, as appropriate.
Configuration Configuration of network devices (such as routers and switches) with default
installation settings leaves a system extremely vulnerable. It is of paramount importance that administrators understand the limitations of default settings. Ideally, configurations should be tested and assured prior to implementation of the devices on
a live network. Often, basic device configurations are set for convenience and not
for control and security. It is easier to operate some devices with just the default
settings, but in many cases, there is a corresponding loss of security.
Improperly configured or improperly secured devices left with default configurations will draw attackers if connected to the Internet. It is important to
understand the ramifications of the settings made on any network device connected to a foreign or uncontrolled network.
Enabling and Disabling Services and Protocols
When considering whether to enable and disable services and protocols in relation
to network hardening, there are extra tasks that must be done to protect the network and its internal systems. As with the OSs and NOSs discussed earlier, it is
important to evaluate the current needs and conditions of the network and infrastructure, and then begin to eliminate unnecessary services and protocols.This leads
to a cleaner network structure, more capacity, and less vulnerability to attack.
It is obvious that unnecessary protocols should be eliminated. For most that
means eliminating Internetwork Packet Exchange (IPX), Sequenced Packet
Exchange (SPX), and/or Netbios Extended User Interface (NetBEUI). It is also
important to look at the specific operational protocols used in a network such as
Internet Control Messaging Protocol (ICMP), Internet Group Management
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Protocol (IGMP), Service Advertising Protocol (SAP), and the Network Basic
Input/Output System (NetBIOS) functionality associated with Server Message
Block (SMB) transmissions in Windows-based systems.
As you begin to evaluate the need to remove protocols and services,
make sure that the items you are removing are within your area of control. Consult with your system administrator on the appropriate action to
take, and make sure you have prepared a plan to back out and recover if
you make a mistake.
While considering removal of non-essential protocols, it is important to look at
every area of the network to determine what is actually occurring and running on
the system.The appropriate tools are needed to do this and the Internet contains a
wealth of resources for tools and information to analyze and inspect systems.
A number of functional (and free) tools can be found at sites such as Among these, tools like SuperScan
3.0 are extremely useful in the evaluation process. If working in a mixed environment with UNIX and Linux machines or NetWare machines, a tool such as Big
Brother may be downloaded and evaluated (or in some cases used without
charge) by visiting Another multiplatform tool with analysis potential is LANGuard Network Security Scanner, available for download and evaluation at tools can be used to monitor and
report on multiple platforms, giving a better view of what is present in a environment. Many tools are also available for free at In Linuxbased systems, non-essential services can be controlled in different ways
depending on the distribution being worked with.This may include editing or
making changes to xinetd.conf or inetd.conf, or use of the graphical Linuxconf or
ntsysv utilities. It may also include use of ipchains or iptables in various versions to
restrict the options available for connection at a firewall.
Windows NT-based platforms allow the configuration of OS and network
services from provided administrative tools.This can include a service applet in a
control panel in NT versions, or a Microsoft Management Console (MMC) tool
in a Windows 2000/XP/.NET environment. It may also be possible to check or
modify configurations at the network adaptor properties and configuration pages.
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Notes From the Underground…
In either case, it is important to restrict access and thus limit vulnerability due to
unused or unnecessary services or protocols.
While discussing the concepts of enabling and disabling protocols and services, we need to take a moment to work with a tool that is used to check the
status of a network and its potential vulnerabilities. Exercise 8.02 uses
Foundstone’s SuperScan 3.0 to look at the configuration of a network, specifically to generate a discussion and overview of the services and protocols that
might be considered when thinking about restricting access at various levels.
SuperScan 3.0 is used to scan ports; it is not a security scanner. Security scanners
that can be used to detail OS, NOS, and hardware or protocol vulnerabilities
include products like Big Brother and LANGuard Network Security Scanner,
mentioned earlier. If using a UNIX-based platform, a number of evaluation tools
have been developed, such as Nmap (Network Mapper), which is capable of both
port and security scans. Although Exercise 8.02 discusses potential vulnerabilities
and the tightening of various OS and NOS platforms, the discussion can also be
applied to the network devices being used.
Eliminate External NetBIOS Traffic
One of the most common methods of obtaining access to a Windowsbased system and then gaining control of that system is through NetBIOS
traffic. Windows-based systems use NetBIOS in conjunction with Server
Message Blocks (SMBs) to exchange service information and establish
secure channel communications between machines for session maintenance. If file and print sharing is enabled on a Windows 9.x, Windows
ME, Windows 2000, XP, or .NET 2003 machine, or server service is enabled
on a Windows NT machine, NetBIOS traffic can be viewed on the external
network unless it has been disabled on the external interface. With the
proliferation of DSL, Broadband, and other “always on” connections to
the Internet, it is vital that this functionality be disabled on all interfaces
exposed to the Internet. If you do not, you might as well publish your network information on your Web site, because it will be available to anyone
who wants it.
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In this exercise, you are going to examine a network to identify open
ports and what could be potential problems or holes in the network
interfaces. For purposes of this exercise, you are going to use
Foundstone’s SuperScan 3.0, which you can download and install for
free prior to starting the exercise by going to
knowledge/free_tools.html and selecting the download tool. This tool
is available for Windows OS machines only, and although not specifically
mentioned, works well on Windows XP machines.
To begin the exercise, launch the SuperScan application. When it is
open, configure the program for the exercise by performing the following steps:
1. In the Scan Type section, select Only Scan Responsive and All
Selected Ports in List.
2. In the Configuration section, select Port List Setup.
3. In the Port List Setup window, scroll through the list and select
any ports that list services you know of, expect to see, or think
may be present on the network. This is accomplished by doubleclicking the port name.
4. When finished selecting the ports you want to scan, save the port
list configuration to the default location.
5. In the Internet Protocol (IP) section, enter the start and end ranges
of the network or the range of addresses you want to explore.
6. Leave the top two fields blank, and press the Start button to initiate scanning.
When the scan is complete, a window should appear that looks like
the one shown in Figure 8.2.
In this figure, notice that you can expand the IP address of the
scanned host, and view the ports from the list configuration that
responded to the probe. You can see from the example that there are a
number of ports open on the hosts that were probed. (Note that these
machines are in an internal network, so some of them are allowed.)
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Figure 8.2 Showing a Completed Scan Operation
Figure 8.3 identifies some characteristics and information about the
probed system that are useful in the tracking and analysis of holes and
vulnerabilities. First, this machine is Windows based, probably of the
Windows 9.x genre. This statement is based on the fact that the machine
has port 139 open for NetBIOS sessions, and Windows-based machines
with file and print sharing enabled use ports 137, 138, or 139 to accommodate traffic. It is unlikely that this machine is a Windows 2000 Class
Figure 8.4 shows what appears to be a Windows 2000-based
machine. This assessment comes from two specific open ports: port 139
indicates NetBIOS communication, and port 445 is used for Microsoft’s
Directory Services only on Windows 2000 class machines.
Figure 8.5 shows different ports as being open than those seen in the
Windows-based scans. Port 22 is for secure communication via Secure
Shell (SSH) login in a terminal session, and port 111 is for Remote
Procedure Calls (RPCs), used for network file system (NFS) commands
and communication in UNIX-based systems, and installed by default in
Linux distributions.
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Figure 8.3 Displaying Open Ports on a Win9.x Machine After Scan
Figure 8.4 Displaying Windows 2000 Class Open Ports After Scanning.
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Figure 8.5 Displaying UNIX-based Open Ports After Scanning
After the scan is complete and the open ports have been evaluated
by the scanning tools, decisions must be made as to which of these
ports are likely to be vulnerable, and then the risks of the vulnerability
weighed against the need for the particular service connected to that
port. Port vulnerabilities are constantly updated by various vendors, and
should be reviewed and evaluated for risk at regular intervals to reduce
potential problems. A list of known uses for ports can be found at
In the Win9.x and Windows 2000 systems, port 139 is open. In an
internal, isolated network, this port is used for NetBIOS traffic, which
allows file sharing and print sharing on Windows platforms. However, on
a network with an external interface, this should be shut off. In Windows
9.x, NetBIOS should be separated from the adapter’s properties pages. In
Windows 2000 and Windows XP, NetBIOS can be disabled by selecting
the WINS tab under Advanced properties in the TCP/IP settings, as illustrated in Figure 8.6. This is a per-adapter setting. If the functionality of
having NetBIOS communication enabled in the network is needed, SMB
signing, which partially secures the shared communication, could offer
some protection to the transmission of information. However, some
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functionality of NetBIOS dependent applications may be lost, which, in
some cases, will not operate without the NetBIOS capability in use.
Figure 8.6 Disabling NetBIOS over TCP/IP in Windows 2000 or
Windows XP
Earlier in this exercise, it was mentioned that the Windows 2000 scan
showed port 445 as open, which is for Microsoft’s Directory Services.
However, port 445 is actually used in a NetBIOS manner for browsing the
network. This port is not used by default; normal communication occurs
on TCP port 139, which carries SMB traffic on the Netbios over TCP/IP
(NBT) transport. If NBT is enabled on a client, it will try to connect at
ports 139 and 445 simultaneously. If there’s a response from port 445, it
sends an RST (TCP reset) to port 139 and only uses port 445 for the SMB
session. If no response, it uses port 139 only. If no response from either,
the session fails.
This is a good alternative if the SMB requirements only include
Windows 2000 or newer Windows systems, because this would eliminate
NetBIOS traffic and its associated vulnerabilities.
In the case of the Linux system seen earlier, ports 111 and 22 are
open. Port 22 is necessary because it is used for SSH authentication and
protection of session communications. Port 111 is used for RPC traffic in
various applications, including the NFS file system. If needed, it can be
left open. However, there are a large number of known vulnerabilities
related to port 111, so all patches must be applied to secure this port.
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More information on the port 111 vulnerabilities can be found at
Access Control Lists
In network devices, an Access Control List (ACL) performs a function much like
those discussed in the Discretionary Access Controls (DACs) section in Chapter
1. However, the functionality of an ACL is slightly different, and its capacity to
control access is limited by the type of device and the control software written to
guide the device. Also, ACL’s are controlled by a device operator or administrator,
not by the “owner” of the resource. Following is a list of the areas of ACLs that
can be controlled:
Protocols allowed
Ports allowed
Source of connection
Destination of connection
Interface type for connection
ACLs are also used as a firewall rules method. A firewall router can be used
with an ACL to filter or block traffic on specific ports, for specific protocols, and
for source or destination network addresses. Packet filter tables are often derived
from the construction of the ACL for the firewall.
Finally, ACL configurations must be checked and verified to restrict access to
the configuration information itself.The number of individuals or services that
have permission to monitor or modify settings on network equipment must be
limited to tighten the security of the device. ACLs should also be set to not allow
use of network services such as Telnet for access if alternatives are available, thus
tightening the access level even more.
Many of the rule sets being defined while using ACL functions are set to
either allow or deny a particular function, protocol, or access at an interface. As
noted above, a number of conditions can be controlled at the hardware device
with the ACL configurations.
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For example:
To deny the use of ICMP on interface <eth0>, a line can be created in
the ACL that reads int <eth0> ICMP deny. This would deny ICMP on
interface <eth0>.
To deny a specific communication protocol, an ACL entry can be created that reads: int <eth0> IPX deny. This would block use of IPX on
the interface.
To deny all protocols on an interface, a line can be added to the ACL
that reads int <eth0> ANY deny.This would effectively eliminate the use
of all protocols on the interface.
An ACL can become complex, and may need to be centrally stored to
be deployed to multiple devices.
When working with ACLs, remember that you will be utilizing some of
the concepts discussed in Chapter 1. However, you will also use some
different procedures to accomplish access control. For example, you may
use static access control list (SACL) configurations to maintain the settings on hardware devices in a network. Along with the SACL configuration, you may use other technologies to centralize the deployment of the
rule sets defining the level of access. Additionally, as you will see later in
this chapter, you may use a Directory Enabled Network (DEN) method
system to manage overall ACL development and deployment.
Application Hardening
The Security+ exam covers a very large area of the concepts of application hardening.This section looks at procedures and best practices in a couple of different
arenas to provide security.This section not only looks at end-user applications
such as browsers, office suites, and e-mail client software applications, but also
evaluates the problems that exist in applications provided through servers and services running on networks.These include Web servers, e-mail servers, File
Transfer Protocol (FTP) servers, DNS servers, and DHCP servers.This section
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also looks at Network News Transfer Protocol (NNTP) servers, file and print
servers, and data repositories. It also explores directory services and databases.
As in the OS and NOS section, as you work to understand and utilize the
updates, hotfixes, service packs, and patches in the application area, be
sure to test these repairs on machines that are in a parallel network environment. It is always prudent to test and try out the patches on non-production equipment prior to implementation in a live production network
Updates Updates are provided by the manufacturer of the application and are usually
intended to enhance features or functionalities of the applications involved.
Updates for end-user applications increase the capability of the software
to perform tasks.
Updates of server applications are often cosmetic in nature, or provided
to expand the capability of a particular type of server beyond its
original uses.
In either case, it is important to evaluate the updates to determine whether or
not they are required or beneficial to the operation. Again, it is imperative to
always test on equipment that is not part of the production environment to limit
problems and downtime.
Hotfixes for applications are provided by the vendors. However, these tend to be
specific to the function operating on a server.These include fixes for server applications such as Sendmail, Exchange, Microsoft Structured Query Language (SQL)
server, or a Berkeley Internet Name Domain (BIND) DNS server.
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Service Packs
Service packs for various application servers are produced nearly as often
as those for OSs and NOSs.
Expect to see service packs, or major collections of hotfixes, provided at
fairly regular intervals.
Service packs may be utilized often to correct the initial problems discovered since the product’s release.
Patches for application servers are provided by the vendor of the
Patches are used to fix compatibility and minor operation issues and
interface problems.
Accumulations of patches are sent out as service packs.
The Security+ exam contains questions about the additional security
configurations required for most of the application servers discussed. Be
sure to review the potential vulnerabilities of the various server types and
the manufacturer-recommended security plans for them. For example,
you may want to review settings relative to e-mail servers on disabling
e-mail relay problems, FTP servers for restricting access, Web servers for
restricting access, and database servers for protecting the databases and
Web Servers Most companies and organizations today have a Web presence on the Internet.
An Internet presence offers numerous business advantages, such as the ability to
advertise to a large audience, to interact with customers and partners, and to provide updated information to interested parties.
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Web pages are stored on servers running Web services software such as
Microsoft’s Internet Information Server (IIS) or Apache (developed for Linux and
UNIX servers, but also now available for Windows).Web servers must be accessible via the Internet if the public is to be able to access the Web pages. However,
this accessibility provides a point of entry to Internet “bad guys” who want to get
into the network, so it is vitally important that Web servers be secured. Protecting
a Web server is no small task. Systems attached to the Internet before they are
fully “hardened” are usually detected and compromised within minutes. Malicious
crackers are always actively searching for systems to infiltrate, making it essential
that a Web server is properly locked down before bringing it online.
First and foremost, administrators must lock down the underlying OS.This
process includes applying updates and patches, removing unneeded protocols and
services, and properly configuring all native security controls. Second, it is wise to
place the Web server behind a protective barrier, such as a firewall or a reverse
proxy. Anything that limits, restricts, filters, or controls traffic into and out of a Web
server reduces the means by which malicious users can attack the system.Third,
administrators must lock down the Web server itself.This process actually has
numerous facets, each of which are important to maintaining a secure Web server.
Many Web servers, such as IIS on Windows NT and Windows 2000, use a
named user account to authenticate anonymous Web visitors.When a Web visitor
accesses a Web site using this methodology, the Web server automatically logs that
user on as the IIS user account.
The visiting user remains anonymous, but the host server platform uses the
IIS user account to control access.This account grants system administrators
granular access control on a Web server.
These specialized Web user accounts should have their access restricted so
they cannot log on locally nor access anything outside the Web root. Additionally,
administrators should be very careful about granting these accounts the ability to
write to files or execute programs; this should be done only when absolutely
necessary. If other named user accounts are allowed to log on over the Web, it is
essential that these accounts not be the same user accounts employed to log onto
the internal network. In other words, if employees log on via the Web using their
own credentials instead of the anonymous Web user account, administrators
should create special accounts for those employees to use just for Web logon.
Authorizations over the Internet should not be considered secure unless strong
encryption mechanisms are in place to protect them. Secure Sockets Layer (SSL)
can be used to protect Web traffic; however, the protection it offers is not significant enough to protect internal accounts on the Internet.
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E-mail Servers E-mail servers have their own set of built-in and application-specific vulnerabili-
ties. All e-mail servers are vulnerable to normal attacks that are mounted against
their specific OS, but they are also vulnerable to Denial of Service (DoS) attacks,
virus attacks, and relay and spoofing attacks that may affect the level of service.
To protect the servers, the OSs and NOSs on the server must be hardened, as
well as the e-mail service applications. In e-mail, no systems are immune to attack.
There are many deficiencies in the various versions of e-mail server software
such as Sendmail for Linux and UNIX, and the Exchange/Outlook platform.
Any problems that have been exposed must be investigated, to evaluate the services and functions that should be included in the e-mail service. For example,
specific vulnerabilities exist if HTML e-mail is used on a system, both on the
e-mail server side and the client side. If HTML e-mail is chosen, arrangements
must be made to apply all security patches to client machines, browsers, and
servers to protect against arbitrary execution of code. It is also important to evaluate the messaging and instant messaging capabilities, as the implementation of
Internet Message Access Protocol (IMAP) technologies may also expose the network to further risk. Additionally, e-mail servers are constant potential sources of
virus attacks, and therefore must have the strongest possible protection for scanning incoming and outgoing messages. Finally, e-mail servers should not have
extraneous services and applications installed, and administrative and system access
permissions should be tightly controlled to block installation or execution of
unauthorized programs and Trojans.
When hardening an e-mail server, it is important to consider the following
attack points:
E-mail relay, which allows unauthorized users to send e-mail through
a e-mail server
Virus propagation; make sure the anti-virus planning and applications are
performing correctly
Spamming, including DoS conditions that exist in response to
“flame wars”
Storage limitations, to limit DoS attacks based on message size or volume
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FTP Servers FTP servers are potential security problems, as they are exposed to outside inter-
faces thereby inviting anyone to access them.The vast majority of FTP servers
open to the Internet support anonymous access to public resources.
Incorrect file system settings in a server hosting an FTP server allows unrestricted access to all resources stored on that server, and could lead to a system
breach. FTP servers exposed to the Internet are best operated in the DMZ, rather
than the internal network.They should be hardened with all of the OS and NOS
fixes available, but all services other than FTP that could lead to breach of the
system should be disabled or removed. Contact from the internal network to the
FTP server through the firewall should be restricted and controlled through ACL
entries, to prevent possible traffic through the FTP server from returning to the
internal network.
FTP servers providing service in an internal network are also susceptible to
attack, therefore administrators should consider establishing access controls
including usernames and passwords, as well as the use of SSL for authentication.
Some of the hardening tasks that should be performed on FTP servers include:
Protection of the server file system
Isolation of the FTP directories
Positive creation of authorization and access control rules
Regular review of logs
Regular review of directory content to detect unauthorized files and
DNS Servers Hardening DNS servers consists of performing normal OS hardening, and then
considering the types of control that can be done with the DNS service itself.
Older versions of BIND DNS were not always easy to configure, but current
versions running on Linux and UNIX platforms can be secured relatively easily.
Microsoft’s initial offering of DNS on NT were plagued with violations of their
integrity, making internetwork attacks much easier to accomplish, since information about the internal network was easy to retrieve.Windows 2000 versions
include the capability to restrict zone transfer operations to specific machines that
are members of a domain, thus better protecting the resources in the zone files
from unauthorized use.
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When hardening a DNS server, it is important to restrict zone transfers so
that they will not be made to unauthorized or rogue servers.
Zone transfers should only be made to designated servers. Additionally, those
users who may successfully query the zone records with utilities such as
NSLookup should be restricted via the ACL settings. Zone files contain all
records of a zone that are entered, therefore an unauthorized entity that retrieves
the records has retrieved a record of what is generally the internal network, with
hostnames and IP addresses.
There are records within a DNS server that can be set for individual machines.
These include host information (HINFO) records, which generally contain
descriptive information about the OS and features of a particular machine. HINFO
records were used in the past to track machine configurations when all records
were maintained statically, and were not as attractive a target as they are today. A
best practice in this case would be to not use HINFO records in the DNS server.
There are a number of known exploits against DNS servers in general. For
example, a major corporation placed all of their DNS servers on a single segment.This made it relatively simple to mount a DOS attack utilizing ICMP to
block or flood traffic to that segment. Other conditions administrators must
harden against are attacks involving cache poisoning, in which a server is fed
altered or spoofed records that are retained and then duplicated elsewhere. In this
case, a basic step for slowing this type of attack is to configure the DNS server to
not do recursive queries. It is also important to realize that BIND servers must
run under the context of root and Windows DNS servers must run under the
context of system to access the ports they need to work with. If the base NOS is
not sufficiently hardened, a compromise can occur.
NNTP Servers Network News Transfer Protocol (NNTP) servers are also vulnerable to some
types of attacks because they are often heavily utilized from a network resource
perspective. NNTP servers that are used to carry high volumes of newsgroup
traffic from Internet feeds are vulnerable to DoS attacks that can be mounted
when “flame wars” occur.This vulnerability also exists in the case of listserv applications used for mailing lists. NNTP servers also have vulnerabilities similar to
e-mail servers, because they are not always configured correctly to set storage
parameters, purge newsgroup records, or limit attachments. It is important to be
aware of malicious code and attachments that can be attached to the messages
that are being accepted and stored. NNTP servers should be restricted to valid
entities, which requires that the network administrator correctly set the limits for
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System Hardening • Chapter 8
access. It is also important to be aware of the platform being used for hosting a
NNTP server. If Windows-based, it will be subject to the same hardening and file
permission issues present in Windows IIS servers.Therefore, there are additional
services and protocols that must be limited for throughput, and defenses such as
virus scanning that must be in place.
File and Print Servers The ability to share files and printers with other members of a network can make
many tasks simpler and, in fact, was the original purpose for networking computers. However, this ability also has a dark side, especially when users are
unaware that they are sharing resources. If a trusted user can gain access, the possibility exists that a malicious user can also obtain access. On systems linked by
broadband connections, crackers have all the time they need to connect to a
shared resources and exploit them.
On Windows OSs, there is a service called file and printer sharing (the Server
service in Windows NT).When enabled, this service, allows others to access the
system across the network to view and retrieve or use resources. Other OSs have
similar services (and thus similar weaknesses).The Microsoft File and Printer
Sharing service uses NetBIOS with SMB traffic to advertise shared resources, but
does not offer security to restrict who can see and access those resources.
This security is controlled by setting permissions on those resources.The
problem is that when a resource is created in a Windows NT-based system, they
are set by default to give full control over the resource to everyone who accesses
that system. By default, the file and printer sharing service (or server service in
Windows NT) is bound to all interfaces being used for communication.
This means that when sharing is enabled for the purpose of sharing resources
with a trusted internal network over a network interface card (NIC), the system
is also sharing those resources with the entire untrusted external network over
the external interface connection. Many users are unaware of these defaults and
do not realize their resources are available to anyone who knows enough about
Windows to find them. For example, users with access to port scanning software,
or using the basic analysis provided through the use of NetBIOS statistics (NBTSTAT) or the net view command in a Windows network, would have the ability
to list shared resources if NetBIOS functionality exists.
At the very least, the file and print sharing service should be unbound from
the external network interface’s adapter. Another solution (or a further precaution
to take in addition to unbinding the external adapter) is to use a different protocol on the internal network.
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Domain 3.0 • Infrastructure Security
Notes From the Underground…
Look at What is Exposed
To look at the resources exposed in a Windows network, open a command window in any version of Windows that is networked. Type command at the Run line in Win9.x, or cmd at the Run line on any NT-based
machine. At the prompt, type net view and press the Return [Enter] key.
You will see a display showing machin