Red Hat Enterprise Linux Guide

EAL3 Evaluated Configuration Guide for Red Hat Enterprise
Linux
Klaus Weidner <[email protected]>
June 29, 2004; v1.2
atsec is a trademark of atsec GmbH
IBM, IBM logo, BladeCenter, eServer, iSeries, OS/400, PowerPC, POWER3, POWER4, POWER4+, pSeries, S390,
xSeries, zSeries, zArchitecture, and z/VM are trademarks or registered trademarks of International Business Machines
Corporation in the United States, other countries, or both.
Intel and Pentium are trademarks of Intel Corporation in the United States, other countries, or both.
Java and all Java-based products are trademarks of Sun Microsystems, Inc., in the United States, other countries, or
both.
Linux is a registered trademark of Linus Torvalds.
UNIX is a registered trademark of The Open Group in the United States and other countries.
This document is provided AS IS with no express or implied warranties. Use the information in this document at your
own risk.
This document may be reproduced or distributed in any form without prior permission provided the copyright notice
is retained on all copies. Modified versions of this document may be freely distributed provided that they are clearly
identified as such, and this copyright is included intact.
Copyright (c) 2003, 2004 by atsec GmbH, and IBM Corporation or its wholly owned subsidiaries.
2
Contents
1
Introduction
1.1 Purpose of this document . . . . . . . . . . . . . . .
1.2 How to use this document . . . . . . . . . . . . . . .
1.3 What is a CC compliant system? . . . . . . . . . . .
1.3.1 Hardware requirements . . . . . . . . . . . .
1.3.2 Software requirements . . . . . . . . . . . .
1.3.3 Environmental requirements . . . . . . . . .
1.3.4 Operational requirements . . . . . . . . . . .
1.4 Requirements for the system’s environment . . . . .
1.5 Requirements for the system’s users . . . . . . . . .
1.6 Overview of the system’s security functions . . . . .
1.6.1 Identification and authentication . . . . . . .
1.6.2 Audit . . . . . . . . . . . . . . . . . . . . .
1.6.3 Discretionary access control . . . . . . . . .
1.6.4 Object reuse . . . . . . . . . . . . . . . . .
1.6.5 Security management and system protection .
1.6.6 Secure communication . . . . . . . . . . . .
1.7 Overview of security relevant events . . . . . . . . .
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Installation
2.1 Supported hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Selection of install options and packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3
Secure initial system configuration
3.1 Creating additional user accounts for administrators . . . . . . . . . . .
3.2 Installing required updates . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Automated configuration of the system . . . . . . . . . . . . . . . . . .
3.4 Configuring filesystem parameters . . . . . . . . . . . . . . . . . . . .
3.5 Add and remove packages . . . . . . . . . . . . . . . . . . . . . . . .
3.6 Disable services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7 Remove SUID/SGID root settings from binaries . . . . . . . . . . . . .
3.8 Update permissions for ’su’ . . . . . . . . . . . . . . . . . . . . . . . .
3.9 Disable root login over the network . . . . . . . . . . . . . . . . . . .
3.10 Setting up SSH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.11 Setting up xinetd . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.12 Setting up FTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.13 Setting up Postfix . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.14 Setting up the audit subsystem . . . . . . . . . . . . . . . . . . . . . .
3.14.1 Installing the packages needed for auditing . . . . . . . . . . .
3.14.2 Setting up the audit configuration files . . . . . . . . . . . . . .
3.14.3 Starting auditd at boot as a system service . . . . . . . . . .
3.14.4 Starting auditd in fail-secure mode from init (OPTIONAL)
3.15 Introduction to Pluggable Authentication Module (PAM) configuration .
3.16 Required Pluggable Authentication Module (PAM) configuration . . . .
3.16.1 /etc/pam.d/system-auth . . . . . . . . . . . . . . . . . . . . . .
3.16.2 /etc/pam.d/login . . . . . . . . . . . . . . . . . . . . . . . . .
3.16.3 /etc/pam.d/other . . . . . . . . . . . . . . . . . . . . . . . . .
3.16.4 /etc/pam.d/sshd . . . . . . . . . . . . . . . . . . . . . . . . . .
3.16.5 /etc/pam.d/su . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.16.6 /etc/pam.d/vsftpd . . . . . . . . . . . . . . . . . . . . . . . . .
3.17 Configuring default account properties . . . . . . . . . . . . . . . . . .
3.18 Configuring the boot loader . . . . . . . . . . . . . . . . . . . . . . . .
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3.18.1 GRUB boot loader configuration .
3.18.2 Yaboot boot loader configuration .
3.18.3 ZIPL boot loader configuration . .
3.18.4 iSeries kernel slots . . . . . . . .
3.19 Reboot and initial network connection . .
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32
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System operation
4.1 System startup, shutdown and crash recovery . . . .
4.2 Backup and restore . . . . . . . . . . . . . . . . . .
4.3 Gaining superuser access . . . . . . . . . . . . . . .
4.4 Installation of additional software . . . . . . . . . .
4.5 Scheduling processes using cron and at . . . . . . . .
4.6 Mounting filesystems . . . . . . . . . . . . . . . . .
4.7 Managing user accounts . . . . . . . . . . . . . . .
4.8 Using serial terminals . . . . . . . . . . . . . . . . .
4.9 SYSV shared memory and IPC objects . . . . . . . .
4.10 Configuring secure network connections with stunnel
4.10.1 Introduction . . . . . . . . . . . . . . . . . .
4.10.2 Creating an externally signed certificate . . .
4.10.3 Creating a self-signed certificate . . . . . . .
4.10.4 Activating the tunnel . . . . . . . . . . . . .
4.10.5 Using the tunnel . . . . . . . . . . . . . . .
4.10.6 Example 1: Secure SMTP delivery . . . . . .
4.10.7 Example 2: Simple web server . . . . . . . .
4.10.8 Example 1: system status view . . . . . . . .
4.11 The Abstract Machine Testing Utility (AMTU) . . .
4.12 Setting the system time and date . . . . . . . . . . .
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Monitoring, Logging & Audit
5.1 Reviewing the system configuration . . . . . . .
5.2 System logging and accounting . . . . . . . . . .
5.3 Configuring the audit subsystem . . . . . . . . .
5.3.1 Intended usage of the audit subsystem . .
5.3.2 Selecting the events to be audited . . . .
5.3.3 Reading and searching the audit records .
5.3.4 Starting and stopping the audit subsystem
5.3.5 Storage of audit records . . . . . . . . .
5.3.6 Reliability of audit data . . . . . . . . . .
5.4 System configuration variables in /etc/sysconfig .
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53
Security guidelines for users
6.1 Online Documentation . . . . . . . .
6.2 Authentication . . . . . . . . . . . . .
6.3 Password policy . . . . . . . . . . . .
6.4 Access control for files and directories
6.5 Data import / export . . . . . . . . . .
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Appendix
7.1 Online Documentation . . . . . . . . . . .
7.2 Literature . . . . . . . . . . . . . . . . . .
7.3 The file /etc/audit/audit.conf . .
7.4 The file /etc/audit/filter.conf .
7.5 The file /etc/audit/filesets.conf
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4
1
1
1.1
INTRODUCTION
5
Introduction
Purpose of this document
The Red Hat Enterprise Linux (RHEL) distribution is designed to provide a secure and reliable operating system for
a variety of purposes. Because security requirements obviously depend on the applications and environment, it is not
possible to simply certify that the system is ”secure”, a more precise definition is needed.
The Common Criteria (CC) provides a widely recognized methodology for security certifications. A CC evaluation is
fundamentally a two-step process, consisting of defining the ”security target” which describes the features that are to
be evaluated, and then testing and verifying that the system actually implements these features with a sufficient level
of assurance.
This document is a security guide that explains how to set up the evaluated configuration, and provides information
to administrators and ordinary users to ensure secure operation of the system. It is intended to be self-contained in
addressing the most important issues at a high level, and refers to other existing documentation where more details are
needed.
The document primarily addresses administrators, but the section ”Security guidelines for users” is intended for
ordinary users of the system as well as administrators.
Knowledge of the Common Criteria is not required for readers of this document.
1.2
How to use this document
The key words ”MUST”, ”MUST NOT”, ”REQUIRED”, ”SHALL”, ”SHALL NOT”, ”SHOULD”, ”SHOULD NOT”,
”RECOMMENDED”, ”MAY”, and ”OPTIONAL” in this document are to be interpreted as described in RFC 2119
<http://www.ietf.org/rfc/rfc2119.txt>.
Note that the terms ”SHOULD” and ”SHOULD NOT” are avoided in this document. Requirements are either absolute
(and marked with MUST and equivalent terms), or entirely optional (in the sense of not affecting required security
functions) and marked with RECOMMENDED, MAY or OPTIONAL.
If you follow the requirements in this document when setting up and using the system, your configuration will match
the evaluated configuration. Certain configuration options are marked as OPTIONAL and you MAY modify them as
needed, but you MUST NOT make other changes, because they will make the system fail to match the evaluated
configuration.
Of course, you MUST always use common sense. This document is not a formal specification, and legitimate reasons
may exist to modify the system setup in ways not described here if that is necessary for the system to fulfill its intended
purpose. Specifically, applying security patches released by the vendor is strongly RECOMMENDED even though that
will cause a deviation from the evaluated configuration.
In cases where the requirements and recommendations in this document conflict with those in other sources (such as
the online documentation), the information in this Configuration Guide has higher precedence. You MUST follow the
steps described here to reach the evaluated configuration, even if other documentation describes different methods.
The usual convention is used in this guide when referring to manual pages that are included in the software distribution.
For example, the notation ls(1) means that running the man -S 1 ls command will display the manual page for the
ls command from section one of the installed documentation. In most cases, the -S flag and the section number may
be omitted from the command, they are only needed if pages with the same name exist in different sections,
1.3
What is a CC compliant system?
A system can be considered to be ”CC compliant” if it matches an evaluated and certified configuration. This
implies various requirements concerning hardware and software, as well as requirements concerning the operating
environment, users, and the ongoing operating procedures.
1
INTRODUCTION
6
Strictly speaking, an evaluation according to the CC represents the results of investigation of the security properties of
the target system according to defined guidelines. It should not be considered as a guarantee for fitness for any specific
purpose, but should provide help in deciding the suitability of the system considering how well the intended use fits
the described capabilities. It is intended to provide a level of assurance about the security functions that have been
examined by a neutral third party.
1.3.1
Hardware requirements
The hardware MUST be the one of the following IBM systems:
IBM xSeries 335 - AS and WS
IBM pSeries 630 - AS only
IBM iSeries 825 type 9406 (OS/400 V5R2 LPAR ) - AS only
IBM zSeries 900 (within VM 4.3 logical partition) - AS only
IBM eServer 325 (AMD64 Opteron) - AS only
Running the certified software on other similar hardware may result in an equivalent security level, but the certification
does not apply if the hardware is different from that used for the testing processes during the evaluation.
1.3.2
Software requirements
The software MUST match the evaluated configuration. In the case of an operating system, this also requires that the
installed kernel, system, and application software are the same. The documentation (including this guide) will specify
permitted variations, such as modifying certain configuration files and settings, and installing software that does not
have the capability to affect the security of the system (typically those that do not require ’root’ privileges).
1.3.3
Environmental requirements
Stated requirements concerning the operating environment MUST be met. Typical requirements include a secure
location for the hardware (protected from physical access by unauthorized persons), as well as restrictions concerning
permitted network connections.
1.3.4
Operational requirements
The operation of the system MUST be in agreement with defined organizational security policies, to ensure that actions
by administrators and users do not undermine the system’s security.
1.4
Requirements for the system’s environment
The security target covers one or more systems running RHEL, networked in a non-hostile network, with a
well-managed and non-hostile user community. It is not intended to address the needs of an Internet-connected server,
or the case where services are to be provided to potentially hostile users.
You MUST set up the server (or servers) in a physically secure environment, where they are protected from theft and
manipulation by unauthorized persons.
1
INTRODUCTION
7
You MUST ensure that all connections to peripheral devices and all network connections are protected against
tampering, tapping and other modifications. Using the secured protocols SSHv2 or SSLv3 is considered sufficient
protection for network connections. All other connections must remain completely within the physically secure server
environment.
All components in the network such as routers, switches, and hubs that are used for communication are assumed to
pass the user data reliably and without modification. Translations on protocols elements (such as NAT) are allowed as
long as those modifications do not lead to a situation where information is routed to somebody other than the intended
recipient system.
Be aware that information passed to another system leaves the control of the sending system, and the protection of
this information against unauthorized access needs to be enforced by the receiving system. If an organization wants
to implement a consistent security policy covering multiple systems on a network, organizational procedures MUST
ensure that all those systems can be trusted and are configured with compatible security configurations enforcing an
organization wide security policy. How to do this is beyond the scope of this Configuration Guide. If you set up a
communication link to a system outside your control, please keep in mind that you will not be able to enforce any
security policy for any information you pass to such a system over the communication link or in other ways (for
example, by using removable storage media).
Every person that has the ability to perform administrative actions by switching to root has full control over the system
and could, either by accident or deliberately, undermine the security of the system and bring it into an insecure state.
This Configuration Guide provides the basic guidance how to set up and operate the system securely, but is not intended
to be the sole information required for a system administrator to learn how to operate Linux securely.
It is assumed, within this Configuration Guide, that administrators who use this guide have a good knowledge and
understanding of operating security principles in general and of Linux administrative commands and configuration
options in particular. We strongly advise that an organization that wants to operate the system in the evaluated
configuration nevertheless have their administrators trained in operating system security principles and RHEL security
functions, properties, and configuration.
Every organization needs to trust their system administrators not to deliberately undermine the security of the system.
Although the evaluated configuration includes audit functions that can be used to make users accountable for their
actions, an administrator is able to stop the audit subsystem and reconfigure it such that his actions no longer
get audited. Well trained and trustworthy administrators are a key element for the secure operation of the system.
This Configuration Guide provides the additional information a system administrator should obey when installing,
configuring and operating the system in compliance with the requirements defined in the Security Target for the
Common Criteria evaluation.
1.5
Requirements for the system’s users
The security target addresses the security needs of cooperating users in a benign environment, who will use the system
responsibly to fulfill their tasks.
Note that system availability is not addressed in this evaluation, and a malicious user could disable a server through
resource exhaustion or similar methods.
The requirements for users specifically include:
• User accounts MUST be assigned only to those users with a need to access the data protected by the system, and
who MUST be sufficiently trustworthy not to abuse those privileges. For example, the system cannot prevent
data from being intentionally redistributed to unauthorized third parties by an authorized user.
• All users of the system MUST be sufficiently skilled to understand the security implications of their actions, and
MUST understand and follow the requirements listed in section §6 ”Security guidelines for users” of this guide.
Appropriate training MUST be available to ensure this.
It is part of your responsibility as a system administrator to verify that these requirements are met, and to be available
to users if they need your help in maintaining the security of their data.
1
INTRODUCTION
1.6
8
Overview of the system’s security functions
This section summarizes the security functions that were covered by the evaluation. Please refer to the appropriate
sections for information on configuring, using and managing these functions.
1.6.1
Identification and authentication
Pluggable Authentication Module (PAM)
Sections §3.15 ”Introduction to Pluggable Authentication Module (PAM) configuration”, §3.16 ”Required
Pluggable Authentication Module (PAM) configuration” of this guide; and the documentation in
/usr/share/doc/pam*/ and the pam(8) man page.
OpenSSH
Section §3.10 ”Setting up SSH” of this guide; and the sshd(8), ssh(1), sshd config(5) man pages.
vsftpd
Section §3.12 ”Setting up FTP” of this guide; and the vsftpd(8), vsftpd.conf (5) man pages.
su
Sections §3.8 ”Update permissions for ’su’”, §4.3 ”Gaining superuser access” of this guide; and the su(8) man
page.
1.6.2
Audit
Sections §3.14 ”Setting up the audit subsystem” and §5.3 ”Configuring the audit subsystem” of this guide; and the
laus(7) man page, whose ”SEE ALSO” section points to the remaining LAuS man pages.
1.6.3
Discretionary access control
Sections §6.4 ”Access control for files and directories” and §4.9 ”SYSV shared memory and IPC objects” of this guide.
1.6.4
Object reuse
See the RHEL High Level Design document, the kernel automatically ensures that new objects (disk files, memory,
IPC) do not contain any traces of previous contents.
1.6.5
Security management and system protection
Chapters §4 ”System operation” and §5 ”Monitoring, Logging & Audit”.
1.6.6
Secure communication
Section §4.10 ”Configuring secure network connections with stunnel” of this guide; and the stunnel(1) man page.
Section §3.10 ”Setting up SSH” of this guide; and the sshd(8), ssh(1), and sshd config(5) man pages.
2
1.7
INSTALLATION
9
Overview of security relevant events
The audit subsystem is intended to be the central interface for collecting and viewing the record of security relevant
events. The events being monitored by default in the evaluated configuration include:
• All authentication done through the PAM library, including the identity and location (where available) of the
user and the success or failure result.
• Use of su(8) to change identity. All actions done as part of a su session are marked in the audit record with the
original user’s login user ID.
• Adding, changing, or deleting users or groups.
• Changes and change attempts to the contents of security critical files.
• Changes to the access permissions or ownership of any files or IPC objects.
• Binding network ports and accepting connections.
Please refer to section §5 ”Monitoring, Logging & Audit” for more information.
2
Installation
The evaluation covers a fresh installation of RHEL AS or WS, Version 3 Update 2, on one of the supported hardware
platforms as defined in section §1.3.1 ”Hardware requirements” of this guide.
On the platforms that support virtualization (VM) or secure logical partitioning (LPAR), other operating systems
MAY be installed and active at the same time as the evaluated configuration. This is if (and only if) the VM or LPAR
configuration ensures that the other operating systems cannot access data belonging to the evaluated configuration or
otherwise interfere with its operation. Setting up this type of configuration is considered to be part of the operating
environment and is not addressed in this guide.
On the other platforms, the evaluated configuration MUST be the only operating system installed on the server.
2.1
Supported hardware
You MAY attach the following peripherals without invalidating the evaluation results. Other hardware MUST NOT be
installed in or attached to the system.
• Any storage devices and backup devices supported by the operating system (this includes hard disks, CD-ROM
drives and tape drives).
• All Ethernet and Token Ring network adapters supported by the operating system. Modems, ISDN and other
WAN adapters are not part of the evaluated environment.
• Any printers supported by the operating system.
• Operator console consisting of a keyboard, video monitor, and optionally mouse. Additionally, you MAY
directly attach supported serial terminals (see section §4.8 ”Using serial terminals” of this guide), but not
modems, ISDN cards, or other remote access terminals.
Hot-pluggable hardware that depends on the dynamic loading of kernel modules is not supported. Examples of such
unsupported hardware are USB and, IEEE1394/FireWire peripherals.
2
10
INSTALLATION
2.2
Selection of install options and packages
This section describes the detailed steps to be performed when installing the RHEL operating system on the target
server.
All settings listed here are REQUIRED unless specifically declared otherwise.
1. It is RECOMMENDED that you disconnect all network connections until the post-install system configuration is
finished. You MAY use a network if required for the installation (for example, zSeries hosts are usually installed
using NFS, because they do not have a CD drive). If you do use a network, you MUST ensure that this network
is secure, for example by directly connecting the new system to a standalone NFS server with no other network
connections.
2. You MUST download the ISO images from the RedHat Network on a separate Internet-connected computer,
and either burn CD-Rs from them, or make the contents available on a NFS file server. The download location
https://rhn.redhat.com/network/software/download isos full.pxt contains links to the platform-specific images.
You MUST use Red Hat Enterprise Linux 3 Update 2, either AS (Advanced Server) or WS (Workstation).
Make sure that you are using the appropriate version for your platform:
xSeries
eServer 325
pSeries
iSeries
zSeries
i386
x86_64
ppc
ppc
s390
AS or WS
AS
AS
AS
AS
You MUST verify that the MD5 checksums of the image files are correct. Run md5sum *.iso to view the
checksums for the downloaded images, and compare them with those shown in this list:
Red Hat Enterprise Linux 3 AS (i386) Update 2
Binary Disc 1
139M
240a6a59d7f2f1c4bb2d017016e46f5c
Binary Disc 2
619M
a45ce3753d0c9a599d4533c8ba4339d2
Binary Disc 3
633M
5bc126d663e681f874a15f55e05c070f
Binary Disc 4
168M
158f58ae5e1307415185e0b4863b40e4
Red Hat Enterprise Linux 3 WS (i386) Update 2
Binary Disc 1
131M
211692ca8fac5894f4f98d1a744f4c27
Binary Disc 2
619M
a45ce3753d0c9a599d4533c8ba4339d2
Binary Disc 3
633M
5bc126d663e681f874a15f55e05c070f
Binary Disc 4
168M
158f58ae5e1307415185e0b4863b40e4
Red Hat Enterprise Linux 3 AS (X86_64) Update 2
Binary Disc 1
142M
32f28eb619907faca2a94bb8e7658dae
Binary Disc 2
625M
2919142a9f3bb46572815bdb327baddc
Binary Disc 3
637M
be55fc8e56d3f1eb53d87f46f97b063b
Binary Disc 4
204M
2d7530d57c5c407bb2d820361a48bb18
Red Hat Enterprise Linux 3 AS (ppc) Update 2
Binary Disc 1
172M
5ed53761d9dfb69568cb7077a9f85f0e
Binary Disc 2
619M
d75085869102710c9803603d55c669af
Binary Disc 3
638M
ab819d81efced28099e3f6ebcf38de52
Binary Disc 4
39M
4089bad2a99ab560cf55ad88e40309da
2
11
INSTALLATION
Red Hat Enterprise Linux 3 AS (s390) Update 2
Binary Disc 1
130M
df70a9aaa1a457306360c7d31ba74711
Binary Disc 2
623M
6d6b3a93d38cfadc1553687bfa05387a
Binary Disc 3
513M
b046f680a279479e3d9d63c53ffcdb42
Binary Disc 4
376K
2a220f9dc346075c6037e73a40e657f0
3. Launch the installer program contained on the CD-ROM. The details of how to do this depend on the hardware
platform, please refer to the installation guide that is part of the printed manual accompanying the CD.
For example:
• xSeries, eServer 325 (Opteron), pSeries: Insert the first CD and boot from CD-ROM.
• zSeries, iSeries: Details depend on the operation mode (VM, LPAR or native). The process generally
involves copying the installer onto the server and launching the installer using the host’s management
interface.
4. You MAY choose text-mode installation instead of the default graphical installation by entering linux text
at the boot prompt.
You MAY also use a serial console to do a text-mode installation. To do so, connect a serial terminal (or a
computer with terminal emulator software; such a computer MUST be appropriately secure) to the server’s
serial port, and boot from the RHEL CD. When the boot prompt is shown on the serial console, enter linux
text console=ttyS0 (use the appropriate name of the serial device if not using ttyS0) and press ENTER
to start the installation.
5. Running the CD media test for all installation CDs is RECOMMENDED.
6. When the ”Welcome” screen appears, press Next.
7. Language Selection: choose English (English) to ensure that the messages shown during the installation match
those described in this guide.
8. Keyboard Configuration: You MAY change the U.S. English setting to match your keyboard.
9. Mouse Configuration: You MAY change the Mouse Selection if the autodetected values are not appropriate,
including choosing ”No mouse” and using the keyboard only.
10. Disk Partitioning Setup. Use Manual partition with Disk Druid to set up the partitions. For CAPP-compliant
auditing, you MUST set up a separate partition for the directory /var/log/.
• Set up the REQUIRED / (root) and /var/log partitions, and as many additional mounted partitions as
appropriate. /var/log REQUIRES at least 100 MB of space in order to be able to install and launch the
audit system, but this does not include the additional space needed for saved audit logs, please refer to
section §5.3 ”Configuring the audit subsystem” of this guide for more information.
It is RECOMMENDED to also use separate partitions for /var, /home and /tmp. Some configurations
(recognized automatically by the installation program) need a separate /boot partition. The following table
shows a RECOMMENDED partitioning scheme together with minimum sizes for the partitions. Using
more space is RECOMMENDED:
/boot
/
/tmp
/home
/var
/var/log
75
1200
200
100
384
100
MB
MB
MB
MB
MB
MB needed for install, >>1GB for use
• All mounted partions MUST be of type ext3 and formatted.
• Configuring a swap partition at least as large as the installed RAM is RECOMMENDED.
3
SECURE INITIAL SYSTEM CONFIGURATION
12
11. Boot Loader Configuration: Setting a boot loader password is RECOMMENDED. You MUST NOT add other
operating systems to the configuration.
12. Network Configuration: Configure all installed network cards (zero or more) as appropriate for the platform. In
the case of virtual network cards on zSeries or iSeries, these options are not available. The following options
MUST be used for non-virtual network cards:
• Use the Edit button to either assign a static IP address by unchecking the Configure using DHCP box
and entering the IP Address and Netmask; or alternatively disable the card by unchecking the Activate
on boot box.
• You MUST NOT use DHCP for any active network card.
• Enter a valid hostname (which is RECOMMENDED to be unique within your network) consisting
of one or more alphanumeric components, separated by ’.’, and each matching the regular expression
[a-zA-Z][-a-zA-Z0-9]*
• OPTIONAL: assign a Gateway address and DNS servers.
• Modems and ISDN adapters MUST NOT be present.
13. Firewall Configuration: RECOMMENDED to select No firewall for the evaluated configuration, it is not needed
on a hardened minimal installation and may cause conflicts with the use of stunnel(8) for secure connections.
You MAY enable the firewall and choose a list of permitted ports.
14. Additional Language Support: RECOMMENDED to leave the default language set as English (USA) to ensure
that system messages match those described in the documentation. (Note that users can individually override
this setting.) You MAY add additional language support.
15. Time Zone Selection: RECOMMENDED to set the Location or UTC Offset as appropriate for the server’s
location, and RECOMMENDED to activate System clock uses UTC.
16. Set Root Password: Choose a Root Password according to the password policy (§6.3), and Confirm it.
17. Package Installation Defaults: Select Customize the set of packages to be installed. When using the graphical
installer, put a check mark on the Minimal set of packages (last item, in the Miscellaneous group), this will
deselect all the other package selections. If using the text-mode installer, you MUST manually deselect all
packages by removing all check marks in the Package Group Selection dialog.
18. About to Install: This is the final confirmation to start the installation. Press Next to start the automated
partitioning, formatting, and installation process. Insert additional disks if prompted to do so. For the x86
architecture, all the needed data is on the first CD-ROM, so you will not be asked to insert additional disks.
19. When the automated install is complete and the Congratulations screen appears, pressing Exit will reboot the
system. It is RECOMMENDED that you now reconfigure the system to boot from the newly installed system
only (typically the first hard disk) and disable all other boot methods such as CD-ROM, network boot (PXE) or
floppy disk. If you choose not to do that, you MUST remove the installation CD-ROM from the drive before
rebooting.
20. Wait for the freshly installed system to start, and verify that the issue message printed above the login prompt
matches the installed system type and version. Then log in as ”root” and proceed with the next section.
3
Secure initial system configuration
After the initial installation, the operating system is not yet in the evaluated configuration. The instructions in this
section explain how to achieve that configuration.
After software upgrades or installation of additional packages, these steps MUST be re-done or at least re-checked to
ensure that the configuration remains secure.
Log in as user ’root’ on the system console for these steps.
3
3.1
SECURE INITIAL SYSTEM CONFIGURATION
13
Creating additional user accounts for administrators
The evaluated configuration disables direct ”root” login over the network. All system administrators MUST log in
using a non-root individual user ID, then use the su(8) command to gain superuser privileges for administrative tasks.
This requires membership in the ’wheel’ group of trusted users.
You MUST define at least one non-root user account with the useradd(8) command, and add this user account to the
’wheel’ group. Note that the enhanced password quality checking mechanisms and the password expiry settings of
the evaluated configuration are not active yet. You must manually set the password properties in accordance with the
password policy.
Here is an example of creating an additional user account:
useradd -m -c "John Doe" -G wheel jdoe
passwd jdoe
chage -m 1 -M 60 -W 7 jdoe
Please refer to sections §4.7 ”Managing user accounts” and §6.3 ”Password policy” of this guide for more information
on creating user accounts.
3.2
Installing required updates
You need to download several additional packages not included in Update 2 to set up the evaluated configuration. The
packages are available at the following location:
ftp://partners.redhat.com/EAL3_RHEL3/U2/
Download the RPMs using an Internet-connected computer, and transfer the RPMs to the system being installed.
You MUST select the appropriate RPM packages for your architecture. The 64bit architectures support execution of
both 64bit and 32bit binaries.
xSeries (i386)
This is a 32bit-only platform. Use *.i686.rpm variants of packages if available, *.i386.rpm or *.noarch.rpm
otherwise.
eSeries 325 (Opteron/x86 64)
This system uses a 64bit kernel and 64bit userspace programs, and also supports running 32bit programs. Use
the *.x86 64.rpm or *.noarch.rpm variants of packages. You may OPTIONALLY install the *.i386.rpm or
*.i686.rpm variants of libraries (package names containing -libs or -devel) in addition to the 64bit versions.
iSeries or pSeries (ppc/ppc64)
These systems use a 64bit kernel, but the installed userspace programs are the 32bit variants. They support
running 64bit programs as well. There are separate kernels available for the iSeries and pSeries patforms,
use ppc64iseries.rpm or ppc64pseries as appropriate. Use the *.ppc64.rpm variants of laus and laus-libs,
*.ppc.rpm or *.noarch.rpm for everything else. You may OPTIONALLY install the *.ppc64.rpm variants of
libraries (package names containing -libs or -devel) in addition to the 32bit versions, and the *.ppc.rpm version
of laus-libs in addition to the default 64bit version.
zSeries (s390)
The evaluated configuration uses a 31bit kernel running 31bit userspace programs. Install the *.s390.rpm
or *.noarch.rpm variants only. Use of 64bit packages (*.s390x.rpm) is NOT supported in the evaluated
configuration.
3
SECURE INITIAL SYSTEM CONFIGURATION
14
The active kernel MUST be one of the listed kernel or kernel-smp packages. It is RECOMMENDED that you uninstall
unused kernel packages, such as the uniprocessor kernel on a SMP machine. The development libraries (*-devel*)
and additional non-default word size libraries as explained above are OPTIONAL. All other packages listed here are
REQUIRED. You MUST verify the MD5 sums against the following list:
### i386
954a3c754a5f8929560dba65d99c5baf amtu-0.1-5RHEL.i386.rpm
34edf418f9e2dc80e681b6ca38cb854a at-3.1.8-48.ent.i386.rpm
00744d4d35e23b78fc6deb49a187c951
kernel-2.4.21-15.0.2.EL.peterm.eal.3.i686.rpm
827f8140f520ff4677bbde524edd6e69
kernel-smp-2.4.21-15.0.2.EL.peterm.eal.3.i686.rpm
cd31e226ffc751e4a490c4c46716c0b6
kernel-source-2.4.21-15.0.2.EL.peterm.eal.3.i386.rpm
942d4e9687cc229ee7866e0810294ed9 laus-0.1-62RHEL3.i386.rpm
79ac3ab71e1917cc464dc2f3b1b9edd1 laus-devel-0.1-62RHEL3.i386.rpm
58e5e19bf98d287576ad7d0c50d3ff74 laus-libs-0.1-62RHEL3.i386.rpm
6789218233e890ce2c5005ce70abea99 passwd-0.68-3.1.i386.rpm
cd62831bd278541bac99f13edf3a93f9 shadow-utils-4.0.3-20.03.i386.rpm
af2f1ff1abb97e16b92b51b89ed69212 vixie-cron-3.0.1-75.i386.rpm
### iSeries
4a638c42ea65b2ba1eae1c82b837e375 amtu-0.1-5RHEL.ppc.rpm
63935344db78a3e7173549fe4f7f57ef at-3.1.8-48.ent.ppc.rpm
1d33d4613000f63c29426b8d82dc6560
kernel-2.4.21-15.0.2.EL.peterm.eal.3.ppc64iseries.rpm
b54313d999396e92627b6d33c7c51058
kernel-source-2.4.21-15.0.2.EL.peterm.eal.3.ppc64.rpm
8f17734994b40665c02f77f1d19ae9d5 laus-0.1-62RHEL3.ppc64.rpm
c6129b9d09330794a5f329acff7def6e laus-devel-0.1-62RHEL3.ppc.rpm
91c6217ba1d27dbefee33452f31423d6 laus-devel-0.1-62RHEL3.ppc64.rpm
2db58f704ade9835b55077a7537546a5 laus-libs-0.1-62RHEL3.ppc.rpm
86dc0501ba9e8942010678806aea9e8c laus-libs-0.1-62RHEL3.ppc64.rpm
1b1203051fe38a4c7d6714948b7cf348 passwd-0.68-3.1.ppc.rpm
e7edac75f05e107df39b82ade751f26f shadow-utils-4.0.3-20.03.ppc.rpm
38bbec2cb8070032130a69d352dc70dd vixie-cron-3.0.1-75.ppc.rpm
### pSeries
4a638c42ea65b2ba1eae1c82b837e375 amtu-0.1-5RHEL.ppc.rpm
63935344db78a3e7173549fe4f7f57ef at-3.1.8-48.ent.ppc.rpm
519d8724bdd022cc18465b8323b8e5c9
kernel-2.4.21-15.0.2.EL.peterm.eal.3.ppc64pseries.rpm
b54313d999396e92627b6d33c7c51058
kernel-source-2.4.21-15.0.2.EL.peterm.eal.3.ppc64.rpm
8f17734994b40665c02f77f1d19ae9d5 laus-0.1-62RHEL3.ppc64.rpm
c6129b9d09330794a5f329acff7def6e laus-devel-0.1-62RHEL3.ppc.rpm
91c6217ba1d27dbefee33452f31423d6 laus-devel-0.1-62RHEL3.ppc64.rpm
2db58f704ade9835b55077a7537546a5 laus-libs-0.1-62RHEL3.ppc.rpm
86dc0501ba9e8942010678806aea9e8c laus-libs-0.1-62RHEL3.ppc64.rpm
1b1203051fe38a4c7d6714948b7cf348 passwd-0.68-3.1.ppc.rpm
e7edac75f05e107df39b82ade751f26f shadow-utils-4.0.3-20.03.ppc.rpm
38bbec2cb8070032130a69d352dc70dd vixie-cron-3.0.1-75.ppc.rpm
### s390
3
SECURE INITIAL SYSTEM CONFIGURATION
15
4480b7c15f8a734544a0670d8e38f48e amtu-0.1-5RHEL.s390.rpm
491ca763be4d1d72bd8b1f9482063623 at-3.1.8-48.ent.s390.rpm
d96c577a3391feb227018d65f3c114b4
kernel-2.4.21-15.0.2.EL.peterm.eal.3.s390.rpm
4bf34cc066affc96937af09cdc7d6bfe
kernel-source-2.4.21-15.0.2.EL.peterm.eal.3.s390.rpm
73de7e7a4a57b15f9feaf81d62f41a9f laus-0.1-62RHEL3.s390.rpm
298b8ae4714d9fbca2c279452a13a0ee laus-devel-0.1-62RHEL3.s390.rpm
ce7cb4b2bb5789992889047794dbb70d laus-libs-0.1-62RHEL3.s390.rpm
bf1c3950d090d33386e9ef7f2e4f91c7 passwd-0.68-3.1.s390.rpm
074298576ec409b7923509a12983442a shadow-utils-4.0.3-20.03.s390.rpm
b2feeb0dd26a9c791cc342066357bc0b vixie-cron-3.0.1-75.s390.rpm
### x86_64
1ba34f27a2392f251417c3d4aeed5abc amtu-0.1-5RHEL.x86_64.rpm
c7ca492b0266ae83f92f09a6d4b94ab0 at-3.1.8-48.ent.x86_64.rpm
77836e69f9cc29e1220dae6e3d3e42e0
kernel-2.4.21-15.0.2.EL.peterm.eal.3.x86_64.rpm
8f4b4f77243e68dfba2feee8c37f6631
kernel-smp-2.4.21-15.0.2.EL.peterm.eal.3.x86_64.rpm
b9bcb2fe3030052aafad5988d1945802
kernel-source-2.4.21-15.0.2.EL.peterm.eal.3.x86_64.rpm
59d191b83642cd3642d173f4041b6d66 laus-0.1-62RHEL3.x86_64.rpm
79ac3ab71e1917cc464dc2f3b1b9edd1 laus-devel-0.1-62RHEL3.i386.rpm
5538d44c8fe6da06ce02d0c787c58eec laus-devel-0.1-62RHEL3.x86_64.rpm
58e5e19bf98d287576ad7d0c50d3ff74 laus-libs-0.1-62RHEL3.i386.rpm
276582e5f9eea630400b32003cbfcfdc laus-libs-0.1-62RHEL3.x86_64.rpm
932c7d5e07e3a172f0248ab06d405410 passwd-0.68-3.1.x86_64.rpm
8cbdcdf09a6945a09ca8f7255f4cbbdb shadow-utils-4.0.3-20.03.x86_64.rpm
14ce77fd0c0def8147ec109b152deae9 vixie-cron-3.0.1-75.x86_64.rpm
When using the automated configuration, copy these RPM files into the directory /root/rpms/ of the system being
installed, the installer will then handle the upgrade automatically. You MUST download the current version of the
eal3-certification RPM package to use the automated configuration as described in the next section.
If installing manually, use the rpm(8) command to install and upgrade the downloaded packages:
rpm -Uvh *.rpm
3.3
Automated configuration of the system
The eal3-certification package SHOULD be installed initially to achieve the evaluated configuration. This RPM
package contains EAL3 specific configuration files, and the script /etc/audit/rhel-eal3.bash that sets up the evaluated
configuration.
It is RECOMMENDED that you use the rhel-eal3.bash script to reset the configuration to its initial state after
any updates, but you MAY also perform the steps listed here manually.
Install the certification RPM with the following command:
rpm -Uvh eal3-certification*.rpm
Run the following command to view a summary of the supported options:
3
SECURE INITIAL SYSTEM CONFIGURATION
16
/etc/audit/rhel-eal3.bash -h
It is RECOMMENDED that you uninstall all unused kernel packages, such as the uniprocessor kernel on a SMP
machine, before running the script. The script will upgrade the installed kernel package(s) to the required version, and
if you have multiple packages, the wrong one might be activated due to the upgrade order. You MAY also manually
upgrade the kernel package (and test it) before running the script.
You will need to specify a directory containing the required update packages (this is /root/rpms/ by default), and also
a directory or media containing the RHEL3 Update2 RPM packages. Specify these with the --rpm-path parameter,
with the update packages listed first. For example:
/etc/audit/rhel-eal3.bash --rpm-path ’/root/rpms /mnt/cd*’
If the RHEL3 Update2 RPM packages are stored on an NFS file server instead of on CD-R media, specify the path
to the RPMS directory as in the following example, using the appropriate path to the mounted directory instead of
/mnt/SERVER/U2/:
/etc/audit/rhel-eal3.bash \
--rpm-path ’/root/rpms /mnt/SERVER/U2/RedHat/RPMS/’
You MAY also add the --add-optional flag to automatically install optional packages (useful for testing).
You MAY use the -a flag to automate the install and have it run without prompting. This is intended for people who
are familiar with the process; if running it for the first time you SHOULD let it run interactively and verify the actions
as described in this guide.
You MUST answer all questions asked by the script that are not marked as ”optional” with y to achieve the evaluated
configuration.
WARNING: The rhel-eal3.bash script will reboot the system as the final step in the process, as described in the
manual instructions in section §3.19 ”Reboot and initial network connection” of this guide. On zSeries, it will run the
zipl boot configuration tool (with no arguments) before rebooting.
If the script has completed successfully, the remaining steps in this chapter were done automatically; you MAY skip
ahead to section §4 ”System operation” of this guide.
3.4
Configuring filesystem parameters
You MUST add the mount option acl in the file /etc/fstab for all ext3 file systems. You MAY also add the option
user xattr. Multiple options are separated with commas (not ”comma space”), for example acl,user xattr.
Edit /etc/fstab and replace the defaults option specification (fourth column) with acl for all file systems with
type ext3 (third column). Then, run mount MOUNTPOINT -o remount for each of the mount points (second
column).
For more information, please refer to section §4.6 ”Mounting filesystems” of this guide.
3.5
Add and remove packages
The minimal system that was initially installed does not contain all packages required for the evaluated configuration,
and some of the initially installed packages need to be removed.
In the following lists, the suffix /cross indicates a package using the non-default word size. For example, the default
”glibc” package on Opteron is named glibc-*.x86 64.rpm, while ”glibc/cross” refers to glibc-*.i686.rpm. Please refer
to section §3.2 ”Installing required updates” for more information. The following table shows the mappings:
3
17
SECURE INITIAL SYSTEM CONFIGURATION
# Architecture
xSeries
iSeries, pSeries
eServer 325
zSeries (31bit)
default
i386 or i686
ppc
x86_64
s390
/cross
[not applicable]
ppc64
i386 or i686
[not applicable]
The evaluated configuration consists of exactly the following packages:
One or both of the following kernel packages:
kernel
kernel-smp
Packages installed on all architectures:
acl amtu ash aspell at attr authconfig autofs basesystem bash
bc beecrypt bind-utils binutils bzip2 bzip2-libs chkconfig
comps coreutils cpio cpp cracklib cracklib-dicts crontabs cups
cups-libs curl cvs cyrus-sasl cyrus-sasl-gssapi cyrus-sasl-md5
cyrus-sasl-plain db4 dev devlabel dhclient dialog diffutils
dos2unix dosfstools dump e2fsprogs ed eject elfutils
elfutils-libelf elinks ethtool expat fbset file filesystem
findutils finger fontconfig freetype ftp gawk gdbm gettext
glib glib2 glibc glibc-common glibc-headers glibc-kernheaders
gmp gnupg gpm grep groff gzip hdparm hesiod hotplug htmlview
hwdata info initscripts iproute ipsec-tools iptables
iptables-ipv6 iputils irda-utils isdn4k-utils jfsutils jwhois
kbd kernel kernel-utils krb5-libs krb5-workstation krbafs
krbafs-utils kudzu laus laus-libs less lftp lha libacl libattr
libcap libgcc libgcj libjpeg libpng libstdc++ libtermcap
libtiff libtool-libs libuser libwvstreams libxml2 lockdev
logrotate logwatch losetup lslk lsof lvm m4 mailcap mailx make
MAKEDEV man man-pages mdadm mgetty mingetty minicom mkinitrd
mktemp modutils mount mtools mtr mt-st nano nc ncompress
ncurses netconfig netdump netpbm netpbm-progs net-tools newt
nfs-utils nscd nss_ldap ntsysv openldap openssh
openssh-clients openssh-server openssl pam pam_krb5
pam_passwdqc pam_smb parted passwd patch pax pciutils pcre
pdksh perl perl-DateManip perl-Filter perl-HTML-Parser
perl-HTML-Tagset perl-libwww-perl perl-URI pinfo popt portmap
postfix ppp prelink procmail procps psacct psmisc pspell
pyOpenSSL python python-optik pyxf86config quota raidtools
rdate rdist readline redhat-config-mouse
redhat-config-network-tui redhat-config-securitylevel-tui
redhat-logos redhat-lsb redhat-menus redhat-release rhnlib
rhpl rmt rootfiles rpm rpmdb-redhat rpm-python rp-pppoe rsh
rsync schedutils sed setarch setserial setup setuptool
shadow-utils sharutils slang slocate specspo star stunnel sudo
symlinks sysklogd sysreport SysVinit talk tar tcl tcp_wrappers
tcpdump tcsh telnet termcap tetex tetex-fonts tetex-latex tftp
time tk tmpwatch traceroute tzdata unix2dos unzip up2date
usbutils usermode utempter util-linux vconfig vim-common
vim-minimal vixie-cron wget which wireless-tools words
3
SECURE INITIAL SYSTEM CONFIGURATION
18
wvdial XFree86-libs XFree86-libs-data XFree86-Mesa-libGL
xinetd ypbind yp-tools zip zlib
additional package on AS (not available on WS):
vsftpd
additional packages on x86 (xSeries):
apmd eject fbset grub hdparm kbd kernel-pcmcia-cs laus minicom
mkbootdisk pyxf86config redhat-config-mouse rp-pppoe setserial
syslinux usbutils wireless-tools
additional packages on x86_64 (eServer 325 (Opteron)):
eject fbset grub hdparm kbd laus minicom pyxf86config
redhat-config-mouse rp-pppoe setserial syslinux usbutils
wireless-tools
additional packages on ppc (pSeries) and ppc (iSeries):
eject fbset hdparm kbd laus-libs/cross laus/cross minicom
ppc64-utils pyxf86config redhat-config-mouse rp-pppoe
setserial usbutils wireless-tools yaboot
additional packages on s390 (zSeries):
laus s390utils
In addition to these packages, certain additional software from the RHEL CDs MAY be installed without invalidating
the evaluated configuration. The rules described in section §4.4 ”Installation of additional software” of this guide
MUST be followed to ensure that the security requirements are not violated.
The following packages are examples of tolerated packages that MAY be added to the system according to these rules.
Note that the software contained in these packages is not intended to be used with ’root’ privileges, but the presence
of the packages does not invalidate the evaluated configuration. The rhel-eal3.bash script does not remove
these packages if they are installed on the system, and MAY be used to install them automatically by specifying the
--add-optional parameter to the command line. The example OPTIONAL packages are:
autoconf automake bison cracklib/cross db4/cross
eal3-certification-doc expect expect-devel flex gcc gcc-c++
glib/cross glibc-devel glibc-devel/cross glibc/cross
kernel-source/any krb5-devel laus-devel laus-devel/cross
laus-libs/cross libacl/cross libattr-devel libattr/cross
libgcc/cross libstdc++-devel libstdc++-devel/cross
libstdc++/cross netpbm netpbm-progs openldap-clients
openssl-devel pam-devel pam-devel/cross perl-Digest-HMAC
perl-Digest-SHA1 rpm-build strace tetex tetex-fonts
tetex-latex texinfo zlib-devel zlib-devel/cross zlib/cross
3
SECURE INITIAL SYSTEM CONFIGURATION
19
The next steps involve installing selected packages from the distribution CD-ROMs. Due to dependency issues, the
RECOMMENDED method is to first copy all needed RPMs to a temporary directory, and then installing them all in
one step using rpm -Uvh *.rpm.
The rhel-eal3.bash script handles the package selection and installation automatically, and will prompt for the
installation media as necessary. After installation, the package selection is again verified, and the script will indicate
which packages are still missing or the wrong version. In this case, verify that the needed RPM packages are available
in the locations specified, and that they are the correct versions and for the correct architecture.
If you are performing this step manually, first create a temporary directory to store the RPM files:
mkdir /root/rpms
Copy all the missing package files to that directory. This step is very time consuming when done manually, the
RECOMMENDED method is to use the rhel-eal3.bash script to do this automatically. The following shows an example
of the manual method, this needs to be repeated until all missing packages are copied:
# Get list of currently installed packages
rpm -qa | sort | less
# Search for one of the missing packages
find /mnt/cd* -name ’vsftpd*’
# Copy missing packages from the installation media
cp /mnt/cdrom/RedHat/RPMS/vsftpd-1.2.0-4.i386.rpm /root/rpms/
# Repeat these steps for the other missing packages
[...]
Once the packages are all copied, install them all in one step with the following single command:
# Install all packages
rpm -Uvh /root/rpms/*.rpm
This MAY result in the following expected warning and error messages that are harmless:
warning: user bhcompile does not exist - using root
warning: group bhcompile does not exist - using root
error: %postun(laus-0.1-54RHEL3) scriptlet failed, exit status 255
Any other errors or warnings indicate that the installation is invalid and needs to be redone.
Now you can remove the temporary directory with the following command:
rm -rf /root/rpms
3
3.6
SECURE INITIAL SYSTEM CONFIGURATION
20
Disable services
Note: The system runlevel as specified in the ’initdefault’ entry in /etc/inittab MUST remain at the default setting of
’3’ for these steps to be valid.
The following services are REQUIRED for runlevel 3:
atd
audit
crond
irqbalance
kudzu
network
random
syslog
#
#
#
#
#
#
#
#
the ’at’ daemon
the audit daemon
vixie-cron
configures SMP IRQ balancing
new device discovery
network interface configuration
random numbers
system logging
The following services are OPTIONAL for runlevel 3:
cups
gpm
mdmonitor
postfix
rawdevices
sshd
vsftpd
xinetd
#
#
#
#
#
#
#
#
print subsystem
console mouse management
software raid monitoring
SMTP MTA
Raw partition management (eg. for Oracle)
Secure Shell
FTP server
Internet Services
You MUST ensure that all REQUIRED services are active. You MAY enable or disable services from the OPTIONAL
list as suitable for your configuration. All other services MUST be deactivated.
Use chkconfig SERVICENAME off to disable a service, and chkconfig SERVICENAME on to enable it. The following
command lists the active services:
chkconfig --list | grep "3:on" | sort
Make sure that the audit subsystem is activated. If auditd is not running, all logins are automatically disabled in the
evaluated configuration as required by CAPP.
3.7
Remove SUID/SGID root settings from binaries
Use of the SUID bit on binaries (to run with root privileges, a.k.a. ”setuid bit”) MUST be limited to those shown in
the following list:
/bin/ping
/bin/su
/usr/bin/at
/usr/bin/chage
/usr/bin/chfn
/usr/bin/chsh
/usr/bin/crontab
/usr/bin/gpasswd
/usr/bin/newgrp
/usr/bin/passwd
3
SECURE INITIAL SYSTEM CONFIGURATION
21
The other binaries that were installed with the SUID bit set MUST have this bit removed. Administrators can still run
these binaries normally, but they are not available for ordinary users.
There are also a number of SGID files on the system that are needed:
/usr/sbin/postdrop
/usr/sbin/postqueue
/usr/sbin/utempter
# group "maildrop"
# group "maildrop"
# group "tty"
Similarly, the SGID bit MUST NOT be used to give group ”root” privileges to any binary.
Generate a list of all SUID/SGID programs on the system by running the following command:
find / -not -fstype ext3 -prune -o \
-type f \( -perm -4000 -o -perm -2000 \) \
-print
Then, for each file in this list that is not one of the permitted SUID or SGID programs, run the command chmod -s
FILE to remove the SUID and SGID bits. When done, re-run the find command to verify that the list matches the
permitted programs.
3.8
Update permissions for ’su’
The ’su’ binary MUST be restricted to members of the trusted ’wheel’ group. This will be enforced both with PAM
configuration (configured later) and the binary’s permissions.
chgrp wheel /bin/su
chmod 4710 /bin/su
You MUST have at least one user account other than ’root’ configured to be a member of the ’wheel’ group, otherwise
system administration will ONLY be possible from the system console.
3.9
Disable root login over the network
Login from the network with user ID 0 (’root’) MUST NOT be permitted over the network. Administrators MUST
use an ordinary user ID to log in, and then use the /bin/su - command to switch identities. For more information,
refer to section §4.3 ”Gaining superuser access” of this guide.
It is RECOMMENDED that you remind administrators of this by adding the following alias to the bash configuration
file /etc/profile that disables the pathless ’su’ command:
alias su="echo \"Always use ’/bin/su -’ (see Configuration Guide)\""
This alias can be disabled for the root user in /root/.bashrc:
unalias su
The restriction for direct root logins is enforced through two separate mechanisms. For network logins using ssh, the
PermitRootLogin no entry in /etc/ssh/sshd config MUST be set (see next section). Console and serial terminal
logins use the pam securetty.so PAM module in the /etc/pam.d/login file that verifies that the terminal character
device used is listed in the file /etc/securetty.
The file /etc/securetty MUST NOT be changed from the secure default settings. The original contents are the following:
3
SECURE INITIAL SYSTEM CONFIGURATION
22
console
vc/1
vc/2
vc/3
vc/4
vc/5
vc/6
vc/7
vc/8
vc/9
vc/10
vc/11
tty1
tty2
tty3
tty4
tty5
tty6
tty7
tty8
tty9
tty10
tty11
3.10
Setting up SSH
SSH protocol version 1 MUST be disabled. It has known security deficiencies.
The ssh client MUST NOT be set up SUID root (the SUID bit was removed in the post-install configuration). This
prevents the use of some authentication methods normally supported by OpenSSH, but does not affect the evaluated
configuration that uses password authentication exclusively.
The SSH Server MUST be configured to reject attempts to log in as root.
The permitted authentication mechanisms are per-user (nonempty) passwords and per-user DSS public key
authentication. All other authentication methods MUST be disabled.
The setting PAMAuthenticationViaKbdInt MUST be disabled, since this would otherwise circumvent the
disabled root logins over the network.
This results in the following option set for the SSH daemon that MUST be set in /etc/ssh/sshd config:
Protocol 2
Ciphers 3des-cbc
SyslogFacility AUTHPRIV
PermitRootLogin no
RSAAuthentication no
PubkeyAuthentication no
IgnoreRhosts yes
RhostsRSAAuthentication no
HostbasedAuthentication no
PasswordAuthentication yes
PermitEmptyPasswords no
ChallengeResponseAuthentication no
KerberosAuthentication no
3
SECURE INITIAL SYSTEM CONFIGURATION
23
PAMAuthenticationViaKbdInt no
X11Forwarding no
Subsystem sftp /usr/libexec/openssh/sftp-server
All other options MUST NOT be changed from the defaults or from those settings specified here. Specifically, you
MUST NOT add other authentication methods (AFS, Kerberos, host-based) to those permitted here.
3.11
Setting up xinetd
The xinetd super server is not used in the evaluated configuration, but MAY be used to start non-root network processes.
The file /etc/xinetd.conf contains default settings, these can be overridden by service-specific entry files stored in the
directory /etc/xinetd.d/.
The log method and the data that is to be logged are defined using the defaults entry in the /etc/xinetd.conf file.
The RECOMMENDED settings are:
defaults
{
instances
log_type
log_on_success
log_on_failure
cps
}
=
=
=
=
=
60
SYSLOG authpriv
HOST PID EXIT DURATION
HOST ATTEMPT
25 30
includedir /etc/xinetd.d
The xinetd.conf (5) man page contains more information on xinetd and configuration examples.
3.12
Setting up FTP
The evaluated configuration OPTIONALLY includes FTP services. Note that FTP does not provide support for
encryption, so this is only RECOMMENDED for anonymous access to non-confidential files. If you do not specifically
need FTP, it is RECOMMENDED that you disable the vsftpd(8) service.
Use the chkconfig(8) command to control the FTP service:
# Activate FTP service
chkconfig vsftpd on
# Disable FTP service
chkconfig vsftpd off
The vsftpd service uses several additional configuration files. In /etc/vsftpd/vsftpd.conf the configuration of the ftp
daemon is specified. In addition, the file /etc/vsftpd.ftpusers is used for access control. Users listed in that file can
NOT log in via FTP. This file initially contains all system IDs and the root user. It can be augmented with other IDs
according to the local needs, but the root entry MUST NOT be removed. The ftpusers file is not checked by the ftp
daemon itself but by a PAM module. Please see section §3.16 ”Required Pluggable Authentication Module (PAM)
configuration” of this guide for details.
The setup of /etc/vsftpd/vsftpd.conf depends on the local needs. Please refer to vsftpd.conf (5) for details.
The default configuration permits only anonymous FTP. This setting is only suitable for distribution of public files for
which no read access control is needed. It is RECOMMENDED disabling anonymous FTP if you do not need this
functionality with the following /etc/vsftpd/vsftpd.conf setting:
3
SECURE INITIAL SYSTEM CONFIGURATION
24
anonymous_enable=NO
You MAY enable FTP authentication for local user accounts. The corresponding setting in /etc/vsftpd/vsftpd.conf is:
local_enable=YES
It is RECOMMENDED to use the more secure alternatives sftp(1) or scp(1) to copy files among users, and to use FTP
only for legacy applications that do not support this alternative.
3.13
Setting up Postfix
The default settings of the postfix MTA are in accordance with the EAL3 requirements. An alias MUST be set up
for root in /etc/aliases, as postfix will not deliver mail while running with UID 0. Specify one or more user names of
administrators to whom mail addressed to root will be forwarded.
Please see postfix(1), master(8), and the documentation in /usr/share/doc/postfix*/ for details.
3.14
Setting up the audit subsystem
This section describes only the initial setup and default configuration of the audit subsystem. Please refer to section
§5.3 ”Configuring the audit subsystem” of this guide for information about how it works and what changes MAY be
made to the configuration.
Since failures in the audit subsystem may result in an unusable system, ensure that the audit subsystem is properly
activated:
# Create the audit device if necessary
ls -l /dev/audit
mknod -m 600 /dev/audit c 10 224
# ensure that auditd gets launched
chkconfig audit on
3.14.1
Installing the packages needed for auditing
The required packages have already been installed in the previous step described in section §3.2 ”Installing required
updates” of this guide. This section describes the further changes that need to be made to reach the initial state of the
evaluated configuration.
The audit subsystem consists of the following packages:
kernel-*
The kernels include the audit modifications, including the driver drivers/audit/* and the required hooks in the
rest of the kernel.
laus, laus-libs
Contains the userspace Linux Auditing Subsystem (LAuS) programs including auditd(8), aucat(8) and
augrep(8), the liblaus.so shared library, the /etc/rc.d/init.d/audit startup script, the configuration in
/etc/sysctl.conf, the /lib/security/pam laus.so PAM module and the corresponding man pages. The
corresponding development libraries and headers are in the laus-devel RPM, which is not installed as part of the
evaluated configuration.
at, cron, shadow-utils
These packages contain audit-enabled versions of the trusted programs, which will generate audit records for
security relevant events.
3
SECURE INITIAL SYSTEM CONFIGURATION
3.14.2
25
Setting up the audit configuration files
It is RECOMMENDED to add the following settings to the file /etc/sysctl.conf :
dev.audit.max-messages = 1024
dev.audit.paranoia = 0
dev.audit.attach-all = 0
dev.audit.allow-suspend = 1
The rhel-eal3.bash script automatically sets up this configuration.
The appendix of this guide lists the RECOMMENDED content of the audit configuration files. The laus package by
default installs these files with the RECOMMENDED contents:
/etc/audit/audit.conf
/etc/audit/filter.conf
/etc/audit/filesets.conf
3.14.3
Starting auditd at boot as a system service
The evaluated configuration runs auditd as a standard daemon service launched as part of the normal startup
sequence, this is activated with the following command:
chkconfig audit on
3.14.4
Starting auditd in fail-secure mode from init (OPTIONAL)
Running auditd as a system service is the standard and recommended method, other system components such as
cron and atd are also launched in this way.
However, if auditd is killed or unexpectedly terminates, audit messages will be lost until the administrator restarts
the service. This failure mode does not violate CAPP requirements, because only the sysadmin can kill the audit
daemon. The only failure mode addressed by CAPP concerns running out of disk space, and that is handled directly
by auditd. Any other abnormal termination would indicate a serious bug that should be investigated, reported and
fixed.
If you want to ensure that an instance of auditd will always be running even in case of these unusual failure modes,
you MAY set up an alternative configuration and launch auditd via the init daemon.
To do this, disable the audit system service, then create an entry in the file /etc/inittab and activate it:
chkconfig audit off
echo "au:35:respawn:/sbin/auditd -F" >> /etc/inittab
init q
This operating mode ensures that an instance of auditd will always be running, because init will automatically
restart auditd immediately if it terminates for any reason. If init cannot restart auditd in this way, it will generate
a syslog warning message and temporarily deactivate the inittab entry for five minutes.
3
26
SECURE INITIAL SYSTEM CONFIGURATION
3.15
Introduction to Pluggable Authentication Module (PAM) configuration
The PAM subsystem is responsible for maintaining passwords and other authentication data. Because this is a
security-critical system, understanding how it works is very important. In addition to the pam(8) manual page,
full documentation is available in /usr/share/doc/pam-*/txts/ and includes ”The Linux-PAM System Administrator’s
Guide” (pam.txt) as well as information for writing PAM applications and modules. Detailed information about
modules is available in /usr/share/doc/pam-*/txts/README.pam * as well as manual pages for individual modules,
such as pam stack(8).
The PAM configuration is stored in the /etc/pam.d/ directory. Note that the documentation refers to a file /etc/pam.conf
that is not used by RHEL (PAM was compiled to ignore this file if the /etc/pam.d/ directory exists).
Each service (application) that uses PAM for authentication uses a service-name to determine its configuration. stored
in the /etc/pam.d/SERVICE NAME file. The special service-name OTHER (case insensitive) is used for default settings
if there are no specific settings.
The configuration file for the service contains one entry for each module, in the format:
module-type
control-flag
module-path
args
Comments MAY be used extending from ’#’ to the end of the line, and entries MAY be split over multiple lines using
a backslash at the end of a line as a continuation character.
The module-type defines the type of action being done. This can be one of four types:
auth
Authenticates users (determines that they are who they claim to be). It can also assign credentials, for example
additional group memberships beyond those specified through /etc/passwd and /etc/groups. This additional
functionality MUST NOT be used.
account
Account management not related to authentication, it can also restrict access based on time of day, available
system resources or the location of the user (network address or system console).
session
Manages resources associated with a service by running specified code at the start and end of the session. Typical
usage includes logging and accounting, and initialization such as auto mounting a home directory.
password
Used for updating the password (or other authentication token), for example when using the passwd(1) utility to
change it.
The control-flag specifies the action that will be taken based on the success or failure of an individual module. The
modules are stacked (executed in sequence), and the control-flags determine which final result (success or failure) will
be returned, thereby specifying the relative importance of the modules.
Stacked modules are executed in the order specified in the configuration file.
The control-flag can be specified as either a single keyword, or alternatively with a more elaborate syntax that allows
greater control. RHEL uses only the single keyword syntax by default.
The following keywords control how a module affects the result of the authentication attempt:
required
If this module returns a failure code, the entire stack will return failure. The failure will be reported to the
application or user only after all other modules in the stack have been run, to prevent leakage of information (for
example, ask for a password even if the entered username is not valid).
3
SECURE INITIAL SYSTEM CONFIGURATION
27
requisite
Same as required, but return failure immediately not executing the other modules in the stack. Can be used to
prevent a user from entering a password over an insecure connection.
sufficient
Return success immediately if no previous required modules in the stack have returned failure. Do not execute
succeeding modules.
optional
The return code of this module is ignored, except if all other modules in the stack return an indeterminate result
(PAM IGNORE).
The module-path specifies the filename of the module to be run (relative to the directory /lib/security/, and the optional
args are passed to the module - refer to the module’s documentation for supported options.
3.16
Required Pluggable Authentication Module (PAM) configuration
You MUST restrict authentication to services that are explicitly specified. The ’other’ fallback MUST be disabled
by specifying the pam deny.so module for each module-type in the ’other’ configuration. This ensures that access
decisions within the PAM system are handled only by the service specific PAM configuration.
Note that RHEL uses the pam stack(8) module to unify commonly used configuration options within single files,
rather than having redundant information in multiple files. You MUST verify that the shared settings are applicable to
services that use pam stack, and keep in mind that a change to the shared file will affect several services.
You MUST add the pam wheel.so module to the ’auth’ module type configuration for the ’su’ service to restrict use of
su(1) to members of the ’wheel’ group.
You MUST add the pam tally.so module to the auth and account module type configurations of login, sshd and
vsftpd. This ensures that accounts are disabled after several failed login attempts.The pam tally.so module is used in
the auth stack to increment a counter in the file /var/log/lastlog, and in the account stack to either deny login after
too many failed attempts, or to reset the counter to zero after successful authentication. The evaluated configuration
uses a lockout after six failed attempts, corresponding to the setting deny=6, you MAY decrease the number for
stricter enforcement. Be aware that this can be used in denial-of-service attacks to lock out legitimate users. Please
refer to section §4.7 ”Managing user accounts” of this guide for more information.
You MUST use the pam passwdqc.so password quality checking module to ensure that users will not use
easily-guessable passwords.
The system supports many other PAM modules apart from the ones shown here. In general, you MAY add PAM
modules that add additional restrictions. You MUST NOT weaken the restrictions through configuration changes of
the modules shown here or via additional modules. Also, you MUST NOT add PAM modules that provide additional
privileges to users (such as the pam console.so module).
You MUST NOT run the authconfig(8) tool to modify the authentication configuration.
Following are the pam configuration files:
3.16.1
/etc/pam.d/system-auth
This file contains common settings that are shared by multiple services using authentication. The pam passwdqc.so
module is configured to enforce the minimum password length of 8 characters. Note that the pam passwdqc.so module
is not part of a default installation, it was added previously as described in section §3.5 ”Add and remove packages”
of this guide.
The pam tally module MUST be used to block the user after 5 failed login attempts.
3
SECURE INITIAL SYSTEM CONFIGURATION
28
The remember option to pam unix.so prevents users from reusing old passwords. Hashes of old passwords are stored
in the file /etc/security/opasswd. Note that this file MUST exist, otherwise users cannot change passwords. Use the
following commands to create it:
touch /etc/security/opasswd
chmod 600 /etc/security/opasswd
The file /etc/pam.d/system-auth MUST be set up with the following content:
#%PAM-1.0
#
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
#
# ... so don’t run authconfig
#
# pam.d/system-auth - PAM master configuration for EAL3/CAPP compliance
#
see the Evaluated Configuration Guide for more info
#
auth
auth
auth
required
required
required
pam_tally.so onerr=fail no_magic_root
pam_env.so
pam_unix.so likeauth nullok
account
account
required
required
pam_unix.so
pam_tally.so deny=5 reset no_magic_root
password
required
password
required
pam_passwdqc.so min=disabled,disabled,16,12,8 \
random=42
pam_unix.so nullok use_authtok md5 \
shadow remember=7
session
session
required
required
3.16.2
pam_limits.so
pam_unix.so
/etc/pam.d/login
This file configures the behavior of the login program. It allows root login only for terminals configured in
/etc/securetty. If the file /etc/nologin is present, then only root can log in.
The pam laus.so module is by default configured to be optional instead of required, which assumes that all
terminals available for login are in physically secure locations and accessible only for authorized administrators. This
permits administrators to log in on the console even if the audit subsystem is not available. If any serial terminals are
attached and available for arbitrary users, you MUST specify the pam laus.so module to be required to ensure the
CAPP-compliant fail-secure operating mode that disables login if audit is not working. Please refer to section §4.8
”Using serial terminals” of this guide for more information.
#%PAM-1.0
#
# pam.d/login - PAM login configuration for EAL3/CAPP certification
#
see the Evaluated Configuration Guide for more info
#
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SECURE INITIAL SYSTEM CONFIGURATION
29
# If serial terminals are in use, pam_laus.so MUST be changed to be ’required’
# for CAPP-complaint fail-secure auditing. The default ’optional’ setting
# assumes that all terminals are in physically secure locations.
#
auth
auth
auth
required
required
required
pam_securetty.so
pam_stack.so service=system-auth
pam_nologin.so
account
required
pam_stack.so service=system-auth
password
required
pam_stack.so service=system-auth
session
#session
session
required
required
optional
pam_stack.so service=system-auth
pam_laus.so # fail-secure mode
pam_laus.so # requires physically secure terminals
3.16.3
/etc/pam.d/other
This configuration applies for all PAM usage for which no explicit service is configured. It will log and block any
attempts.
#%PAM-1.0
#
# pam.d/other - PAM other configuration for EAL3/CAPP compliance
#
see the Evaluated Configuration Guide for more info
#
auth
auth
required
required
pam_warn.so
pam_deny.so
account
account
required
required
pam_warn.so
pam_deny.so
password required
password required
pam_warn.so
pam_deny.so
session
session
pam_warn.so
pam_deny.so
3.16.4
required
required
/etc/pam.d/sshd
This file configures the PAM usage for SSH. This is similar to the login configuration. The securetty entry is not
applicable to network logins, and the pam laus.so module MUST be configured to prevent network login if the audit
system is not available. Note that pam laus.so MUST run in the account stack, it does not work in the account or auth
stacks due to the OpenSSH privilege separation mechanism.
#%PAM-1.0
#
# pam.d/sshd - pam.d/sshd configuration for EAL3/CAPP compliance
#
see the Evaluated Configuration Guide for more info
#
3
SECURE INITIAL SYSTEM CONFIGURATION
auth
auth
required
required
pam_stack.so service=system-auth
pam_nologin.so
account
account
required
required
pam_stack.so service=system-auth
pam_laus.so detach
password
required
pam_stack.so service=system-auth
session
required
pam_stack.so service=system-auth
3.16.5
30
/etc/pam.d/su
This file configures the behavior of the ’su’ command. Only users in the trusted ’wheel’ group can use it to become
’root’, as configured with the pam wheel module.
#%PAM-1.0
#
# pam.d/su - PAM su configuration from EAL3/CAPP compliance
#
see the Evaluated Configuration Guide for more info
#
auth
auth
auth
sufficient
required
required
pam_rootok.so
pam_wheel.so use_uid
pam_stack.so service=system-auth
account
required
pam_stack.so service=system-auth
password
required
pam_deny.so
session
session
required
optional
pam_stack.so service=system-auth
pam_xauth.so
The password branch is disabled because forcing the root user to change the root password is not desired for this
program,
3.16.6
/etc/pam.d/vsftpd
This file configures the authentication for the FTP daemon. With the listfile module, users listed in /etc/vsftpd.ftpusers
are denied FTP access to the system. Note that the setting is relevant only for authentication of incoming connections,
and does not prevent local users from using the ftp(1) client to access other machines on the network.
#%PAM-1.0
#
# pam.d/vsftpd - vsftpd configuration for EAL3/CAPP compliance
#
see the Evaluated Configuration Guide for more info
auth
required
auth
auth
required
required
pam_listfile.so item=user sense=deny \
file=/etc/vsftpd.ftpusers onerr=succeed
pam_stack.so service=system-auth
pam_shells.so
3
SECURE INITIAL SYSTEM CONFIGURATION
account
account
required
required
pam_stack.so service=system-auth
pam_laus.so detach
password
required
pam_deny.so
session
required
pam_stack.so service=system-auth
31
pam deny.so is used in the password stack because the FTP protocol has no provisions for changing passwords.
3.17
Configuring default account properties
The file /etc/login.defs defines settings that will be used by user management tools such as useradd(8). The file is not
used during the authentication process itself.
The password aging settings defined in this file are used when creating users and when changing passwords, and stored
in the user’s /etc/shadow entry. Note that only the /etc/shadow entries are considered during authentication, so changes
in /etc/login.defs will not retroactively change the settings for existing users.
The PASS MIN LEN setting has no effect in the evaluated configuration, the relevant settings are instead configured
using the min= parameter to pam passwdqc.so in the /etc/pam.d/system-auth file.
#
Directory where mailboxes reside, _or_ name of file, relative to the
#
home directory. If you _do_ define both, MAIL_DIR takes precedence.
#
QMAIL_DIR is for Qmail
#
# The setting is used only when creating or deleting users, and has
# no effect on the mail delivery system. MAY be changed as required.
#
#QMAIL_DIR
Maildir
#MAIL_FILE
.mail
MAIL_DIR
/var/spool/mail
# Password aging controls:
#
#
PASS_MAX_DAYS
Maximum number of days a password may be used.
#
PASS_MIN_DAYS
Minimum number of days allowed between password changes.
#
PASS_MIN_LEN
Minimum acceptable password length.
#
PASS_WARN_AGE
Number of days warning given before a password expires.
#
PASS_MAX_DAYS
60
# MAY be changed, must be <= 60
PASS_MIN_DAYS
1
# MAY be changed, 0 < PASS_MIN_DAYS < PASS_MAX_DAYS
PASS_WARN_AGE
7
# MAY be changed
PASS_MIN_LEN
5
# no effect in the evaluated configuration
#
# Min/max values for automatic uid selection in useradd
#
# MAY be changed, 100 < UID_MIN < UID_MAX < 65535
#
UID_MIN
500
UID_MAX
60000
3
SECURE INITIAL SYSTEM CONFIGURATION
32
#
# Min/max values for automatic gid selection in groupadd
#
# MAY be changed, 100 < GID_MIN < GID_MAX < 65535
#
GID_MIN
500
GID_MAX
60000
#
# If defined, this command is run when removing a user.
# It should remove any at/cron/print jobs etc. owned by
# the user to be removed (passed as the first argument).
#
# MAY be activated as described in the "Managing user accounts"
# section of the ECG.
#
#USERDEL_CMD
/usr/sbin/userdel_local
#
# If useradd should create home directories for users by default
# On RH systems, we do. This option is ORed with the -m flag on
# useradd command line.
#
# MAY be changed.
#
CREATE_HOME
yes
3.18
Configuring the boot loader
You MUST set up the server in a secure location where it is protected from unauthorized access. Even though that
is sufficient to protect the boot process, it is RECOMMENDED to configure the following additional protection
mechanisms:
• Ensure that the installed system boots exclusively from the disk partition containing RHEL, and not from floppy
disks, USB drives, CD-ROMs, network adapters, or other devices.
• Ensure that this setting cannot be modified, for example by using a BootProm/BIOS password to protect access
to the configuration.
3.18.1
GRUB boot loader configuration
The GRUB boot loader is used on the xSeries and eServer 325 (Opteron) platforms. It is highly configurable, and
permits flexible modifications at boot time through a special-purpose command line interface. Please refer to the
grub(8) man page or run info grub for more information.
• Use the password command in /boot/grub/menu.lst to prevent unauthorized use of the boot loader interface.
Using md5 encoded passwords is RECOMMENDED, run the command grub-md5-crypt to generate the encoded
version of a password.
• Protect all menu entries other than the default RHEL boot with the lock option, so that the boot loader
will prompt for a password when the user attempts to boot from other media (such as a floppy) or sets other
non-default options for the boot process. To implement this, add a line containing just the keyword lock after
the title entry in the /boot/grub/menu.lst file.
3
SECURE INITIAL SYSTEM CONFIGURATION
33
• Remove group and world read permissions from the grub configuration file if it contains a password by running
the following command:
chmod 600 /boot/grub/menu.lst
All changes to the configuration take effect automatically on the next boot, there is no need to re-run an activation
program.
The following example of the /boot/grub/menu.lst configuration file shows RECOMMENDED settings:
default=0
timeout=10
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
password --md5 $1$O471l/$H/JW2MYeugX6Y1h3v.1Iz0
title Red Hat Enterprise Linux AS (2.4.21-15.EL)
lock
root (hd0,0)
kernel /boot/vmlinuz-2.4.21-15.EL ro root=LABEL=/
initrd /boot/initrd-2.4.21-15.EL.img
Note that the configuration shown here might not be exactly the configuration used on the installed system, depending
on the kernel options needed for the hardware.
3.18.2
Yaboot boot loader configuration
Yaboot is used on the pSeries machines, it is an OpenFirmware-based boot loader, and can be reconfigured at boot
time from a specialized command line.
Yaboot and GRUB are very similar, both support MD5-encrypted passwords specified in the configuration file.
You need to re-run the ybin(8) tool when you have modified the configuration file, this is however not necessary if you
replace a kernel and keep all path names unchanged.
Please refer to the yaboot.conf (5) and ybin(8) manual pages and the yaboot HOWTO for more information:
http://penguinppc.org/projects/yaboot/doc/yaboot-howto.shtml
3.18.3
ZIPL boot loader configuration
The ZIPL boot loader is used on the zSeries mainframe when the system is set up using the VM virtualization layer.
In this context, ”booting” refers to the initial program load (IPL) done from the CP command prompt, which affects
only a single specific Linux instance (a.k.a. ”partition”, which refers to the running system and not the disk partition
in this context).
Configuration of the VM system is beyond the scope of this document. You MUST ensure that the configuration
settings and virtual devices used are only accessible to the authorized administrators. Do NOT use unencrypted 3270
sessions for console access on insecure networks.
ZIPL writes a boot record on the virtual disk (DASD) used by this Linux instance, this boot record then proceeds to load
and run the Linux kernel itself. The zipl command must be re-run after any kernel or boot argument modifications.
Please refer to the zipl(8) man page for more information.
The following example shows a typical /etc/zipl.conf file:
4
SYSTEM OPERATION
34
[defaultboot]
default=ipl
[ipl]
target=/boot/zipl
image=/boot/kernel/image
ramdisk=/boot/initrd
parameters="dasd=0200 root=/dev/dasda1"
3.18.4
iSeries kernel slots
Similar to zSeries, the iSeries hosts use an initial program load (IPL) system to load and initialize a virtual Linux
instance. There is no boot loader program on the Linux side, the host platform’s boot loader is configured through
device drivers accessed via virtual files in the /proc/ file system.
The system supports multiple kernel slots. Usually, slot A contains the production kernel, and slot B is reserved for
experimental kernels. The default boot image is selected via the /proc/iSeries/mf/side virtual file.
The kernel slot may contain either just a plain kernel (file name ”vmlinux” or similar), or a combined kernel plus initial
root disk (file name ”vmlinitrd” or similar). Use the combined kernel+initrd if available to ensure that all necessary
modules will be available for booting.
There are usually several different kernels and/or kernel+initrd files in /boot/, be careful to use the right file based on
the version number information contained in the file name.
Here is a sample session to copy an image to kernel slot B, and activate it:
dd if=/boot/vmlinitrd of=/proc/iSeries/mf/B/vmlinux bs=4k
cat /proc/cmdline > /proc/iSeries/mf/B/cmdline
echo "B" > /proc/iSeries/mf/side
For more information, please refer to:
http://www-1.ibm.com/servers/eserver/iseries/linux/tech_faq.html
3.19
Reboot and initial network connection
After all the changes described in this chapter have been done, you MUST reboot the system to ensure that all unwanted
tasks are stopped, and that the running kernel, modules and applications all correspond to the evaluated configuration.
Please make sure that the boot loader is configured correctly for your platform. On zSeries, remember to run the zipl(8)
tool to write the boot record.
The system will then match the evaluated configuration. The server MAY then be connected to a secure network as
described above.
4
System operation
To ensure that the systems remains in a secure state, special care MUST be taken during system operation.
4
4.1
SYSTEM OPERATION
35
System startup, shutdown and crash recovery
Use the shutdown(8), halt(8) or reboot(8) programs as needed to shut down or reboot the system.
When powered on (or on initial program load of the logical partition on a host system), the system will boot into the
RHEL operating system. If necessary (for example after a crash), a filesystem check will be performed automatically.
In rare cases manual intervention is necessary, please refer to the e2fsck(8) and debugfs(8) documentation for details
in this case.
In case a nonstandard boot process is needed (such as booting from floppy disk or CD-ROM to replace a defective hard
drive), interaction with the boot loader and/or the host’s management system can be used to modify the boot procedure
for recovery.
For example, on xSeries you can use the following grub commands to launch a shell directly from the kernel, bypassing
the normal init/login mechanism:
# view the current grub configuration
grub> cat (hd0,1)/boot/grub/menu.lst
# manually enter the modified settings
grub> kernel (hd0,1)/boot/vmlinuz root=/dev/sda1 init=/bin/sh
grub> initrd (hd0,1)/boot/initrd
grub> boot
Please refer to the relevant documentation of the boot loader, as well as the RHEL administrator guide, for more
information.
4.2
Backup and restore
Whenever you make changes to security-critical files, you MAY need to be able to track the changes made and revert
to previous versions, but this is not required for compliance with the evaluated configuration.
The star(1) archiver is RECOMMENDED for backups of complete directory contents, please refer to section §6.5
”Data import / export” of this guide. Regular backups of the following files and directories (on removable media such
as tapes or CD-R, or on a separate host) are RECOMMENDED:
/etc/
/var/spool/cron/
/var/spool/at/
Depending on your site’s audit requirements, also include the contents of /var/log/ in the backup plan. In that case, the
automatic daily log file rotation needs to be disabled or synchronized with the backup mechanism, refer to sections
§5.2 ”System logging and accounting” and §5.3 ”Configuring the audit subsystem” of this guide for more information.
You MUST protect the backup media from unauthorized access, because the copied data does not have the access
control mechanisms of the original file system. Among other critical data, it contains the secret keys used by the SSH
and stunnel servers, as well as the /etc/shadow password database. Store the backup media at least as securely as the
server itself.
A RECOMMENDED method to track changes is to use a version control system. RCS is easy to set up because
it does not require setting up a central repository for the changes, and you can use shell scripting to automate the
change tracking. RCS is not included in the evaluated configuration, see rcsintro(1) in the rcs RPM package for more
information. Alternatively, you can create manually create backup copies of the files and/or copy them to other servers
using scp(1).
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4.3
SYSTEM OPERATION
36
Gaining superuser access
System administration tasks require superuser privileges. Since directly logging on over the network as user ’root’ is
disabled, you MUST first authenticate using an unprivileged user ID, and then use the su command to switch identities.
Note that you MUST NOT use the ’root’ rights for anything other than those administrative tasks that require these
privileges, all other tasks MUST be done using your normal (non-root) user ID.
You MUST use exactly the following su(1) command line to gain superuser access:
/bin/su This ensures that the correct binary is executed irrespective of PATH settings or shell aliases, and that the root shell
starts with a clean environment not contaminated with the starting user’s settings. This is necessary because the .profile
shell configuration and other similar files are writable for the unprivileged ID, which would allow an attacker to easily
elevate privileges to root if able to subvert these settings.
Administrators MUST NOT add any directory to the root user’s PATH that are writable for anyone other than ’root’,
and similarly MUST NOT use or execute any scripts, binaries or configuration files that are writable for anyone other
than ’root’, or where any containing directory is writable for a user other than ’root’.
4.4
Installation of additional software
Additional software packages MAY be installed as needed, provided that they do not conflict with the security
requirements.
Any additional software added is not intended to be used with superuser privileges. The administrator MUST use only
those programs that are part of the original evaluated configuration for administration tasks, except if the administrator
has independently ensured that use of the additional software is not a security risk.
Administrators MAY add scripts to automate tasks as long as those only depend on and run programs that are part of
the evaluated configuration.
The security requirements for additional software are:
• Kernel modules other than those provided as part of the evaluated configuration MUST NOT be installed or
loaded. You MUST NOT load the tux kernel module (the in-kernel web server is not supported). You MUST
NOT add support for non-ELF binary formats or foreign binary format emulation that circumvents system call
auditing. You MUST NOT activate knfsd or export NFS file systems.
• Device special nodes MUST NOT be added to the system.
• SUID root or SGID root programs MUST NOT be added to the system. Programs which use the SUID or SGID
bits to run with identities other than ’root’ MAY be added.
• The content, permissions, and ownership of all existing filesystem objects (including directories and device
nodes) that are part of the evaluated configuration MUST NOT be modified. Files and directories MAY be
added to existing directories provided that this does not violate any other requirement.
• Programs automatically launched with ’root’ privileges MUST NOT be added to the system. Exception:
processes that immediately and permanently switch to a non privileged identity on launch are permitted,
for example by using su USERID -c LAUNCH COMMAND in the startup file, or alternatively by using the
setgroups(2), setgid(2) and setuid(2) system calls in a binary. (seteuid(2) etc. are insufficient.)
Automatic launch mechanisms are:
– Entries in /etc/inittab
– Executable files or links in /etc/rc.d/init.d/ and its subdirectories
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37
– Entries in /etc/xinetd.conf
– Scheduled jobs using cron (including entries in /etc/cron* files) or at
Examples of programs that usually do not conflict with these requirements and MAY be installed are compilers,
interpreters, network services running with non-root rights, and similar programs. The requirements listed above
MUST be verified in each specific case.
4.5
Scheduling processes using cron and at
The cron(8) program schedules programs for execution at regular intervals. Entries can be modified using the
crontab(1) program - the file format is documented in the crontab(5) manual page.
You MUST follow the rules specified for installation of additional programs for all entries that will be executed by the
’root’ user. Use non-root crontab entries in all cases where ’root’ privileges are not absolutely necessary.
The at(1) and batch(1) programs execute a command line at a specific single point of time. The same rules apply as
for jobs scheduled via cron(8). Use atq(1) and atrm(1) to manage the scheduled jobs.
Errors in the non interactive jobs executed by cron and at are reported in the system log files in /var/log/, and
additionally via e-mail to the user who scheduled it.
Permission for users to schedule jobs with cron and at is controlled through the following allow and deny files:
/etc/at.allow
/etc/at.deny
/etc/cron.allow
/etc/cron.deny
The allow file has precedence if it exists, then only those users whose usernames are listed in it are permitted to use the
service. If it does not exist, the deny file is used instead and all users who are not listed in that file can use the service.
Note that the contents of these files are only relevant when the scheduling commands are executed, and changes have
no effect on already scheduled commands.
In the RHEL distribution, the allow files do not exist, and deny files are used to prevent system-internal IDs and/or
guest users from using these services. By default, the evaluated configuration permits everybody to use cron and at.
It is RECOMMENDED to restrict the use of cron and at to human users and disallow system accounts from using
these mechanisms. For example, the following commands add all system accounts other than root to the deny files:
awk -F: ’{if ($3>0 && $3<100) print $1}’ /etc/passwd >/etc/at.deny
chmod 600 /etc/at.deny
cp /etc/at.deny /etc/cron.deny
Administrators MAY schedule jobs that will be run with the privileges of a specified user by editing the file /etc/crontab
with an appropriate username in the sixth field. Entries in /etc/crontab are not restricted by the contents of the allow
and deny files.
You MAY create /etc/at.allow and/or /etc/cron.allow files to explicitly list users who are permitted to use these services.
If you do create these files, they MUST be owned by the user ’root’ and have file permissions 0600 (no access for group
or others).
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4.6
38
Mounting filesystems
If any filesystems need to be mounted in addition to those set up at installation time, appropriate mount options MUST
be used to ensure that mounting the filesystem does not introduce capabilities that could violate the security policy.
A new file system can be integrated as part of the evaluated configuration, for example by installing an additional hard
disk, under the following conditions:
• The device is protected against theft or manipulation in the same way as the server itself, for example by being
installed inside the server.
• One or more new, empty, file systems in EXT3 format are created on it.
• The file systems are mounted using the acl option, for example with the following setting in the /etc/fstab file:
/dev/sdc1 /home2 ext3 acl 1 2
Existing files and directories MAY then be moved onto the new file systems.
• If a device containing a file system is ever removed from the system, the device MUST be stored within the
secure server facility, or alternatively MUST be destroyed in a way that the data on it is reliably erased.
Alternatively, media MAY be accessed without integrating them into the evaluated configuration, for example
CD-ROMs.
The following mount options MUST be used if the filesystems contain data that is not part of the evaluated
configuration:
ro,nodev,nosuid
Adding the noexec mount option to avoid accidental execution of files or scripts on additional mounted filesystems is
RECOMMENDED.
Note that these settings do not completely protect against malicious code and data, you MUST also verify that the
data originates from a trustworthy source and does not compromise the server’s security. Specifically, be aware of the
following issues:
• Even unprivileged programs and scripts can contain malicious code that uses the calling user’s rights in
unintended ways, such as corrupting the user’s data, introducing trojan horses in the system, attacking other
machines on the network, revealing confidential documents, or sending unsolicited commercial e-mail (”spam”).
• Data on the additional filesystem MUST have appropriate access rights to prevent disclosure to or modification
by unauthorized users. Be aware that imported data may have been created using user names and permissions
that do not match your system’s security policies.
• You MUST NOT write data on removable file systems such as floppy disks, since it cannot be adequately
protected by the system’s access control mechanisms after being removed from the system. Please refer to
section §4.2 ”Backup and restore” of this guide for more information regarding non-filesystem-based backup.
Each new file system MUST be mounted on an empty directory that is not used for any other purpose. It is
RECOMMENDED using subdirectories of /mnt for temporary disk and removeable storage media mounts.
For example:
# mount /dev/cdrom /mnt/cdrom -t iso9660 -o ro,nodev,nosuid,noexec
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You MAY also add an equivalent configuration to /etc/fstab, for example:
/dev/cdrom /mnt/cdrom iso9660 ro,noauto,nodev,nosuid,noexec 0 0
You MUST NOT include the user flag, ordinary users are not permitted to mount filesystems. This is also enforced by
the deletion of the SUID bit on the mount command.
4.7
Managing user accounts
Use the useradd(8) command to create new user accounts, then use the passwd(1) command to assign an initial
password for the user. Alteratively, if the user is present when the account is created, permit them to choose their own
password. Refer to the manual pages for useradd(8) and passwd(1) for more information.
If you assign an initial password for a new user, you MUST transfer this initial password in a secure way to the user,
ensuring that no third party gets the information. For example, you can tell the password to a user personally known
to you. If this is not possible, you MAY send the password in written form in a sealed letter. This applies also when
you set a new password for a user in case the user has forgotten the password or it has expired. You need to advise
the user that he MUST change this initial password when he first logs into the system and select his own password in
accordance with the rules defined in section §6.3 ”Password policy” of this guide.
You MUST NOT use the -p option to useradd(8), specifying a password in that way would bypass the password
quality checking mechanism.
The temporary password set by the administrator MUST be changed by the user as soon as possible. Use the chage(8)
command with the -d option to set the last password change date to a value where the user will be reminded to change
the password. The RECOMMENDED value is based on the settings in /etc/login.defs and is equivalent to today’s date
plus PASS WARN AGE minus PASS MAX DAYS.
Example:
useradd -m -c "John Doe" jdoe
passwd jdoe
chage -d $(date +%F -d "53 days ago") jdoe
The -m option to useradd(8) creates a home directory for the user based on a copy of the contents of the /etc/skel/
directory. Note that you MAY modify some default configuration settings for users, such as the default umask(2)
setting or time zone, by editing the corresponding global configuration files:
/etc/profile
/etc/bashrc
/etc/csh.cshrc
If necessary, you MAY reset the user’s password to a known value using passwd USER, and entering the new
password. You cannot recover the previously used password, since the hash function used is not reversible.
You MAY use the usermod(8) command to change a user’s properties. For example, if you want to add the user ’jdoe’
to the wheel group, you could use the following:
# List the groups the user is currently a member of:
groups jdoe
# Add the additional group
usermod -G $(su jdoe -c groups | sed ’s/ /,/g’),wheel jdoe
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Users MAY be locked out (disabled) using passwd -l USER, and re-enabled using passwd -u USER.
The pam tally.so PAM module enforces automatic lockout after excessive failed authentication attempts,
as described in section §3.16 ”Required Pluggable Authentication Module (PAM) configuration” of this
guide. Use the program pam tally to view and reset the counter if necessary, as documented in the file
/usr/share/doc/pam-*/txts/README.pam tally. Note that the pam tally mechanism does not prevent password
guessing attacks, it only prevents use of the account after such an attack has been detected. Therefore, you MUST
assign a new password for the user before reactivating an account. For example:
# view the current counter value
pam_tally --user jdoe
# set new password, and reset the counter
passwd jdoe
pam_tally --user jdoe --reset
The chage(1) utility MAY be used to view and modify the expiry settings for user accounts. Unprivileged users are
able to view but not modify their own expiry settings.
The userdel(8) utility removes the user account from the system, but does not remove files outside the home directory
(and the mail spool file), or kill processes belonging to this user. Use kill (or reboot the system) and find to do so
manually if necessary, for example:
# Which user to delete?
U=jdoe
# Lock user account, but don’t remove it yet
passwd -l $U
# Kill all user processes, repeat if needed (or reboot)
kill -9 ‘ps -la --User $U|awk ’{print $4}’‘
# Recursively remove all files and directories belonging to user
# (Careful - this may delete files belonging to others if they
# are stored in a directory owned by this user.)
find / -depth \( ! -fstype ext3 -prune -false \) \
-o -user $U -exec rm -rf {} \;
# Remove cron and at jobs
crontab -u $U -r
find /var/spool/at -user $U -exec rm {} \;
# Now delete the account
userdel $U
If you need to create additional groups or modify existing groups, use the groupadd(8), groupmod(8) and groupdel(8)
commands.
Group passwords are NOT supported in the evaluated configuration, and have been disabled by removing the SUID
bit from the newgrp(8) program. You MUST NOT re-enable this feature and MUST NOT use passwd(1) with the -g
switch or the gpasswd(1) command to set group passwords.
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4.8
41
Using serial terminals
You MAY attach serial terminals to the system. They are activated by adding an entry in the file /etc/inittab for each
serial terminal that causes init(8) to launch an agetty(8) process to monitor the serial line. agetty runs login(1) to handle
user authentication and set up the user’s session.
If you use serial terminals and require the CAPP-compliant fail-safe audit mode, you MUST ensure that the file
/etc/pam.d/login is configured to require the pam laus.so module in the session stack. Please refer to section
§3.16.2 ”/etc/pam.d/login” of this guide for more information about the needed PAM configuration.
For example, adding the following line to /etc/inittab activates a VT102-compatible serial terminal on serial port
/dev/ttyS1, communicating at 19200 bits/s:
S1:3:respawn:/sbin/agetty 19200 ttyS1 vt102
The first field MUST be an unique identifier for the entry (typically the last characters of the device name). Please
refer to the agetty(8) and inittab(5) man pages for further information about the format of entries.
You MUST reinitialize the init daemon after any changes to /etc/inittab by running the following command:
init q
4.9
SYSV shared memory and IPC objects
The system supports SYSV-compatible shared memory, IPC objects, and message queues. If programs fail to release
resources they have used (for example, due to a crash), the administrator MAY use the ipcs(8) utility to list information
about them, and ipcrm(8) to force deletion of unneeded objects. Note that these resources are also released when the
system is rebooted.
For additional information, please refer to the msgctl(2), msgget(2), msgrcv(2), msgsnd(2), semctl(2), semget(2),
semop(2), shmat(2), shmctl(2), shmdt(2), shmget(2) and ftok(3) manual pages.
4.10
Configuring secure network connections with stunnel
4.10.1
Introduction
The stunnel program is a flexible and secure solution for setting up encrypted network connections, enabling the use of
strong encryption even for applications that are not able to use encryption natively. stunnel uses the OpenSSL library
for its encryption functions, and the corresponding openssl(1) command line tool for key management.
Stunnel has three main operating modes:
• Accept incoming SSL-encrypted TCP connections, and run a specific program to handle the request.
This is similar to how xinetd launches programs, and any program compatible with xinetd can also be used for
this purpose. It must read and write the communication data on the stdin and stdout file descriptors and stay in
the foreground. stunnel also supports switching user and group IDs before launching the program.
• Open a SSL connection to a remote SSL-capable TCP server, and copy data to and from stdin and stdout.
• Bind a TCP port to accept incoming unencrypted connections, and forward data using SSL to a prespecified
remote server.
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SYSTEM OPERATION
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The following diagram shows a sample usage scenario:
+-----------+
+-----------+
|
|
|
|
|
|
encrypted data stream
|
|
|
stunnel=+==================================+=stunnel
|
|
|\
//||
|
|-----------| \
local
/ |-----------|
|1024
| \
local
plain- /
|
1024|
|
|
\ plaintext
\
|
|
|
|
/ text
data
\ |
|
|
| /
data
stream
\ |
|
|
||/
stream
\_=Client
|
|
Server=+*|
|
|
|
|
|
|
|
|
|
+-----------+
+-----------+
TCP ports
TCP ports
In this scenario, neither the client nor the server have administrator privileges, they are running as normal user
processes. Also, the client and server do not support encryption directly.
stunnel makes a secure communication channel available for the client and server. On the client, stunnel is accepting
connections on TCP port 82. The client connects to this port on the local machine using normal unencrypted TCP,
stunnel accepts the connection, and opens a new TCP connection to the stunnel server running on the remote machine.
The stunnel instances use cryptographic certificates to ensure that the data stream has not been intercepted or tampered
with, and then the remote stunnel opens a third TCP connection to the server, which is again a local unencrypted
connection.
Any data sent by either the client or server is accepted by the corresponding stunnel instance, encrypted, sent to the
other stunnel, decrypted and finally forwarded to the receiving program. This way, no modifications are required to
the client and server.
To set up a secure connection compliant with the evaluated configuration, you MUST start the stunnel server(s) with
administrator rights, and you MUST use a TCP port in the administrator-reserved range 1-1023 to accept incoming
connections. A corresponding client which connects to the server MAY be started by any user, not just administrators.
stunnel MAY also be used by non-administratorive users to receive encrypted connections on ports in the range
1024-65536. This is permitted, but it is outside of the scope of the evaluated configuration and not considered to
be a trusted connection.
Any network servers and clients other than the trusted programs described in this guide (stunnel, sshd, vsftpd, postfix
and cupsd) MUST be run using non-administrator normal user identities. Programs run from stunnel MUST be
switched to a non-root user ID by using the setuid and setgid parameters in the /etc/stunnel/*.conf configuration
files.
It is RECOMMENDED configuring any such servers to accept connections only from machine-local clients, either
by binding only the localhost IP address 127.0.0.1, or by software filtering inside the application. This ensures that
the only encrypted connections are possible over the network. Details on how to do this depend on the software being
used and are beyond the scope of this guide.
Please refer to the stunnel(8) and openssl(1) man pages for more information.
4.10.2
Creating an externally signed certificate
It is strongly RECOMMENDED that you have your server’s certificate signed by an established Certificate Authority
(CA), which acts as a trusted third party to vouch for the certificate’s authenticity for clients. Please refer to the
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SYSTEM OPERATION
43
openssl(1) and req(1) man pages for instructions on how to generate and use a certificate signing request.
Create the server’s private key and a certificate signing request (CSR) with the following commands:
touch /etc/stunnel/stunnel.pem
chmod 400 /etc/stunnel/stunnel.pem
openssl req -newkey rsa:1024 -nodes \
-keyout /etc/stunnel/stunnel.pem -out /etc/stunnel/stunnel.csr
You will be prompted for the information that will be contained in the certificate. Most important is the ”Common
Name”, because the connecting clients will check if the hostname in the certificate matches the server they were trying
to connect to. If they do not match, the connection will be refused, to prevent a ’man-in-the-middle’ attack.
Here is a sample interaction:
Generating a 1024 bit RSA private key
..........++++++
.......++++++
writing new private key to ’/etc/stunnel/stunnel.pem’
----You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ’.’, the field will be left blank.
----Country Name (2 letter code) [PL]:US
State or Province Name (full name) [Some-State]:TX
Locality Name (eg, city) []:Austin
Organization Name (eg, company) [Stunnel Developers Ltd]:Example Inc.
Organizational Unit Name (eg, section) []:
Common Name (FQDN of your server) []:www.example.com
Common Name (default) []:localhost
The file /etc/stunnel/stunnel.pem will contain both the certificate (public key) and also the secret key needed by the
server. The secret key will be used by non-interactive server processes, and cannot be protected with a passphrase. You
MUST protect the secret key from being read by unauthorized users, to ensure that you are protected against someone
impersonating your server.
Next, send the generated CSR file /etc/stunnel/stunnel.csr (not the private key) to the CA along with whatever
authenticating information they require to verify your identity and your server’s identity. The CA will then generate
a signed certificate from the CSR, using a process analogous to openssl req -x509 -in stunnel.csr
-key CA-key.pem -out signed-cert.pem.
When you receive the signed certificate back from the CA, append it to the file /etc/stunnel/stunnel.pem containing the
private key using the following command:
echo >> /etc/stunnel/stunnel.pem
cat signed-cert.pem >> /etc/stunnel/stunnel.pem
Make sure that the resulting file contains no extra whitespace or other text in addition to the key and certificate, with
one blank line separating the private key and certificate:
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SYSTEM OPERATION
44
-----BEGIN RSA PRIVATE KEY----MIICXQIBAAKBgQCzF3ezbZFLjgv1YHNXnBnI8jmeQ5MmkvdNw9XkLnA2ONKQmvPQ
[...]
4tjzwTFxPKYvAW3DnXxRAkAvaf1mbc+GTMoAiepXPVfqSpW2Qy5r/wa04d9phD5T
oUNbDU+ezu0Pana7mmmvg3Mi+BuqwlQ/iU+G/qrG6VGj
-----END RSA PRIVATE KEY---------BEGIN CERTIFICATE----MIIC1jCCAj+gAwIBAgIBADANBgkqhkiG9w0BAQQFADBXMQswCQYDVQQGEwJQTDET
[...]
bIbYKL6Q1kE/vhGmRXcXQrZzkfu8sgJv7JsDpoTpAdUnmvssUY0bchqFo4Hhzkvs
U/whL2/8RFv5jw==
-----END CERTIFICATE----You MAY distribute the original signed certificate (signed-cert.pem in this example) to clients, it does not contain any
confidential information. Never distribute the file containing the private key, that is for use by the stunnel server
only.
When using externally signed certificates, you MUST use the option CApath in stunnel client configuration files along
with the setting verify=2 or verify=3 to enable the clients to verify the certificate.
4.10.3
Creating a self-signed certificate
Alternatively, you MAY use a self-signed certificate instead of one signed by an external CA. This saves some time
and effort when first setting up the server, but each connecting client will need to manually verify the certificate’s
validity. Experience shows that most users will not do the required checking and simply click ”OK” for whatever
warning dialogs that are shown, resulting in significantly reduced security. Self-signed certificates can be appropriate
for controlled environments with a small number of users, but are not recommended for general production use.
Create a self-signed host certificate with the following commands:
cd /usr/share/ssl/certs
make stunnel.pem
mv stunnel.pem /etc/stunnel/
chmod 400 /etc/stunnel/stunnel.pem
The secret key contained in this file MUST be kept secret.
You MAY extract the public certificate from this file for distribution to clients. Make sure you do not accidentally
distribute the secret key:
cd /etc/stunnel
sed ’1,/END/d’ < stunnel.pem > signed-cert.pem
The client has no independent way to verify the validity of a self-signed certificate, each client MUST manually verify
and confirm the validity of the certificate.
One method is to give a copy of the self-signed certificate to the client (using a secure transport mechanism, not
e-mail), and import it into the client directly. The stunnel client uses the CAfile option for this purpose.
Alternatively, many client programs (not stunnel) can interactively import the certificate when connecting to the
server. The client will display information about the server’s certificate including an MD5 key fingerprint. You need
to compare this fingerprint with the original fingerprint of the server’s certificate.
Run the following command on the server to display the original certificate’s fingerprint:
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SYSTEM OPERATION
45
openssl x509 -fingerprint -in /etc/stunnel/stunnel.pem
Most clients will store the certificate for future reference, and will not need to do this verification step on further
invocations.
4.10.4
Activating the tunnel
In the evaluated configuration, you MUST use the RC4-SHA cipher suite as defined in the SSL v3 protocol, also
known as SSL RSA WITH RC4 128 SHA (SC1.8).
You MUST specify the cipher list in all stunnel client and server configuration files:
ciphers = RC4-SHA
For a service or tunnel that will only be used temporarily, simply launch the stunnel program from the command
line and specify an appropriate configuration file. The tunnel will be available for multiple clients, but will not be
started automatically after a reboot. To shut down the tunnel, search for the command line in the ps ax process
listing, and use the kill(1) command with the PID shown for the stunnel process.
The RECOMMENDED method is to use two separate configuration files, one for server definitions (incoming
connections use SSL), and one for client definitions (outgoing connections use SSL). More complex configurations will
require additional configuration files containing individual service-specific settings. You MUST use the REQUIRED
settings in all stunnel configuration files.
Use the following content for the file /etc/stunnel/stunnel-server.conf :
### /etc/stunnel/stunnel-server.conf
#
# The following settings are REQUIRED for CAPP compliance when used
# as a server, see ECG. File names MAY be changed as needed.
cert = /etc/stunnel/stunnel.pem
ciphers = RC4-SHA
#
# User and group ID MUST NOT be "root", but MAY be changed as needed.
setuid = nobody
setgid = nobody
#
# The following settings are RECOMMENDED
debug = 6
output = /var/log/stunnel-server.log
pid =
foreground = yes
#
# Individual service definitions follow
Use the following content for the file /etc/stunnel/stunnel-client.conf :
### /etc/stunnel/stunnel-client.conf
#
# The following settings are REQUIRED for CAPP compliance when used
# as a client, see ECG. File names MAY be changed as needed. You
# MAY use CApath instead of CAfile for externally signed certificates.
CAfile = /etc/stunnel/signed-cert.pem
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46
SYSTEM OPERATION
ciphers = RC4-SHA
client = yes
verify = 2
#
# User and group ID MUST NOT be "root", but MAY be changed as needed.
setuid = nobody
setgid = nobody
#
# The following settings are RECOMMENDED
debug = 6
output = /var/log/stunnel-client.log
pid =
foreground = yes
#
# Individual service definitions follow
The RECOMMENDED launch method for stunnel(8) is via the init(8) process. This requires adding new entries to
/etc/inittab, the tunnels will be re-launched automatically whenever they are terminated, as well as after a reboot. The
following are the RECOMMENDED /etc/inittab entries:
ts:3:respawn:/usr/sbin/stunnel /etc/stunnel/stunnel-server.conf
tc:3:respawn:/usr/sbin/stunnel /etc/stunnel/stunnel-client.conf
Make sure you use the option foreground = yes in the configuration file when running from init (otherwise
init will misinterpret the backgrounded server as having died and will try to restart it immediately, causing a loop),
and use the output option to redirect the output to a log file.
4.10.5
Using the tunnel
If the client program supports SSL encryption, it will be able to communicate with the stunnel service directly. You
will need to verify and accept the server’s certificate if the client cannot recognize it as valid according to its known
certification authorities.
If the client program does not support SSL directly, you can use stunnel as a client, or indirectly by setting up a
proxy that allows the client to connect to an unencrypted local TCP port.
WARNING: The stunnel client does not verify the server’s certificate by default. You MUST specify either
verify = 2 or verify = 3 on the client command line to switch on certificate verification.
You MAY also activate client certificate verification in the server’s configuration file, so that the server can verify the
client’s identity as well.
As described in the previous section, you MUST use the option ciphers = RC4-SHA in the configuration file to
ensure that the cipher selection supported in the evaluated configuration will be used.
4.10.6
Example 1: Secure SMTP delivery
Normal SMTP e-mail delivery is not encrypted, but most mail clients support the enhanced SMTPS protocol that uses
SSL encryption. The protocol itself is unchanged other than being encrypted.
stunnel can easily be used as a proxy to receive SMTPS connections on the standard port expected by clients
(465/tcp), and then forward the data to the mail server listening on the SMTP port (25/tcp). The mail server
configuration does not need to be modified to support encryption of incoming mail.
To implement SSL support for incoming
/etc/stunnel/stunnel-server.conf configuration:
mail,
add
the
following
service
definition
to
the
4
SYSTEM OPERATION
47
[inbound_mail]
accept = 465
connect = 127.0.0.1:25
4.10.7
Example 2: Simple web server
The following shell script acts as a simple web server, reading requests from standard input and writing HTTP/HTML
to standard output:
cat > /usr/local/sbin/webserver_test <<-__EOF__
#!/bin/sh
# Simple web server, can be run via stunnel or xinetd
#
# read and discard client data
dd bs=65536 count=1 >/dev/null 2>&1
#
# Send HTTP header
echo -e "HTTP/1.0 200\r"
echo -e "Content-type: text/html\r"
echo -e "\r"
#
# Send HTML output
echo "<html>"
echo "<h1>Test Page</h1>"
date
echo "<h2>Memory usage</h2>"
echo "<pre>"
free
echo "</pre>"
echo "</html>"
__EOF__
chmod +x /usr/local/sbin/webserver_test
Add the following entry to the /etc/stunnel/stunnel-server.conf configuration to make this service available using the
encrypted HTTPS protocol:
[webserver_test]
accept = 443
exec = /usr/local/sbin/webserver_test
TIMEOUTclose = 0
Then, use a SSL-capable web browser to connect to port 443:
elinks https://localhost/
4.10.8
Example 1: system status view
This example shows how to combine stunnel client and server definitions to implement an encrypted tunnel for
applications that do not themselves support encryption.
First, on the server machine, set up a stunnel server definition that accepts SSL connections on TCP port 444, and
reports memory usage statistics for the server to connecting clients. Add the following service definition to the
/etc/stunnel/stunnel-server.conf configuration:
4
SYSTEM OPERATION
48
[free]
accept = 444
exec = /usr/bin/free
execargs = free
Then, on the client machine, add the following entry to the /etc/stunnel/stunnel-client.conf configuration, using the
server’s IP address instead of ”127.0.0.1”:
[free]
accept = 81
connect = 127.0.0.1:444
On the client machine, connect to the local stunnel proxy by running the following command as a normal user:
telnet localhost 81
This will open an unencrypted TCP connection to the client’s local port 81, then stunnel builds an encrypted tunnel to
the server’s port 444 and transfers the decrypted data (in this case, the ”free” output) back to the client. All unencrypted
connections are machine local, and the data transferred over the network is encrypted.
4.11
The Abstract Machine Testing Utility (AMTU)
The security of the operating system depends on correctly functioning hardware. For example, the memory subsystem
uses hardware support to ensure that the memory spaces used by different processes are protected from each other.
The Abstract Machine Testing Utility (AMTU) is distributed as an RPM, and was installed previously as described in
section §3.5 ”Add and remove packages” of this guide.
To run all supported tests, simply execute the amtu program:
amtu
A successful run is indicated by the following output:
Executing Memory Test...
Memory Test SUCCESS!
Executing Memory Separation Test...
Memory Separation Test SUCCESS!
Executing Network I/O Tests...
Network I/O Controller Test SUCCESS!
Executing I/O Controller - Disk Test...
I/O Controller - Disk Test SUCCESS!
Executing Supervisor Mode Instructions Test...
Privileged Instruction Test SUCCESS!
The program will return a nonzero exit code on failure, which MAY be used to automatically detect failures of the
tested systems and take appropriate action.
Please refer to the amtu(8) man page for more details.
5
MONITORING, LOGGING & AUDIT
4.12
49
Setting the system time and date
You MUST verify periodically that the system clock is sufficiently accurate, otherwise log and audit files will contain
misleading information. When starting the system, the time and date are copied from the computer’s hardware clock
to the kernel’s software clock, and written back to the hardware clock on system shutdown.
All internal dates and times used by the kernel, such as file modification stamps, use universal time (UTC), and do not
depend on the current time zone settings. Userspace utilities usually adjust these values to the currently active time
zone for display. Note that text log files will contain ASCII time and date representations in local time, often without
explicitly specifying the time zone.
The date(1) command displays the current time and date, and can be used by administrators to set the software clock,
using the argument mmddHHMMyyyy to specify the numeric month, day, hour, minute and year respectively. For
example, the following command sets the clock to May 1st 2004, 1pm in the local time zone:
date 050113002004
The hwclock(8) can query and modify the hardware clock on supported platforms, but is not available in virtual
environments such as z/VM or LPAR. The typical use is to copy the current value of the software clock to the hardware
clock. Note that the hardware clock MAY be running in either local time or universal time, as indicated by the UTC
setting in the /etc/sysconfig/clock file. The following command sets the hardware clock to the current time using UTC:
hwclock -u -w
Use the command tzselect(8) to change the default time zone for the entire system. Note that users MAY individually
configure a different time zone by setting the TZ environment variable appropriately in their shell profile, such as the
$HOME/.bashrc file.
5
5.1
Monitoring, Logging & Audit
Reviewing the system configuration
It is RECOMMENDED that you review the system’s configuration at regular intervals to verify if it still agrees with
the evaluated configuration. This primarily concerns those processes that may run with ’root’ privileges.
The permissions of the device files /dev/* MUST NOT be modified.
In particular, review settings in the following files and directories to ensure that the contents and permissions have not
been modified:
/etc/at.allow
/etc/at.deny
/etc/audit/*
/etc/cron.allow
/etc/cron.d/*
/etc/cron.daily/*
/etc/cron.deny
/etc/cron.hourly/*
/etc/cron.monthly/*
/etc/cron.weekly/*
/etc/crontab
/etc/group
/etc/gshadow
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MONITORING, LOGGING & AUDIT
50
/etc/hosts
/etc/inittab
/etc/ld.so.conf
/etc/login.defs
/etc/modules.conf
/etc/pam.d/*
/etc/passwd
/etc/rc.d/init.d/*
/etc/securetty
/etc/security/opasswd
/etc/shadow
/etc/ssh/ssh_config
/etc/ssh/sshd_config
/etc/stunnel/*
/etc/sysconfig/*
/etc/vsftpd.ftpusers
/etc/vsftpd/vsftpd.conf
/etc/xinetd.conf
/var/log/audit.d/*
/var/log/faillog
/var/log/lastlog
/var/spool/at/*
/var/spool/cron/*
Use the command lastlog to detect unusual patterns of logins.
Also verify the output of the following commands (run as ’root’):
atq
crontab -l
find / \( -perm -4000 -o -perm -2000 \) -ls
find / \( -type f -o -type d -o -type b \) -perm -0002 -ls
find /bin /boot /etc /lib /sbin /usr \
! -type l \( ! -uid 0 -o -perm +022 \)
5.2
System logging and accounting
System log messages are stored in the /var/log/ directory tree in plain text format, most are logged through the
syslogd(8) and klogd(8) programs, which MAY be configured via the /etc/syslog.conf file.
The logrotate(8) utility, launched from /etc/cron.daily/logrotate, starts a fresh log file every week or when they
reach a maximum size and automatically removes or archives old log files. You MAY change the configuration files
/etc/logrotate.conf and /etc/logrotate.d/* as required.
In addition to the syslog messages, various other log files and status files are generated in /var/log by other programs:
File
audit.d
boot.msg
lastlog
vsftpd.log
Source
Directory for LAuS logs
Messages from system startup
Last successful log in (see lastlog(8))
Transaction log of the VSFTP daemon
5
MONITORING, LOGGING & AUDIT
localmessages
mail
messages
news/
warn
wtmp
51
Written by syslog
Written by syslog, contains messages from the MTA (postfix)
Written by syslog, contains messages from su and ssh
syslog news entries (not used in the evaluated configuration)
Written by syslog
Written by the PAM susbystem, see who(1)
Please see syslog(3), syslog.conf (5) and syslogd(8) man pages for details on syslog configuration.
The ps(1) command can be used to monitor the currently running processes. Using ps faux will show all currently
running processes and threads.
5.3
Configuring the audit subsystem
The audit subsystem implements a central monitoring solution to keep track of security relevant events, such as changes
and change attempts to security critical files.
This is accomplished through two separate mechanisms. All system calls are intercepted, and the kernel writes the
parameters and return value to the audit log for those calls that are marked as security relevant in the filter configuration.
In addition, some trusted programs contain audit-specific code to write audit trails of the actions they are requested to
perform.
Please see auditd(8), laus(7), auditd.conf (5), aucat(8) and augrep(8) for details.
5.3.1
Intended usage of the audit subsystem
The Controlled Access Protection Profile (CAPP) specifies the auditing capabilities that a compliant system must
support. The evaluated configuration described here is based on these requirements.
WARNING: Some of the CAPP requirements may conflict with your specific requirements for the system. For
example, a CAPP-compliant system MUST disable logins if the audit subsystem is not working. Please ensure that
you are aware of the consequences if you enable auditing.
CAPP is designed for a multiuser system, with multiple unique users who maintain both shared and private resources.
The auditing features are intended to support this mode of operation with a reliable trail of security-relevant operations.
It is less useful for a pure application server with no interactive users.
Please be aware that the auditing subsystem will, when activated, cause some slowdown for applications on the
server. The impact depends on what the application is doing and how the audit subsystem is configured. As a rule
of thumb, applications that open a large number of separate files are most affected, and CPU-bound programs should
not be measurably affected. You will need to balance the performance requirements against your security needs when
deciding if and how you want to use auditing.
5.3.2
Selecting the events to be audited
You MAY make changes to the set of system calls and events that are to be audited. CAPP requires that the system
has the capability to audit security relevant events, but it is up to you to choose how you want to use these capabilities.
It is acceptable to turn off system call auditing completely even in an evaluated configuration, for example on a pure
application server with no interactive users on the system.
The configuration file /etc/audit/filter.conf by default contains a suggested setup for a typical multiuser system, all
access to the security relevant files (as configured in /etc/audit/filter.conf and /etc/audit/filesets.conf ) is audited, along
with other security relevant events such as system reconfiguration.
You MAY selectively disable and enable auditing for specific events or users as required by setting up predicates and
filters in the filter.conf file. The following excerpt from the default configuration is an example:
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MONITORING, LOGGING & AUDIT
52
predicate is-non-root-uid = !eq(0);
filter not-root-user = is-non-root-uid(login-uid);
tag "Open_Denied"
syscall open = denied(result)
&& (( not-root-user || effectivenonroot )
&& is-sysdir(arg0));
Please refer to the audit-filter(5) man page for more details.
5.3.3
Reading and searching the audit records
Use the aucat(8) and augrep(8) tools to retrieve information from the audit logs. The information available for retrieval
depends on the active filter configuration. If you modify the filter configuration, it is RECOMMENDED keeping a
datestamped copy of the applicable configuration with the log files for future reference.
For example:
# view the last 100 audit records
aucat | tail -100
# view all successful PAM authentications
augrep -e TEXT -U AUTH_success
# all actions recorded for a specified login UID (this includes
# actions done by this user with a different effective UID,
# for example, via SUID programs or as part of a "su" session)
augrep -l kw
# file removals
augrep -e SYSCALL -S unlink
Of course, you can use other tools such as plain grep(1) or scripting languages such as awk(1), python(1) or perl(1) to
further analyze the text output generated by the low-level audit tools.
5.3.4
Starting and stopping the audit subsystem
The audit subsystem is only active when all of the following conditions are met:
• The audit.o kernel module must be loaded.
• The audit daemon auditd must be running.
• Processes are attached to the audit subsystem by explicitly launching them with the aurun(8) wrapper program;
starting them from an interactive shell session that used the pam laus.so PAM module when logging in;
or when syscall auditing is enabled globally for all processes (setting dev.audit.attach-all=1 in
/etc/sysctl.conf ).
If the audit daemon is terminated, no audit events are generated until it is restarted. To avoid lost audit records when
you have modified the filter configuration, you MUST use the command auditd -r to re-load the filters.
WARNING: auditd -r will not reload /etc/audit/audit.conf, it only reloads the filter configuration file. To activate
changes to this configuration file you MUST restart the audit daemon:
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MONITORING, LOGGING & AUDIT
53
/etc/rc.d/init.d/audit restart
You MUST NOT attempt to reload the configuration by sending auditd a HUP signal or by running
/etc/rc.d/init.d/audit reload, because that will not write the required audit record showing the
reconfiguration. You MUST use one of the two restart methods described above.
If the audit module is unloaded with rmmod, all processes are detached permanently from the audit subsystem. They
can only be re-attached when using the AUDIT ATTACH ALL=1 option in /etc/sysconfig/audit.
5.3.5
Storage of audit records
The REQUIRED operating mode for the audit records is ”bin mode” (”bin” as in bucket), using several preallocated
files of constant size for the audit records. auditd will write data to the first file until it is filled, then switch to the
next one re-using each one in turn in a round-robin fashion.
Each time a bin is filled, auditd will launch the configured notification program to process the file. The default
configuration saves a copy of each filled file before re-using the storage. If the notification program exits with a failure
status, for example, due to lack of disk space, auditd will then take the configured action, by default setting the
message queue size to zero and thereby blocking all processes that try to write new records. These audited processes
will sleep until auditd resumes processing (typically once disk space has been freed by the administrator), then they
will be woken up by the kernel and proceed running normally.
You MAY instead configure round-robin reuse of the files without saving, to keep the disk space used by the audit logs
constant. To do that, remove the ”-S /var/log/audit.d/save.%u” option in /etc/audit/audit.conf. In this configuration,
you have access to a fixed amount of historical audit data, but any new events will cyclically overwrite old data. A user
could exploit this mechanism by intentionally generating a large number of irrelevant entries to wipe out the previously
generated records. The default configuration uses four files of only 20 MiB size each. You SHOULD increase these
numbers in /etc/audit/audit.conf according to available disk space, your organizational requirements, and the system’s
usage patterns to ensure that a sufficient amount of historic audit data will be saved.
5.3.6
Reliability of audit data
By default, the audit records are written using the normal Linux filesystem buffering, which means that information
may be lost in a crash because it has not been written to the physical disk yet. Any applications that read the records
while the system is running will always get the most current data out of the buffer cache, even if it has not yet been
committed to disk, so this does not affect normal operation. If you want to ensure that auditd always forces a disk
write for each record, you MAY set the ”sync = yes;” option in /etc/audit/audit.conf, but be aware that this will result
in significantly reduced performance and high strain on the disk.
The audit record files are not protected against a malicious administrator, and are not intended for an environment
where the administrators are not trustworthy.
5.4
System configuration variables in /etc/sysconfig
The system uses various files in /etc/sysconfig to configure the system. Most files in this directory tree contain variable
definitions in the form of shell variables that are either read by the rc scripts at system boot time or are evaluated by
other commands at runtime. Note that changes will not take effect until the affected service is restarted or the system
is rebooted.
6
6
6.1
SECURITY GUIDELINES FOR USERS
54
Security guidelines for users
Online Documentation
The system provides a large amount of online documentation, usually in text format. Use the man program to read
entries in the online manual, for example:
man ls
man man
to read information about the ls and man commands respectively. You can search for keywords in the online manual
with the apropos(1) utility, for example:
apropos password
When this guide refers to manual pages, it uses the syntax ENTRY(SECTION), for example ls(1). Usually you do not
need to provide the section number, but if there are several entries in different sections, you can use the optional -S
switch and pick a specific one.
Some programs provide additional information GNU ’texinfo’ format, use the info program to read it, for example:
info diff
Additional information, sorted by software package, can be found in the /usr/share/doc/*/ directories. Use the less(1)
pager to read it, for example:
/usr/share/doc/bash*/FAQ
Many programs also support a --help, -? or -h switch you can use to get a usage summary of supported
command-line parameters.
A collection of How-To documents in HTML format can be found under /usr/share/doc/howto/en/html if the optional
howtoenh package is installed.
Please see /usr/share/doc/howto/en/html/Security-HOWTO for security information. The HTML files can be read with
the w3m browser.
The RHEL server documentation is also available in electronic form in the directories /usr/share/doc/rhel*.
Note that this Configuration Guide has precedence over other documents in case of conflicting recommendations.
6.2
Authentication
You MUST authenticate (prove your identity) before being permitted to use the system. When the administrator created
your user account, he or she will have assigned a user name and default password, and provided that information for
you along with instructions how to access the system.
Logging in to the system will usually be done using the Secure Shell (SSH) protocol, alternatively a serial terminal
may be available. Use the ssh command to connect to the system unless instructed otherwise by the administrator,
for example:
ssh [email protected]
6
55
SECURITY GUIDELINES FOR USERS
The ssh(1) manual page provides more information on available options. If you need to transfer files between systems,
use the scp(1) or sftp(1) tools.
If this is the first time you are connecting to the target system, you will be prompted if you want to accept the host
key. If the administrator has provided a key fingerprint for comparison, verify that they match, otherwise type yes to
continue. You MUST immediately change your initially assigned password with the passwd(1) utility.
You MUST NOT under any circumstances attempt to log in from an insecure device, such as a public terminal or a
computer belonging to a friend. Even if the person owning the computer is trustworthy, the computer may not be due
to having been infected with malicious code. Always remember that the device you are typing your password into
has the ability to save and re-use your authentication information, so you are in effect giving the computer you are
using the right to do any and all actions in your name. Insecure handling of authentication information is the leading
cause for exploits of otherwise secure systems, and SSH can only protect the information during transit, and offers no
protection at all against an insecure end point.
When you log out from the system and leave the device you have used for access (such as a terminal or a workstation
with terminal emulation), you MUST ensure that you have not left information on the screen or within an internal
buffer that should not be accessible to another user. You should be aware that some terminals also store information
not displayed on the terminal (such as passwords, or the contents of a scrollback buffer). Nevertheless this information
may be extractable by the next user unless the terminal buffer has been cleared. Safe options include completely
shutting down the client software used for access, powering down a hardware terminal, or clearing the scrollback
buffer by switching among virtual terminals in addition to clearing the visible screen area.
If you ever forget your password, contact your administrator who will be able to assign a new password.
You MAY use the chsh(1) and chfn(1) programs to update your login shell and personal information if necessary. Not
all settings can be changed this way, contact your administrator if you need to change settings that require additional
privileges.
6.3
Password policy
All users, including the administrators, MUST ensure that their authentication passwords are strong (hard to guess)
and handled with appropriate security precautions. The password policy described here is designed to satisfy the
requirements of the evaluated configuration. If your organization already has a password policy defined, your
administrator MAY refer you to that policy if it is equivalently strong.
You MUST change the initial password set by the administrator when you first log into the system. You MUST select
your own password in accordance with the rules defined here. You MUST also change the password if the administrator
has set a new password, for example if you have forgotten your password and requested the administrator to reset the
password.
Use the passwd(1) program to change passwords. It will first prompt you for your old password to confirm your
identity, then for the new password. You need to enter the new password twice, to catch mistyped passwords.
The passwd(1) program will automatically perform some checks on your new password to help ensure that it is not
easily guessable, but you MUST nevertheless follow the requirements in this chapter.
Note that the administrators MUST also ensure that their own passwords comply with this password policy, even in
cases where the automatic checking is not being done, such as when first installing the system.
• Your password MUST be a minimum of 8 characters in length. More than 8 characters MAY be used (it is
RECOMMENDED to use more than 8, best is to use passphrases), and all characters are significant.
• Use at least one character each from the following sets for passwords:
Lowercase letters:
Uppercase letters:
Digits:
Punctuation:
abcdefghijklmnopqrstuvwxyz
ABCDEFGHIJKLMNOPQRSTUVWXYZ
0123456789
!"#$%&’()*+,-./:;<=>?[\]ˆ_‘{|}˜
6
SECURITY GUIDELINES FOR USERS
56
• You MUST NOT base the password on a dictionary word, your real name, login name, or other personal details
(such as dates, names of relatives or pets), or names of real people or fictional characters.
• Instead of a password, you MAY use a passphrase consisting of multiple unrelated words (at least three) joined
with random punctuation characters. Such a passphrase MUST have a length of at least 16 characters.
• You MUST NOT use a simple alphabetic string, palindrome or combinations of adjacent keyboard keys.
• When you choose a new password, it MUST NOT be a simple variation or permutation of a previously used
one.
• You MUST NOT write the password on paper or store it on electronic devices in unprotected form. Storage in a
secure location (such as an envelope in a safety deposit box, or encrypted storage on an electronic device) MAY
be acceptable, contact your administrator first to ensure that the protection is strong enough to make password
recovery infeasible for the types of attackers the system is intended to protect against.
• The password is for you and you only. A password is like a toothbrush - you do not want to share it with anybody,
even your best friend. You MUST NOT disclose your password to anybody else, or permit anybody else to use
the system using your identity.
Note that administrators will never ask you for your password, since they do not need it even if they are required
to modify settings affecting your user account.
• You MUST NOT use the same password for access to any systems under external administration, including
Internet sites. You MAY however use the same password for accounts on multiple machines within one
administrative unit, as long as they are all of an equivalent security level and under the control of the same
administrators.
• You MUST inform the administrator and select a new password if you have reason to believe that your password
was accidentally disclosed to a third party.
• If the system notifies you that your password will expire soon or has expired, choose a new one as instructed.
Contact your administrator in case of difficulty.
A RECOMMENDED method of generating passwords that fits these criteria while still being easy to memorize is to
base it on letters of words in a sentence (NOT a famous quotation), including capitalization and punctuation and one
or two variations. Example:
"Ask not for whom the bell tolls."
=> An4wtbt.
"Password ’P’9tw;ciSd’ too weak; contained in RHEL documentation"
=> P’9tw;ciRd
6.4
Access control for files and directories
Linux is a multiuser operating system. You can control which other users will be able to read or modify your files
by setting the Unix permission bits and user/group IDs, or (if more precise control is needed) by using POSIX-style
access control lists (ACLs).
Note that the administrators (’root’) are able to override these permissions and access all files on the system. Use of
encryption is RECOMMENDED for additional protection of sensitive data.
The ’umask’ setting controls the permissions of newly created files and directories and specifies the access bits that
will be removed from new objects. Ensure that the setting is appropriate, and never grant write access to others by
default. The umask MUST include at least the 002 bit (no write access for others), and the RECOMMENDED setting
is 027 (read-only and execute access for the group, no access at all for others).
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APPENDIX
57
Do not set up world-writable areas in the filesystem - if you want to share files in a controlled manner with a fixed
group of other users (such as a project group), please contact your administrator and request the creation of a user
group for that purpose.
Always remember that you are responsible for the security of the data you create and use. Choose permissions that
match the protection goals appropriate for the content, and that correspond to your organization’s security policy.
Access to confidential data MUST be on a need-to-know basis, do not make data world-readable unless the information
is intended to be public.
Whenever you start a program or script, it will execute with your access rights. This implies that a malicious program
would be able to read and modify all files that you have access to. Never execute any code that you have received
from untrustworthy sources, and do not run commands that you do not understand. Be aware that manipulations to
the environment a program is run in can also cause security flaws, such as leaking sensitive information. Do not
use the shell variables LD LIBRARY PATH or LD PRELOAD that modify the shared library configuration used by
dynamically linked programs.
Programs can be configured to run with the access rights of the program file’s owner and/or group instead of the rights
of the calling user. This is the SUID/SGID mechanism, which utilities such as passwd(1) use to be able to access
security-critical files. You could also create your own SUID/SGID programs via chmod(1), but DO NOT do that
unless you fully understand the security implications - you would be giving away your access privileges to whoever
launches the SUID program. Please refer to the ”Secure Programming HOWTO” in the unlikely case that you need to
create such a program, there you will find explanations of the many aspects that must be considered, such as the risk of
unintended shell escapes, buffer overflows, resource exhaustion attacks and many other factors. Note that SUID root
programs MUST NOT be added to the evaluated configuration, the only permitted use of the SUID bit is for setting
non-root user IDs.
Please refer to the chmod(1), umask(2), chown(1), chgrp(1), acl(5), getfacl(1), and setfacl(1) manual pages for
information, or any of the many available books covering Linux security (cf. Appendix ’Literature’), or ask your
system administrator for advice.
6.5
Data import / export
The system comes with various tools to archive data (tar, star, cpio). If ACLs are used, then only star MUST be used
to handle the files and directories as the other commands do not support ACLs. The options -H=exustar -acl must be
used with star.
Please see the star(1) man page for more information.
7
7.1
Appendix
Online Documentation
If there are conflicting recommendations in this guide and in one of the sources listed here, the Configuration Guide
has precedence concerning the evaluated configuration.
”Red Hat Enterprise Linux 3 Installation Guide for the x86, Itanium and AMD64 Architectures”,
/usr/share/doc/rhel-ig-x8664-multi-en-3/index.html
”Red Hat Enterprise Linux 3 Installation Guide for the IBM eServer iSeries and IBM eServer pSeries Architectures”,
/usr/share/doc/rhel-ig-ppc-multi-en-3/index.html
”Red Hat Enterprise Linux 3 Installation Guide for the IBM S/390 and IBM eServer zSeries Architectures”,
/usr/share/doc/rhel-ig-s390-multi-en-3/index.html
”Red Hat Enterprise Linux 3 System Administration Guide”, /usr/share/doc/rhel-sag-en-3/index.html
7
58
APPENDIX
”Red Hat Enterprise Linux 3 Reference Guide”, /usr/share/doc/rhel-rg-en-3/index.html
”Red Hat Enterprise Linux 3 Security Guide”, /usr/share/doc/rhel-sg-en-3/index.html
David
A.
Wheeler,
”Secure
Programming
for
Linux
and
Unix
HOWTO”,
/usr/share/doc/howto/en/html single/Secure-Programs-HOWTO.html, http://tldp.org/HOWTO/Secure-Programs-HOWTO/
Kevin Fenzi, Dave Wreski, ”Linux Security HOWTO”, /usr/share/doc/howto/en/html single/Security-HOWTO.html,
http://www.linuxsecurity.com/docs/LDP/Security-HOWTO/
7.2
Literature
Ellen Siever, Stephen Spainhour, Stephen Figgins, & Jessica P. Hekman, ”Linux in a Nutshell, 3rd Edition”, O’Reilly
2000, ISBN 0596000251
Simson Garfinkel, Gene Spafford, Alan Schwartz, ”Practical Unix & Internet Security, 3rd Edition”, O’Reilly 2003,
ISBN 0596003234
Aeleen Frisch, ”Essential System Administration, 3rd Edition”, O’Reilly 2002, ISBN 0596003439
Daniel J. Barrett, Richard Silverman, ”SSH, The Secure Shell: The Definitive Guide”, O’Reilly 2001, ISBN
0596000111
David N. Blank-Edelman, ”Perl for System Administration”, O’Reilly 2000, ISBN 1565926099
Shelley Powers, Jerry Peek, Tim O’Reilly, Mike Loukides, ”Unix Power Tools, 3rd Edition”, O’Reilly 2002, ISBN
0596003307
W. Richard Stevens, ”Advanced Programming in the UNIX(R) Environment”, Addison-Wesley 1992, ISBN
0201563177
Linda Mui, ”When You Can’t Find Your UNIX System Administrator”, O’Reilly 1995, ISBN 1565921046
7.3
The file /etc/audit/audit.conf
# kernel interface
device-file = "/dev/audit";
# filter config
filter-config = "/etc/audit/filter.conf";
# Standard output method is bin mode.
#
output {
mode
= bin;
num-files
= 4;
file-size
= 20M;
file-name
= "/var/log/audit.d/bin";
notify
= "/usr/sbin/audbin -S /var/log/audit.d/save.%u -C";
# The following symlink is created whenever we switch to
# a new bin.
current
= "/var/log/audit";
sync
= no;
7
59
APPENDIX
# uncomment these to cause audit records to be
# flushed to the disk after sync-after records
# are written to the log
#
#
sync
= yes;
sync-after
= 16;
error {
action {
type = suspend;
};
};
};
#
#
#
#
#
#
#
Alternatively, write to /var/log/audit in normal
append mode
output {
mode
= append;
file-name
= "/var/log/audit";
sync
= yes;
};
# Alternative output
# output {
#
mode
#
command
# };
= stream;
= "/usr/local/sbin/send_to_syslog"
# Disk usage thresholds.
# These thresholds are checked at regular intervals when
# append mode is used.
# (bin mode doesn’t require these checks as the bin files
# are preallocated).
threshold disk-space-low {
space-left = 10M;
action {
type = syslog;
facility = security;
priority = warning;
};
action {
type = notify;
command = "/usr/local/bin/page-admin";
};
action {
type = audit;
event = AUDIT_disklow;
};
};
threshold disk-full {
space-left = 20K;
action {
type = syslog;
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60
APPENDIX
facility = security;
priority = crit;
};
action {
type = audit;
event = AUDIT_diskfull;
};
};
7.4
#
#
#
#
#
#
#
The file /etc/audit/filter.conf
This is a sample filter.conf file.
Please take a look at filesets.conf first if you
wish to customize what system calls will be logged.
The syntax of this file is described in filter.conf(5).
#
# Various primitive predicates
predicate
is-null
predicate
is-negative
predicate
is-system-uid
predicate
is-lower-1024
=
=
=
=
eq(0);
lt(0);
lt(100);
lt(-1024);
#
# Predicate to check open(2) mode: true iff
# (mode & O_ACCMODE) == O_RDONLY
predicate
is-rdonly
= mask(O_ACCMODE, O_RDONLY);
#
# Predicates for testing file type, valid when applied
# to a file type argument
predicate
__isreg
= mask(S_IFMT, S_IFREG);
predicate
__isdir
= mask(S_IFMT, S_IFDIR);
predicate
__ischr
= mask(S_IFMT, S_IFCHR);
predicate
__isblk
= mask(S_IFMT, S_IFBLK);
predicate
__issock
= mask(S_IFMT, S_IFSOCK);
predicate
__islnk
= mask(S_IFMT, S_IFLNK);
predicate
s_isreg
= __isreg(file-mode);
predicate
s_isdir
= __isdir(file-mode);
predicate
s_ischr
= __ischr(file-mode);
predicate
s_isblk
= __isblk(file-mode);
predicate
s_issock
= __issock(file-mode);
predicate
s_islnk
= __islnk(file-mode);
predicate
is-tempdir
= mask(01777, 01777);
predicate
is-world-writable = mask(0666, 0666);
#
# Predicates dealing with process exit code
predicate
if-crash-signal =
7
61
APPENDIX
!mask(__WSIGMASK, 0)
&& (mask(__WSIGMASK,
mask(__WSIGMASK,
mask(__WSIGMASK,
mask(__WSIGMASK,
__WSIGILL) ||
__WSIGABRT) ||
__WSIGSEGV) ||
__WSIGSTKFLT));
#
# Predicates for audit-tags
predicate
is-o-creat
predicate
is-ipc-remove
predicate
is-ipc-setperms
predicate
is-ipc-creat
predicate
is-auditdevice
predicate
is-cmd-set-auditid
predicate
is-cmd-set-loginid
=
=
=
=
=
=
=
mask(O_CREAT, O_CREAT);
eq(IPC_RMID);
eq(IPC_SET);
mask(IPC_CREAT, IPC_CREAT);
prefix("/dev/audit");
eq(AUIOCSETAUDITID);
eq(AUIOCLOGIN);
#
# Misc filters
filter
filter
filter
filter
predicate
predicate
predicate
=
=
=
=
=
=
=
is-null(uid);
is-null(dumpable);
is-negative(result);
is-lower-1024(result);
eq(AF_PACKET);
eq(AF_NETLINK);
eq(SOCK_RAW);
is-root
is-setuid
syscall-failed
syscall-addr-succeed
is-af-packet
is-af-netlink
is-sock-raw
#
# Include filesets.
#
include "filesets.conf";
#
# "Secret" files should not be read by everyone # we also log read access to these files
#
predicate
is-secret = prefix(@secret-files);
#
# All regular files owned by a system uid are deemed sensitive
#
predicate
is-system-file = is-system-uid(file-uid)
&& !prefix("/var")
&& !is-world-writable(file-mode);
#
# Define ioctls we track
#
set
sysconf-ioctls = {
SIOCADDDLCI,
SIOCADDMULTI,
SIOCADDRT,
SIOCBONDCHANGEACTIVE,
7
62
APPENDIX
SIOCBONDENSLAVE,
SIOCBONDRELEASE,
SIOCBONDSETHWADDR,
SIOCDARP,
SIOCDELDLCI,
SIOCDELMULTI,
SIOCDELRT,
SIOCDIFADDR,
SIOCDRARP,
SIOCETHTOOL,
SIOCGIFBR,
SIOCSARP,
SIOCSIFADDR,
SIOCSIFBR,
SIOCSIFBRDADDR,
SIOCSIFDSTADDR,
SIOCSIFENCAP,
SIOCSIFFLAGS,
SIOCSIFHWADDR,
SIOCSIFHWBROADCAST,
SIOCSIFLINK,
SIOCSIFMAP,
SIOCSIFMEM,
SIOCSIFMETRIC,
SIOCSIFMTU,
SIOCSIFNAME,
SIOCSIFNETMASK,
SIOCSIFPFLAGS,
SIOCSIFSLAVE,
SIOCSIFTXQLEN,
SIOCSMIIREG
};
predicate is-sysconf-ioctl
= eq(@sysconf-ioctls);
#
# System calls on file names
#
set
file-ops = {
"mkdir", "rmdir", "unlink",
"chmod",
"chown", "lchown",
"chown32", "lchown32",
};
#
# General system related ops
#
set
system-ops = {
swapon, swapoff,
create_module, init_module, delete_module,
sethostname, setdomainname,
};
set
priv-ops = {
7
63
APPENDIX
"setuid",
"setuid32",
"seteuid",
"seteuid32",
"setreuid",
"setreuid32",
"setresuid",
"setresuid32",
"setgid",
"setgid32",
"setegid",
"setegid32",
"setregid",
"setregid32",
"setresgid",
"setresgid32",
"setgroups",
"setgroups32",
"capset",
};
#
# Audit-Tags (only syscall related tags are handled here)
#
# define sets of syscalls related to audit-tags
# System calls for changing file modes
set
mode-ops = {
"chmod",
"fchmod",
};
# System calls for changing file owner
set
owner-ops = {
"chown", "lchown",
"chown32", "lchown32",
"fchown",
};
# System calls doing file link operations
set
link-ops = {
"link", "symlink",
};
# System calls for creating device files
set
mknod-ops = {
"mknod",
};
# System calls for opening a file
set
open-ops = {
"open",
};
7
64
APPENDIX
# File renaming
set
rename-ops = {
"rename",
};
# File truncation
set
truncate-ops = {
"truncate", "truncate64",
"ftruncate", "ftruncate64",
};
# Unlink files
set
unlink-ops = {
"unlink",
};
# Deletion of directories
set
rmdir-ops = {
"rmdir",
};
# Mounting of filesystems
set
mount-ops = {
"mount",
};
# Unounting of filesystems
set
umount-ops = {
"umount",
"umount2"
};
# Changing user (-role)
set
userchange-ops = {
"setuid",
"setuid32",
"seteuid",
"seteuid32",
"setreuid",
"setreuid32",
"setresuid",
"setresuid32",
};
# Execute another program
set
execute-ops = {
"execve",
};
# Set real user-ID
set
realuid-ops = {
"setuid",
"setuid32",
};
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65
APPENDIX
# Set user-IDS in gerneral
set
setuserids-ops = {
"setuid",
"setuid32",
"seteuid",
"seteuid32",
"setreuid",
"setreuid32",
"setresuid",
"setresuid32",
};
# Set real group-ID
set
realgid-ops = {
"setgid",
"setgid32",
"setgroups",
"setgroups32",
};
# Set group-IDs in gerneral
set
setgroups-ops = {
"setgid",
"setgid32",
"setegid",
"setegid32",
"setregid",
"setregid32",
"setresgid",
"setresgid32",
"setgroups",
"setgroups32",
};
# Set other kind of privileges (capabilities)
set
privilege-ops = {
"capset",
};
# Change system-time
set
timechange-ops = {
"adjtimex",
"stime",
"settimeofday",
};
# bring sets and tags in conjunction
tag "FILE_mode"
syscall @mode-ops = always;
tag "FILE_owner"
syscall @owner-ops = always;
7
APPENDIX
tag "FILE_link"
syscall @link-ops = always;
tag "FILE_mknod"
syscall @mknod-ops = always;
tag "FILE_create"
syscall open = is-o-creat(arg1);
tag "FILE_create"
syscall creat = always;
#tag "FILE_open"
#syscall @open-ops = always;
tag "FILE_open"
syscall @open-ops = (is-system-file(arg0) && !(is-rdonly(arg1)))
|| is-secret(arg0);
tag "FILE_rename"
syscall @rename-ops = always;
tag "FILE_truncate"
syscall @truncate-ops = always;
tag "FILE_unlink"
syscall @unlink-ops = always;
tag "FS_rmdir"
syscall @rmdir-ops = always;
tag "FS_mount"
syscall @mount-ops = always;
tag "FS_umount"
syscall @umount-ops = always;
# I think owner changing doesnt make much sense
tag "MSG_owner"
syscall msgctl = is-ipc-setperms(arg1);
tag "MSG_mode"
syscall msgctl = is-ipc-setperms(arg1);
tag "MSG_delete"
syscall msgctl = is-ipc-remove(arg1);
tag "MSG_create"
syscall msgget = always;
tag "SEM_owner"
syscall semctl = is-ipc-setperms(arg2);
66
7
APPENDIX
tag "SEM_mode"
syscall semctl = is-ipc-setperms(arg2);
tag "SEM_delete"
syscall semctl = is-ipc-remove(arg2);
tag "SEM_create"
syscall semget = always;
tag "SHM_owner"
syscall shmctl = is-ipc-setperms(arg1);
tag "SHM_mode"
syscall shmctl = is-ipc-setperms(arg1);
tag "SHM_delete"
syscall shmctl = is-ipc-remove(arg1);
tag "SHM_create"
syscall shmget = always;
tag "PRIV_userchange"
syscall @userchange-ops = always;
tag "PROC_execute"
syscall @execute-ops = always;
tag "PROC_realuid"
syscall @realuid-ops = always;
tag "PROC_auditid"
syscall ioctl = (is-auditdevice(arg0) && is-cmd-set-auditid(arg1));
tag "PROC_loginid"
syscall ioctl = (is-auditdevice(arg0) && is-cmd-set-loginid(arg1));
tag "PROC_setuserids"
syscall @setuserids-ops = always;
tag "PROC_realgid"
syscall @realgid-ops = always;
tag "PROC_setgroups"
syscall @setgroups-ops = always;
tag "PROC_privilege"
syscall @privilege-ops = always;
tag "SYS_timechange"
syscall @timechange-ops = always;
67
7
APPENDIX
# not required by CAPP
syscall ipc = always;
syscall socket = is-af-packet(arg0) || is-sock-raw(arg1);
syscall ioctl = is-sysconf-ioctl(arg1);
#
# Special filters for process/termination
event process-exit = if-crash-signal(exitcode);
#
# Events we want to log unconditionally:
event network-config = always;
event user-message = always;
event process-login = always;
7.5
The file /etc/audit/filesets.conf
#
# This file contains file name sets etc used in the default
# audit filter configuration file.
#
# The syntax of this file is described in filter.conf(5).
#
#
# Set of files for which we track read access.
#
set
secret-files = {
"/etc/shadow",
"/etc/gshadow",
"/var/log/audit",
"/var/log/audit.d",
"/var/log/audit.d/bin.0",
"/var/log/audit.d/bin.1",
"/var/log/audit.d/bin.2",
"/var/log/audit.d/bin.3",
};
68
">