CIS CentOS Linux 6 Benchmark

CIS CentOS Linux 6 Benchmark
v2.0.1 - 06-02-2016
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Table of Contents
Overview ............................................................................................................................................................... 12
Intended Audience ........................................................................................................................................ 12
Consensus Guidance..................................................................................................................................... 12
Typographical Conventions ...................................................................................................................... 13
Scoring Information ..................................................................................................................................... 13
Profile Definitions ......................................................................................................................................... 14
Acknowledgements ...................................................................................................................................... 15
Recommendations ............................................................................................................................................. 16
1 Initial Setup .................................................................................................................................................. 16
1.1 Filesystem Configuration ............................................................................................................... 16
1.1.1.1 Ensure mounting of cramfs filesystems is disabled (Scored) .............................. 17
1.1.1.2 Ensure mounting of freevxfs filesystems is disabled (Scored)............................ 19
1.1.1.3 Ensure mounting of jffs2 filesystems is disabled (Scored) ................................... 20
1.1.1.4 Ensure mounting of hfs filesystems is disabled (Scored) ...................................... 21
1.1.1.5 Ensure mounting of hfsplus filesystems is disabled (Scored) ............................. 22
1.1.1.6 Ensure mounting of squashfs filesystems is disabled (Scored) .......................... 23
1.1.1.7 Ensure mounting of udf filesystems is disabled (Scored) ..................................... 24
1.1.1.8 Ensure mounting of FAT filesystems is disabled (Scored) ................................... 25
1.1.2 Ensure separate partition exists for /tmp (Scored) .................................................... 26
1.1.3 Ensure nodev option set on /tmp partition (Scored) ................................................. 28
1.1.4 Ensure nosuid option set on /tmp partition (Scored) ................................................ 29
1.1.5 Ensure noexec option set on /tmp partition (Scored) ............................................... 30
1.1.6 Ensure separate partition exists for /var (Scored) ..................................................... 31
1.1.7 Ensure separate partition exists for /var/tmp (Scored) ........................................... 32
1.1.8 Ensure nodev option set on /var/tmp partition (Scored) ........................................ 33
1.1.9 Ensure nosuid option set on /var/tmp partition (Scored) ....................................... 34
1.1.10 Ensure noexec option set on /var/tmp partition (Scored).................................... 35
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1.1.11 Ensure separate partition exists for /var/log (Scored) .......................................... 36
1.1.12 Ensure separate partition exists for /var/log/audit (Scored) ............................. 37
1.1.13 Ensure separate partition exists for /home (Scored) .............................................. 38
1.1.14 Ensure nodev option set on /home partition (Scored) ........................................... 39
1.1.15 Ensure nodev option set on /dev/shm partition (Scored) .................................... 40
1.1.16 Ensure nosuid option set on /dev/shm partition (Scored) ................................... 41
1.1.17 Ensure noexec option set on /dev/shm partition (Scored) .................................. 42
1.1.18 Ensure nodev option set on removable media partitions (Not Scored) ........... 43
1.1.19 Ensure nosuid option set on removable media partitions (Not Scored) .......... 44
1.1.20 Ensure noexec option set on removable media partitions (Not Scored) ......... 45
1.1.21 Ensure sticky bit is set on all world-writable directories (Scored) .................... 46
1.1.22 Disable Automounting (Scored) ....................................................................................... 47
1.2 Configure Software Updates ......................................................................................................... 49
1.2.1 Ensure package manager repositories are configured (Not Scored) ................... 49
1.2.2 Ensure GPG keys are configured (Not Scored) .............................................................. 50
1.2.3 Ensure gpgcheck is globally activated (Scored) ........................................................... 51
1.3 Filesystem Integrity Checking ...................................................................................................... 52
1.3.1 Ensure AIDE is installed (Scored) ...................................................................................... 52
1.3.2 Ensure filesystem integrity is regularly checked (Scored) ....................................... 54
1.4 Secure Boot Settings ........................................................................................................................ 55
1.4.1 Ensure permissions on bootloader config are configured (Scored) ..................... 55
1.4.2 Ensure bootloader password is set (Scored) ................................................................. 56
1.4.3 Ensure authentication required for single user mode (Scored) ............................. 57
1.4.4 Ensure interactive boot is not enabled (Scored) .......................................................... 58
1.5 Additional Process Hardening ..................................................................................................... 59
1.5.1 Ensure core dumps are restricted (Scored) ................................................................... 59
1.5.2 Ensure XD/NX support is enabled (Not Scored) .......................................................... 61
1.5.3 Ensure address space layout randomization (ASLR) is enabled (Scored) ......... 63
1.5.4 Ensure prelink is disabled (Scored) .................................................................................. 64
1.6 Mandatory Access Control ............................................................................................................. 64
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1.6.1.1 Ensure SELinux is not disabled in bootloader configuration (Scored) ............ 67
1.6.1.2 Ensure the SELinux state is enforcing (Scored) ........................................................ 68
1.6.1.3 Ensure SELinux policy is configured (Scored) ........................................................... 69
1.6.1.4 Ensure SETroubleshoot is not installed (Scored) ..................................................... 70
1.6.1.5 Ensure the MCS Translation Service (mcstrans) is not installed (Scored) ..... 71
1.6.1.6 Ensure no unconfined daemons exist (Scored) ......................................................... 72
1.6.2 Ensure SELinux is installed (Scored) ................................................................................ 73
1.7 Warning Banners............................................................................................................................... 73
1.7.1.1 Ensure message of the day is configured properly (Scored) ............................... 75
1.7.1.2 Ensure local login warning banner is configured properly (Not Scored) ....... 77
1.7.1.3 Ensure remote login warning banner is configured properly (Not Scored) .. 79
1.7.1.4 Ensure permissions on /etc/motd are configured (Not Scored) ....................... 81
1.7.1.5 Ensure permissions on /etc/issue are configured (Scored) ................................ 82
1.7.1.6 Ensure permissions on /etc/issue.net are configured (Not Scored) ................ 83
1.7.2 Ensure GDM login banner is configured (Scored) ........................................................ 84
1.8 Ensure updates, patches, and additional security software are installed (Not
Scored) ..................................................................................................................................................... 86
2 Services .......................................................................................................................................................... 86
2.1 inetd Services ...................................................................................................................................... 88
2.1.1 Ensure chargen services are not enabled (Scored) ..................................................... 88
2.1.2 Ensure daytime services are not enabled (Scored) ..................................................... 89
2.1.3 Ensure discard services are not enabled (Scored) ...................................................... 90
2.1.4 Ensure echo services are not enabled (Scored) ............................................................ 91
2.1.5 Ensure time services are not enabled (Scored) ............................................................ 92
2.1.6 Ensure rsh server is not enabled (Scored)...................................................................... 93
2.1.7 Ensure talk server is not enabled (Scored) .................................................................... 94
2.1.8 Ensure telnet server is not enabled (Scored) ................................................................ 95
2.1.9 Ensure tftp server is not enabled (Scored) ..................................................................... 96
2.1.10 Ensure rsync service is not enabled (Scored) ............................................................. 97
2.1.11 Ensure xinetd is not enabled (Scored) ........................................................................... 98
2.2 Special Purpose Services ................................................................................................................ 98
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2.2.1.1 Ensure time synchronization is in use (Not Scored) ............................................... 99
2.2.1.2 Ensure ntp is configured (Scored) ................................................................................ 100
2.2.1.3 Ensure chrony is configured (Scored) ........................................................................ 102
2.2.2 Ensure X Window System is not installed (Scored) .................................................. 103
2.2.3 Ensure Avahi Server is not enabled (Scored) .............................................................. 104
2.2.4 Ensure CUPS is not enabled (Scored) ............................................................................. 105
2.2.5 Ensure DHCP Server is not enabled (Scored) .............................................................. 106
2.2.6 Ensure LDAP server is not enabled (Scored) ............................................................... 107
2.2.7 Ensure NFS and RPC are not enabled (Scored) ........................................................... 108
2.2.8 Ensure DNS Server is not enabled (Scored) ................................................................. 109
2.2.9 Ensure FTP Server is not enabled (Scored) .................................................................. 110
2.2.10 Ensure HTTP server is not enabled (Scored) ............................................................ 111
2.2.11 Ensure IMAP and POP3 server is not enabled (Scored)........................................ 112
2.2.12 Ensure Samba is not enabled (Scored) ........................................................................ 113
2.2.13 Ensure HTTP Proxy Server is not enabled (Scored) ............................................... 114
2.2.14 Ensure SNMP Server is not enabled (Scored) ........................................................... 115
2.2.15 Ensure mail transfer agent is configured for local-only mode (Scored)......... 116
2.2.16 Ensure NIS Server is not enabled (Scored) ................................................................ 118
2.3 Service Clients .................................................................................................................................. 119
2.3.1 Ensure NIS Client is not installed (Scored) ................................................................... 119
2.3.2 Ensure rsh client is not installed (Scored) .................................................................... 121
2.3.3 Ensure talk client is not installed (Scored) ................................................................... 122
2.3.4 Ensure telnet client is not installed (Scored) ............................................................... 123
2.3.5 Ensure LDAP client is not installed (Scored) ............................................................... 124
3 Network Configuration.......................................................................................................................... 124
3.1 Network Parameters (Host Only) ............................................................................................. 125
3.1.1 Ensure IP forwarding is disabled (Scored) ................................................................... 125
3.1.2 Ensure packet redirect sending is disabled (Scored) ............................................... 126
3.2 Network Parameters (Host and Router) ................................................................................ 127
3.2.1 Ensure source routed packets are not accepted (Scored) ...................................... 127
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3.2.2 Ensure ICMP redirects are not accepted (Scored) ..................................................... 129
3.2.3 Ensure secure ICMP redirects are not accepted (Scored) ...................................... 130
3.2.4 Ensure suspicious packets are logged (Scored) .......................................................... 131
3.2.5 Ensure broadcast ICMP requests are ignored (Scored) ........................................... 132
3.2.6 Ensure bogus ICMP responses are ignored (Scored) ................................................ 133
3.2.7 Ensure Reverse Path Filtering is enabled (Scored) ................................................... 134
3.2.8 Ensure TCP SYN Cookies is enabled (Scored).............................................................. 135
3.3 IPv6 ....................................................................................................................................................... 136
3.3.1 Ensure IPv6 router advertisements are not accepted (Scored) ........................... 136
3.3.2 Ensure IPv6 redirects are not accepted (Scored) ...................................................... 137
3.3.3 Ensure IPv6 is disabled (Not Scored) ............................................................................. 138
3.4 TCP Wrappers................................................................................................................................... 139
3.4.1 Ensure TCP Wrappers is installed (Scored) ................................................................. 139
3.4.2 Ensure /etc/hosts.allow is configured (Scored) ......................................................... 141
3.4.3 Ensure /etc/hosts.deny is configured (Scored) .......................................................... 142
3.4.4 Ensure permissions on /etc/hosts.allow are configured (Scored) ..................... 143
3.4.5 Ensure permissions on /etc/hosts.deny are configured (Scored) ...................... 144
3.5 Uncommon Network Protocols ................................................................................................. 145
3.5.1 Ensure DCCP is disabled (Not Scored) ........................................................................... 145
3.5.2 Ensure SCTP is disabled (Not Scored) ............................................................................ 146
3.5.3 Ensure RDS is disabled (Not Scored) .............................................................................. 147
3.5.4 Ensure TIPC is disabled (Not Scored) ............................................................................. 148
3.6 Firewall Configuration .................................................................................................................. 149
3.6.1 Ensure iptables is installed (Scored)............................................................................... 149
3.6.2 Ensure default deny firewall policy (Scored) .............................................................. 151
3.6.3 Ensure loopback traffic is configured (Scored) .......................................................... 152
3.6.4 Ensure outbound and established connections are configured (Not Scored) 154
3.6.5 Ensure firewall rules exist for all open ports (Scored) ............................................ 155
3.7 Ensure wireless interfaces are disabled (Not Scored) ................................................. 157
4 Logging and Auditing ............................................................................................................................. 157
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4.1 Configure System Accounting (auditd) ................................................................................... 158
4.1.1.1 Ensure audit log storage size is configured (Not Scored) ................................... 160
4.1.1.2 Ensure system is disabled when audit logs are full (Scored) ............................ 161
4.1.1.3 Ensure audit logs are not automatically deleted (Scored) .................................. 162
4.1.2 Ensure auditd service is enabled (Scored) ................................................................... 163
4.1.3 Ensure auditing for processes that start prior to auditd is enabled (Scored) 164
4.1.4 Ensure events that modify date and time information are collected (Scored)
................................................................................................................................................................... 165
4.1.5 Ensure events that modify user/group information are collected (Scored) ... 167
4.1.6 Ensure events that modify the system's network environment are collected
(Scored) ................................................................................................................................................. 168
4.1.7 Ensure events that modify the system's Mandatory Access Controls are
collected (Scored) .............................................................................................................................. 170
4.1.8 Ensure login and logout events are collected (Scored) ............................................ 171
4.1.9 Ensure session initiation information is collected (Scored) .................................. 172
4.1.10 Ensure discretionary access control permission modification events are
collected (Scored) .............................................................................................................................. 173
4.1.11 Ensure unsuccessful unauthorized file access attempts are collected (Scored)
................................................................................................................................................................... 175
4.1.12 Ensure use of privileged commands is collected (Scored)................................... 177
4.1.13 Ensure successful file system mounts are collected (Scored) ............................ 179
4.1.14 Ensure file deletion events by users are collected (Scored)................................ 181
4.1.15 Ensure changes to system administration scope (sudoers) is collected
(Scored) ................................................................................................................................................. 183
4.1.16 Ensure system administrator actions (sudolog) are collected (Scored) ........ 184
4.1.17 Ensure kernel module loading and unloading is collected (Scored) ................ 185
4.1.18 Ensure the audit configuration is immutable (Scored) ......................................... 187
4.2 Configure Logging ........................................................................................................................... 187
4.2.1.1 Ensure rsyslog Service is enabled (Scored) .............................................................. 188
4.2.1.2 Ensure logging is configured (Not Scored) ............................................................... 189
4.2.1.3 Ensure rsyslog default file permissions configured (Scored) ............................ 191
4.2.1.4 Ensure rsyslog is configured to send logs to a remote log host (Scored) ..... 192
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4.2.1.5 Ensure remote rsyslog messages are only accepted on designated log hosts.
(Not Scored) ......................................................................................................................................... 193
4.2.2.1 Ensure syslog-ng service is enabled (Scored) .......................................................... 195
4.2.2.2 Ensure logging is configured (Not Scored) ............................................................... 196
4.2.2.3 Ensure syslog-ng default file permissions configured (Scored) ....................... 198
4.2.2.4 Ensure syslog-ng is configured to send logs to a remote log host (Not Scored)
................................................................................................................................................................... 199
4.2.2.5 Ensure remote syslog-ng messages are only accepted on designated log hosts
(Not Scored) ......................................................................................................................................... 200
4.2.3 Ensure rsyslog or syslog-ng is installed (Scored) ...................................................... 202
4.2.4 Ensure permissions on all logfiles are configured (Scored) .................................. 203
4.3 Ensure logrotate is configured (Not Scored) ................................................................... 204
5 Access, Authentication and Authorization ..................................................................................... 204
5.1 Configure cron .................................................................................................................................. 205
5.1.1 Ensure cron daemon is enabled (Scored) ..................................................................... 205
5.1.2 Ensure permissions on /etc/crontab are configured (Scored) ............................ 206
5.1.3 Ensure permissions on /etc/cron.hourly are configured (Scored)..................... 207
5.1.4 Ensure permissions on /etc/cron.daily are configured (Scored) ........................ 208
5.1.5 Ensure permissions on /etc/cron.weekly are configured (Scored) ................... 209
5.1.6 Ensure permissions on /etc/cron.monthly are configured (Scored) ................. 210
5.1.7 Ensure permissions on /etc/cron.d are configured (Scored) ............................... 211
5.1.8 Ensure at/cron is restricted to authorized users (Scored) .................................... 212
5.2 SSH Server Configuration ............................................................................................................. 214
5.2.1 Ensure permissions on /etc/ssh/sshd_config are configured (Scored) ............ 214
5.2.2 Ensure SSH Protocol is set to 2 (Scored) ....................................................................... 216
5.2.3 Ensure SSH LogLevel is set to INFO (Scored) .............................................................. 217
5.2.4 Ensure SSH X11 forwarding is disabled (Scored) ...................................................... 218
5.2.5 Ensure SSH MaxAuthTries is set to 4 or less (Scored) ............................................. 219
5.2.6 Ensure SSH IgnoreRhosts is enabled (Scored) ............................................................ 220
5.2.7 Ensure SSH HostbasedAuthentication is disabled (Scored) .................................. 221
5.2.8 Ensure SSH root login is disabled (Scored) .................................................................. 222
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5.2.9 Ensure SSH PermitEmptyPasswords is disabled (Scored) ..................................... 223
5.2.10 Ensure SSH PermitUserEnvironment is disabled (Scored) ................................. 224
5.2.11 Ensure only approved ciphers are used (Scored) ................................................... 225
5.2.12 Ensure only approved MAC algorithms are used (Scored) .................................. 226
5.2.13 Ensure SSH Idle Timeout Interval is configured (Scored) ................................... 228
5.2.14 Ensure SSH LoginGraceTime is set to one minute or less (Scored).................. 230
5.2.15 Ensure SSH access is limited (Scored) ......................................................................... 231
5.2.16 Ensure SSH warning banner is configured (Scored) .............................................. 233
5.3 Configure PAM.................................................................................................................................. 234
5.3.1 Ensure password creation requirements are configured (Scored) .................... 234
5.3.2 Ensure lockout for failed password attempts is configured (Scored)................ 236
5.3.3 Ensure password reuse is limited (Scored).................................................................. 238
5.3.4 Ensure password hashing algorithm is SHA-512 (Scored) .................................... 239
5.4 User Accounts and Environment .............................................................................................. 240
5.4.1.1 Ensure password expiration is 90 days or less (Scored) ..................................... 241
5.4.1.2 Ensure minimum days between password changes is 7 or more (Scored) . 243
5.4.1.3 Ensure password expiration warning days is 7 or more (Scored) .................. 245
5.4.1.4 Ensure inactive password lock is 30 days or less (Scored) ................................ 246
5.4.2 Ensure system accounts are non-login (Scored) ........................................................ 248
5.4.3 Ensure default group for the root account is GID 0 (Scored) ................................ 249
5.4.4 Ensure default user umask is 027 or more restrictive (Scored) .......................... 250
5.5 Ensure root login is restricted to system console (Not Scored)............................... 252
5.6 Ensure access to the su command is restricted (Scored) ........................................... 253
6 System Maintenance............................................................................................................................... 253
6.1 System File Permissions ............................................................................................................... 255
6.1.1 Audit system file permissions (Not Scored) ................................................................. 255
6.1.2 Ensure permissions on /etc/passwd are configured (Scored) ............................. 257
6.1.3 Ensure permissions on /etc/shadow are configured (Scored) ............................ 258
6.1.4 Ensure permissions on /etc/group are configured (Scored) ................................ 259
6.1.5 Ensure permissions on /etc/gshadow are configured (Scored) .......................... 260
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6.1.6 Ensure permissions on /etc/passwd- are configured (Scored) ........................... 261
6.1.7 Ensure permissions on /etc/shadow- are configured (Scored) ........................... 262
6.1.8 Ensure permissions on /etc/group- are configured (Scored) .............................. 263
6.1.9 Ensure permissions on /etc/gshadow- are configured (Scored) ........................ 264
6.1.10 Ensure no world writable files exist (Scored) .......................................................... 265
6.1.11 Ensure no unowned files or directories exist (Scored) ......................................... 266
6.1.12 Ensure no ungrouped files or directories exist (Scored) ...................................... 267
6.1.13 Audit SUID executables (Not Scored) ........................................................................... 268
6.1.14 Audit SGID executables (Not Scored) ........................................................................... 269
6.2 User and Group Settings ............................................................................................................... 270
6.2.1 Ensure password fields are not empty (Scored) ........................................................ 270
6.2.2 Ensure no legacy "+" entries exist in /etc/passwd (Scored) ................................. 271
6.2.3 Ensure no legacy "+" entries exist in /etc/shadow (Scored) ................................. 272
6.2.4 Ensure no legacy "+" entries exist in /etc/group (Scored) .................................... 273
6.2.5 Ensure root is the only UID 0 account (Scored).......................................................... 274
6.2.6 Ensure root PATH Integrity (Scored) ............................................................................. 275
6.2.7 Ensure all users' home directories exist (Scored) ..................................................... 277
6.2.8 Ensure users' home directories permissions are 750 or more restrictive
(Scored) ................................................................................................................................................. 278
6.2.9 Ensure users own their home directories (Scored) .................................................. 279
6.2.10 Ensure users' dot files are not group or world writable (Scored) .................... 280
6.2.11 Ensure no users have .forward files (Scored) ........................................................... 281
6.2.12 Ensure no users have .netrc files (Scored) ................................................................. 282
6.2.13 Ensure users' .netrc Files are not group or world accessible (Scored) ........... 283
6.2.14 Ensure no users have .rhosts files (Scored) ............................................................... 285
6.2.15 Ensure all groups in /etc/passwd exist in /etc/group (Scored) ....................... 286
6.2.16 Ensure no duplicate UIDs exist (Scored) .................................................................... 287
6.2.17 Ensure no duplicate GIDs exist (Scored)..................................................................... 288
6.2.18 Ensure no duplicate user names exist (Scored) ....................................................... 289
6.2.19 Ensure no duplicate group names exist (Scored) .................................................... 290
Appendix: Change History ............................................................................................................................ 299
10 | P a g e
11 | P a g e
Overview
This document provides prescriptive guidance for establishing a secure configuration
posture for CentOS Linux 6 systems running on x86 and x64 platforms. This document was
tested against CentOS 6.7.
The guidance within broadly assumes that operations are being performed as the root
user. Non-root users may not be able to access certain areas of the system, especially after
remediation has been performed. It is advisable to verify root users path integrity and the
integrity of any programs being run prior to execution of commands and scripts included in
this benchmark.
To obtain the latest version of this guide, please visit http://benchmarks.cisecurity.org. If
you have questions, comments, or have identified ways to improve this guide, please write
us at feedback@cisecurity.org.
Intended Audience
This benchmark is intended for system and application administrators, security specialists,
auditors, help desk, and platform deployment personnel who plan to develop, deploy,
assess, or secure solutions that incorporate CentOS Linux 6 on a x86 platform.
Consensus Guidance
This benchmark was created using a consensus review process comprised of subject
matter experts. Consensus participants provide perspective from a diverse set of
backgrounds including consulting, software development, audit and compliance, security
research, operations, government, and legal.
Each CIS benchmark undergoes two phases of consensus review. The first phase occurs
during initial benchmark development. During this phase, subject matter experts convene
to discuss, create, and test working drafts of the benchmark. This discussion occurs until
consensus has been reached on benchmark recommendations. The second phase begins
after the benchmark has been published. During this phase, all feedback provided by the
Internet community is reviewed by the consensus team for incorporation in the
benchmark. If you are interested in participating in the consensus process, please visit
https://community.cisecurity.org.
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Typographical Conventions
The following typographical conventions are used throughout this guide:
Convention
Meaning
Stylized Monospace font
Used for blocks of code, command, and script examples.
Text should be interpreted exactly as presented.
Monospace font
Used for inline code, commands, or examples. Text should
be interpreted exactly as presented.
<italic font in brackets>
Italic texts set in angle brackets denote a variable
requiring substitution for a real value.
Italic font
Used to denote the title of a book, article, or other
publication.
Note
Additional information or caveats
Scoring Information
A scoring status indicates whether compliance with the given recommendation impacts the
assessed target's benchmark score. The following scoring statuses are used in this
benchmark:
Scored
Failure to comply with "Scored" recommendations will decrease the final benchmark score.
Compliance with "Scored" recommendations will increase the final benchmark score.
Not Scored
Failure to comply with "Not Scored" recommendations will not decrease the final
benchmark score. Compliance with "Not Scored" recommendations will not increase the
final benchmark score.
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Profile Definitions
The following configuration profiles are defined by this Benchmark:

Level 1 - Server
Items in this profile intend to:
o
o
o
be practical and prudent;
provide a clear security benefit; and
not inhibit the utility of the technology beyond acceptable means.
This profile is intended for servers.

Level 2 - Server
This profile extends the "Level 1 - Server" profile. Items in this profile exhibit one or
more of the following characteristics:
o
o
o
are intended for environments or use cases where security is paramount.
acts as defense in depth measure.
may negatively inhibit the utility or performance of the technology.
This profile is intended for servers.

Level 1 - Workstation
Items in this profile intend to:
o
o
o
be practical and prudent;
provide a clear security benefit; and
not inhibit the utility of the technology beyond acceptable means.
This profile is intended for workstations.

Level 2 - Workstation
This profile extends the "Level 1 - Workstation" profile. Items in this profile exhibit
one or more of the following characteristics:
o
o
o
are intended for environments or use cases where security is paramount.
acts as defense in depth measure.
may negatively inhibit the utility or performance of the technology.
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This profile is intended for workstations.
Acknowledgements
This benchmark exemplifies the great things a community of users, vendors, and subject matter
experts can accomplish through consensus collaboration. The CIS community thanks the entire
consensus team with special recognition to the following individuals who contributed greatly to
the creation of this guide:
Contributor
Rakesh Jain Research Engineer, Intel
William E. Triest III , The Ohio State University
Editor
Rael Daruszka , Center for Internet Security
Jonathan Lewis Christopherson
This benchmark is based upon previous Linux benchmarks published and would not be
possible without the contributions provided over the history of all of these benchmarks
including the previous version of the CentOS and Red Hat benchmarks. The CIS community
thanks everyone who has contributed to the Linux benchmarks.
15 | P a g e
Recommendations
1 Initial Setup
Items in this section are advised for all systems, but may be difficult or require extensive
preparation after the initial setup of the system.
1.1 Filesystem Configuration
Directories that are used for system-wide functions can be further protected by placing
them on separate partitions. This provides protection for resource exhaustion and enables
the use of mounting options that are applicable to the directory's intended use. Users' data
can be stored on separate partitions and have stricter mount options. A user partition is a
filesystem that has been established for use by the users and does not contain software for
system operations.
The recommendations in this section are easier to perform during initial system
installation. If the system is already installed, it is recommended that a full backup be
performed before repartitioning the system.
Note: If you are repartitioning a system that has already been installed, make sure the data
has been copied over to the new partition, unmount it and then remove the data from the
directory that was in the old partition. Otherwise it will still consume space in the old
partition that will be masked when the new filesystem is mounted. For example, if a system
is in single-user mode with no filesystems mounted and the administrator adds a lot of data
to the /tmp directory, this data will still consume space in / once the /tmp filesystem is
mounted unless it is removed first.
16 | P a g e
1.1.1 Disable unused filesystems
A number of uncommon filesystem types are supported under Linux. Removing support
for unneeded filesystem types reduces the local attack surface of the system. If a filesystem
type is not needed it should be disabled. Native Linux file systems are designed to ensure
that built-in security controls function as expected. Non-native filesystems can lead to
unexpected consequences to both the security and functionality of the system and should
be used with caution. Many filesystems are created for niche use cases and are not
maintained and supported as the operating systems are updated and patched. Users of
non-native filesystems should ensure that there is attention and ongoing support for them,
especially in light of frequent operating system changes.
Standard network connectivity and Internet access to cloud storage may make the use of
non-standard filesystem formats to directly attach heterogeneous devices much less
attractive.
Note: This should not be considered a comprehensive list of filesystems. You may wish to
consider additions to those listed here for your environment.
1.1.1.1 Ensure mounting of cramfs filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The cramfs filesystem type is a compressed read-only Linux filesystem embedded in small
footprint systems. A cramfs image can be used without having to first decompress the
image.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
server. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
17 | P a g e
# modprobe -n -v cramfs
install /bin/true
# lsmod | grep cramfs
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install cramfs /bin/true
18 | P a g e
1.1.1.2 Ensure mounting of freevxfs filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The freevxfs filesystem type is a free version of the Veritas type filesystem. This is the
primary filesystem type for HP-UX operating systems.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v freevxfs
install /bin/true
# lsmod | grep freevxfs
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install freevxfs /bin/true
19 | P a g e
1.1.1.3 Ensure mounting of jffs2 filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The jffs2 (journaling flash filesystem 2) filesystem type is a log-structured filesystem
used in flash memory devices.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v jffs2
install /bin/true
# lsmod | grep jffs2
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install jffs2 /bin/true
20 | P a g e
1.1.1.4 Ensure mounting of hfs filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The hfs filesystem type is a hierarchical filesystem that allows you to mount Mac OS
filesystems.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v hfs
install /bin/true
# lsmod | grep hfs
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install hfs /bin/true
21 | P a g e
1.1.1.5 Ensure mounting of hfsplus filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The hfsplus filesystem type is a hierarchical filesystem designed to replace hfs that
allows you to mount Mac OS filesystems.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v hfsplus
install /bin/true
# lsmod | grep hfsplus
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install hfsplus /bin/true
22 | P a g e
1.1.1.6 Ensure mounting of squashfs filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The squashfs filesystem type is a compressed read-only Linux filesystem embedded in
small footprint systems (similar to cramfs). A squashfs image can be used without having
to first decompress the image.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v squashfs
install /bin/true
# lsmod | grep squashfs
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install squashfs /bin/true
23 | P a g e
1.1.1.7 Ensure mounting of udf filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The udf filesystem type is the universal disk format used to implement ISO/IEC 13346 and
ECMA-167 specifications. This is an open vendor filesystem type for data storage on a
broad range of media. This filesystem type is necessary to support writing DVDs and newer
optical disc formats.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v udf
install /bin/true
# lsmod | grep udf
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install udf /bin/true
24 | P a g e
1.1.1.8 Ensure mounting of FAT filesystems is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 2 - Workstation
Description:
The FAT filesystem format is primarily used on older windows systems and portable USB
drives or flash modules. It comes in three types FAT12, FAT16, and FAT32 all of which are
supported by the vfat kernel module.
Rationale:
Removing support for unneeded filesystem types reduces the local attack surface of the
system. If this filesystem type is not needed, disable it.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v vfat
install /bin/true
# lsmod | grep vfat
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install vfat /bin/true
Impact:
FAT filesystems are often used on portable USB sticks and other flash media are commonly
used to transfer files between workstations, removing VFAT support may prevent the
ability to transfer files in this way.
25 | P a g e
1.1.2 Ensure separate partition exists for /tmp (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The /tmp directory is a world-writable directory used for temporary storage by all users
and some applications.
Rationale:
Since the /tmp directory is intended to be world-writable, there is a risk of resource
exhaustion if it is not bound to a separate partition. In addition, making /tmp its own file
system allows an administrator to set the noexec option on the mount, making /tmp
useless for an attacker to install executable code. It would also prevent an attacker from
establishing a hardlink to a system setuid program and wait for it to be updated. Once the
program was updated, the hardlink would be broken and the attacker would have his own
copy of the program. If the program happened to have a security vulnerability, the attacker
could continue to exploit the known flaw.
Audit:
Run the following command and verify output shows /tmp is mounted:
# mount | grep /tmp
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
For new installations, during installation create a custom partition setup and specify a
separate partition for /tmp.
For systems that were previously installed, create a new partition and configure
/etc/fstab as appropriate.
Impact:
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem
partitions may prevent successful resizing, or may require the installation of additional
tools solely for the purpose of resizing operations. The use of these additional tools may
introduce their own security considerations.
26 | P a g e
References:
1. AJ Lewis, "LVM HOWTO", http://tldp.org/HOWTO/LVM-HOWTO/
Notes:
systemd includes the tmp.mount service which should be used instead of
configuring /etc/fstab.
27 | P a g e
1.1.3 Ensure nodev option set on /tmp partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nodev mount option specifies that the filesystem cannot contain special devices.
Rationale:
Since the /tmp filesystem is not intended to support devices, set this option to ensure that
users cannot attempt to create block or character special devices in /tmp.
Audit:
If a /tmp partition exists run the following command and verify that the nodev option is set
on /tmp:
# mount | grep /tmp
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add nodev to the fourth field (mounting options) for
the /tmp partition. See the fstab(5) manual page for more information.
Run the following command to remount /tmp:
# mount -o remount,nodev /tmp
28 | P a g e
1.1.4 Ensure nosuid option set on /tmp partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nosuid mount option specifies that the filesystem cannot contain setuid files.
Rationale:
Since the /tmp filesystem is only intended for temporary file storage, set this option to
ensure that users cannot create setuid files in /tmp.
Audit:
If a /tmp partition exists run the following command and verify that the nosuid option is set
on /tmp:
# mount | grep /tmp
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add nosuid to the fourth field (mounting options) for
the /tmp partition. See the fstab(5) manual page for more information.
Run the following command to remount /tmp:
# mount -o remount,nosuid /tmp
29 | P a g e
1.1.5 Ensure noexec option set on /tmp partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The noexec mount option specifies that the filesystem cannot contain executable binaries.
Rationale:
Since the /tmp filesystem is only intended for temporary file storage, set this option to
ensure that users cannot run executable binaries from /tmp.
Audit:
If a /tmp partition exists run the following command and verify that the noexec option is set
on /tmp:
# mount | grep /tmp
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add noexec to the fourth field (mounting options) for the
/tmp partition. See the fstab(5) manual page for more information.
Run the following command to remount /tmp:
# mount -o remount,noexec /tmp
30 | P a g e
1.1.6 Ensure separate partition exists for /var (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The /var directory is used by daemons and other system services to temporarily store
dynamic data. Some directories created by these processes may be world-writable.
Rationale:
Since the /var directory may contain world-writable files and directories, there is a risk of
resource exhaustion if it is not bound to a separate partition.
Audit:
Run the following command and verify output shows /var is mounted:
# mount | grep /var
/dev/xvdg1 on /var type ext4 (rw,relatime,data=ordered)
Remediation:
For new installations, during installation create a custom partition setup and specify a
separate partition for /var.
For systems that were previously installed, create a new partition and
configure /etc/fstab as appropriate.
Impact:
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem
partitions may prevent successful resizing, or may require the installation of additional
tools solely for the purpose of resizing operations. The use of these additional tools may
introduce their own security considerations.
References:
1. AJ Lewis, "LVM HOWTO", http://tldp.org/HOWTO/LVM-HOWTO/
31 | P a g e
1.1.7 Ensure separate partition exists for /var/tmp (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The /var/tmp directory is a world-writable directory used for temporary storage by all
users and some applications.
Rationale:
Since the /var/tmp directory is intended to be world-writable, there is a risk of resource
exhaustion if it is not bound to a separate partition. In addition, making /var/tmp its own
file system allows an administrator to set the noexec option on the mount,
making /var/tmp useless for an attacker to install executable code. It would also prevent
an attacker from establishing a hardlink to a system setuid program and wait for it to be
updated. Once the program was updated, the hardlink would be broken and the attacker
would have his own copy of the program. If the program happened to have a security
vulnerability, the attacker could continue to exploit the known flaw.
Audit:
Run the following command and verify output shows /var/tmp is mounted:
# mount | grep /var/tmp
tmpfs on /var/tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
For new installations, during installation create a custom partition setup and specify a
separate partition for /var/tmp.
For systems that were previously installed, create a new partition and
configure /etc/fstab as appropriate.
Impact:
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem
partitions may prevent successful resizing, or may require the installation of additional
tools solely for the purpose of resizing operations. The use of these additional tools may
introduce their own security considerations.
32 | P a g e
1.1.8 Ensure nodev option set on /var/tmp partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nodev mount option specifies that the filesystem cannot contain special devices.
Rationale:
Since the /var/tmp filesystem is not intended to support devices, set this option to ensure
that users cannot attempt to create block or character special devices in /var/tmp.
Audit:
If a /var/tmp partition exists run the following command and verify that the nodev option is
set on /var/tmp.
# mount | grep /var/tmp
tmpfs on /var/tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add nodev to the fourth field (mounting options) for
the /var/tmp partition. See the fstab(5) manual page for more information.
Run the following command to remount /var/tmp:
# mount -o remount,nodev /var/tmp
33 | P a g e
1.1.9 Ensure nosuid option set on /var/tmp partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nosuid mount option specifies that the filesystem cannot contain setuid files.
Rationale:
Since the /var/tmp filesystem is only intended for temporary file storage, set this option to
ensure that users cannot create setuid files in /var/tmp.
Audit:
If a /var/tmp partition exists run the following command and verify that the nosuid option
is set on /var/tmp.
# mount | grep /var/tmp
tmpfs on /var/tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add nosuid to the fourth field (mounting options) for
the /var/tmp partition. See the fstab(5) manual page for more information.
Run the following command to remount /var/tmp:
# mount -o remount,nosuid /var/tmp
34 | P a g e
1.1.10 Ensure noexec option set on /var/tmp partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The noexec mount option specifies that the filesystem cannot contain executable binaries.
Rationale:
Since the /var/tmp filesystem is only intended for temporary file storage, set this option to
ensure that users cannot run executable binaries from /var/tmp.
Audit:
If a /var/tmp partition exists run the following command and verify that the noexec option
is set on /var/tmp.
# mount | grep /var/tmp
tmpfs on /var/tmp type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add noexec to the fourth field (mounting options) for the
/var/tmp partition. See the fstab(5) manual page for more information.
Run the following command to remount /var/tmp:
# mount -o remount,noexec /var/tmp
35 | P a g e
1.1.11 Ensure separate partition exists for /var/log (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The /var/log directory is used by system services to store log data .
Rationale:
There are two important reasons to ensure that system logs are stored on a separate
partition: protection against resource exhaustion (since logs can grow quite large) and
protection of audit data.
Audit:
Run the following command and verify output shows /var/log is mounted:
# mount | grep /var/log
/dev/xvdh1 on /var/log type ext4 (rw,relatime,data=ordered)
Remediation:
For new installations, during installation create a custom partition setup and specify a
separate partition for /var/log.
For systems that were previously installed, create a new partition and
configure /etc/fstab as appropriate.
Impact:
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem
partitions may prevent successful resizing, or may require the installation of additional
tools solely for the purpose of resizing operations. The use of these additional tools may
introduce their own security considerations.
References:
1. AJ Lewis, "LVM HOWTO", http://tldp.org/HOWTO/LVM-HOWTO/
36 | P a g e
1.1.12 Ensure separate partition exists for /var/log/audit (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The auditing daemon, auditd, stores log data in the /var/log/audit directory.
Rationale:
There are two important reasons to ensure that data gathered by auditd is stored on a
separate partition: protection against resource exhaustion (since the audit.log file can
grow quite large) and protection of audit data. The audit daemon calculates how much free
space is left and performs actions based on the results. If other processes (such as syslog)
consume space in the same partition as auditd, it may not perform as desired.
Audit:
Run the following command and verify output shows /var/log/audit is mounted:
# mount | grep /var/log/audit
/dev/xvdi1 on /var/log/audit type ext4 (rw,relatime,data=ordered)
Remediation:
For new installations, during installation create a custom partition setup and specify a
separate partition for /var/log/audit.
For systems that were previously installed, create a new partition and
configure /etc/fstab as appropriate.
Impact:
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem
partitions may prevent successful resizing, or may require the installation of additional
tools solely for the purpose of resizing operations. The use of these additional tools may
introduce their own security considerations.
References:
1. AJ Lewis, "LVM HOWTO", http://tldp.org/HOWTO/LVM-HOWTO/
37 | P a g e
1.1.13 Ensure separate partition exists for /home (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The /home directory is used to support disk storage needs of local users.
Rationale:
If the system is intended to support local users, create a separate partition for the /home
directory to protect against resource exhaustion and restrict the type of files that can be
stored under /home.
Audit:
Run the following command and verify output shows /home is mounted:
# mount | grep /home
/dev/xvdf1 on /home type ext4 (rw,nodev,relatime,data=ordered)
Remediation:
For new installations, during installation create a custom partition setup and specify a
separate partition for /home.
For systems that were previously installed, create a new partition and
configure /etc/fstab as appropriate.
Impact:
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem
partitions may prevent successful resizing, or may require the installation of additional
tools solely for the purpose of resizing operations. The use of these additional tools may
introduce their own security considerations.
References:
1. AJ Lewis, "LVM HOWTO", http://tldp.org/HOWTO/LVM-HOWTO/
38 | P a g e
1.1.14 Ensure nodev option set on /home partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nodev mount option specifies that the filesystem cannot contain special devices.
Rationale:
Since the user partitions are not intended to support devices, set this option to ensure that
users cannot attempt to create block or character special devices.
Audit:
If a /home partition exists run the following command and verify that the nodev option is set
on /home.
# mount | grep /home
/dev/xvdf1 on /home type ext4 (rw,nodev,relatime,data=ordered)
Remediation:
Edit the /etc/fstab file and add nodev to the fourth field (mounting options) for the
/home partition. See the fstab(5) manual page for more information.
# mount -o remount,nodev /home
Notes:
The actions in this recommendation refer to the /home partition, which is the default user
partition that is defined. If you have created other user partitions, it is recommended that
the Remediation and Audit steps be applied to these partitions as well.
39 | P a g e
1.1.15 Ensure nodev option set on /dev/shm partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nodev mount option specifies that the filesystem cannot contain special devices.
Rationale:
Since the /dev/shm filesystem is not intended to support devices, set this option to ensure
that users cannot attempt to create special devices in /dev/shm partitions.
Audit:
Run the following command and verify that the nodev option is set on /dev/shm.
# mount | grep /dev/shm
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add nodev to the fourth field (mounting options) for
the /dev/shm partition. See the fstab(5) manual page for more information.
Run the following command to remount /dev/shm:
# mount -o remount,nodev /dev/shm
40 | P a g e
1.1.16 Ensure nosuid option set on /dev/shm partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nosuid mount option specifies that the filesystem cannot contain setuid files.
Rationale:
Setting this option on a file system prevents users from introducing privileged programs
onto the system and allowing non-root users to execute them.
Audit:
Run the following command and verify that the nosuid option is set on /dev/shm.
# mount | grep /dev/shm
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add nosuid to the fourth field (mounting options) for
the /dev/shm partition. See the fstab(5) manual page for more information.
Run the following command to remount /dev/shm:
# mount -o remount,nosuid /dev/shm
41 | P a g e
1.1.17 Ensure noexec option set on /dev/shm partition (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The noexec mount option specifies that the filesystem cannot contain executable binaries.
Rationale:
Setting this option on a file system prevents users from executing programs from shared
memory. This deters users from introducing potentially malicious software on the system.
Audit:
Run the following command and verify that the noexec option is set on /dev/shm.
# mount | grep /dev/shm
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime)
Remediation:
Edit the /etc/fstab file and add noexec to the fourth field (mounting options) for
the /dev/shm partition. See the fstab(5) manual page for more information.
Run the following command to remount /dev/shm:
# mount -o remount,noexec /dev/shm
42 | P a g e
1.1.18 Ensure nodev option set on removable media partitions (Not
Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nodev mount option specifies that the filesystem cannot contain special devices.
Rationale:
Removable media containing character and block special devices could be used to
circumvent security controls by allowing non-root users to access sensitive device files
such as /dev/kmem or the raw disk partitions.
Audit:
Run the following command and verify that the nodev option is set on all removable media
partitions.
# mount
Remediation:
Edit the /etc/fstab file and add nodev to the fourth field (mounting options) of all
removable media partitions. Look for entries that have mount points that contain words
such as floppy or cdrom. See the fstab(5) manual page for more information.
43 | P a g e
1.1.19 Ensure nosuid option set on removable media partitions (Not
Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The nosuid mount option specifies that the filesystem cannot contain setuid files.
Rationale:
Setting this option on a file system prevents users from introducing privileged programs
onto the system and allowing non-root users to execute them.
Audit:
Run the following command and verify that the nosuid option is set on all removable media
partitions.
# mount
Remediation:
Edit the /etc/fstab file and add nosuid to the fourth field (mounting options) of all
removable media partitions. Look for entries that have mount points that contain words
such as floppy or cdrom. See the fstab(5) manual page for more information.
44 | P a g e
1.1.20 Ensure noexec option set on removable media partitions (Not
Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The noexec mount option specifies that the filesystem cannot contain executable binaries.
Rationale:
Setting this option on a file system prevents users from executing programs from the
removable media. This deters users from being able to introduce potentially malicious
software on the system.
Audit:
Run the following command and verify that the noexec option is set on all removable media
partitions.
# mount
Remediation:
Edit the /etc/fstab file and add noexec to the fourth field (mounting options) of all
removable media partitions. Look for entries that have mount points that contain words
such as floppy or cdrom. See the fstab(5) manual page for more information.
45 | P a g e
1.1.21 Ensure sticky bit is set on all world-writable directories (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Setting the sticky bit on world writable directories prevents users from deleting or
renaming files in that directory that are not owned by them.
Rationale:
This feature prevents the ability to delete or rename files in world writable directories
(such as /tmp) that are owned by another user.
Audit:
Run the following command to verify no world writable directories exist without the sticky
bit set:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -type d
\( -perm -0002 -a ! -perm -1000 \) 2>/dev/null
No output should be returned.
Remediation:
Run the following command to set the sticky bit on all world writable directories:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -type d
-perm -0002 2>/dev/null | xargs chmod a+t
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1.1.22 Disable Automounting (Scored)
Profile Applicability:
 Level 1 - Server
 Level 2 - Workstation
Description:
autofs allows automatic mounting of devices, typically including CD/DVDs and USB drives.
Rationale:
With automounting enabled anyone with physical access could attach a USB drive or disc
and have its contents available in system even if they lacked permissions to mount it
themselves.
Audit:
Run the following command and verify all runlevels are listed as "off" or autofs is not
available:
# chkconfig --list autofs
autofs
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable autofs:
# chkconfig autofs off
Impact:
The use portable hard drives is very common for workstation users. If your organization
allows the use of portable storage or media on workstations and physical access controls to
workstations is considered adequate there is little value add in turning off automounting.
Notes:
This control should align with the tolerance of the use of portable drives and optical media
in the organization. On a server requiring an admin to manually mount media can be part
of defense-in-depth to reduce the risk of unapproved software or information being
introduced or proprietary software or information being exfiltrated. If admins commonly
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use flash drives and Server access has sufficient physical controls, requiring manual
mounting may not increase security.
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1.2 Configure Software Updates
CentOS 6 uses the yum package manager to install and update software packages. Patch
management procedures may vary widely between enterprises. Large enterprises may
choose to install a local updates server that can be used in place of CentOS's servers,
whereas a single deployment of a system may prefer to get updates directly. Updates can
be performed automatically or manually, depending on the site's policy for patch
management. Many large enterprises prefer to test patches on a non-production system
before rolling out to production.
For the purpose of this benchmark, the requirement is to ensure that a patch management
system is configured and maintained. The specifics on patch update procedures are left to
the organization.
1.2.1 Ensure package manager repositories are configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Systems need to have package manager repositories configured to ensure they receive the
latest patches and updates.
Rationale:
If a system's package repositories are misconfigured important patches may not be
identified or a rogue repository could introduce compromised software.
Audit:
Run the following command and verify repositories are configured correctly:
# yum repolist
Remediation:
Configure your package manager repositories according to site policy.
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1.2.2 Ensure GPG keys are configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Most packages managers implement GPG key signing to verify package integrity during
installation.
Rationale:
It is important to ensure that updates are obtained from a valid source to protect against
spoofing that could lead to the inadvertent installation of malware on the system.
Audit:
Run the following command and verify GPG keys are configured correctly:
# rpm -q gpg-pubkey --qf '%{name}-%{version}-%{release} --> %{summary}\n'
Remediation:
Update your package manager GPG keys in accordance with site policy.
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1.2.3 Ensure gpgcheck is globally activated (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The gpgcheck option, found in the main section of the /etc/yum.conf and individual
/etc/yum/repos.d/* files determines if an RPM package's signature is checked prior to its
installation.
Rationale:
It is important to ensure that an RPM's package signature is always checked prior to
installation to ensure that the software is obtained from a trusted source.
Audit:
Run the following command and verify gpgcheck is set to '1':
# grep ^gpgcheck /etc/yum.conf
gpgcheck=1
Run the following command and verify that all instances of gpgcheck returned are set to '1':
# grep ^gpgcheck /etc/yum.repos.d/*
Remediation:
Edit /etc/yum.conf and set 'gpgcheck=1' in the [main] section.
Edit any failing files in /etc/yum.repos.d/* and set all instances of gpgcheck to '1'.
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1.3 Filesystem Integrity Checking
AIDE is a file integrity checking tool, similar in nature to Tripwire. While it cannot prevent
intrusions, it can detect unauthorized changes to configuration files by alerting when the
files are changed. When setting up AIDE, decide internally what the site policy will be
concerning integrity checking. Review the AIDE quick start guide and AIDE documentation
before proceeding.
1.3.1 Ensure AIDE is installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
AIDE takes a snapshot of filesystem state including modification times, permissions, and
file hashes which can then be used to compare against the current state of the filesystem to
detect modifications to the system.
Rationale:
By monitoring the filesystem state compromised files can be detected to prevent or limit
the exposure of accidental or malicious misconfigurations or modified binaries.
Audit:
Run the following command and verify aide is installed:
# rpm -q aide
aide-<version>
Remediation:
Run the following command to install aide:
# yum install aide
Configure AIDE as appropriate for your environment. Consult the AIDE documentation for
options.
Initialize AIDE:
# aide --init
# mv /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
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References:
1. AIDE stable manual: http://aide.sourceforge.net/stable/manual.html
Notes:
The prelinking feature can interfere with AIDE because it alters binaries to speed up their
start up times. Run prelink -ua to restore the binaries to their prelinked state, thus
avoiding false positives from AIDE.
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1.3.2 Ensure filesystem integrity is regularly checked (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Periodic checking of the filesystem integrity is needed to detect changes to the filesystem.
Rationale:
Periodic file checking allows the system administrator to determine on a regular basis if
critical files have been changed in an unauthorized fashion.
Audit:
Run the following commands to determine if there is a cron job scheduled to run the aide
check.
# crontab -u root -l | grep aide
# grep -r aide /etc/cron.* /etc/crontab
Ensure a cron job in compliance with site policy is returned.
Remediation:
Run the following command:
# crontab -u root -e
Add the following line to the crontab:
0 5 * * * /usr/sbin/aide --check
Notes:
The checking in this recommendation occurs every day at 5am. Alter the frequency and
time of the checks in compliance with site policy.
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1.4 Secure Boot Settings
The recommendations in this section focus on securing the bootloader and settings
involved in the boot process directly.
1.4.1 Ensure permissions on bootloader config are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The grub configuration file contains information on boot settings and passwords for
unlocking boot options. The grub configuration is usually located at
/boot/grub/grub.conf and linked as /boot/grub/menu.lst and /etc/grub.conf.
Rationale:
Setting the permissions to read and write for root only prevents non-root users from
seeing the boot parameters or changing them. Non-root users who read the boot
parameters may be able to identify weaknesses in security upon boot and be able to exploit
them.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /boot/grub/grub.conf
Access: (0600/-rw-------) Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on your grub configuration:
# chown root:root /boot/grub/grub.conf
# chmod og-rwx /boot/grub/grub.conf
Notes:
This recommendation is designed around the grub bootloader, if LILO or another
bootloader is in use in your environment enact equivalent settings.
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1.4.2 Ensure bootloader password is set (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Setting the boot loader password will require that anyone rebooting the system must enter
a password before being able to set command line boot parameters
Rationale:
Requiring a boot password upon execution of the boot loader will prevent an unauthorized
user from entering boot parameters or changing the boot partition. This prevents users
from weakening security (e.g. turning off SELinux at boot time).
Audit:
Run the following command and verify output matches:
# grep "^password" /boot/grub/grub.conf
password --md5 <encrypted-password>
Remediation:
Create an encrypted password with grub-md5-crypt:
# grub-md5-crypt
Password: <password>
Retype Password: <password>
<encrypted-password>
Copy and paste the <encrypted-password> into the global section of /boot/grub/grub.conf:
password --md5 <encrypted-password>
Notes:
This recommendation is designed around the grub bootloader, if LILO or another
bootloader is in use in your environment enact equivalent settings.
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1.4.3 Ensure authentication required for single user mode (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Single user mode is used for recovery when the system detects an issue during boot or by
manual selection from the bootloader.
Rationale:
Requiring authentication in single user mode prevents an unauthorized user from
rebooting the system into single user to gain root privileges without credentials.
Audit:
Run the following command and verify SINGLE is set to '/sbin/sulogin':
# grep ^SINGLE /etc/sysconfig/init
SINGLE=/sbin/sulogin
Remediation:
Edit /etc/sysconfig/init and set SINGLE to '/sbin/sulogin':
SINGLE=/sbin/sulogin
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1.4.4 Ensure interactive boot is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Interactive boot allows console users to interactively select which services start on boot.
The PROMPT option provides console users the ability to interactively boot the system and
select which services to start on boot .
Rationale:
Turn off the PROMPT option on the console to prevent console users from potentially
overriding established security settings.
Audit:
Run the following command and verify PROMPT is set to 'no':
# grep "^PROMPT=" /etc/sysconfig/init
PROMPT=no
Remediation:
Edit the /etc/sysconfig/init file and set PROMPT to 'no':
PROMPT=no
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1.5 Additional Process Hardening
1.5.1 Ensure core dumps are restricted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
A core dump is the memory of an executable program. It is generally used to determine
why a program aborted. It can also be used to glean confidential information from a core
file. The system provides the ability to set a soft limit for core dumps, but this can be
overridden by the user.
Rationale:
Setting a hard limit on core dumps prevents users from overriding the soft variable. If core
dumps are required, consider setting limits for user groups (see limits.conf(5)). In
addition, setting the fs.suid_dumpable variable to 0 will prevent setuid programs from
dumping core.
Audit:
Run the following commands and verify output matches:
# grep "hard core" /etc/security/limits.conf /etc/security/limits.d/*
* hard core 0
# sysctl fs.suid_dumpable
fs.suid_dumpable = 0
Remediation:
Add the following line to the /etc/security/limits.conf file or a
/etc/security/limits.d/* file:
* hard core 0
Set the following parameter in the /etc/sysctl.conf file:
fs.suid_dumpable = 0
Run the following command to set the active kernel parameter:
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# sysctl -w fs.suid_dumpable=0
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1.5.2 Ensure XD/NX support is enabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Recent processors in the x86 family support the ability to prevent code execution on a per
memory page basis. Generically and on AMD processors, this ability is called No Execute
(NX), while on Intel processors it is called Execute Disable (XD). This ability can help
prevent exploitation of buffer overflow vulnerabilities and should be activated whenever
possible. Extra steps must be taken to ensure that this protection is enabled, particularly on
32-bit x86 systems. Other processors, such as Itanium and POWER, have included such
support since inception and the standard kernel for those platforms supports the feature.
Rationale:
Enabling any feature that can protect against buffer overflow attacks enhances the security
of the system.
Audit:
Run the following command and verify your kernel has identified and activated NX/XD
protection.
# dmesg | grep NX
NX (Execute Disable) protection: active
Remediation:
On 32 bit systems install a kernel with PAE support, no installation is required on 64 bit
systems:
If necessary configure your bootloader to load the new kernel and reboot the system.
You may need to enable NX or XD support in your bios.
Notes:
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Ensure your system supports the XD or NX bit and has PAE support before implementing
this recommendation as this may prevent it from booting if these are not supported by
your hardware.
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1.5.3 Ensure address space layout randomization (ASLR) is enabled
(Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Address space layout randomization (ASLR) is an exploit mitigation technique which
randomly arranges the address space of key data areas of a process.
Rationale:
Randomly placing virtual memory regions will make it difficult to write memory page
exploits as the memory placement will be consistently shifting.
Audit:
Run the following command and verify output matches:
# sysctl kernel.randomize_va_space
kernel.randomize_va_space = 2
Remediation:
Set the following parameter in the /etc/sysctl.conf file:
kernel.randomize_va_space = 2
Run the following command to set the active kernel parameter:
# sysctl -w kernel.randomize_va_space=2
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1.5.4 Ensure prelink is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
is a program that modifies ELF shared libraries and ELF dynamically linked
binaries in such a way that the time needed for the dynamic linker to perform relocations
at startup significantly decreases.
prelink
Rationale:
The prelinking feature can interfere with the operation of AIDE, because it changes
binaries. Prelinking can also increase the vulnerability of the system if a malicious user is
able to compromise a common library such as libc.
Audit:
Run the following command and verify prelink is not installed:
# rpm -q prelink
package prelink is not installed
Remediation:
Run the following commands to restore binaries to normal and uninstall prelink:
# prelink -ua
# yum remove prelink
1.6 Mandatory Access Control
Mandatory Access Control (MAC) provides an additional layer of access restrictions to
processes on top of the base Discretionary Access Controls. By restricting how processes
can access files and resources on a system the potential impact from vulnerabilities in the
processes can be reduced.
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Impact: Mandatory Access Control limits the capabilities of applications and daemons on a
system, while this can prevent unauthorized access the configuration of MAC can be
complex and difficult to implement correctly preventing legitimate access from occurring.
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1.6.1 Configure SELinux
SELinux provides a Mandatory Access Control (MAC) system that greatly augments the
default Discretionary Access Control (DAC) model. Under SELinux, every process and every
object (files, sockets, pipes) on the system is assigned a security context, a label that
includes detailed type information about the object. The kernel allows processes to access
objects only if that access is explicitly allowed by the policy in effect. The policy defines
transitions, so that a user can be allowed to run software, but the software can run under a
different context than the user's default. This automatically limits the damage that the
software can do to files accessible by the calling user. The user does not need to take any
action to gain this benefit. For an action to occur, both the traditional DAC permissions
must be satisfied as well as the SELinux MAC rules. The action will not be allowed if either
one of these models does not permit the action. In this way, SELinux rules can only make a
system's permissions more restrictive and secure. SELinux requires a complex policy to
allow all the actions required of a system under normal operation. Three such policies have
been designed for use with RHEL7 and are included with the system: targeted, strict, and
mls. These are described as follows:



targeted: consists mostly of Type Enforcement (TE) rules, and a small number of
Role-Based Access Control (RBAC) rules. Targeted restricts the actions of many
types of programs, but leaves interactive users largely unaffected.
strict: also uses TE and RBAC rules, but on more programs and more aggressively.
mls: implements Multi-Level Security (MLS), which introduces even more kinds of
labels (sensitivity and category) and rules that govern access based on these.
This section provides guidance for the configuration of the targeted policy.
Note: This section only applies if SELinux is in use on the system. Recommendations for
AppArmor are included in the Distribution Independent Linux benchmark, and additional
Mandatory Access Control systems exist beyond these two.
References:
1. NSA SELinux resources:
1. http://www.nsa.gov/research/selinux
2. http://www.nsa.gov/research/selinux/list.shtml
2. Fedora SELinux resources:
1. FAQ: http://docs.fedoraproject.org/selinux-faq
2. User Guide: http://docs.fedoraproject.org/selinux-user-guide
3. Managing Services Guide: http://docs.fedoraproject.org/selinux-managingconfined-services-guide
3. SELinux Project web page and wiki:
1. http://www.selinuxproject.org
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4. Chapters 43-45 of Red Hat Enterprise Linux 5: Deployment Guide (Frank Mayer,
Karl MacMillan and David Caplan),
5. SELinux by Example: Using Security Enhanced Linux (Prentice Hall, August 6, 2006)
1.6.1.1 Ensure SELinux is not disabled in bootloader configuration
(Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Configure SELINUX to be enabled at boot time and verify that it has not been overwritten
by the grub boot parameters.
Rationale:
SELinux must be enabled at boot time in your grub configuration to ensure that the
controls it provides are not overridden.
Audit:
Run the following command and verify that no kernel line has the selinux=0 or
enforcing=0 parameters set:
# grep "^\s*kernel" /boot/grub/grub.conf
Remediation:
Edit /boot/grub/grub.conf and remove all instances of selinux=0 and enforcing=0 on
all kernel lines.
Notes:
This recommendation is designed around the grub bootloader, if LILO or another
bootloader is in use in your environment enact equivalent settings.
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1.6.1.2 Ensure the SELinux state is enforcing (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Set SELinux to enable when the system is booted.
Rationale:
SELinux must be enabled at boot time in to ensure that the controls it provides are in effect
at all times.
Audit:
Run the following commands and ensure output matches:
# grep SELINUX=enforcing /etc/selinux/config
SELINUX=enforcing
# sestatus
SELinux status: enabled
Current mode: enforcing
Mode from config file: enforcing
Remediation:
Edit the /etc/selinux/config file to set the SELINUX parameter:
SELINUX=enforcing
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1.6.1.3 Ensure SELinux policy is configured (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Configure SELinux to meet or exceed the default targeted policy, which constrains daemons
and system software only.
Rationale:
Security configuration requirements vary from site to site. Some sites may mandate a
policy that is stricter than the default policy, which is perfectly acceptable. This item is
intended to ensure that at least the default recommendations are met.
Audit:
Run the following commands and ensure output matches either "targeted" or "mls":
# grep SELINUXTYPE=targeted /etc/selinux/config
SELINUXTYPE=targeted
# sestatus
Policy from config file: targeted
Remediation:
Edit the /etc/selinux/config file to set the SELINUXTYPE parameter:
SELINUXTYPE=targeted
Notes:
If your organization requires stricter policies, ensure that they are set in
the /etc/selinux/config file.
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1.6.1.4 Ensure SETroubleshoot is not installed (Scored)
Profile Applicability:
 Level 2 - Server
Description:
The SETroubleshoot service notifies desktop users of SELinux denials through a userfriendly interface. The service provides important information around configuration errors,
unauthorized intrusions, and other potential errors.
Rationale:
The SETroubleshoot service is an unnecessary daemon to have running on a server,
especially if X Windows is disabled.
Audit:
Run the following command and verify setroubleshoot is not installed:
# rpm -q setroubleshoot
package setroubleshoot is not installed
Remediation:
Run the following command to uninstall setroubleshoot:
# yum remove setroubleshoot
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1.6.1.5 Ensure the MCS Translation Service (mcstrans) is not installed
(Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The mcstransd daemon provides category label information to client processes requesting
information. The label translations are defined in /etc/selinux/targeted/setrans.conf
Rationale:
Since this service is not used very often, remove it to reduce the amount of potentially
vulnerable code running on the system.
Audit:
Run the following command and verify mcstrans is not installed:
# rpm -q mcstrans
package mcstrans is not installed
Remediation:
Run the following command to uninstall mcstrans:
# yum remove mcstrans
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1.6.1.6 Ensure no unconfined daemons exist (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Daemons that are not defined in SELinux policy will inherit the security context of their
parent process.
Rationale:
Since daemons are launched and descend from the init process, they will inherit the
security context label initrc_t. This could cause the unintended consequence of giving the
process more permission than it requires.
Audit:
Run the following command and verify not output is produced:
# ps -eZ | egrep "initrc" | egrep -vw "tr|ps|egrep|bash|awk" | tr ':' ' ' | awk '{
print $NF }'
Remediation:
Investigate any unconfined daemons found during the audit action. They may need to have
an existing security context assigned to them or a policy built for them.
Notes:
Occasionally certain daemons such as backup or centralized management software may
require running unconfined. Any such software should be carefully analyzed and
documented before such an exception is made.
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1.6.2 Ensure SELinux is installed (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
SELinux provides Mandatory Access Controls.
Rationale:
Without a Mandatory Access Control system installed only the default Discretionary Access
Control system will be available.
Audit:
Run the following command and verify libselinux is installed:
# rpm -q libselinux
libselinux-<version>
Remediation:
Run the following command to install libselinux:
# yum install libselinux
1.7 Warning Banners
Presenting a warning message prior to the normal user login may assist in the prosecution
of trespassers on the computer system. Changing some of these login banners also has the
side effect of hiding OS version information and other detailed system information from
attackers attempting to target specific exploits at a system.
Guidelines published by the US Department of Defense require that warning messages
include at least the name of the organization that owns the system, the fact that the system
is subject to monitoring and that such monitoring is in compliance with local statutes, and
that use of the system implies consent to such monitoring. It is important that the
organization's legal counsel review the content of all messages before any system
modifications are made, as these warning messages are inherently site-specific. More
information (including citations of relevant case law) can be found at
http://www.justice.gov/criminal/cybercrime/
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Note: The text provided in the remediation actions for these items is intended as an
example only. Please edit to include the specific text for your organization as approved by
your legal department.
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1.7.1 Command Line Warning Banners
The /etc/motd, /etc/issue, and /etc/issue.net files govern warning banners for
standard command line logins for both local and remote users.
1.7.1.1 Ensure message of the day is configured properly (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The contents of the /etc/motd file are displayed to users after login and function as a
message of the day for authenticated users.
Unix-based systems have typically displayed information about the OS release and patch
level upon logging in to the system. This information can be useful to developers who are
developing software for a particular OS platform. If mingetty(8) supports the following
options, they display operating system information:
\m - machine architecture (uname -m)
\r - operating system release (uname -r)
\s - operating system name
\v - operating system version (uname -v)
Rationale:
Warning messages inform users who are attempting to login to the system of their legal
status regarding the system and must include the name of the organization that owns the
system and any monitoring policies that are in place. Displaying OS and patch level
information in login banners also has the side effect of providing detailed system
information to attackers attempting to target specific exploits of a system. Authorized users
can easily get this information by running the "uname -a" command once they have logged
in.
Audit:
Run the following command and verify that the contents match site policy:
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# cat /etc/motd
Run the following command and verify no results are returned:
# egrep '(\\v|\\r|\\m|\\s)' /etc/motd
Remediation:
Edit the /etc/motd file with the appropriate contents according to your site policy, remove
any instances of \m, \r, \s, or \v.
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1.7.1.2 Ensure local login warning banner is configured properly (Not
Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The contents of the /etc/issue file are displayed to users prior to login for local terminals.
Unix-based systems have typically displayed information about the OS release and patch
level upon logging in to the system. This information can be useful to developers who are
developing software for a particular OS platform. If mingetty(8) supports the following
options, they display operating system information:
\m - machine architecture (uname -m)
\r - operating system release (uname -r)
\s - operating system name
\v - operating system version (uname -v)
Rationale:
Warning messages inform users who are attempting to login to the system of their legal
status regarding the system and must include the name of the organization that owns the
system and any monitoring policies that are in place. Displaying OS and patch level
information in login banners also has the side effect of providing detailed system
information to attackers attempting to target specific exploits of a system. Authorized users
can easily get this information by running the "uname -a" command once they have logged
in.
Audit:
Run the following command and verify that the contents match site policy:
# cat /etc/issue
Run the following command and verify no results are returned:
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# egrep '(\\v|\\r|\\m|\\s)' /etc/issue
Remediation:
Edit the /etc/issue file with the appropriate contents according to your site policy,
remove any instances of \m, \r, \s, or \v:
# echo "Authorized uses only. All activity may be monitored and reported." >
/etc/issue
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1.7.1.3 Ensure remote login warning banner is configured properly (Not
Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The contents of the /etc/issue.net file are displayed to users prior to login for remote
connections from configured services.
Unix-based systems have typically displayed information about the OS release and patch
level upon logging in to the system. This information can be useful to developers who are
developing software for a particular OS platform. If mingetty(8) supports the following
options, they display operating system information:
\m - machine architecture (uname -m)
\r - operating system release (uname -r)
\s - operating system name
\v - operating system version (uname -v)
Rationale:
Warning messages inform users who are attempting to login to the system of their legal
status regarding the system and must include the name of the organization that owns the
system and any monitoring policies that are in place. Displaying OS and patch level
information in login banners also has the side effect of providing detailed system
information to attackers attempting to target specific exploits of a system. Authorized users
can easily get this information by running the "uname -a" command once they have logged
in.
Audit:
Run the following command and verify that the contents match site policy:
# cat /etc/issue.net
Run the following command and verify no results are returned:
# egrep '(\\v|\\r|\\m|\\s)' /etc/issue.net
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Remediation:
Edit the /etc/issue.net file with the appropriate contents according to your site policy,
remove any instances of \m, \r, \s, or \v:
# echo "Authorized uses only. All activity may be monitored and reported." >
/etc/issue.net
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1.7.1.4 Ensure permissions on /etc/motd are configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The contents of the /etc/motd file are displayed to users after login and function as a
message of the day for authenticated users.
Rationale:
If the /etc/motd file does not have the correct ownership it could be modified by
unauthorized users with incorrect or misleading information.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/motd
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on /etc/motd:
# chown root:root /etc/motd
# chmod 644 /etc/motd
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1.7.1.5 Ensure permissions on /etc/issue are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The contents of the /etc/issue file are displayed to users prior to login for local terminals.
Rationale:
If the /etc/issue file does not have the correct ownership it could be modified by
unauthorized users with incorrect or misleading information.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/issue
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on /etc/issue:
# chown root:root /etc/issue
# chmod 644 /etc/issue
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1.7.1.6 Ensure permissions on /etc/issue.net are configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The contents of the /etc/issue.net file are displayed to users prior to login for remote
connections from configured services.
Rationale:
If the /etc/issue.net file does not have the correct ownership it could be modified by
unauthorized users with incorrect or misleading information.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/issue.net
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on /etc/issue.net:
# chown root:root /etc/issue.net
# chmod 644 /etc/issue.net
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1.7.2 Ensure GDM login banner is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
GDM is the GNOME Display Manager which handles graphical login for GNOME based
systems.
Rationale:
Warning messages inform users who are attempting to login to the system of their legal
status regarding the system and must include the name of the organization that owns the
system and any monitoring policies that are in place.
Audit:
If GDM is installed on the system verify that /etc/dconf/profile/gdm exists and contains
the following:
user-db:user
system-db:gdm
file-db:/usr/share/gdm/greeter-dconf-defaults
Then verify the banner-message-enable and banner-message-text options are configured
in /etc/dconf/db/gdm.d/01-banner-message:
[org/gnome/login-screen]
banner-message-enable=true
banner-message-text='<banner message>'
Remediation:
Create the /etc/dconf/profile/gdm file with the following contents:
user-db:user
system-db:gdm
file-db:/usr/share/gdm/greeter-dconf-defaults
Create or edit the banner-message-enable and banner-message-text options
in /etc/dconf/db/gdm.d/01-banner-message:
[org/gnome/login-screen]
banner-message-enable=true
banner-message-text='Authorized uses only. All activity may be monitored and
reported.'
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Run the following command to update the system databases:
# dconf update
Notes:
Additional options and sections may appear in the /etc/dconf/db/gdm.d/01-bannermessage file.
If a different GUI login service is in use, consult your documentation and apply an
equivalent banner.
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1.8 Ensure updates, patches, and additional security software are
installed (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Periodically patches are released for included software either due to security flaws or to
include additional functionality.
Rationale:
Newer patches may contain security enhancements that would not be available through the
latest full update. As a result, it is recommended that the latest software patches be used to
take advantage of the latest functionality. As with any software installation, organizations
need to determine if a given update meets their requirements and verify the compatibility
and supportability of any additional software against the update revision that is selected.
Audit:
Run the following command and verify there are no updates or patches to install:
# yum check-update
Remediation:
Use your package manager to update all packages on the system according to site
policy. The following command will install all available updates:
# yum update
Notes:
Site policy may mandate a testing period before install onto production systems for
available updates.
2 Services
While applying system updates and patches helps correct known vulnerabilities, one of the
best ways to protect the system against as yet unreported vulnerabilities is to disable all
86 | P a g e
services that are not required for normal system operation. This prevents the exploitation
of vulnerabilities discovered at a later date. If a service is not enabled, it cannot be
exploited. The actions in this section of the document provide guidance on some services
which can be safely disabled and under which circumstances, greatly reducing the number
of possible threats to the resulting system. Additionally some services which should
remain enabled but with secure configuration are covered as well as insecure service
clients.
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2.1 inetd Services
inetd is a super-server daemon that provides internet services and passes connections to
configured services. While not commonly used inetd and any unneeded inetd based
services should be disabled if possible.
2.1.1 Ensure chargen services are not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
is a network service that responds with 0 to 512 ASCII characters for each
connection it receives. This service is intended for debugging and testing purposes. It is
recommended that this service be disabled.
chargen
Rationale:
Disabling this service will reduce the remote attack surface of the system.
Audit:
Run the following command and verify chargen-dgram and chargen-stream are off or
missing:
# chkconfig --list
xinetd based services:
chargen-dgram: off
chargen-stream: off
Remediation:
Run the following commands to disable chargen-dgram and chargen-stream:
# chkconfig chargen-dgram off
# chkconfig chargen-stream off
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2.1.2 Ensure daytime services are not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
daytime is a network service that responds with the server's current date and time. This
service is intended for debugging and testing purposes. It is recommended that this service
be disabled.
Rationale:
Disabling this service will reduce the remote attack surface of the system.
Audit:
Run the following command and verify daytime-dgram and daytime-stream are off or
missing:
# chkconfig --list
xinetd based services:
daytime-dgram: off
daytime-stream: off
Remediation:
Run the following commands to disable daytime-dgram and daytime-stream:
# chkconfig daytime-dgram off
# chkconfig daytime-stream off
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2.1.3 Ensure discard services are not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
is a network service that simply discards all data it receives. This service is
intended for debugging and testing purposes. It is recommended that this service be
disabled.
discard
Rationale:
Disabling this service will reduce the remote attack surface of the system.
Audit:
Run the following command and verify discard-dgram and discard-stream are off or
missing:
# chkconfig --list
xinetd based services:
discard-dgram: off
discard-stream: off
Remediation:
Run the following commands to disable discard-dgram and discard-stream:
# chkconfig discard-dgram off
# chkconfig discard-stream off
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2.1.4 Ensure echo services are not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
is a network service that responds to clients with the data sent to it by the client. This
service is intended for debugging and testing purposes. It is recommended that this service
be disabled.
echo
Rationale:
Disabling this service will reduce the remote attack surface of the system.
Audit:
Run the following command and verify echo-dgram and echo-stream are off or missing:
# chkconfig --list
xinetd based services:
echo-dgram:
echo-stream:
off
off
Remediation:
Run the following commands to disable echo-dgram and echo-stream:
# chkconfig echo-dgram off
# chkconfig echo-stream off
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2.1.5 Ensure time services are not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
is a network service that responds with the server's current date and time as a 32 bit
integer. This service is intended for debugging and testing purposes. It is recommended
that this service be disabled.
time
Rationale:
Disabling this service will reduce the remote attack surface of the system.
Audit:
Run the following command and verify time-dgram and time-stream are off or missing:
# chkconfig --list
xinetd based services:
time-dgram:
time-stream:
off
off
Remediation:
Run the following commands to disable time-dgram and time-stream:
# chkconfig time-dgram off
# chkconfig time-stream off
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2.1.6 Ensure rsh server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Berkeley rsh-server (rsh, rlogin, rexec) package contains legacy services that
exchange credentials in clear-text.
Rationale:
These legacy services contain numerous security exposures and have been replaced with
the more secure SSH package.
Audit:
Run the following command and verify rsh, rlogin, and rexec are off or missing:
# chkconfig --list
xinetd based services:
rexec:
rlogin:
rsh:
off
off
off
Remediation:
Run the following commands to disable rsh, rlogin, and rexec:
# chkconfig rexec off
# chkconfig rlogin off
# chkconfig rsh off
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2.1.7 Ensure talk server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The talk software makes it possible for users to send and receive messages across systems
through a terminal session. The talk client (allows initiate of talk sessions) is installed by
default.
Rationale:
The software presents a security risk as it uses unencrypted protocols for communication.
Audit:
Run the following command and verify talk is off or missing:
# chkconfig --list
xinetd based services:
talk:
off
Remediation:
Run the following command to disable talk:
# chkconfig talk off
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2.1.8 Ensure telnet server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The telnet-server package contains the telnet daemon, which accepts connections
from users from other systems via the telnet protocol.
Rationale:
The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission
medium could allow a user with access to sniff network traffic the ability to steal
credentials. The ssh package provides an encrypted session and stronger security.
Audit:
Run the following command and verify telnet is off or missing:
# chkconfig --list
xinetd based services:
telnet:
off
Remediation:
Run the following command to disable telnet:
# chkconfig telnet off
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2.1.9 Ensure tftp server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol, typically used to
automatically transfer configuration or boot machines from a boot server. The packages
tftp and atftp are both used to define and support a TFTP server.
Rationale:
TFTP does not support authentication nor does it ensure the confidentiality or integrity of
data. It is recommended that TFTP be removed, unless there is a specific need for TFTP. In
that case, extreme caution must be used when configuring the services.
Audit:
Run the following command and verify tftp is off or missing:
# chkconfig --list
xinetd based services:
tftp:
off
Remediation:
Run the following command to disable tftp:
# chkconfig tftp off
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2.1.10 Ensure rsync service is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The rsyncd service can be used to synchronize files between systems over network links.
Rationale:
The rsyncd service presents a security risk as it uses unencrypted protocols for
communication.
Audit:
Run the following command and verify rsync is of or missing:
# chkconfig --list
xinetd based services:
rsync:
off
Remediation:
Run the following command to disable rsync:
# chkconfig rsync off
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2.1.11 Ensure xinetd is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The eXtended InterNET Daemon (xinetd) is an open source super daemon that replaced
the original inetd daemon. The xinetd daemon listens for well known services and
dispatches the appropriate daemon to properly respond to service requests.
Rationale:
If there are no xinetd services required, it is recommended that the daemon be disabled.
Audit:
Run the following command and verify all runlevels are listed as "off" or xinetd is not
available:
# chkconfig --list xinetd
xinetd
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run one of the following command to disable xinetd:
# chkconfig xinetd off
2.2 Special Purpose Services
This section describes services that are installed on systems that specifically need to run
these services. If any of these services are not required, it is recommended that they be
disabled or deleted from the system to reduce the potential attack surface.
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2.2.1 Time Synchronization
It is recommended that physical systems and virtual guests lacking direct access to the
physical host's clock be configured to synchronize their time using a service such as NTP or
chrony.
2.2.1.1 Ensure time synchronization is in use (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
System time should be synchronized between all systems in an environment. This is
typically done by establishing an authoritative time server or set of servers and having all
systems synchronize their clocks to them.
Rationale:
Time synchronization is important to support time sensitive security mechanisms like
Kerberos and also ensures log files have consistent time records across the enterprise,
which aids in forensic investigations.
Audit:
On physical systems or virtual systems where host based time synchronization is not
available run the following commands and verify either ntp or chrony is installed:
# rpm -q ntp
# rpm -q chrony
On virtual systems where host based time synchronization is available consult your
virtualization software documentation and verify that host based synchronization is in use.
Remediation:
On physical systems or virtual systems where host based time synchronization is not
available run one of the following commands to install either ntp or chrony:
# yum install ntp
# yum install chrony
On virtual systems where host based time synchronization is available consult your
virtualization software documentation and setup host based synchronization.
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2.2.1.2 Ensure ntp is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
ntp is a daemon which implements the Network Time Protocol (NTP).
It is designed to
synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on NTP can be found at http://www.ntp.org. ntp can be
configured to be a client and/or a server.
This recommendation only applies if ntp is in use on the system.
Rationale:
If ntp is in use on the system proper configuration is vital to ensuring time synchronization
is working properly.
Audit:
Run the following command and verify output matches:
# grep "^restrict" /etc/ntp.conf
restrict -4 default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
The -4 in the first line is optional and options after default can appear in any
order. Additional restriction lines may exist.
Run the following command and verify remote server is configured properly:
# grep "^server" /etc/ntp.conf
server <remote-server>
Multiple servers may be configured.
Run the following command and verify that '-u ntp:ntp' is included in OPTIONS:
# grep "^OPTIONS" /etc/sysconfig/ntpd
OPTIONS="-u ntp:ntp"
Additional options may be present.
Remediation:
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Add or edit restrict lines in /etc/ntp.conf to match the following:
restrict -4 default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
Add or edit server lines to /etc/ntp.conf as appropriate:
server <remote-server>
Add or edit the OPTIONS in /etc/sysconfig/ntpd to include '-u ntp:ntp':
OPTIONS="-u ntp:ntp"
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2.2.1.3 Ensure chrony is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
chrony is a daemon which implements the Network Time Protocol (NTP) is designed to
synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on chrony can be found
at http://chrony.tuxfamily.org/. chrony can be configured to be a client and/or a server.
Rationale:
If chrony is in use on the system proper configuration is vital to ensuring time
synchronization is working properly.
This recommendation only applies if chrony is in use on the system.
Audit:
Run the following command and verify remote server is configured properly:
# grep "^server" /etc/chrony.conf
server <remote-server>
Multiple servers may be configured.
Run the following command and verify OPTIONS includes '-u chrony':
# grep ^OPTIONS /etc/sysconfig/chronyd
OPTIONS="-u chrony"
Additional options may be present.
Remediation:
Add or edit server lines to /etc/chrony.conf as appropriate:
server <remote-server>
Add or edit the OPTIONS in /etc/sysconfig/chronyd to include '-u chrony':
OPTIONS="-u chrony"
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2.2.2 Ensure X Window System is not installed (Scored)
Profile Applicability:
 Level 1 - Server
Description:
The X Window System provides a Graphical User Interface (GUI) where users can have
multiple windows in which to run programs and various add on. The X Windows system is
typically used on workstations where users login, but not on servers where users typically
do not login.
Rationale:
Unless your organization specifically requires graphical login access via X Windows,
remove it to reduce the potential attack surface.
Audit:
Run the following command and verify no output is returned:
# rpm -qa xorg-x11*
Remediation:
Run the following command to remove the X Windows System packages:
# yum remove xorg-x11*
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2.2.3 Ensure Avahi Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Avahi is a free zeroconf implementation, including a system for multicast DNS/DNS-SD
service discovery. Avahi allows programs to publish and discover services and hosts
running on a local network with no specific configuration. For example, a user can plug a
computer into a network and Avahi automatically finds printers to print to, files to look at
and people to talk to, as well as network services running on the machine.
Rationale:
Automatic discovery of network services is not normally required for system
functionality. It is recommended to disable the service to reduce the potential attack
surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or avahi-daemon is
not available:
# chkconfig --list avahi-daemon
avahi-daemon
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable avahi-daemon:
# chkconfig avahi-daemon off
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2.2.4 Ensure CUPS is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 2 - Workstation
Description:
The Common Unix Print System (CUPS) provides the ability to print to both local and
network printers. A system running CUPS can also accept print jobs from remote systems
and print them to local printers. It also provides a web based remote administration
capability.
Rationale:
If the system does not need to print jobs or accept print jobs from other systems, it is
recommended that CUPS be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or cups is not
available:
# chkconfig --list cups
cups
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable cups:
# chkconfig cups off
Impact:
Disabling CUPS will prevent printing from the system, a common task for workstation
systems.
References:
1. More detailed documentation on CUPS is available at the project homepage at
http://www.cups.org.
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2.2.5 Ensure DHCP Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Dynamic Host Configuration Protocol (DHCP) is a service that allows machines to be
dynamically assigned IP addresses.
Rationale:
Unless a system is specifically set up to act as a DHCP server, it is recommended that this
service be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or dhcpd is not
available:
# chkconfig --list dhcpd
dhcpd
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable dhcpd:
# chkconfig dhcpd off
References:
1. More detailed documentation on DHCP is available at
http://www.isc.org/software/dhcp.
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2.2.6 Ensure LDAP server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Lightweight Directory Access Protocol (LDAP) was introduced as a replacement for
NIS/YP. It is a service that provides a method for looking up information from a central
database.
Rationale:
If the system will not need to act as an LDAP server, it is recommended that the software be
disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or slapd is not
available:
# chkconfig --list slapd
slapd
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable slapd:
# chkconfig slapd off
References:
1. For more detailed documentation on OpenLDAP, go to the project homepage at
http://www.openldap.org.
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2.2.7 Ensure NFS and RPC are not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Network File System (NFS) is one of the first and most widely distributed file systems
in the UNIX environment. It provides the ability for systems to mount file systems of other
servers through the network.
Rationale:
If the system does not export NFS shares or act as an NFS client, it is recommended that
these services be disabled to reduce remote attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or nfs is not
available:
# chkconfig --list nfs
nfs
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Run the following command and verify all runlevels are listed as "off" or rpcbind is not
available:
# chkconfig --list rpcbind
rpcbind
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following commands to disable nfs and rpcbind:
# chkconfig nfs off
# chkconfig rpcbind off
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2.2.8 Ensure DNS Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Domain Name System (DNS) is a hierarchical naming system that maps names to IP
addresses for computers, services and other resources connected to a network.
Rationale:
Unless a system is specifically designated to act as a DNS server, it is recommended that
the service be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or named is not
available:
# chkconfig --list named
named
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable named:
# chkconfig named off
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2.2.9 Ensure FTP Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The File Transfer Protocol (FTP) provides networked computers with the ability to transfer
files.
Rationale:
FTP does not protect the confidentiality of data or authentication credentials. It is
recommended sftp be used if file transfer is required. Unless there is a need to run the
system as a FTP server (for example, to allow anonymous downloads), it is recommended
that the service be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or vsftpd is not
available:
# chkconfig --list vsftpd
vsftpd
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable vsftpd:
# chkconfig vsftpd off
Notes:
Additional FTP servers also exist and should be audited.
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2.2.10 Ensure HTTP server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
HTTP or web servers provide the ability to host web site content.
Rationale:
Unless there is a need to run the system as a web server, it is recommended that the service
be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or httpd is not
available:
# chkconfig --list httpd
httpd
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable httpd:
# chkconfig httpd off
Notes:
Several httpd servers exist and can use other service names. apache, apache2, lighttpd,
and nginx are example services that provide an HTTP server. These and other services
should also be audited.
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2.2.11 Ensure IMAP and POP3 server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
dovecot is an open source IMAP and POP3 server for Linux based systems.
Rationale:
Unless POP3 and/or IMAP servers are to be provided by this system, it is recommended
that the service be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or dovecot is not
available.:
# chkconfig --list dovecot
dovecot
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable dovecot:
# chkconfig dovecot off
Notes:
Several IMAP/POP3 servers exist and can use other service names. cyrus-imapd is an
example service that provides an IMAP/POP3 server. These and other services should also
be audited.
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2.2.12 Ensure Samba is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Samba daemon allows system administrators to configure their Linux systems to share
file systems and directories with Windows desktops. Samba will advertise the file systems
and directories via the Small Message Block (SMB) protocol. Windows desktop users will
be able to mount these directories and file systems as letter drives on their systems.
Rationale:
If there is no need to mount directories and file systems to Windows systems, then this
service can be disabled to reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or smb is not
available:
# chkconfig --list smb
smb
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable smb:
# chkconfig smb off
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2.2.13 Ensure HTTP Proxy Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Squid is a standard proxy server used in many environments.
Rationale:
If there is no need for a proxy server, it is recommended that the squid proxy be disabled to
reduce the potential attack surface.
Audit:
Run the following command and verify all runlevels are listed as "off" or squid is not
available:
# chkconfig --list squid
squid
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable squid:
# chkconfig squid off
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2.2.14 Ensure SNMP Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Simple Network Management Protocol (SNMP) server is used to listen for SNMP
commands from an SNMP management system, execute the commands or collect the
information and then send results back to the requesting system.
Rationale:
The SNMP server communicates using SNMP v1, which transmits data in the clear and does
not require authentication to execute commands. Unless absolutely necessary, it is
recommended that the SNMP service not be used.
Audit:
Run the following command and verify all runlevels are listed as "off" or snmpd is not
available:
# chkconfig --list snmpd
snmpd
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable snmpd:
# chkconfig snmpd off
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2.2.15 Ensure mail transfer agent is configured for local-only mode
(Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Mail Transfer Agents (MTA), such as sendmail and Postfix, are used to listen for incoming
mail and transfer the messages to the appropriate user or mail server. If the system is not
intended to be a mail server, it is recommended that the MTA be configured to only process
local mail.
Rationale:
The software for all Mail Transfer Agents is complex and most have a long history of
security issues. While it is important to ensure that the system can process local mail
messages, it is not necessary to have the MTA's daemon listening on a port unless the
server is intended to be a mail server that receives and processes mail from other systems.
Audit:
Run the following command and verify that the MTA is not listening on any non-loopback
address (127.0.0.1 or ::1):
# netstat -an | grep LIST | grep ":25[[:space:]]"
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
Remediation:
Edit /etc/postfix/main.cf and add the following line to the RECEIVING MAIL section. If
the line already exists, change it to look like the line below:
inet_interfaces = localhost
Restart postfix:
# service postfix restart
Notes:
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This recommendation is designed around the postfix mail server, depending on your
environment you may have an alternative MTA installed such as sendmail. If this is the
case consult the documentation for your installed MTA to configure the recommended
state.
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2.2.16 Ensure NIS Server is not enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Network Information Service (NIS) (formally known as Yellow Pages) is a client-server
directory service protocol for distributing system configuration files. The NIS server is a
collection of programs that allow for the distribution of configuration files.
Rationale:
The NIS service is inherently an insecure system that has been vulnerable to DOS attacks,
buffer overflows and has poor authentication for querying NIS maps. NIS generally been
replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is
recommended that the service be disabled and other, more secure services be used
Audit:
Run the following command and verify all runlevels are listed as "off" or ypserv is not
available:
# chkconfig --list ypserv
ypserv
0:off
1:off
2:off
3:off
4:off
5:off
6:off
Remediation:
Run the following command to disable ypserv:
# chkconfig ypserv off
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2.3 Service Clients
A number of insecure services exist. While disabling the servers prevents a local attack
against these services, it is advised to remove their clients unless they are required.
Note: This should not be considered a comprehensive list of insecure service clients. You
may wish to consider additions to those listed here for your environment.
2.3.1 Ensure NIS Client is not installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Network Information Service (NIS), formerly known as Yellow Pages, is a client-server
directory service protocol used to distribute system configuration files. The NIS client
(ypbind) was used to bind a machine to an NIS server and receive the distributed
configuration files.
Rationale:
The NIS service is inherently an insecure system that has been vulnerable to DOS attacks,
buffer overflows and has poor authentication for querying NIS maps. NIS generally has
been replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is
recommended that the service be removed.
Audit:
Run the following command and verify ypbind is not installed:
# rpm -q ypbind
Remediation:
Run the following command to uninstall ypbind:
# yum remove ypbind
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Impact:
Many insecure service clients are used as troubleshooting tools and in testing
environments. Uninstalling them can inhibit capability to test and troubleshoot. If they are
required it is advisable to remove the clients after use to prevent accidental or intentional
misuse.
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2.3.2 Ensure rsh client is not installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The rsh package contains the client commands for the rsh services.
Rationale:
These legacy clients contain numerous security exposures and have been replaced with the
more secure SSH package. Even if the server is removed, it is best to ensure the clients are
also removed to prevent users from inadvertently attempting to use these commands and
therefore exposing their credentials. Note that removing the rsh package removes the
clients for rsh, rcp and rlogin.
Audit:
Run the following command and verify rsh is not installed:
# rpm -q rsh
Remediation:
Run the following command to uninstall rsh:
# yum remove rsh
Impact:
Many insecure service clients are used as troubleshooting tools and in testing
environments. Uninstalling them can inhibit capability to test and troubleshoot. If they are
required it is advisable to remove the clients after use to prevent accidental or intentional
misuse.
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2.3.3 Ensure talk client is not installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The talk software makes it possible for users to send and receive messages across
systems through a terminal session. The talk client, which allows initialization of talk
sessions, is installed by default.
Rationale:
The software presents a security risk as it uses unencrypted protocols for communication.
Audit:
Run the following command and verify talk is not installed:
# rpm -q talk
Remediation:
Run the following command to uninstall talk:
# yum remove talk
Impact:
Many insecure service clients are used as troubleshooting tools and in testing
environments. Uninstalling them can inhibit capability to test and troubleshoot. If they are
required it is advisable to remove the clients after use to prevent accidental or intentional
misuse.
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2.3.4 Ensure telnet client is not installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The telnet package contains the telnet client, which allows users to start connections to
other systems via the telnet protocol.
Rationale:
The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission
medium could allow an unauthorized user to steal credentials. The ssh package provides
an encrypted session and stronger security and is included in most Linux distributions.
Audit:
Run the following command and verify telnet is not installed:
# rpm -q telnet
Remediation:
Run the following command to uninstall telnet:
# yum remove telnet
Impact:
Many insecure service clients are used as troubleshooting tools and in testing
environments. Uninstalling them can inhibit capability to test and troubleshoot. If they are
required it is advisable to remove the clients after use to prevent accidental or intentional
misuse.
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2.3.5 Ensure LDAP client is not installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Lightweight Directory Access Protocol (LDAP) was introduced as a replacement for
NIS/YP. It is a service that provides a method for looking up information from a central
database.
Rationale:
If the system will not need to act as an LDAP client, it is recommended that the software be
removed to reduce the potential attack surface.
Audit:
Run the following command and verify openldap-clients is not installed:
# rpm -q openldap-clients
Remediation:
Run the following command to uninstall openldap-clients:
# yum remove openldap-clients
Impact:
Removing the LDAP client will prevent or inhibit using LDAP for authentication in your
environment.
3 Network Configuration
This section provides guidance on for securing the network configuration of the system
through kernel parameters, access list control, and firewall settings.
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3.1 Network Parameters (Host Only)
The following network parameters are intended for use if the system is to act as a host
only. A system is considered host only if the system has a single interface, or has multiple
interfaces but will not be configured as a router.
3.1.1 Ensure IP forwarding is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The net.ipv4.ip_forward flag is used to tell the system whether it can forward packets or
not.
Rationale:
Setting the flag to 0 ensures that a system with multiple interfaces (for example, a hard
proxy), will never be able to forward packets, and therefore, never serve as a router.
Audit:
Run the following command and verify output matches:
# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0
Remediation:
Set the following parameter in the /etc/sysctl.conf file:
net.ipv4.ip_forward = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.ip_forward=0
# sysctl -w net.ipv4.route.flush=1
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3.1.2 Ensure packet redirect sending is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
ICMP Redirects are used to send routing information to other hosts. As a host itself does
not act as a router (in a host only configuration), there is no need to send redirects.
Rationale:
An attacker could use a compromised host to send invalid ICMP redirects to other router
devices in an attempt to corrupt routing and have users access a system set up by the
attacker as opposed to a valid system.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.conf.all.send_redirects
net.ipv4.conf.all.send_redirects = 0
# sysctl net.ipv4.conf.default.send_redirects
net.ipv4.conf.default.send_redirects = 0
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.send_redirects=0
# sysctl -w net.ipv4.conf.default.send_redirects=0
# sysctl -w net.ipv4.route.flush=1
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3.2 Network Parameters (Host and Router)
The following network parameters are intended for use on both host only and router
systems. A system acts as a router if it has at least two interfaces and is configured to
perform routing functions.
3.2.1 Ensure source routed packets are not accepted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
In networking, source routing allows a sender to partially or fully specify the route packets
take through a network. In contrast, non-source routed packets travel a path determined
by routers in the network. In some cases, systems may not be routable or reachable from
some locations (e.g. private addresses vs. Internet routable), and so source routed packets
would need to be used.
Rationale:
Setting net.ipv4.conf.all.accept_source_route and
net.ipv4.conf.default.accept_source_route to 0 disables the system from accepting
source routed packets. Assume this system was capable of routing packets to Internet
routable addresses on one interface and private addresses on another interface. Assume
that the private addresses were not routable to the Internet routable addresses and vice
versa. Under normal routing circumstances, an attacker from the Internet routable
addresses could not use the system as a way to reach the private address systems. If,
however, source routed packets were allowed, they could be used to gain access to the
private address systems as the route could be specified, rather than rely on routing
protocols that did not allow this routing.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.conf.all.accept_source_route
net.ipv4.conf.all.accept_source_route = 0
# sysctl net.ipv4.conf.default.accept_source_route
net.ipv4.conf.default.accept_source_route = 0
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Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.accept_source_route=0
# sysctl -w net.ipv4.conf.default.accept_source_route=0
# sysctl -w net.ipv4.route.flush=1
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3.2.2 Ensure ICMP redirects are not accepted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
ICMP redirect messages are packets that convey routing information and tell your host
(acting as a router) to send packets via an alternate path. It is a way of allowing an outside
routing device to update your system routing tables. By setting
net.ipv4.conf.all.accept_redirects to 0, the system will not accept any ICMP redirect
messages, and therefore, won't allow outsiders to update the system's routing tables.
Rationale:
Attackers could use bogus ICMP redirect messages to maliciously alter the system routing
tables and get them to send packets to incorrect networks and allow your system packets
to be captured.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.conf.all.accept_redirects
net.ipv4.conf.all.accept_redirects = 0
# sysctl net.ipv4.conf.default.accept_redirects
net.ipv4.conf.default.accept_redirects = 0
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.accept_redirects=0
# sysctl -w net.ipv4.conf.default.accept_redirects=0
# sysctl -w net.ipv4.route.flush=1
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3.2.3 Ensure secure ICMP redirects are not accepted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Secure ICMP redirects are the same as ICMP redirects, except they come from gateways
listed on the default gateway list. It is assumed that these gateways are known to your
system, and that they are likely to be secure.
Rationale:
It is still possible for even known gateways to be compromised. Setting
net.ipv4.conf.all.secure_redirects to 0 protects the system from routing table
updates by possibly compromised known gateways.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.conf.all.secure_redirects
net.ipv4.conf.all.secure_redirects = 0
# sysctl net.ipv4.conf.default.secure_redirects
net.ipv4.conf.default.secure_redirects = 0
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.secure_redirects=0
# sysctl -w net.ipv4.conf.default.secure_redirects=0
# sysctl -w net.ipv4.route.flush=1
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3.2.4 Ensure suspicious packets are logged (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
When enabled, this feature logs packets with un-routable source addresses to the kernel
log.
Rationale:
Enabling this feature and logging these packets allows an administrator to investigate the
possibility that an attacker is sending spoofed packets to their system.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.conf.all.log_martians
net.ipv4.conf.all.log_martians = 1
# sysctl net.ipv4.conf.default.log_martians
net.ipv4.conf.default.log_martians = 1
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.log_martians=1
# sysctl -w net.ipv4.conf.default.log_martians=1
# sysctl -w net.ipv4.route.flush=1
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3.2.5 Ensure broadcast ICMP requests are ignored (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Setting net.ipv4.icmp_echo_ignore_broadcasts to 1 will cause the system to ignore all
ICMP echo and timestamp requests to broadcast and multicast addresses.
Rationale:
Accepting ICMP echo and timestamp requests with broadcast or multicast destinations for
your network could be used to trick your host into starting (or participating) in a Smurf
attack. A Smurf attack relies on an attacker sending large amounts of ICMP broadcast
messages with a spoofed source address. All hosts receiving this message and responding
would send echo-reply messages back to the spoofed address, which is probably not
routable. If many hosts respond to the packets, the amount of traffic on the network could
be significantly multiplied.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.icmp_echo_ignore_broadcasts
net.ipv4.icmp_echo_ignore_broadcasts = 1
Remediation:
Set the following parameter in the /etc/sysctl.conf file:
net.ipv4.icmp_echo_ignore_broadcasts = 1
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1
# sysctl -w net.ipv4.route.flush=1
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3.2.6 Ensure bogus ICMP responses are ignored (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Setting icmp_ignore_bogus_error_responses to 1 prevents the kernel from logging bogus
responses (RFC-1122 non-compliant) from broadcast reframes, keeping file systems from
filling up with useless log messages.
Rationale:
Some routers (and some attackers) will send responses that violate RFC-1122 and attempt
to fill up a log file system with many useless error messages.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.icmp_ignore_bogus_error_responses
net.ipv4.icmp_ignore_bogus_error_responses = 1
Remediation:
Set the following parameter in the /etc/sysctl.conf file:
net.ipv4.icmp_ignore_bogus_error_responses = 1
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1
# sysctl -w net.ipv4.route.flush=1
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3.2.7 Ensure Reverse Path Filtering is enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Setting net.ipv4.conf.all.rp_filter and net.ipv4.conf.default.rp_filter to 1
forces the Linux kernel to utilize reverse path filtering on a received packet to determine if
the packet was valid. Essentially, with reverse path filtering, if the return packet does not
go out the same interface that the corresponding source packet came from, the packet is
dropped (and logged if log_martians is set).
Rationale:
Setting these flags is a good way to deter attackers from sending your system bogus
packets that cannot be responded to. One instance where this feature breaks down is if
asymmetrical routing is employed. This would occur when using dynamic routing protocols
(bgp, ospf, etc) on your system. If you are using asymmetrical routing on your system, you
will not be able to enable this feature without breaking the routing.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.conf.all.rp_filter
net.ipv4.conf.all.rp_filter = 1
# sysctl net.ipv4.conf.default.rp_filter
net.ipv4.conf.default.rp_filter = 1
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.rp_filter=1
# sysctl -w net.ipv4.conf.default.rp_filter=1
# sysctl -w net.ipv4.route.flush=1
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3.2.8 Ensure TCP SYN Cookies is enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
When tcp_syncookies is set, the kernel will handle TCP SYN packets normally until the
half-open connection queue is full, at which time, the SYN cookie functionality kicks in. SYN
cookies work by not using the SYN queue at all. Instead, the kernel simply replies to the
SYN with a SYN|ACK, but will include a specially crafted TCP sequence number that
encodes the source and destination IP address and port number and the time the packet
was sent. A legitimate connection would send the ACK packet of the three way handshake
with the specially crafted sequence number. This allows the system to verify that it has
received a valid response to a SYN cookie and allow the connection, even though there is no
corresponding SYN in the queue.
Rationale:
Attackers use SYN flood attacks to perform a denial of service attacked on a system by
sending many SYN packets without completing the three way handshake. This will quickly
use up slots in the kernel's half-open connection queue and prevent legitimate connections
from succeeding. SYN cookies allow the system to keep accepting valid connections, even if
under a denial of service attack.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv4.tcp_syncookies
net.ipv4.tcp_syncookies = 1
Remediation:
Set the following parameter in the /etc/sysctl.conf file:
net.ipv4.tcp_syncookies = 1
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.tcp_syncookies=1
# sysctl -w net.ipv4.route.flush=1
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3.3 IPv6
IPv6 is a networking protocol that supersedes IPv4. It has more routable addresses and has
built in security. If IPv6 is to be used, follow this section of the benchmark to configure
IPv6, otherwise disable IPv6.
3.3.1 Ensure IPv6 router advertisements are not accepted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
This setting disables the system's ability to accept IPv6 router advertisements.
Rationale:
It is recommended that systems not accept router advertisements as they could be tricked
into routing traffic to compromised machines. Setting hard routes within the system
(usually a single default route to a trusted router) protects the system from bad routes.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv6.conf.all.accept_ra
net.ipv6.conf.all.accept_ra = 0
# sysctl net.ipv6.conf.default.accept_ra
net.ipv6.conf.default.accept_ra = 0
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv6.conf.all.accept_ra=0
# sysctl -w net.ipv6.conf.default.accept_ra=0
# sysctl -w net.ipv6.route.flush=1
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3.3.2 Ensure IPv6 redirects are not accepted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
This setting prevents the system from accepting ICMP redirects. ICMP redirects tell the
system about alternate routes for sending traffic.
Rationale:
It is recommended that systems not accept ICMP redirects as they could be tricked into
routing traffic to compromised machines. Setting hard routes within the system (usually a
single default route to a trusted router) protects the system from bad routes.
Audit:
Run the following commands and verify output matches:
# sysctl net.ipv6.conf.all.accept_redirects
net.ipv6.conf.all.accept_redirect = 0
# sysctl net.ipv6.conf.default.accept_redirects
net.ipv6.conf.default.accept_redirect = 0
Remediation:
Set the following parameters in the /etc/sysctl.conf file:
net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv6.conf.all.accept_redirects=0
# sysctl -w net.ipv6.conf.default.accept_redirects=0
# sysctl -w net.ipv6.route.flush=1
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3.3.3 Ensure IPv6 is disabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Although IPv6 has many advantages over IPv4, few organizations have implemented IPv6.
Rationale:
If IPv6 is not to be used, it is recommended that it be disabled to reduce the attack surface
of the system.
Audit:
Run the following command and verify output includes indicated line:
# modprobe -c | grep ipv6
...
options ipv6 disable=1
...
Remediation:
Create the file /etc/modprobe.d/CIS.conf and add the following line:
options ipv6 disable=1
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3.4 TCP Wrappers
3.4.1 Ensure TCP Wrappers is installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
TCP Wrappers provides a simple access list and standardized logging method for services
capable of supporting it. In the past, services that were called from inetd and xinetd
supported the use of tcp wrappers. As inetd and xinetd have been falling in disuse, any
service that can support tcp wrappers will have the libwrap.so library attached to it.
Rationale:
TCP Wrappers provide a good simple access list mechanism to services that may not have
that support built in. It is recommended that all services that can support TCP Wrappers,
use it.
Audit:
Run the following command and verify tcp_wrappers is installed:
# rpm -q tcp_wrappers
tcp_wrappers-<version>
Run the following command and verify libwrap.so is installed:
# rpm -q tcp_wrappers-libs
tcp_wrappers-libs-<version>
Remediation:
Run the following command to install tcp_wrappers:
# yum install tcp_wrappers
Notes:
To verify if a service supports TCP Wrappers, run the following command:
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# ldd <path-to-daemon> | grep libwrap.so
If there is any output, then the service supports TCP Wrappers.
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3.4.2 Ensure /etc/hosts.allow is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/hosts.allow file specifies which IP addresses are permitted to connect to the
host. It is intended to be used in conjunction with the /etc/hosts.deny file.
Rationale:
The /etc/hosts.allow file supports access control by IP and helps ensure that only
authorized systems can connect to the system.
Audit:
Run the following command and verify the contents of the /etc/hosts.allow file:
# cat /etc/hosts.allow
Remediation:
Run the following command to create /etc/hosts.allow:
# echo "ALL: <net>/<mask>, <net>/<mask>, ..." >/etc/hosts.allow
where each <net>/<mask> combination (for example, "192.168.1.0/255.255.255.0")
represents one network block in use by your organization that requires access to this
system.
Notes:
Contents of the /etc/hosts.allow file will vary depending on your network configuration.
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3.4.3 Ensure /etc/hosts.deny is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/hosts.deny file specifies which IP addresses are not permitted to connect to the
host. It is intended to be used in conjunction with the /etc/hosts.allow file.
Rationale:
The /etc/hosts.deny file serves as a failsafe so that any host not specified in
/etc/hosts.allow is denied access to the system.
Audit:
Run the following command and verify the contents of the /etc/hosts.deny file:
# cat /etc/hosts.deny
ALL: ALL
Remediation:
Run the following command to create /etc/hosts.deny:
# echo "ALL: ALL" >> /etc/hosts.deny
Notes:
Contents of the /etc/hosts.deny file may include additional options depending on your
network configuration.
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3.4.4 Ensure permissions on /etc/hosts.allow are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/hosts.allow file contains networking information that is used by many
applications and therefore must be readable for these applications to operate.
Rationale:
It is critical to ensure that the /etc/hosts.allow file is protected from unauthorized write
access. Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/hosts.allow
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on /etc/hosts.allow:
# chown root:root /etc/hosts.allow
# chmod 644 /etc/hosts.allow
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3.4.5 Ensure permissions on /etc/hosts.deny are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/hosts.deny file contains network information that is used by many system
applications and therefore must be readable for these applications to operate.
Rationale:
It is critical to ensure that the /etc/hosts.deny file is protected from unauthorized write
access. Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/hosts.deny
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on /etc/hosts.deny:
# chown root:root /etc/hosts.deny
# chmod 644 /etc/hosts.deny
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3.5 Uncommon Network Protocols
The Linux kernel modules support several network protocols that are not commonly used.
If these protocols are not needed, it is recommended that they be disabled in the kernel.
Note: This should not be considered a comprehensive list of uncommon network protocols,
you may wish to consider additions to those listed here for your environment.
3.5.1 Ensure DCCP is disabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Datagram Congestion Control Protocol (DCCP) is a transport layer protocol that
supports streaming media and telephony. DCCP provides a way to gain access to
congestion control, without having to do it at the application layer, but does not provide insequence delivery.
Rationale:
If the protocol is not required, it is recommended that the drivers not be installed
to reduce the potential attack surface.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v dccp
install /bin/true
# lsmod | grep dccp
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install dccp /bin/true
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3.5.2 Ensure SCTP is disabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Stream Control Transmission Protocol (SCTP) is a transport layer protocol used to
support message oriented communication, with several streams of messages in one
connection. It serves a similar function as TCP and UDP, incorporating features of both. It is
message-oriented like UDP, and ensures reliable in-sequence transport of messages with
congestion control like TCP.
Rationale:
If the protocol is not being used, it is recommended that kernel module not be loaded,
disabling the service to reduce the potential attack surface.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v sctp
install /bin/true
# lsmod | grep sctp
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install sctp /bin/true
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3.5.3 Ensure RDS is disabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Reliable Datagram Sockets (RDS) protocol is a transport layer protocol designed to
provide low-latency, high-bandwidth communications between cluster nodes. It was
developed by the Oracle Corporation.
Rationale:
If the protocol is not being used, it is recommended that kernel module not be loaded,
disabling the service to reduce the potential attack surface.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v rds
install /bin/true
# lsmod | grep rds
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install rds /bin/true
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3.5.4 Ensure TIPC is disabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Transparent Inter-Process Communication (TIPC) protocol is designed to provide
communication between cluster nodes.
Rationale:
If the protocol is not being used, it is recommended that kernel module not be loaded,
disabling the service to reduce the potential attack surface.
Audit:
Run the following commands and verify the output is as indicated:
# modprobe -n -v tipc
install /bin/true
# lsmod | grep tipc
<No output>
Remediation:
Edit or create the file /etc/modprobe.d/CIS.conf and add the following line:
install tipc /bin/true
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3.6 Firewall Configuration
IPtables is an application that allows a system administrator to configure the IPv4 tables,
chains and rules provided by the Linux kernel firewall. While several methods of
configuration exist this section is intended only to ensure the resulting IPtables rules are in
place, not how they are configured. If IPv6 is in use in your environment, similar settings
should be applied to the IP6tables as well.
Note: This section broadly assumes starting with an empty IPtables firewall ruleset
(established by flushing the rules with iptables -F). Remediation steps included only
affect the live system, you will also need to configure your default firewall configuration to
apply on boot. Configuration of a live systems firewall directly over a remote connection
will often result in being locked out. It is advised to have a known good firewall
configuration set to run on boot and to configure an entire firewall structure in a script that
is then run and tested before saving to boot. The following script will implement the
firewall rules of this section and open port 22(ssh) from anywhere:
#!/bin/bash
# Flush IPtables rules
iptables -F
# Ensure
iptables
iptables
iptables
default deny firewall policy
-P INPUT DROP
-P OUTPUT DROP
-P FORWARD DROP
# Ensure
iptables
iptables
iptables
loopback traffic is configured
-A INPUT -i lo -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
-A INPUT -s 127.0.0.0/8 -j DROP
# Ensure
iptables
iptables
iptables
iptables
iptables
iptables
outbound and established connections are configured
-A OUTPUT -p tcp -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p udp -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p icmp -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p udp -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p icmp -m state --state ESTABLISHED -j ACCEPT
# Open inbound ssh(tcp port 22) connections
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -j ACCEPT
3.6.1 Ensure iptables is installed (Scored)
Profile Applicability:
 Level 1 - Server
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 Level 1 - Workstation
Description:
iptables allows configuration of the IPv4 tables in the linux kernel and the rules stored
within them. Most firewall configuration utilities operate as a front end to iptables.
Rationale:
iptables is required for firewall management and configuration.
Audit:
Run the following command and verify iptables is installed:
# rpm -q iptables
iptables-<version>
Remediation:
Run the following command to install iptables:
# yum install iptables
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3.6.2 Ensure default deny firewall policy (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
A default deny all policy on connections ensures that any unconfigured network usage will
be rejected.
Rationale:
With a default accept policy the firewall will accept any packet that is not configured to be
denied. It is easier to white list acceptable usage than to black list unacceptable usage.
Audit:
Run the following command and verify that the policy for the INPUT, OUTPUT, and FORWARD
chains is DROP or REJECT:
# iptables -L
Chain INPUT (policy DROP)
Chain FORWARD (policy DROP)
Chain OUTPUT (policy DROP)
Remediation:
Run the following commands to implement a default DROP policy:
# iptables -P INPUT DROP
# iptables -P OUTPUT DROP
# iptables -P FORWARD DROP
Notes:
Changing firewall settings while connected over network can result in being locked out of
the system.
Remediation will only affect the active system firewall, be sure to configure the default
policy in your firewall management to apply on boot as well.
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3.6.3 Ensure loopback traffic is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Configure the loopback interface to accept traffic. Configure all other interfaces to deny
traffic to the loopback network (127.0.0.0/8).
Rationale:
Loopback traffic is generated between processes on machine and is typically critical to
operation of the system. The loopback interface is the only place that loopback network
(127.0.0.0/8) traffic should be seen, all other interfaces should ignore traffic on this
network as an anti-spoofing measure.
Audit:
Run the following commands and verify output includes the listed rules in order (packet
and byte counts may differ):
# iptables -L INPUT -v -n
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target
prot opt in
out
0
0 ACCEPT
all -- lo
*
0
0 DROP
all -- *
*
source
0.0.0.0/0
127.0.0.0/8
destination
0.0.0.0/0
0.0.0.0/0
# iptables -L OUTPUT -v -n
Chain OUTPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target
prot opt in
out
0
0 ACCEPT
all -- *
lo
source
0.0.0.0/0
destination
0.0.0.0/0
Remediation:
Run the following commands to implement the loopback rules:
# iptables -A INPUT -i lo -j ACCEPT
# iptables -A OUTPUT -o lo -j ACCEPT
# iptables -A INPUT -s 127.0.0.0/8 -j DROP
Notes:
Changing firewall settings while connected over network can result in being locked out of
the system.
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Remediation will only affect the active system firewall, be sure to configure the default
policy in your firewall management to apply on boot as well.
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3.6.4 Ensure outbound and established connections are configured (Not
Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Configure the firewall rules for new outbound, and established connections.
Rationale:
If rules are not in place for new outbound, and established connections all packets will be
dropped by the default policy preventing network usage.
Audit:
Run the following command and verify all rules for new outbound, and established
connections match site policy:
# iptables -L -v -n
Remediation:
Configure iptables in accordance with site policy. The following commands will implement
a policy to allow all outbound connections and all established connections:
#
#
#
#
#
#
iptables
iptables
iptables
iptables
iptables
iptables
-A
-A
-A
-A
-A
-A
OUTPUT -p tcp -m state --state NEW,ESTABLISHED -j ACCEPT
OUTPUT -p udp -m state --state NEW,ESTABLISHED -j ACCEPT
OUTPUT -p icmp -m state --state NEW,ESTABLISHED -j ACCEPT
INPUT -p tcp -m state --state ESTABLISHED -j ACCEPT
INPUT -p udp -m state --state ESTABLISHED -j ACCEPT
INPUT -p icmp -m state --state ESTABLISHED -j ACCEPT
Notes:
Changing firewall settings while connected over network can result in being locked out of
the system.
Remediation will only affect the active system firewall, be sure to configure the default
policy in your firewall management to apply on boot as well.
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3.6.5 Ensure firewall rules exist for all open ports (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Any ports that have been opened on non-loopback addresses need firewall rules to govern
traffic.
Rationale:
Without a firewall rule configured for open ports default firewall policy will drop all
packets to these ports.
Audit:
Run the following command to determine open ports:
# netatat -ln
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address
tcp
0
0 0.0.0.0:22
Foreign Address
0.0.0.0:*
State
LISTEN
Run the following command to determine firewall rules:
# iptables -L INPUT -v -n
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target
prot opt in
out
0
0 ACCEPT
all -- lo
*
0
0 DROP
all -- *
*
0
0 ACCEPT
tcp -- *
*
tcp dpt:22 state NEW
source
0.0.0.0/0
127.0.0.0/8
0.0.0.0/0
destination
0.0.0.0/0
0.0.0.0/0
0.0.0.0/0
Verify all open ports listening on non-localhost addresses have at least one firewall rule.
The last line identified by the "tcp dpt:22 state NEW" identifies it as a firewall rule for new
connections on tcp port 22.
Remediation:
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For each port identified in the audit which does not have a firewall rule establish a proper
rule for accepting inbound connections:
# iptables -A INPUT -p <protocol> --dport <port> -m state --state NEW -j ACCEPT
Notes:
Changing firewall settings while connected over network can result in being locked out of
the system.
Remediation will only affect the active system firewall, be sure to configure the default
policy in your firewall management to apply on boot as well.
The remediation command opens up the port to traffic from all sources. Consult iptables
documentation and set any restrictions in compliance with site policy.
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3.7 Ensure wireless interfaces are disabled (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 2 - Workstation
Description:
Wireless networking is used when wired networks are unavailable. CentOS 6 contains a
wireless tool kit to allow system administrators to configure and use wireless networks.
Rationale:
If wireless is not to be used, wireless devices can be disabled to reduce the potential attack
surface.
Audit:
Run the following command to determine wireless interfaces on the system:
# iwconfig
Run the following command and verify wireless interfaces are active:
# ip link show up
Remediation:
Run the following command to disable any wireless interfaces:
# ip link set <interface> down
Disable any wireless interfaces in your network configuration.
Impact:
Many if not all laptop workstations and some desktop workstations will connect via
wireless requiring these interfaces be enabled.
4 Logging and Auditing
The items in this section describe how to configure logging, log monitoring, and auditing,
using tools included in most distributions.
It is recommended that rsyslog be used for logging (with logwatch providing
summarization) and auditd be used for auditing (with aureport providing
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summarization) to automatically monitor logs for intrusion attempts and other suspicious
system behavior.
In addition to the local log files created by the steps in this section, it is also recommended
that sites collect copies of their system logs on a secure, centralized log server via an
encrypted connection. Not only does centralized logging help sites correlate events that
may be occurring on multiple systems, but having a second copy of the system log
information may be critical after a system compromise where the attacker has modified the
local log files on the affected system(s). If a log correlation system is deployed, configure it
to process the logs described in this section.
Because it is often necessary to correlate log information from many different systems
(particularly after a security incident) it is recommended that the time be synchronized
among systems and devices connected to the local network. The standard Internet protocol
for time synchronization is the Network Time Protocol (NTP), which is supported by most
network-ready devices. See the ntpd(8) manual page for more information on configuring
NTP.
It is important that all logs described in this section be monitored on a regular basis and
correlated to determine trends. A seemingly innocuous entry in one log could be more
significant when compared to an entry in another log.
Note on log file permissions: There really isn't a "one size fits all" solution to the
permissions on log files. Many sites utilize group permissions so that administrators who
are in a defined security group, such as "wheel" do not have to elevate privileges to root in
order to read log files. Also, if a third party log aggregation tool is used, it may need to have
group permissions to read the log files, which is preferable to having it run setuid to root.
Therefore, there are two remediation and audit steps for log file permissions. One is for
systems that do not have a secured group method implemented that only permits root to
read the log files (root:root 600). The other is for sites that do have such a setup and are
designated as root:securegrp 640 where securegrp is the defined security group (in
some cases wheel).
4.1 Configure System Accounting (auditd)
System auditing, through auditd, allows system administrators to monitor their systems
such that they can detect unauthorized access or modification of data. By default, auditd
will audit SELinux AVC denials, system logins, account modifications, and authentication
events. Events will be logged to /var/log/audit/audit.log. The recording of these events
will use a modest amount of disk space on a system. If significantly more events are
captured, additional on system or off system storage may need to be allocated.
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The recommendations in this section implement an audit policy that produces large
quantities of logged data. In some environments it can be challenging to store or process
these logs and as such they are marked as Level 2 for both Servers and Workstations.
Note: For 64 bit systems that have arch as a rule parameter, you will need two rules: one
for 64 bit and one for 32 bit systems. For 32 bit systems, only one rule is needed.
Note: Once all configuration changes have been made to /etc/audit/audit.rules, the
auditd configuration must be reloaded:
# service auditd reload
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4.1.1 Configure Data Retention
When auditing, it is important to carefully configure the storage requirements for audit
logs. By default, auditd will max out the log files at 5MB and retain only 4 copies of them.
Older versions will be deleted. It is possible on a system that the 20 MBs of audit logs may
fill up the system causing loss of audit data. While the recommendations here provide
guidance, check your site policy for audit storage requirements.
4.1.1.1 Ensure audit log storage size is configured (Not Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Configure the maximum size of the audit log file. Once the log reaches the maximum size, it
will be rotated and a new log file will be started.
Rationale:
It is important that an appropriate size is determined for log files so that they do not impact
the system and audit data is not lost.
Audit:
Run the following command and ensure output is in compliance with site policy:
# grep max_log_file /etc/audit/auditd.conf
max_log_file = <MB>
Remediation:
Set the following parameter in /etc/audit/auditd.conf in accordance with site policy:
max_log_file = <MB>
Notes:
The max_log_file parameter is measured in megabytes.
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4.1.1.2 Ensure system is disabled when audit logs are full (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The auditd daemon can be configured to halt the system when the audit logs are full.
Rationale:
In high security contexts, the risk of detecting unauthorized access or nonrepudiation
exceeds the benefit of the system's availability.
Audit:
Run the following commands and verify output matches:
# grep space_left_action /etc/audit/auditd.conf
space_left_action = email
# grep action_mail_acct /etc/audit/auditd.conf
action_mail_acct = root
# grep admin_space_left_action /etc/audit/auditd.conf
admin_space_left_action = halt
Remediation:
Set the following parameters in /etc/audit/auditd.conf:
space_left_action = email
action_mail_acct = root
admin_space_left_action = halt
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4.1.1.3 Ensure audit logs are not automatically deleted (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The max_log_file_action setting determines how to handle the audit log file reaching the
max file size. A value of keep_logs will rotate the logs but never delete old logs.
Rationale:
In high security contexts, the benefits of maintaining a long audit history exceed the cost of
storing the audit history.
Audit:
Run the following command and verify output matches:
# grep max_log_file_action /etc/audit/auditd.conf
max_log_file_action = keep_logs
Remediation:
Set the following parameter in /etc/audit/auditd.conf:
max_log_file_action = keep_logs
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4.1.2 Ensure auditd service is enabled (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Turn on the auditd daemon to record system events.
Rationale:
The capturing of system events provides system administrators with information to allow
them to determine if unauthorized access to their system is occurring.
Audit:
Run the following command and verify runlevels 2 through 5 are "on":
# chkconfig --list auditd
auditd
0:off
1:off
2:on
3:on
4:on
5:on
6:off
Remediation:
Run the following command to enable auditd:
# chkconfig auditd on
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4.1.3 Ensure auditing for processes that start prior to auditd is enabled
(Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Configure grub so that processes that are capable of being audited can be audited even if
they start up prior to auditd startup.
Rationale:
Audit events need to be captured on processes that start up prior to auditd, so that
potential malicious activity cannot go undetected.
Audit:
Run the following command and verify that each kernel line has the audit=1 parameter set:
# grep "^\s*kernel" /boot/grub/grub.conf
Remediation:
Edit /boot/grub/grub.conf to include audit=1 on all kernel lines.
Notes:
This recommendation is designed around the grub bootloader, if LILO or another
bootloader is in use in your environment enact equivalent settings.
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4.1.4 Ensure events that modify date and time information are collected
(Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Capture events where the system date and/or time has been modified. The parameters in
this section are set to determine if the adjtimex (tune kernel clock), settimeofday (Set
time, using timeval and timezone structures) stime (using seconds since 1/1/1970) or
clock_settime (allows for the setting of several internal clocks and timers) system calls
have been executed and always write an audit record to the /var/log/audit.log file upon
exit, tagging the records with the identifier "time-change"
Rationale:
Unexpected changes in system date and/or time could be a sign of malicious activity on the
system.
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep time-change /etc/audit/audit.rules
-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
On a 64 bit system run the following command and verify the output matches:
# grep time-change /etc/audit/audit.rules
-a always,exit -F arch=b64 -S adjtimex -S settimeofday -k time-change
-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b64 -S clock_settime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
Remediation:
For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
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-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-a
-a
-a
-a
-w
always,exit -F
always,exit -F
always,exit -F
always,exit -F
/etc/localtime
arch=b64
arch=b32
arch=b64
arch=b32
-p wa -k
-S adjtimex -S settimeofday -k time-change
-S adjtimex -S settimeofday -S stime -k time-change
-S clock_settime -k time-change
-S clock_settime -k time-change
time-change
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4.1.5 Ensure events that modify user/group information are collected
(Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Record events affecting the group, passwd (user IDs), shadow and gshadow (passwords) or
/etc/security/opasswd (old passwords, based on remember parameter in the PAM
configuration) files. The parameters in this section will watch the files to see if they have
been opened for write or have had attribute changes (e.g. permissions) and tag them with
the identifier "identity" in the audit log file.
Rationale:
Unexpected changes to these files could be an indication that the system has been
compromised and that an unauthorized user is attempting to hide their activities or
compromise additional accounts.
Audit:
Run the following command and verify output matches:
# grep identity /etc/audit/audit.rules
-w /etc/group -p wa -k identity
-w /etc/passwd -p wa -k identity
-w /etc/gshadow -p wa -k identity
-w /etc/shadow -p wa -k identity
-w /etc/security/opasswd -p wa -k identity
Remediation:
Add the following lines to the /etc/audit/audit.rules file:
-w
-w
-w
-w
-w
/etc/group -p wa -k identity
/etc/passwd -p wa -k identity
/etc/gshadow -p wa -k identity
/etc/shadow -p wa -k identity
/etc/security/opasswd -p wa -k identity
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4.1.6 Ensure events that modify the system's network environment are
collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Record changes to network environment files or system calls. The below parameters
monitor the sethostname (set the systems host name) or setdomainname (set the systems
domainname) system calls, and write an audit event on system call exit. The other
parameters monitor the /etc/issue and /etc/issue.net files (messages displayed prelogin), /etc/hosts (file containing host names and associated IP addresses) and
/etc/sysconfig/network (directory containing network interface scripts and
configurations) files.
Rationale:
Monitoring sethostname and setdomainname will identify potential unauthorized changes
to host and domainname of a system. The changing of these names could potentially break
security parameters that are set based on those names. The /etc/hosts file is monitored
for changes in the file that can indicate an unauthorized intruder is trying to change
machine associations with IP addresses and trick users and processes into connecting to
unintended machines. Monitoring /etc/issue and /etc/issue.net is important, as
intruders could put disinformation into those files and trick users into providing
information to the intruder. Monitoring /etc/sysconfig/network is important as it can
show if network interfaces or scripts are being modified in a way that can lead to the
machine becoming unavailable or compromised. All audit records will be tagged with the
identifier "system-locale."
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep system-locale /etc/audit/audit.rules
-a always,exit -F arch=b32 -S sethostname -S setdomainname -k system-locale
-w /etc/issue -p wa -k system-locale
-w /etc/issue.net -p wa -k system-locale
-w /etc/hosts -p wa -k system-locale
-w /etc/sysconfig/network -p wa -k system-locale
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On a 64 bit system run the following command and verify the output matches:
# grep system-locale /etc/audit/audit.rules
-a always,exit -F arch=b64 -S sethostname -S setdomainname -k system-locale
-a always,exit -F arch=b32 -S sethostname -S setdomainname -k system-locale
-w /etc/issue -p wa -k system-locale
-w /etc/issue.net -p wa -k system-locale
-w /etc/hosts -p wa -k system-locale
-w /etc/sysconfig/network -p wa -k system-locale
Remediation:
For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
-a
-w
-w
-w
-w
always,exit -F arch=b32 -S sethostname -S setdomainname -k system-locale
/etc/issue -p wa -k system-locale
/etc/issue.net -p wa -k system-locale
/etc/hosts -p wa -k system-locale
/etc/sysconfig/network -p wa -k system-locale
For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-a
-a
-w
-w
-w
-w
always,exit -F arch=b64 -S sethostname -S setdomainname -k system-locale
always,exit -F arch=b32 -S sethostname -S setdomainname -k system-locale
/etc/issue -p wa -k system-locale
/etc/issue.net -p wa -k system-locale
/etc/hosts -p wa -k system-locale
/etc/sysconfig/network -p wa -k system-locale
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4.1.7 Ensure events that modify the system's Mandatory Access
Controls are collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor SELinux mandatory access controls. The parameters below monitor any write
access (potential additional, deletion or modification of files in the directory) or attribute
changes to the /etc/selinux directory.
Rationale:
Changes to files in these directories could indicate that an unauthorized user is attempting
to modify access controls and change security contexts, leading to a compromise of the
system.
Audit:
Run the following command and verify output matches:
# grep MAC-policy /etc/audit/audit.rules
-w /etc/selinux/ -p wa -k MAC-policy
Remediation:
Add the following line to the /etc/audit/audit.rules file:
-w /etc/selinux/ -p wa -k MAC-policy
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4.1.8 Ensure login and logout events are collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor login and logout events. The parameters below track changes to files associated
with login/logout events. The file /var/log/lastlog maintain records of the last time a
user successfully logged in. The /var/run/failock directory maintains records of login
failures via the pam_faillock module.
Rationale:
Monitoring login/logout events could provide a system administrator with information
associated with brute force attacks against user logins.
Audit:
Run the following command and verify output matches:
# grep logins /etc/audit/audit.rules
-w /var/log/lastlog -p wa -k logins
-w /var/run/faillock/ -p wa -k logins
Remediation:
Add the following lines to the /etc/audit/audit.rules file:
-w /var/log/lastlog -p wa -k logins
-w /var/run/faillock/ -p wa -k logins
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4.1.9 Ensure session initiation information is collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor session initiation events. The parameters in this section track changes to the files
associated with session events. The file /var/run/utmp file tracks all currently logged in
users. The /var/log/wtmp file tracks logins, logouts, shutdown, and reboot events. All
audit records will be tagged with the identifier "session." The file /var/log/btmp keeps
track of failed login attempts and can be read by entering the command /usr/bin/last -f
/var/log/btmp. All audit records will be tagged with the identifier "logins."
Rationale:
Monitoring these files for changes could alert a system administrator to logins occurring at
unusual hours, which could indicate intruder activity (i.e. a user logging in at a time when
they do not normally log in).
Audit:
Run the following command and verify output matches:
# grep session /etc/audit/audit.rules
-w /var/run/utmp -p wa -k session
-w /var/log/wtmp -p wa -k session
-w /var/log/btmp -p wa -k session
Remediation:
Add the following lines to the /etc/audit/audit.rules file:
-w /var/run/utmp -p wa -k session
-w /var/log/wtmp -p wa -k session
-w /var/log/btmp -p wa -k session
Notes:
The last command can be used to read /var/log/wtmp (last with no parameters)
and /var/run/utmp (last -f /var/run/utmp)
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4.1.10 Ensure discretionary access control permission modification
events are collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor changes to file permissions, attributes, ownership and group. The parameters in
this section track changes for system calls that affect file permissions and attributes. The
chmod, fchmod and fchmodat system calls affect the permissions associated with a file. The
chown, fchown, fchownat and lchown system calls affect owner and group attributes on a
file. The setxattr, lsetxattr, fsetxattr (set extended file attributes) and removexattr,
lremovexattr, fremovexattr (remove extended file attributes) control extended file
attributes. In all cases, an audit record will only be written for non-system user ids (auid >=
500) and will ignore Daemon events (auid = 4294967295). All audit records will be tagged
with the identifier "perm_mod."
Rationale:
Monitoring for changes in file attributes could alert a system administrator to activity that
could indicate intruder activity or policy violation.
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep perm_mod /etc/audit/audit.rules
-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S
lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod
On a 64 bit system run the following command and verify the output matches:
# grep perm_mod /etc/audit/audit.rules
-a always,exit -F arch=b64 -S chmod -S fchmod -S fchmodat -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b64 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F
auid!=4294967295 -k perm_mod
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-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b64 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S
lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S
lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod
Remediation:
For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S
lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod
For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b64 -S chmod -S fchmod -S fchmodat -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b64 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F
auid!=4294967295 -k perm_mod
-a always,exit -F arch=b64 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S
lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S
lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod
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4.1.11 Ensure unsuccessful unauthorized file access attempts are
collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor for unsuccessful attempts to access files. The parameters below are associated
with system calls that control creation (creat), opening (open, openat) and truncation
(truncate, ftruncate) of files. An audit log record will only be written if the user is a nonprivileged user (auid > = 500), is not a Daemon event (auid=4294967295) and if the system
call returned EACCES (permission denied to the file) or EPERM (some other permanent
error associated with the specific system call). All audit records will be tagged with the
identifier "access."
Rationale:
Failed attempts to open, create or truncate files could be an indication that an individual or
process is trying to gain unauthorized access to the system.
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep access /etc/audit/audit.rules
-a always,exit -F arch=b32 -S creat -S open -S openat -S truncate -S ftruncate -F
exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b32 -S creat -S open -S openat -S truncate -S ftruncate -F
exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access
On a 64 bit system run the following command and verify the output matches:
# grep access /etc/audit/audit.rules
-a always,exit -F arch=b64 -S creat -S open -S openat -S
exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b32 -S creat -S open -S openat -S
exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b64 -S creat -S open -S openat -S
exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b32 -S creat -S open -S openat -S
exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access
truncate -S ftruncate -F
truncate -S ftruncate -F
truncate -S ftruncate -F
truncate -S ftruncate -F
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Remediation:
For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S creat -S open -S openat -S truncate -S ftruncate -F
exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b32 -S creat -S open -S openat -S truncate -S ftruncate -F
exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access
For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b64 -S creat -S open -S openat -S
exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b32 -S creat -S open -S openat -S
exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b64 -S creat -S open -S openat -S
exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access
-a always,exit -F arch=b32 -S creat -S open -S openat -S
exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access
truncate -S ftruncate -F
truncate -S ftruncate -F
truncate -S ftruncate -F
truncate -S ftruncate -F
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4.1.12 Ensure use of privileged commands is collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor privileged programs (those that have the setuid and/or setgid bit set on execution)
to determine if unprivileged users are running these commands.
Rationale:
Execution of privileged commands by non-privileged users could be an indication of
someone trying to gain unauthorized access to the system.
Audit:
Run the following command replacing <partition> with a list of partitions where programs
can be executed from on your system:
# find <partition> -xdev \( -perm -4000 -o -perm -2000 \) -type f | awk '{print \
"-a always,exit -F path=" $1 " -F perm=x -F auid>=500 -F auid!=4294967295 \
-k privileged" }'
Verify all resulting lines are in the /etc/audit/audit.rules file.
Remediation:
To remediate this issue, the system administrator will have to execute a find command to
locate all the privileged programs and then add an audit line for each one of them. The
audit parameters associated with this are as follows:
-F path=" $1 " - will populate each file name found through the find command and
processed by awk.
-F perm=x - will write an audit record if the file is executed.
-F auid>=500 - will write a record if the user executing the command is not a privileged
user.
-F auid!= 4294967295 - will ignore Daemon events
All audit records should be tagged with the identifier "privileged".
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Run the following command replacing <partition> with a list of partitions where programs
can be executed from on your system:
# find <partition> -xdev \( -perm -4000 -o -perm -2000 \) -type f | awk '{print "-a
always,exit -F path=" $1 " -F perm=x -F auid>=500 -F auid!=4294967295 -k privileged"
}'
Add all resulting lines to the /etc/audit/audit.rules file.
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4.1.13 Ensure successful file system mounts are collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor the use of the mount system call. The mount (and umount) system call controls the
mounting and unmounting of file systems. The parameters below configure the system to
create an audit record when the mount system call is used by a non-privileged user
Rationale:
It is highly unusual for a non privileged user to mount file systems to the system. While
tracking mount commands gives the system administrator evidence that external media
may have been mounted (based on a review of the source of the mount and confirming it's
an external media type), it does not conclusively indicate that data was exported to the
media. System administrators who wish to determine if data were exported, would also
have to track successful open, creat and truncate system calls requiring write access to a
file under the mount point of the external media file system. This could give a fair
indication that a write occurred. The only way to truly prove it, would be to track
successful writes to the external media. Tracking write system calls could quickly fill up the
audit log and is not recommended. Recommendations on configuration options to track
data export to media is beyond the scope of this document.
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep mounts /etc/audit/audit.rules
-a always,exit -F arch=b32 -S mount -F auid>=500 -F auid!=4294967295 -k mounts
On a 64 bit system run the following command and verify the output matches:
# grep mounts /etc/audit/audit.rules
-a always,exit -F arch=b64 -S mount -F auid>=500 -F auid!=4294967295 -k mounts
-a always,exit -F arch=b32 -S mount -F auid>=500 -F auid!=4294967295 -k mounts
Remediation:
For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
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-a always,exit -F arch=b32 -S mount -F auid>=500 -F auid!=4294967295 -k mounts
For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b64 -S mount -F auid>=500 -F auid!=4294967295 -k mounts
-a always,exit -F arch=b32 -S mount -F auid>=500 -F auid!=4294967295 -k mounts
Notes:
This tracks successful and unsuccessful mount commands. File system mounts do not have
to come from external media and this action still does not verify write (e.g. CD ROMS).
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4.1.14 Ensure file deletion events by users are collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor the use of system calls associated with the deletion or renaming of files and file
attributes. This configuration statement sets up monitoring for the unlink (remove a file),
unlinkat (remove a file attribute), rename (rename a file) and renameat (rename a file
attribute) system calls and tags them with the identifier "delete".
Rationale:
Monitoring these calls from non-privileged users could provide a system administrator
with evidence that inappropriate removal of files and file attributes associated with
protected files is occurring. While this audit option will look at all events, system
administrators will want to look for specific privileged files that are being deleted or
altered.
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep delete /etc/audit/audit.rules
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F
auid!=4294967295 -k delete
On a 64 bit system run the following command and verify the output matches:
# grep delete /etc/audit/audit.rules
-a always,exit -F arch=b64 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F
auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F
auid!=4294967295 -k delete
Remediation:
For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F
auid!=4294967295 -k delete
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For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-a always,exit -F arch=b64 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F
auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F
auid!=4294967295 -k delete
Notes:
At a minimum, configure the audit system to collect file deletion events for all users and
root.
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4.1.15 Ensure changes to system administration scope (sudoers) is
collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor scope changes for system administrations. If the system has been properly
configured to force system administrators to log in as themselves first and then use the
sudo command to execute privileged commands, it is possible to monitor changes in scope.
The file /etc/sudoers will be written to when the file or its attributes have changed. The
audit records will be tagged with the identifier "scope."
Rationale:
Changes in the /etc/sudoers file can indicate that an unauthorized change has been made
to scope of system administrator activity.
Audit:
Run the following command and verify output matches:
# grep scope /etc/audit/audit.rules
-w /etc/sudoers -p wa -k scope
-w /etc/sudoers.d -p wa -k scope
Remediation:
Add the following line to the /etc/audit/audit.rules file:
-w /etc/sudoers -p wa -k scope
-w /etc/sudoers.d -p wa -k scope
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4.1.16 Ensure system administrator actions (sudolog) are collected
(Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor the sudo log file. If the system has been properly configured to disable the use of
the su command and force all administrators to have to log in first and then use sudo to
execute privileged commands, then all administrator commands will be logged to
/var/log/sudo.log. Any time a command is executed, an audit event will be triggered as
the /var/log/sudo.log file will be opened for write and the executed administration
command will be written to the log.
Rationale:
Changes in /var/log/sudo.log indicate that an administrator has executed a command or
the log file itself has been tampered with. Administrators will want to correlate the events
written to the audit trail with the records written to /var/log/sudo.log to verify if
unauthorized commands have been executed.
Audit:
Run the following command and verify output matches:
# grep actions /etc/audit/audit.rules
-w /var/log/sudo.log -p wa -k actions
Remediation:
Add the following lines to the /etc/audit/audit.rules file:
-w /var/log/sudo.log -p wa -k actions
Notes:
The system must be configured with su disabled (See Item 5.6 Ensure access to the su
command is restricted) to force all command execution through sudo. This will not be
effective on the console, as administrators can log in as root.
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4.1.17 Ensure kernel module loading and unloading is collected (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Monitor the loading and unloading of kernel modules. The programs insmod (install a
kernel module), rmmod (remove a kernel module), and modprobe (a more sophisticated
program to load and unload modules, as well as some other features) control loading and
unloading of modules. The init_module (load a module) and delete_module (delete a
module) system calls control loading and unloading of modules. Any execution of the
loading and unloading module programs and system calls will trigger an audit record with
an identifier of "modules".
Rationale:
Monitoring the use of insmod, rmmod and modprobe could provide system administrators
with evidence that an unauthorized user loaded or unloaded a kernel module, possibly
compromising the security of the system. Monitoring of the init_module and
delete_module system calls would reflect an unauthorized user attempting to use a
different program to load and unload modules.
Audit:
On a 32 bit system run the following command and verify the output matches:
# grep modules /etc/audit/audit.rules
-w /sbin/insmod -p x -k modules
-w /sbin/rmmod -p x -k modules
-w /sbin/modprobe -p x -k modules
-a always,exit arch=b32 -S init_module -S delete_module -k modules
On a 64 bit system run the following command and verify the output matches:
# grep modules /etc/audit/audit.rules
-w /sbin/insmod -p x -k modules
-w /sbin/rmmod -p x -k modules
-w /sbin/modprobe -p x -k modules
-a always,exit arch=b64 -S init_module -S delete_module -k modules
Remediation:
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For 32 bit systems add the following lines to the /etc/audit/audit.rules file:
-w
-w
-w
-a
/sbin/insmod -p x -k modules
/sbin/rmmod -p x -k modules
/sbin/modprobe -p x -k modules
always,exit arch=b32 -S init_module -S delete_module -k modules
For 64 bit systems add the following lines to the /etc/audit/audit.rules file:
-w
-w
-w
-a
/sbin/insmod -p x -k modules
/sbin/rmmod -p x -k modules
/sbin/modprobe -p x -k modules
always,exit arch=b64 -S init_module -S delete_module -k modules
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4.1.18 Ensure the audit configuration is immutable (Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
Set system audit so that audit rules cannot be modified with auditctl. Setting the flag "-e
2" forces audit to be put in immutable mode. Audit changes can only be made on system
reboot.
Rationale:
In immutable mode, unauthorized users cannot execute changes to the audit system to
potentially hide malicious activity and then put the audit rules back. Users would most
likely notice a system reboot and that could alert administrators of an attempt to make
unauthorized audit changes.
Audit:
Run the following command and verify output matches:
# grep "^\s*[^#]" /etc/audit/audit.rules | tail -1
-e 2
Remediation:
Add the following line to the end of the/etc/audit/audit.rules file.
-e 2
4.2 Configure Logging
Logging services should be configured to prevent information leaks and to aggregate logs
on a remote server so that they can be reviewed in the event of a system compromise and
ease log analysis.
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4.2.1 Configure rsyslog
The rsyslog software is recommended as a replacement for the syslogd daemon and
provides improvements over syslogd, such as connection-oriented (i.e. TCP) transmission
of logs, the option to log to database formats, and the encryption of log data en route to a
central logging server.
Note: This section only applies if rsyslog is installed on the system.
4.2.1.1 Ensure rsyslog Service is enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Once the rsyslog package is installed it needs to be activated.
Rationale:
If the rsyslog service is not activated the system may default to the syslogd service or lack
logging instead.
Audit:
Run the following command and verify runlevels 2 through 5 are "on":
# chkconfig --list rsyslog
rsyslog
0:off
1:off
2:on
3:on
4:on
5:on
6:off
Remediation:
Run the following command to enable rsyslog:
# chkconfig rsyslog on
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4.2.1.2 Ensure logging is configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/rsyslog.conf file specifies rules for logging and which files are to be used to log
certain classes of messages.
Rationale:
A great deal of important security-related information is sent via rsyslog (e.g., successful
and failed su attempts, failed login attempts, root login attempts, etc.).
Audit:
Review the contents of the /etc/rsyslog.conf file to ensure appropriate logging is set. In
addition, run the following command and verify that the log files are logging information:
# ls -l /var/log/
Remediation:
Edit the following lines in the /etc/rsyslog.conf file as appropriate for your
environment:
*.emerg
mail.*
mail.info
mail.warning
mail.err
news.crit
news.err
news.notice
*.=warning;*.=err
*.crit
*.*;mail.none;news.none
local0,local1.*
local2,local3.*
local4,local5.*
local6,local7.*
:omusrmsg:*
-/var/log/mail
-/var/log/mail.info
-/var/log/mail.warn
/var/log/mail.err
-/var/log/news/news.crit
-/var/log/news/news.err
-/var/log/news/news.notice
-/var/log/warn
/var/log/warn
-/var/log/messages
-/var/log/localmessages
-/var/log/localmessages
-/var/log/localmessages
-/var/log/localmessages
Run the following command to restart rsyslogd:
# pkill -HUP rsyslogd
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References:
1. See the rsyslog.conf(5) man page for more information.
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4.2.1.3 Ensure rsyslog default file permissions configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
rsyslog will create logfiles that do not already exist on the system. This setting controls
what permissions will be applied to these newly created files.
Rationale:
It is important to ensure that log files have the correct permissions to ensure that sensitive
data is archived and protected.
Audit:
Run the following command and verify that $FileCreateMode is 0640 or more restrictive:
# grep ^\$FileCreateMode /etc/rsyslog.conf
Remediation:
Edit the /etc/rsyslog.conf and set $FileCreateMode to 0640 or more restrictive:
$FileCreateMode 0640
References:
1. See the rsyslog.conf(5) man page for more information.
Notes:
You should also ensure this is not overridden with less restrictive settings in
any /etc/rsyslog.d/* conf file.
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4.2.1.4 Ensure rsyslog is configured to send logs to a remote log host
(Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The rsyslog utility supports the ability to send logs it gathers to a remote log host running
syslogd(8) or to receive messages from remote hosts, reducing administrative overhead.
Rationale:
Storing log data on a remote host protects log integrity from local attacks. If an attacker
gains root access on the local system, they could tamper with or remove log data that is
stored on the local system
Audit:
Review the /etc/rsyslog.conf file and verify that logs are sent to a central host (where
logfile.example.com is the name of your central log host):
# grep "^*.*[^I][^I]*@" /etc/rsyslog.conf
*.* @@loghost.example.com
Remediation:
Edit the /etc/rsyslog.conf file and add the following line (where logfile.example.com is
the name of your central log host).
*.* @@loghost.example.com
Run the following command to restart rsyslog:
# pkill -HUP rsyslogd
References:
1. See the rsyslog.conf(5) man page for more information.
Notes:
The double "at" sign (@@) directs rsyslog to use TCP to send log messages to the server,
which is a more reliable transport mechanism than the default UDP protocol.
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4.2.1.5 Ensure remote rsyslog messages are only accepted on
designated log hosts. (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
By default, rsyslog does not listen for log messages coming in from remote systems. The
ModLoad tells rsyslog to load the imtcp.so module so it can listen over a network via
TCP. The InputTCPServerRun option instructs rsyslogd to listen on the specified TCP
port.
Rationale:
The guidance in the section ensures that remote log hosts are configured to only accept
rsyslog data from hosts within the specified domain and that those systems that are not
designed to be log hosts do not accept any remote rsyslog messages. This provides
protection from spoofed log data and ensures that system administrators are reviewing
reasonably complete syslog data in a central location.
Audit:
Run the following commands and verify the resulting lines are uncommented on
designated log hosts and commented or removed on all others:
# grep '$ModLoad imtcp.so' /etc/rsyslog.conf
$ModLoad imtcp.so
# grep '$InputTCPServerRun' /etc/rsyslog.conf
$InputTCPServerRun 514
Remediation:
For hosts that are designated as log hosts, edit the /etc/rsyslog.conf file and uncomment or add the following lines:
$ModLoad imtcp.so
$InputTCPServerRun 514
For hosts that are not designated as log hosts, edit the /etc/rsyslog.conf file and
comment or remove the following lines:
# $ModLoad imtcp.so
# $InputTCPServerRun 514
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Run the following command to restart rsyslogd:
# pkill -HUP rsyslogd
References:
1. See the rsyslog(8) man page for more information.
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4.2.2 Configure syslog-ng
The syslog-ng software is recommended as a replacement for the syslogd daemon and
provides improvements over syslogd, such as connection-oriented (i.e. TCP) transmission
of logs, the option to log to database formats, and the encryption of log data en route to a
central logging server.
Note: This section only applies if syslog-ng is installed on the system.
4.2.2.1 Ensure syslog-ng service is enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Once the syslog-ng package is installed it needs to be activated.
Rationale:
If the syslog-ng service is not activated the system may default to the syslogd service or
lack logging instead.
Audit:
Run the following command and verify runlevels 2 through 5 are "on":
# chkconfig --list syslog-ng
syslog-ng
0:off
1:off
2:on
3:on
4:on
5:on
6:off
Remediation:
Run the following command to enable syslog-ng:
# chkconfig syslog-ng off
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4.2.2.2 Ensure logging is configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/syslog-ng/syslog-ng.conf file specifies rules for logging and which files are to
be used to log certain classes of messages.
Rationale:
A great deal of important security-related information is sent via syslog-ng (e.g.,
successful and failed su attempts, failed login attempts, root login attempts, etc.).
Audit:
Review the contents of the /etc/syslog-ng/syslog-ng.conf file to ensure appropriate
logging is set. In addition, run the following command and ensure that the log files are
logging information:
# ls -l /var/log/
Remediation:
Edit the log lines in the /etc/syslog-ng/syslog-ng.conf file as appropriate for your
environment:
log { source(src);
log { source(src);
log { source(src);
log { source(src);
log { source(src);
log { source(src);
log { source(src);
log { source(src);
log { source(src);
log { source(src);
};
log { source(src);
flags(final); };
log { source(src);
flags(final); };
log { source(src);
flags(final); };
log { source(src);
log { source(src);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
source(chroots);
filter(f_console); destination(console); };
filter(f_console); destination(xconsole); };
filter(f_newscrit); destination(newscrit); };
filter(f_newserr); destination(newserr); };
filter(f_newsnotice); destination(newsnotice); };
filter(f_mailinfo); destination(mailinfo); };
filter(f_mailwarn); destination(mailwarn); };
filter(f_mailerr); destination(mailerr); };
filter(f_mail); destination(mail); };
filter(f_acpid); destination(acpid); flags(final);
source(chroots); filter(f_acpid_full); destination(devnull);
source(chroots); filter(f_acpid_old); destination(acpid);
source(chroots); filter(f_netmgm); destination(netmgm);
source(chroots); filter(f_local); destination(localmessages); };
source(chroots); filter(f_messages); destination(messages); };
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log { source(src); source(chroots); filter(f_iptables); destination(firewall); };
log { source(src); source(chroots); filter(f_warn); destination(warn); };
Run the following command to restart syslog-ng:
# pkill -HUP syslog-ng
References:
1. See the syslog-ng man page for more information.
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4.2.2.3 Ensure syslog-ng default file permissions configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
syslog-ng will create logfiles that do not already exist on the system. This setting controls
what permissions will be applied to these newly created files.
Rationale:
It is important to ensure that log files exist and have the correct permissions to ensure that
sensitive syslog-ng data is archived and protected.
Audit:
Run the following command and verify the perm option is 0640 or more restrictive:
# grep ^options /etc/syslog-ng/syslog-ng.conf
options { chain_hostnames(off); flush_lines(0); perm(0640); stats_freq(3600);
threaded(yes); };
Remediation:
Edit the /etc/syslog-ng/syslog-ng.conf and set perm option to 0640 or more restrictive:
options { chain_hostnames(off); flush_lines(0); perm(0640); stats_freq(3600);
threaded(yes); };
References:
1. See the syslog-ng man pages for more information.
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4.2.2.4 Ensure syslog-ng is configured to send logs to a remote log host
(Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The syslog-ng utility supports the ability to send logs it gathers to a remote log host or to
receive messages from remote hosts, reducing administrative overhead.
Rationale:
Storing log data on a remote host protects log integrity from local attacks. If an attacker
gains root access on the local system, they could tamper with or remove log data that is
stored on the local system
Audit:
Review the /etc/syslog-ng/syslog-ng.conf file and verify that logs are sent to a central
host (where logfile.example.com is the name of your central log host):
destination logserver { tcp("logfile.example.com" port(514)); };
log { source(src); destination(logserver); };
Remediation:
Edit the /etc/syslog-ng/syslog-ng.conf file and add the following lines (where
logfile.example.com is the name of your central log host).
destination logserver { tcp("logfile.example.com" port(514)); };
log { source(src); destination(logserver); };
Run the following command to restart syslog-ng:
# pkill -HUP syslog-ng
References:
1. See the rsyslog.conf(5) man page for more information.
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4.2.2.5 Ensure remote syslog-ng messages are only accepted on
designated log hosts (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
By default, syslog-ng does not listen for log messages coming in from remote systems.
Rationale:
The guidance in the section ensures that remote log hosts are configured to only accept
syslog-ng data from hosts within the specified domain and that those systems that are not
designed to be log hosts do not accept any remote syslog-ng messages. This provides
protection from spoofed log data and ensures that system administrators are reviewing
reasonably complete syslog data in a central location.
Audit:
Review the /etc/syslog-ng/syslog-ng.conf file and verify the following lines are configured
appropriately on designated log hosts:
source net{ tcp(); };
destination remote { file("/var/log/remote/${FULLHOST}-log"); };
log { source(net); destination(remote); };
Remediation:
On designated log hosts edit the /etc/syslog-ng/syslog-ng.conf file and configure the
following lines are appropriately:
source net{ tcp(); };
destination remote { file("/var/log/remote/${FULLHOST}-log"); };
log { source(net); destination(remote); };
On non designated log hosts edit the /etc/syslog-ng/syslog-ng.conf file and remove or
edit any sources that accept network sourced log messages.
Run the following command to restart rsyslogd:
# pkill -HUP rsyslogd
References:
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1. See the rsyslog(8) man page for more information.
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4.2.3 Ensure rsyslog or syslog-ng is installed (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The rsyslog and syslog-ng software are recommended replacements to the original
syslogd daemon which provide improvements over syslogd, such as connection-oriented
(i.e. TCP) transmission of logs, the option to log to database formats, and the encryption of
log data en route to a central logging server.
Rationale:
The security enhancements of rsyslog and syslog-ng such as connection-oriented (i.e.
TCP) transmission of logs, the option to log to database formats, and the encryption of log
data en route to a central logging server) justify installing and configuring the package.
Audit:
Run the following commands and verify at least one indicates the package is installed:
# rpm -q rsyslog
# rpm -q syslog-ng
Remediation:
Install rsyslog or syslog-ng using one of the following commands:
# yum install rsyslog
# yum install syslog-ng
Notes:
The syslog-ng package requires the EPEL6 and Optional repositories be
enabled. See https://czanik.blogs.balabit.com/2015/09/installing-syslog-ng-ose-3-7-1-onrhel6-and-centos6/ for more information.
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4.2.4 Ensure permissions on all logfiles are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Log files stored in /var/log/ contain logged information from many services on the system,
or on log hosts others as well.
Rationale:
It is important to ensure that log files have the correct permissions to ensure that
sensitive data is archived and protected.
Audit:
Run the following command and verify that other has no permissions on any files and
group does not have write or execute permissions on any files:
# find /var/log -type f -ls
Remediation:
Run the following command to set permissions on all existing log files:
# find /var/log -type f -exec chmod g-wx,o-rwx {} +
Notes:
You may also need to change the configuration for your logging software or services for any
logs that had incorrect permissions.
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4.3 Ensure logrotate is configured (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The system includes the capability of rotating log files regularly to avoid filling up the
system with logs or making the logs unmanageable large. The file
/etc/logrotate.d/syslog is the configuration file used to rotate log files created by
syslog or rsyslog.
Rationale:
By keeping the log files smaller and more manageable, a system administrator can easily
archive these files to another system and spend less time looking through inordinately
large log files.
Audit:
Review /etc/logrotate.conf and /etc/logrotate.d/* and verify logs are rotated
according to site policy.
Remediation:
Edit /etc/logrotate.conf and /etc/logrotate.d/* to ensure logs are rotated according
to site policy.
5 Access, Authentication and Authorization
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5.1 Configure cron
5.1.1 Ensure cron daemon is enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The cron daemon is used to execute batch jobs on the system.
Rationale:
While there may not be user jobs that need to be run on the system, the system does have
maintenance jobs that may include security monitoring that have to run, and cron is used
to execute them.
Audit:
Run the following command and verify runlevels 2 through 5 are "on":
# chkconfig --list crond
crond
0:off
1:off
2:on
3:on
4:on
5:on
6:off
Remediation:
Run the following command to enable cron:
# chkconfig crond on
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5.1.2 Ensure permissions on /etc/crontab are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/crontab file is used by cron to control its own jobs. The commands in this item
make sure that root is the user and group owner of the file and that only the owner can
access the file.
Rationale:
This file contains information on what system jobs are run by cron. Write access to these
files could provide unprivileged users with the ability to elevate their privileges. Read
access to these files could provide users with the ability to gain insight on system jobs that
run on the system and could provide them a way to gain unauthorized privileged access.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/crontab
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/crontab:
# chown root:root /etc/crontab
# chmod og-rwx /etc/crontab
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5.1.3 Ensure permissions on /etc/cron.hourly are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
This directory contains system cron jobs that need to run on an hourly basis. The files in
this directory cannot be manipulated by the crontab command, but are instead edited by
system administrators using a text editor. The commands below restrict read/write and
search access to user and group root, preventing regular users from accessing this
directory.
Rationale:
Granting write access to this directory for non-privileged users could provide them the
means for gaining unauthorized elevated privileges. Granting read access to this directory
could give an unprivileged user insight in how to gain elevated privileges or circumvent
auditing controls.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/cron.hourly
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/cron.hourly:
# chown root:root /etc/cron.hourly
# chmod og-rwx /etc/cron.hourly
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5.1.4 Ensure permissions on /etc/cron.daily are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/cron.daily directory contains system cron jobs that need to run on a daily
basis. The files in this directory cannot be manipulated by the crontab command, but are
instead edited by system administrators using a text editor. The commands below restrict
read/write and search access to user and group root, preventing regular users from
accessing this directory.
Rationale:
Granting write access to this directory for non-privileged users could provide them the
means for gaining unauthorized elevated privileges. Granting read access to this directory
could give an unprivileged user insight in how to gain elevated privileges or circumvent
auditing controls.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/cron.daily
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/cron.daily:
# chown root:root /etc/cron.daily
# chmod og-rwx /etc/cron.daily
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5.1.5 Ensure permissions on /etc/cron.weekly are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/cron.weekly directory contains system cron jobs that need to run on a weekly
basis. The files in this directory cannot be manipulated by the crontab command, but are
instead edited by system administrators using a text editor. The commands below restrict
read/write and search access to user and group root, preventing regular users from
accessing this directory.
Rationale:
Granting write access to this directory for non-privileged users could provide them the
means for gaining unauthorized elevated privileges. Granting read access to this directory
could give an unprivileged user insight in how to gain elevated privileges or circumvent
auditing controls.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/cron.weekly
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/cron.weekly:
# chown root:root /etc/cron.weekly
# chmod og-rwx /etc/cron.weekly
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5.1.6 Ensure permissions on /etc/cron.monthly are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/cron.monthly directory contains system cron jobs that need to run on a monthly
basis. The files in this directory cannot be manipulated by the crontab command, but are
instead edited by system administrators using a text editor. The commands below restrict
read/write and search access to user and group root, preventing regular users from
accessing this directory.
Rationale:
Granting write access to this directory for non-privileged users could provide them the
means for gaining unauthorized elevated privileges. Granting read access to this directory
could give an unprivileged user insight in how to gain elevated privileges or circumvent
auditing controls.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/cron.monthly
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/cron.monthly:
# chown root:root /etc/cron.monthly
# chmod og-rwx /etc/cron.monthly
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5.1.7 Ensure permissions on /etc/cron.d are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/cron.d directory contains system cron jobs that need to run in a similar manner
to the hourly, daily weekly and monthly jobs from /etc/crontab, but require more
granular control as to when they run. The files in this directory cannot be manipulated by
the crontab command, but are instead edited by system administrators using a text editor.
The commands below restrict read/write and search access to user and group root,
preventing regular users from accessing this directory.
Rationale:
Granting write access to this directory for non-privileged users could provide them the
means for gaining unauthorized elevated privileges. Granting read access to this directory
could give an unprivileged user insight in how to gain elevated privileges or circumvent
auditing controls.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/cron.d
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/cron.d:
# chown root:root /etc/cron.d
# chmod og-rwx /etc/cron.d
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5.1.8 Ensure at/cron is restricted to authorized users (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Configure /etc/cron.allow and /etc/at.allow to allow specific users to use these
services. If /etc/cron.allow or /etc/at.allow do not exist, then /etc/at.deny and
/etc/cron.deny are checked. Any user not specifically defined in those files is allowed to
use at and cron. By removing the files, only users in /etc/cron.allow and /etc/at.allow
are allowed to use at and cron. Note that even though a given user is not listed in
cron.allow, cron jobs can still be run as that user. The cron.allow file only controls
administrative access to the crontab command for scheduling and modifying cron jobs.
Rationale:
On many systems, only the system administrator is authorized to schedule cron jobs. Using
the cron.allow file to control who can run cron jobs enforces this policy. It is easier to
manage an allow list than a deny list. In a deny list, you could potentially add a user ID to
the system and forget to add it to the deny files.
Audit:
Run the following commands and ensure /etc/cron.deny and /etc/at.deny do not exist:
# stat /etc/cron.deny
stat: cannot stat `/etc/cron.deny': No such file or directory
# stat /etc/at.deny
stat: cannot stat `/etc/at.deny': No such file or directory
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other for both /etc/cron.allow and /etc/at.allow:
# stat /etc/cron.allow
Access: (0600/-rw-------)
# stat /etc/at.allow
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to remove /etc/cron.deny and /etc/at.deny and create and
set permissions and ownership for /etc/cron.allow and /etc/at.allow:
212 | P a g e
#
#
#
#
#
#
#
#
rm /etc/cron.deny
rm /etc/at.deny
touch /etc/cron.allow
touch /etc/at.allow
chmod og-rwx /etc/cron.allow
chmod og-rwx /etc/at.allow
chown root:root /etc/cron.allow
chown root:root /etc/at.allow
213 | P a g e
5.2 SSH Server Configuration
SSH is a secure, encrypted replacement for common login services such as telnet, ftp,
rlogin, rsh, and rcp. It is strongly recommended that sites abandon older clear-text login
protocols and use SSH to prevent session hijacking and sniffing of sensitive data off the
network.
Note: The recommendations in this section only apply if the SSH daemon is installed on the
system, if remote access is not required the SSH daemon can be removed and this section
skipped.
Note: Once all configuration changes have been made to /etc/ssh/sshd_config, the sshd
configuration must be reloaded:
# service sshd reload
5.2.1 Ensure permissions on /etc/ssh/sshd_config are configured
(Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/ssh/sshd_config file contains configuration specifications for sshd. The
command below sets the owner and group of the file to root.
Rationale:
The /etc/ssh/sshd_config file needs to be protected from unauthorized changes by nonprivileged users, but needs to be readable as this information is used with many nonprivileged programs.
Audit:
214 | P a g e
Run the following command and verify Uid and Gid are both 0/root and Access does not
grant permissions to group or other:
# stat /etc/ssh/sshd_config
Access: (0600/-rw-------) Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set ownership and permissions on /etc/ssh/sshd_config:
# chown root:root /etc/ssh/sshd_config
# chmod og-rwx /etc/ssh/sshd_config
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5.2.2 Ensure SSH Protocol is set to 2 (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
SSH supports two different and incompatible protocols: SSH1 and SSH2. SSH1 was the
original protocol and was subject to security issues. SSH2 is more advanced and secure.
Rationale:
SSH v1 suffers from insecurities that do not affect SSH v2.
Audit:
Run the following command and verify that output matches:
# grep "^Protocol" /etc/ssh/sshd_config
Protocol 2
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
Protocol 2
216 | P a g e
5.2.3 Ensure SSH LogLevel is set to INFO (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The INFO parameter specifies that login and logout activity will be logged.
Rationale:
SSH provides several logging levels with varying amounts of verbosity. DEBUG is specifically
not recommended other than strictly for debugging SSH communications since it provides
so much data that it is difficult to identify important security information. INFO level is the
basic level that only records login activity of SSH users. In many situations, such as Incident
Response, it is important to determine when a particular user was active on a system. The
logout record can eliminate those users who disconnected, which helps narrow the field.
Audit:
Run the following command and verify that output matches:
# grep "^LogLevel" /etc/ssh/sshd_config
LogLevel INFO
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
LogLevel INFO
217 | P a g e
5.2.4 Ensure SSH X11 forwarding is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The X11Forwarding parameter provides the ability to tunnel X11 traffic through the
connection to enable remote graphic connections.
Rationale:
Disable X11 forwarding unless there is an operational requirement to use X11 applications
directly. There is a small risk that the remote X11 servers of users who are logged in via
SSH with X11 forwarding could be compromised by other users on the X11 server. Note
that even if X11 forwarding is disabled, users can always install their own forwarders.
Audit:
Run the following command and verify that output matches:
# grep "^X11Forwarding" /etc/ssh/sshd_config
X11Forwarding no
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
X11Forwarding no
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5.2.5 Ensure SSH MaxAuthTries is set to 4 or less (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The MaxAuthTries parameter specifies the maximum number of authentication attempts
permitted per connection. When the login failure count reaches half the number, error
messages will be written to the syslog file detailing the login failure.
Rationale:
Setting the MaxAuthTries parameter to a low number will minimize the risk of successful
brute force attacks to the SSH server. While the recommended setting is 4, set the number
based on site policy.
Audit:
Run the following command and verify that output MaxAuthTries is 4 or less:
# grep "^MaxAuthTries" /etc/ssh/sshd_config
MaxAuthTries 4
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
MaxAuthTries 4
219 | P a g e
5.2.6 Ensure SSH IgnoreRhosts is enabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The IgnoreRhosts parameter specifies that .rhosts and .shosts files will not be used in
RhostsRSAAuthentication or HostbasedAuthentication.
Rationale:
Setting this parameter forces users to enter a password when authenticating with ssh.
Audit:
Run the following command and verify that output matches:
# grep "^IgnoreRhosts" /etc/ssh/sshd_config
IgnoreRhosts yes
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
IgnoreRhosts yes
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5.2.7 Ensure SSH HostbasedAuthentication is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The HostbasedAuthentication parameter specifies if authentication is allowed through
trusted hosts via the user of .rhosts, or /etc/hosts.equiv, along with successful public
key client host authentication. This option only applies to SSH Protocol Version 2.
Rationale:
Even though the .rhosts files are ineffective if support is disabled in /etc/pam.conf,
disabling the ability to use .rhosts files in SSH provides an additional layer of protection .
Audit:
Run the following command and verify that output matches:
# grep "^HostbasedAuthentication" /etc/ssh/sshd_config
HostbasedAuthentication no
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
HostbasedAuthentication no
221 | P a g e
5.2.8 Ensure SSH root login is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The PermitRootLogin parameter specifies if the root user can log in using ssh(1). The
default is no.
Rationale:
Disallowing root logins over SSH requires system admins to authenticate using their own
individual account, then escalating to root via sudo or su. This in turn limits opportunity
for non-repudiation and provides a clear audit trail in the event of a security incident
Audit:
Run the following command and verify that output matches:
# grep "^PermitRootLogin" /etc/ssh/sshd_config
PermitRootLogin no
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
PermitRootLogin no
222 | P a g e
5.2.9 Ensure SSH PermitEmptyPasswords is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The PermitEmptyPasswords parameter specifies if the SSH server allows login to accounts
with empty password strings.
Rationale:
Disallowing remote shell access to accounts that have an empty password reduces the
probability of unauthorized access to the system
Audit:
Run the following command and verify that output matches:
# grep "^PermitEmptyPasswords" /etc/ssh/sshd_config
PermitEmptyPasswords no
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
PermitEmptyPasswords no
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5.2.10 Ensure SSH PermitUserEnvironment is disabled (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The PermitUserEnvironment option allows users to present environment options to the
ssh daemon.
Rationale:
Permitting users the ability to set environment variables through the SSH daemon could
potentially allow users to bypass security controls (e.g. setting an execution path that has
ssh executing trojan'd programs)
Audit:
Run the following command and verify that output matches:
# grep PermitUserEnvironment /etc/ssh/sshd_config
PermitUserEnvironment no
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
PermitUserEnvironment no
224 | P a g e
5.2.11 Ensure only approved ciphers are used (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
This variable limits the types of ciphers that SSH can use during communication.
Rationale:
Based on research conducted at various institutions, it was determined that the symmetric
portion of the SSH Transport Protocol (as described in RFC 4253) has security weaknesses
that allowed recovery of up to 32 bits of plaintext from a block of ciphertext that was
encrypted with the Cipher Block Chaining (CBD) method. From that research, new Counter
mode algorithms (as described in RFC4344) were designed that are not vulnerable to these
types of attacks and these algorithms are now recommended for standard use.
Audit:
Run the following command and verify that output does not contain any cipher block
chaining (-cbc) algorithms:
# grep "Ciphers" /etc/ssh/sshd_config
Ciphers aes256-ctr,aes192-ctr,aes128-ctr,aes256-gcm@openssh.com,aes128gcm@openssh.com,chacha20-poly1305@openssh.com
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
Ciphers aes256-ctr,aes192-ctr,aes128-ctr
References:
1. For more information on the Counter mode algorithms, read RFC4344 at
http://www.ietf.org/rfc/rfc4344.txt
Notes:
Some organizations may have stricter requirements for approved ciphers. Ensure that
ciphers used are in compliance with site policy.
225 | P a g e
5.2.12 Ensure only approved MAC algorithms are used (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
This variable limits the types of MAC algorithms that SSH can use during communication.
Rationale:
MD5 and 96-bit MAC algorithms are considered weak and have been shown to increase
exploitability in SSH downgrade attacks. Weak algorithms continue to have a great deal of
attention as a weak spot that can be exploited with expanded computing power. An
attacker that breaks the algorithm could take advantage of a MiTM position to decrypt the
SSH tunnel and capture credentials and information
Audit:
Run the following command and verify that output does not contain any unlisted MAC
algorithms:
# grep "MACs" /etc/ssh/sshd_config
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com,curve25519sha256@libssh.org,diffie-hellman-group-exchange-sha256
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter in accordance with site
policy. The following includes all supported and accepted MACs:
MACs hmac-sha2-512,hmac-sha2-256
References:
1. More information on SSH downgrade attacks can be found here:
http://www.mitls.org/pages/attacks/SLOTH
Notes:
226 | P a g e
Some organizations may have stricter requirements for approved ciphers. Ensure that
MACs used are in compliance with site policy.
227 | P a g e
5.2.13 Ensure SSH Idle Timeout Interval is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The two options ClientAliveInterval and ClientAliveCountMax control the timeout of
ssh sessions. When the ClientAliveInterval variable is set, ssh sessions that have no
activity for the specified length of time are terminated. When the ClientAliveCountMax
variable is set, sshd will send client alive messages at every ClientAliveInterval
interval. When the number of consecutive client alive messages are sent with no response
from the client, the ssh session is terminated. For example, if the ClientAliveInterval is
set to 15 seconds and the ClientAliveCountMax is set to 3, the client ssh session will be
terminated after 45 seconds of idle time.
Rationale:
Having no timeout value associated with a connection could allow an unauthorized user
access to another user's ssh session (e.g. user walks away from their computer and doesn't
lock the screen). Setting a timeout value at least reduces the risk of this happening..
While the recommended setting is 300 seconds (5 minutes), set this timeout value based on
site policy. The recommended setting for ClientAliveCountMax is 0. In this case, the client
session will be terminated after 5 minutes of idle time and no keepalive messages will be
sent.
Audit:
Run the following commands and verify ClientAliveInterval is 300 or less and
ClientAliveCountMax is 3 or less:
# grep "^ClientAliveInterval" /etc/ssh/sshd_config
ClientAliveInterval 300
# grep "^ClientAliveCountMax" /etc/ssh/sshd_config
ClientAliveCountMax 0
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameters as follows:
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ClientAliveInterval 300
ClientAliveCountMax 0
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5.2.14 Ensure SSH LoginGraceTime is set to one minute or less (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The LoginGraceTime parameter specifies the time allowed for successful authentication to
the SSH server. The longer the Grace period is the more open unauthenticated connections
can exist. Like other session controls in this session the Grace Period should be limited to
appropriate organizational limits to ensure the service is available for needed access.
Rationale:
Setting the LoginGraceTime parameter to a low number will minimize the risk of
successful brute force attacks to the SSH server. It will also limit the number of concurrent
unauthenticated connections While the recommended setting is 60 seconds (1 Minute), set
the number based on site policy.
Audit:
Run the following command and verify that output LoginGraceTime is 60 or less:
# grep "^LoginGraceTime" /etc/ssh/sshd_config
LoginGraceTime 60
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
LoginGraceTime 60
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5.2.15 Ensure SSH access is limited (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
There are several options available to limit which users and group can access the system
via SSH. It is recommended that at least one of the following options be leveraged:
AllowUsers
The AllowUsers variable gives the system administrator the option of allowing specific
users to ssh into the system. The list consists of space separated user names. Numeric user
IDs are not recognized with this variable. If a system administrator wants to restrict user
access further by only allowing the allowed users to log in from a particular host, the entry
can be specified in the form of user@host.
AllowGroups
The AllowGroups variable gives the system administrator the option of allowing specific
groups of users to ssh into the system. The list consists of space separated group names.
Numeric group IDs are not recognized with this variable.
DenyUsers
The DenyUsers variable gives the system administrator the option of denying specific
users to ssh into the system. The list consists of space separated user names. Numeric user
IDs are not recognized with this variable. If a system administrator wants to restrict user
access further by specifically denying a user's access from a particular host, the entry can
be specified in the form of user@host.
DenyGroups
The DenyGroups variable gives the system administrator the option of denying specific
groups of users to ssh into the system. The list consists of space separated group names.
Numeric group IDs are not recognized with this variable.
Rationale:
Restricting which users can remotely access the system via SSH will help ensure that only
authorized users access the system.
231 | P a g e
Audit:
Run the following commands and verify that output matches for at least one:
# grep "^AllowUsers" /etc/ssh/sshd_config
AllowUsers <userlist>
# grep "^AllowGroups" /etc/ssh/sshd_config
AllowGroups <grouplist>
# grep "^DenyUsers" /etc/ssh/sshd_config
DenyUsers <userlist>
# grep "^DenyGroups" /etc/ssh/sshd_config
DenyGroups <grouplist>
Remediation:
Edit the /etc/ssh/sshd_config file to set one or more of the parameter as follows:
AllowUsers <userlist>
AllowGroups <grouplist>
DenyUsers <userlist>
DenyGroups <grouplist>
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5.2.16 Ensure SSH warning banner is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The Banner parameter specifies a file whose contents must be sent to the remote user
before authentication is permitted. By default, no banner is displayed.
Rationale:
Banners are used to warn connecting users of the particular site's policy regarding
connection. Presenting a warning message prior to the normal user login may assist the
prosecution of trespassers on the computer system.
Audit:
Run the following command and verify that output matches:
# grep "^Banner" /etc/ssh/sshd_config
Banner /etc/issue.net
Remediation:
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
Banner /etc/issue.net
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5.3 Configure PAM
PAM (Pluggable Authentication Modules) is a service that implements modular
authentication modules on UNIX systems. PAM is implemented as a set of shared objects
that are loaded and executed when a program needs to authenticate a user. Files for PAM
are typically located in the /etc/pam.d directory. PAM must be carefully configured to
secure system authentication. While this section covers some of PAM, please consult other
PAM resources to fully understand the configuration capabilities.
5.3.1 Ensure password creation requirements are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The pam_cracklib.so module checks the strength of passwords. It performs checks such
as making sure a password is not a dictionary word, it is a certain length, contains a mix of
characters (e.g. alphabet, numeric, other) and more. The following are definitions of the
pam_cracklib.so options.

try_first_pass - retrieve the password from a previous stacked PAM module. If






not available, then prompt the user for a password.
retry=3 - Allow 3 tries before sending back a failure.
minlen=14 - password must be 14 characters or more
dcredit=-1 - provide at least one digit
ucredit=-1 - provide at least one uppercase character
ocredit=-1 - provide at least one special character
lcredit=-1 - provide at least one lowercase character
The settings shown above are one possible policy. Alter these values to conform to your
own organization's password policies.
Rationale:
Strong passwords protect systems from being hacked through brute force methods.
Audit:
Run the following commands and verify all password requirements are as listed or stricter:
234 | P a g e
# grep pam_cracklib.so /etc/pam.d/password-auth
password requisite pam_cracklib.so try_first_pass retry=3 minlen=14 dcredit=-1
ucredit=-1 ocredit=-1 lcredit=-1
# grep pam_cracklib.so /etc/pam.d/system-auth
password requisite pam_cracklib.so try_first_pass retry=3 minlen=14 dcredit=-1
ucredit=-1 ocredit=-1 lcredit=-1
Additional options may be present, 'requisite' may be 'required'.
Remediation:
Edit the /etc/pam.d/password-auth and /etc/pam.d/system-auth files to include the
appropriate options for pam_cracklib.so and to conform to site policy:
password requisite pam_cracklib.so try_first_pass retry=3 minlen=14 dcredit=-1
ucredit=-1 ocredit=-1 lcredit=-1
Notes:
authconfig may overwrite any changes made as part of this recommendation.
It is
advisable to maintain a backup and audit this recommendation anytime authconfig is
used.
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5.3.2 Ensure lockout for failed password attempts is configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Lock out users after n unsuccessful consecutive login attempts. The first sets of changes are
made to the PAM configuration files. The second set of changes are applied to the program
specific PAM configuration file. The second set of changes must be applied to each program
that will lock out users. Check the documentation for each secondary program for
instructions on how to configure them to work with PAM.
Set the lockout number to the policy in effect at your site.
Rationale:
Locking out user IDs after n unsuccessful consecutive login attempts mitigates brute force
password attacks against your systems.
Audit:
Review the /etc/pam.d/password-auth and /etc/pam.d/system-auth files and verify the
following pam_faillock.so lines appear surrounding a pam_unix.so line and the
pam_unix.so is [success=1 default=bad] as listed in both:
auth
auth
auth
auth
required pam_faillock.so preauth audit silent deny=5 unlock_time=900
[success=1 default=bad] pam_unix.so
[default=die] pam_faillock.so authfail audit deny=5 unlock_time=900
sufficient pam_faillock.so authsucc audit deny=5 unlock_time=900
Remediation:
Edit the /etc/pam.d/password-auth and /etc/pam.d/system-auth files and add the
following pam_faillock.so lines surrounding a pam_unix.so line modify
the pam_unix.so is [success=1 default=bad] as listed in both:
auth
auth
auth
auth
required pam_faillock.so preauth audit silent deny=5 unlock_time=900
[success=1 default=bad] pam_unix.so
[default=die] pam_faillock.so authfail audit deny=5 unlock_time=900
sufficient pam_faillock.so authsucc audit deny=5 unlock_time=900
Notes:
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Additional module options may be set, recommendation only covers those listed here.
If a user has been locked out because they have reached the maximum consecutive failure
count defined by deny= in the pam_faillock.so module, the user can be unlocked by
issuing the command faillock -u --reset respectively. This command sets the failed
count to 0, effectively unlocking the user.
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5.3.3 Ensure password reuse is limited (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/security/opasswd file stores the users' old passwords and can be checked to
ensure that users are not recycling recent passwords.
Rationale:
Forcing users not to reuse their past 5 passwords make it less likely that an attacker will be
able to guess the password.
Note that these change only apply to accounts configured on the local system.
Audit:
Run the following commands and ensure the remember option is '5' or more and included in
all results:
# egrep '^password\s+sufficient\s+pam_unix.so' /etc/pam.d/password-auth
password sufficient pam_unix.so remember=5
# egrep '^password\s+sufficient\s+pam_unix.so' /etc/pam.d/system-auth
password sufficient pam_unix.so remember=5
Remediation:
Edit the /etc/pam.d/password-auth and /etc/pam.d/system-auth files to include the
remember option and conform to site policy as shown:
password sufficient pam_unix.so remember=5
Notes:
Additional module options may be set, recommendation only covers those listed here.
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5.3.4 Ensure password hashing algorithm is SHA-512 (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The commands below change password encryption from md5 to sha512 (a much stronger
hashing algorithm). All existing accounts will need to perform a password change to
upgrade the stored hashes to the new algorithm.
Rationale:
The SHA-512 algorithm provides much stronger hashing than MD5, thus providing
additional protection to the system by increasing the level of effort for an attacker to
successfully determine passwords.
Note that these change only apply to accounts configured on the local system.
Audit:
Run the following commands and ensure the sha512 option is included in all results:
# egrep '^password\s+sufficient\s+pam_unix.so' /etc/pam.d/password-auth
password sufficient pam_unix.so sha512
# egrep '^password\s+sufficient\s+pam_unix.so' /etc/pam.d/system-auth
password sufficient pam_unix.so sha512
Remediation:
Edit the /etc/pam.d/password-auth and /etc/pam.d/system-auth files to include the
sha512 option for pam_unix.so as shown:
password sufficient pam_unix.so sha512
Notes:
Additional module options may be set, recommendation only covers those listed here.
If it is determined that the password algorithm being used is not SHA-512, once it is
changed, it is recommended that all user ID's be immediately expired and forced to change
their passwords on next login. To accomplish that, the following commands can be used.
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Any system accounts that need to be expired should be carefully done separately by the
system administrator to prevent any potential problems.
# cat /etc/passwd | awk -F: '( $3 >= 500 && $1 != "nfsnobody" ) { print $1 }' | xargs
-n 1 chage -d 0
5.4 User Accounts and Environment
This section provides guidance on setting up secure defaults for system and user accounts
and their environment.
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5.4.1 Set Shadow Password Suite Parameters
While a majority of the password control parameters have been moved to PAM, some
parameters are still available through the shadow password suite. Any changes made to
/etc/login.defs will only be applied if the usermod command is used. If user IDs are
added a different way, use the chage command to effect changes to individual user IDs.
5.4.1.1 Ensure password expiration is 90 days or less (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The PASS_MAX_DAYS parameter in /etc/login.defs allows an administrator to force
passwords to expire once they reach a defined age. It is recommended that the
PASS_MAX_DAYS parameter be set to less than or equal to 90 days.
Rationale:
The window of opportunity for an attacker to leverage compromised credentials or
successfully compromise credentials via an online brute force attack is limited by the age of
the password. Therefore, reducing the maximum age of a password also reduces an
attacker's window of opportunity.
Audit:
Run the following command and verify PASS_MAX_DAYS is 90 or less:
# grep PASS_MAX_DAYS /etc/login.defs
PASS_MAX_DAYS 90
Verify all users with a password have their maximum days between password change set
to 90 or less:
# egrep ^[^:]+:[^\!*] /etc/shadow | cut -d: -f1
<list of users>
# chage --list <user>
Maximum number of days between password change
: 90
Remediation:
Set the PASS_MAX_DAYS parameter to 90 in /etc/login.defs:
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PASS_MAX_DAYS 90
Modify user parameters for all users with a password set to match:
# chage --maxdays 90 <user>
Notes:
You can also check this setting in /etc/shadow directly. The 5th field should be 90 or less
for all users with a password.
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5.4.1.2 Ensure minimum days between password changes is 7 or more
(Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The PASS_MIN_DAYS parameter in /etc/login.defs allows an administrator to prevent
users from changing their password until a minimum number of days have passed since the
last time the user changed their password. It is recommended that PASS_MIN_DAYS
parameter be set to 7 or more days.
Rationale:
By restricting the frequency of password changes, an administrator can prevent users from
repeatedly changing their password in an attempt to circumvent password reuse controls.
Audit:
Run the following command and verify PASS_MIN_DAYS is 7 or more:
# grep PASS_MIN_DAYS /etc/login.defs
PASS_MIN_DAYS 7
Verify all users with a password have their minimum days between password change set to
7 or more:
# egrep ^[^:]+:[^\!*] /etc/shadow | cut -d: -f1
<list of users>
# chage --list <user>
Minimum number of days between password change
: 7
Remediation:
Set the PASS_MIN_DAYS parameter to 7 in /etc/login.defs:
PASS_MIN_DAYS 7
Modify user parameters for all users with a password set to match:
# chage --mindays 7 <user>
Notes:
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You can also check this setting in /etc/shadow directly. The 5th field should be 7 or more
for all users with a password.
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5.4.1.3 Ensure password expiration warning days is 7 or more (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The PASS_WARN_AGE parameter in /etc/login.defs allows an administrator to notify users
that their password will expire in a defined number of days. It is recommended that the
PASS_WARN_AGE parameter be set to 7 or more days.
Rationale:
Providing an advance warning that a password will be expiring gives users time to think of
a secure password. Users caught unaware may choose a simple password or write it down
where it may be discovered.
Audit:
Run the following command and verify PASS_WARN_AGE is 7 or more:
# grep PASS_WARN_AGE /etc/login.defs
PASS_WARN_AGE 7
Verify all users with a password have their number of days of warning before password
expires set to 7 or more:
# egrep ^[^:]+:[^\!*] /etc/shadow | cut -d: -f1
<list of users>
# chage --list <user>
Number of days of warning before password expires
: 7
Remediation:
Set the PASS_WARN_AGE parameter to 7 in /etc/login.defs:
PASS_WARN_AGE 7
Modify user parameters for all users with a password set to match:
# chage --warndays 7 <user>
Notes:
You can also check this setting in /etc/shadow directly. The 6th field should be 7 or more
for all users with a password.
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5.4.1.4 Ensure inactive password lock is 30 days or less (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
User accounts that have been inactive for over a given period of time can be automatically
disabled. It is recommended that accounts that are inactive for 30 days after password
expiration be disabled.
Rationale:
Inactive accounts pose a threat to system security since the users are not logging in to
notice failed login attempts or other anomalies.
Audit:
Run the following command and verify INACTIVE is 30 or less:
# useradd -D | grep INACTIVE
INACTIVE=30
Verify all users with a password have Password inactive no more than 30 days after
password expires:
# egrep ^[^:]+:[^\!*] /etc/shadow | cut -d: -f1
<list of users>
# chage --list <user>
Password inactive
: <date>
Remediation:
Run the following command to set the default password inactivity period to 30 days:
# useradd -D -f 30
Modify user parameters for all users with a password set to match:
# chage --inactive 30 <user>
Notes:
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You can also check this setting in /etc/shadow directly. The 7th field should be 30 or less
for all users with a password.
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5.4.2 Ensure system accounts are non-login (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
There are a number of accounts provided with CentOS 6 that are used to manage
applications and are not intended to provide an interactive shell.
Rationale:
It is important to make sure that accounts that are not being used by regular users are
prevented from being used to provide an interactive shell. By default, CentOS 6 sets the
password field for these accounts to an invalid string, but it is also recommended that the
shell field in the password file be set to /sbin/nologin. This prevents the account from
potentially being used to run any commands.
Audit:
Run the following script and verify no results are returned:
egrep -v "^\+" /etc/passwd | awk -F: '($1!="root" && $1!="sync" && $1!="shutdown" &&
$1!="halt" && $3<500 && $7!="/sbin/nologin" && $7!="/bin/false") {print}'
Remediation:
Set the shell for any accounts returned by the audit script to /sbin/nologin:
# usermod -s /sbin/nologin <user>
The following script will automatically set all user shells required to /sbin/nologin and
lock the sync, shutdown, and halt users:
#!/bin/bash
for user in `awk -F: '($3 < 500) {print $1 }' /etc/passwd`; do
if [ $user != "root" ]; then
usermod -L $user
if [ $user != "sync" ] && [ $user != "shutdown" ] && [ $user != "halt" ]; then
usermod -s /sbin/nologin $user
fi
fi
done
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5.4.3 Ensure default group for the root account is GID 0 (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The usermod command can be used to specify which group the root user belongs to. This
affects permissions of files that are created by the root user.
Rationale:
Using GID 0 for the root account helps prevent root-owned files from accidentally
becoming accessible to non-privileged users.
Audit:
Run the following command and verify the result is 0:
# grep "^root:" /etc/passwd | cut -f4 -d:
0
Remediation:
Run the following command to set the root user default group to GID 0:
# usermod -g 0 root
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5.4.4 Ensure default user umask is 027 or more restrictive (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The default umask determines the permissions of files created by users. The user creating
the file has the discretion of making their files and directories readable by others via the
chmod command. Users who wish to allow their files and directories to be readable by
others by default may choose a different default umask by inserting the umask command
into the standard shell configuration files (.profile, .bashrc, etc.) in their home
directories.
Rationale:
Setting a very secure default value for umask ensures that users make a conscious choice
about their file permissions. A default umask setting of 077 causes files and directories
created by users to not be readable by any other user on the system. A umask of 027 would
make files and directories readable by users in the same Unix group, while a umask of 022
would make files readable by every user on the system.
Audit:
Run the following commands and verify all umask lines returned are 027 or more
restrictive.
# grep "^umask" /etc/bashrc
umask 027
# grep "^umask" /etc/profile
umask 027
Remediation:
Edit the /etc/bashrc and /etc/profile files (and the appropriate files for any other shell
supported on your system) and add or edit any umask parameters as follows:
umask 027
Notes:
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The audit and remediation in this recommendation apply to bash and shell. If other shells
are supported on the system, it is recommended that their configuration files also are
checked.
Other methods of setting a default user umask exist however the shell configuration files
are the last run and will override other settings if they exist therefor our recommendation
is to configure in the shell configuration files. If other methods are in use in your
environment they should be audited and the shell configs should be verified to not
override.
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5.5 Ensure root login is restricted to system console (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The file /etc/securetty contains a list of valid terminals that may be logged in directly as
root.
Rationale:
Since the system console has special properties to handle emergency situations, it is
important to ensure that the console is in a physically secure location and that
unauthorized consoles have not been defined.
Audit:
# cat /etc/securetty
Remediation:
Remove entries for any consoles that are not in a physically secure location.
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5.6 Ensure access to the su command is restricted (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The su command allows a user to run a command or shell as another user. The program
has been superseded by sudo, which allows for more granular control over privileged
access. Normally, the su command can be executed by any user. By uncommenting the
pam_wheel.so statement in /etc/pam.d/su, the su command will only allow users in the
wheel group to execute su.
Rationale:
Restricting the use of su, and using sudo in its place, provides system administrators better
control of the escalation of user privileges to execute privileged commands. The sudo utility
also provides a better logging and audit mechanism, as it can log each command executed
via sudo, whereas su can only record that a user executed the su program.
Audit:
Run the following command and verify output includes matching line:
# grep pam_wheel.so /etc/pam.d/su
auth required pam_wheel.so use_uid
Run the following command and verify users in wheel group match site policy:
# grep wheel /etc/group
wheel:x:10:root,<user list>
Remediation:
Add the following line to the /etc/pam.d/su file:
auth required pam_wheel.so use_uid
Create a comma separated list of users in the wheel statement in the /etc/group file:
wheel:x:10:root,<user list>
6 System Maintenance
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Recommendations in this section are intended as maintenance and are intended to be
checked on a frequent basis to ensure system stability. Many recommendations do not
have quick remediations and require investigation into the cause and best fix available and
may indicate an attempted breach of system security.
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6.1 System File Permissions
This section provides guidance on securing aspects of system files and directories.
6.1.1 Audit system file permissions (Not Scored)
Profile Applicability:
 Level 2 - Server
 Level 2 - Workstation
Description:
The RPM package manager has a number of useful options. One of these, the --verify (or V) option, can be used to verify that system packages are correctly installed. The -verify option can be used to verify a particular package or to verify all system packages. If
no output is returned, the package is installed correctly. The following table describes the
meaning of output from the verify option:
Code
S
M
5
D
L
U
G
T
Meaning
File size differs.
File mode differs (includes permissions and file type).
The MD5 checksum differs.
The major and minor version numbers differ on a device file.
A mismatch occurs in a link.
The file ownership differs.
The file group owner differs.
The file time (mtime) differs.
The rpm -qf command can be used to determine which package a particular file belongs to.
For example the following commands determines which package the /bin/bash file
belongs to:
# rpm -qf /bin/bash
bash-4.1.2-29.el6.x86_64
To verify the settings for the package that controls the /bin/bash file, run the following:
# rpm -V bash-4.1.2-29.el6.x86_64
.M.......
/bin/bash
Note that you can feed the output of the rpm -qf command to the rpm -V command:
# rpm -V `rpm -qf /etc/passwd`
.M...... c /etc/passwd
S.5....T c /etc/printcap
Rationale:
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It is important to confirm that packaged system files and directories are maintained with
the permissions they were intended to have from the OS vendor.
Audit:
Run the following command to review all installed packages. Note that this may be very
time consuming and may be best scheduled via the cron utility. It is recommended that the
output of this command be redirected to a file that can be reviewed later.
# rpm -Va --nomtime --nosize --nomd5 --nolinkto > <filename>
Remediation:
Correct any discrepancies found and rerun the audit until output is clean or risk is
mitigated or accepted.
References:
1. http://docs.fedoraproject.org/enUS/Fedora_Draft_Documentation/0.1/html/RPM_Guide/index.html
Notes:
Since packages and important files may change with new updates and releases, it is
recommended to verify everything, not just a finite list of files. This can be a time
consuming task and results may depend on site policy therefore it is not a scorable
benchmark item, but is provided for those interested in additional security measures.
Some of the recommendations of this benchmark alter the state of files audited by this
recommendation. The audit command will alert for all changes to a file permissions even if
the new state is more secure than the default.
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6.1.2 Ensure permissions on /etc/passwd are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/passwd file contains user account information that is used by many system
utilities and therefore must be readable for these utilities to operate.
Rationale:
It is critical to ensure that the /etc/passwd file is protected from unauthorized write
access. Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/passwd
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following command to set permissions on /etc/passwd:
# chown root:root /etc/passwd
# chmod 644 /etc/passwd
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6.1.3 Ensure permissions on /etc/shadow are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/shadow file is used to store the information about user accounts that is critical to
the security of those accounts, such as the hashed password and other security
information.
Rationale:
If attackers can gain read access to the /etc/shadow file, they can easily run a password
cracking program against the hashed password to break it. Other security information that
is stored in the /etc/shadow file (such as expiration) could also be useful to subvert the
user accounts.
Audit:
Run the following command and verify Uid and Gid are 0/root, and Access is 000:
# stat /etc/shadow
Access: (0000/----------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following commands to set permissions on /etc/shadow:
# chown root:root /etc/shadow
# chmod 000 /etc/shadow
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6.1.4 Ensure permissions on /etc/group are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/group file contains a list of all the valid groups defined in the system. The
command below allows read/write access for root and read access for everyone else.
Rationale:
The /etc/group file needs to be protected from unauthorized changes by non-privileged
users, but needs to be readable as this information is used with many non-privileged
programs.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 644:
# stat /etc/group
Access: (0644/-rw-r--r--)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following command to set permissions on /etc/group:
# chown root:root /etc/group
# chmod 644 /etc/group
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6.1.5 Ensure permissions on /etc/gshadow are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/gshadow file is used to store the information about groups that is critical to the
security of those accounts, such as the hashed password and other security information.
Rationale:
If attackers can gain read access to the /etc/gshadow file, they can easily run a password
cracking program against the hashed password to break it. Other security information that
is stored in the /etc/gshadow file (such as group administrators) could also be useful to
subvert the group.
Audit:
Run the following command and verify Uid and Gid are 0/root, and Access is 000:
# stat /etc/gshadow
Access: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following chown to set permissions on /etc/gshadow:
# chown root:root /etc/gshadow
# chmod 000 /etc/gshadow
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6.1.6 Ensure permissions on /etc/passwd- are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/passwd- file contains backup user account information.
Rationale:
It is critical to ensure that the /etc/passwd- file is protected from unauthorized access.
Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 600 or
more restrictive:
# stat /etc/passwdAccess: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following command to set permissions on /etc/passwd-:
# chown root:root /etc/passwd# chmod 600 /etc/passwd-
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6.1.7 Ensure permissions on /etc/shadow- are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/shadow- file is used to store backup information about user accounts that is
critical to the security of those accounts, such as the hashed password and other security
information.
Rationale:
It is critical to ensure that the /etc/shadow- file is protected from unauthorized access.
Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 600 or
more restrictive:
# stat /etc/shadowAccess: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following command to set permissions on /etc/shadow-:
# chown root:root /etc/shadow# chmod 600 /etc/shadow-
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6.1.8 Ensure permissions on /etc/group- are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/group- file contains a backup list of all the valid groups defined in the system.
Rationale:
It is critical to ensure that the /etc/group- file is protected from unauthorized access.
Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 600 or
more restrictive:
# stat /etc/groupAccess: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following command to set permissions on /etc/group-:
# chown root:root /etc/group# chmod 600 /etc/group-
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6.1.9 Ensure permissions on /etc/gshadow- are configured (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The /etc/gshadow- file is used to store backup information about groups that is critical to
the security of those accounts, such as the hashed password and other security
information.
Rationale:
It is critical to ensure that the /etc/gshadow- file is protected from unauthorized access.
Although it is protected by default, the file permissions could be changed either
inadvertently or through malicious actions.
Audit:
Run the following command and verify Uid and Gid are both 0/root and Access is 600 or
more restrictive:
# stat /etc/gshadowAccess: (0600/-rw-------)
Uid: (
0/
root)
Gid: (
0/
root)
Remediation:
Run the following command to set permissions on /etc/gshadow-:
# chown root:root /etc/gshadow# chmod 600 /etc/gshadow-
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6.1.10 Ensure no world writable files exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Unix-based systems support variable settings to control access to files. World writable files
are the least secure. See the chmod(2) man page for more information.
Rationale:
Data in world-writable files can be modified and compromised by any user on the system.
World writable files may also indicate an incorrectly written script or program that could
potentially be the cause of a larger compromise to the system's integrity.
Audit:
Run the following command and verify no files are returned:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -type f
-perm -0002
The command above only searches local filesystems, there may still be compromised items
on network mounted partitions. The following command can be run manually for
individual partitions if needed:
# find <partition> -xdev -type f -perm -0002
Remediation:
Removing write access for the "other" category (chmod o-w <filename>) is advisable, but
always consult relevant vendor documentation to avoid breaking any application
dependencies on a given file.
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6.1.11 Ensure no unowned files or directories exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Sometimes when administrators delete users from the password file they neglect to
remove all files owned by those users from the system.
Rationale:
A new user who is assigned the deleted user's user ID or group ID may then end up
"owning" these files, and thus have more access on the system than was intended.
Audit:
Run the following command and verify no files are returned:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -nouser
The command above only searches local filesystems, there may still be compromised items
on network mounted partitions. The following command can be run manually for
individual partitions if needed:
# find <partition> -xdev -nouser
Remediation:
Locate files that are owned by users or groups not listed in the system configuration files,
and reset the ownership of these files to some active user on the system as appropriate.
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6.1.12 Ensure no ungrouped files or directories exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Sometimes when administrators delete users or groups from the system they neglect to
remove all files owned by those users or groups.
Rationale:
A new user who is assigned the deleted user's user ID or group ID may then end up
"owning" these files, and thus have more access on the system than was intended.
Audit:
Run the following command and verify no files are returned:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -nogroup
The command above only searches local filesystems, there may still be compromised items
on network mounted partitions. The following command can be run manually for
individual partitions if needed:
# find <partition> -xdev -nogroup
Remediation:
Locate files that are owned by users or groups not listed in the system configuration files,
and reset the ownership of these files to some active user on the system as appropriate.
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6.1.13 Audit SUID executables (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The owner of a file can set the file's permissions to run with the owner's or group's
permissions, even if the user running the program is not the owner or a member of the
group. The most common reason for a SUID program is to enable users to perform
functions (such as changing their password) that require root privileges.
Rationale:
There are valid reasons for SUID programs, but it is important to identify and review such
programs to ensure they are legitimate.
Audit:
Run the following command to list SUID files:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -type f
-perm -4000
The command above only searches local filesystems, there may still be compromised items
on network mounted partitions. The following command can be run manually for
individual partitions if needed:
# find <partition> -xdev -type f -perm -4000
Remediation:
Ensure that no rogue SUID programs have been introduced into the system. Review the
files returned by the action in the Audit section and confirm the integrity of these binaries.
268 | P a g e
6.1.14 Audit SGID executables (Not Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The owner of a file can set the file's permissions to run with the owner's or group's
permissions, even if the user running the program is not the owner or a member of the
group. The most common reason for a SGID program is to enable users to perform
functions (such as changing their password) that require root privileges.
Rationale:
There are valid reasons for SGID programs, but it is important to identify and review such
programs to ensure they are legitimate. Review the files returned by the action in the audit
section and check to see if system binaries have a different md5 checksum than what from
the package. This is an indication that the binary may have been replaced.
Audit:
Run the following command to list SGID files:
# df --local -P | awk {'if (NR!=1) print $6'} | xargs -I '{}' find '{}' -xdev -type f
-perm -2000
The command above only searches local filesystems, there may still be compromised items
on network mounted partitions. The following command can be run manually for
individual partitions if needed:
# find <partition> -xdev -type f -perm -2000
Remediation:
Ensure that no rogue SGID programs have been introduced into the system. Review the
files returned by the action in the Audit section and confirm the integrity of these binaries.
269 | P a g e
6.2 User and Group Settings
This section provides guidance on securing aspects of the users and groups.
6.2.1 Ensure password fields are not empty (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
An account with an empty password field means that anybody may log in as that user
without providing a password.
Rationale:
All accounts must have passwords or be locked to prevent the account from being used by
an unauthorized user.
Audit:
Run the following command and verify that no output is returned:
# cat /etc/shadow | awk -F: '($2 == "" ) { print $1 " does not have a password "}'
Remediation:
If any accounts in the /etc/shadow file do not have a password, run the following
command to lock the account until it can be determined why it does not have a password:
# passwd -l <username>
Also, check to see if the account is logged in and investigate what it is being used for to
determine if it needs to be forced off.
270 | P a g e
6.2.2 Ensure no legacy "+" entries exist in /etc/passwd (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The character + in various files used to be markers for systems to insert data from NIS
maps at a certain point in a system configuration file. These entries are no longer required
on most systems, but may exist in files that have been imported from other platforms.
Rationale:
These entries may provide an avenue for attackers to gain privileged access on the system.
Audit:
Run the following command and verify that no output is returned:
# grep '^+:' /etc/passwd
Remediation:
Remove any legacy '+' entries from /etc/passwd if they exist.
271 | P a g e
6.2.3 Ensure no legacy "+" entries exist in /etc/shadow (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The character + in various files used to be markers for systems to insert data from NIS
maps at a certain point in a system configuration file. These entries are no longer required
on most systems, but may exist in files that have been imported from other platforms.
Rationale:
These entries may provide an avenue for attackers to gain privileged access on the system.
Audit:
Run the following command and verify that no output is returned:
# grep '^+:' /etc/shadow
Remediation:
Remove any legacy '+' entries from /etc/shadow if they exist.
272 | P a g e
6.2.4 Ensure no legacy "+" entries exist in /etc/group (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The character + in various files used to be markers for systems to insert data from NIS
maps at a certain point in a system configuration file. These entries are no longer required
on most systems, but may exist in files that have been imported from other platforms.
Rationale:
These entries may provide an avenue for attackers to gain privileged access on the system.
Audit:
Run the following command and verify that no output is returned:
# grep '^+:' /etc/group
Remediation:
Remove any legacy '+' entries from /etc/group if they exist.
273 | P a g e
6.2.5 Ensure root is the only UID 0 account (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Any account with UID 0 has superuser privileges on the system.
Rationale:
This access must be limited to only the default root account and only from the system
console. Administrative access must be through an unprivileged account using an approved
mechanism as noted in Item 5.6 Ensure access to the su command is restricted.
Audit:
Run the following command and verify that only "root" is returned:
# cat /etc/passwd | awk -F: '($3 == 0) { print $1 }'
root
Remediation:
Remove any users other than root with UID 0 or assign them a new UID if appropriate.
274 | P a g e
6.2.6 Ensure root PATH Integrity (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The root user can execute any command on the system and could be fooled into executing
programs unintentionally if the PATH is not set correctly.
Rationale:
Including the current working directory (.) or other writable directory in root's executable
path makes it likely that an attacker can gain superuser access by forcing an administrator
operating as root to execute a Trojan horse program.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
if [ "`echo $PATH | grep :: `" != "" ]; then
echo "Empty Directory in PATH (::)"
fi
if [ "`echo $PATH | grep :$`"
echo "Trailing : in PATH"
fi
!= "" ]; then
p=`echo $PATH | sed -e 's/::/:/' -e 's/:$//' -e 's/:/ /g'`
set -- $p
while [ "$1" != "" ]; do
if [ "$1" = "." ]; then
echo "PATH contains ."
shift
continue
fi
if [ -d $1 ]; then
dirperm=`ls -ldH $1 | cut -f1 -d" "`
if [ `echo $dirperm | cut -c6 ` != "-" ]; then
echo "Group Write permission set on directory $1"
fi
if [ `echo $dirperm | cut -c9 ` != "-" ]; then
echo "Other Write permission set on directory $1"
fi
dirown=`ls -ldH $1 | awk '{print $3}'`
if [ "$dirown" != "root" ] ; then
echo $1 is not owned by root
fi
else
echo $1 is not a directory
275 | P a g e
fi
shift
done
Remediation:
Correct or justify any items discovered in the Audit step.
276 | P a g e
6.2.7 Ensure all users' home directories exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Users can be defined in /etc/passwd without a home directory or with a home directory
that does not actually exist.
Rationale:
If the user's home directory does not exist or is unassigned, the user will be placed in "/"
and will not be able to write any files or have local environment variables set.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
cat /etc/passwd | awk -F: '{ print $1 " " $3 " " $6 }' | while read user uid dir; do
if [ $uid -ge 500 -a ! -d "$dir" -a $user != "nfsnobody" ]; then
echo "The home directory ($dir) of user $user does not exist."
fi
done
Remediation:
If any users' home directories do not exist, create them and make sure the respective user
owns the directory. Users without an assigned home directory should be removed or
assigned a home directory as appropriate.
277 | P a g e
6.2.8 Ensure users' home directories permissions are 750 or more
restrictive (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
While the system administrator can establish secure permissions for users' home
directories, the users can easily override these.
Rationale:
Group or world-writable user home directories may enable malicious users to steal or
modify other users' data or to gain another user's system privileges.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for dir in `cat /etc/passwd | egrep -v '(root|halt|sync|shutdown)' | awk -F: '($7 !=
"/sbin/nologin") { print $6 }'`; do
dirperm=`ls -ld $dir | cut -f1 -d" "`
if [ `echo $dirperm | cut -c6 ` != "-" ]; then
echo "Group Write permission set on directory $dir"
fi
if [ `echo $dirperm | cut -c8 ` != "-" ]; then
echo "Other Read permission set on directory $dir"
fi
if [ `echo $dirperm | cut -c9 ` != "-" ]; then
echo "Other Write permission set on directory $dir"
fi
if [ `echo $dirperm | cut -c10 ` != "-" ]; then
echo "Other Execute permission set on directory $dir"
fi
done
Remediation:
Making global modifications to user home directories without alerting the user community
can result in unexpected outages and unhappy users. Therefore, it is recommended that a
monitoring policy be established to report user file permissions and determine the action
to be taken in accordance with site policy.
278 | P a g e
6.2.9 Ensure users own their home directories (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The user home directory is space defined for the particular user to set local environment
variables and to store personal files.
Rationale:
Since the user is accountable for files stored in the user home directory, the user must be
the owner of the directory.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
cat /etc/passwd | awk -F: '{ print $1 " " $3 " " $6 }' | while read user uid dir; do
if [ $uid -ge 500 -a -d "$dir" -a $user != "nfsnobody" ]; then
owner=$(stat -L -c "%U" "$dir")
if [ "$owner" != "$user" ]; then
echo "The home directory ($dir) of user $user is owned by $owner."
fi
fi
done
Remediation:
Change the ownership of any home directories that are not owned by the defined user to
the correct user.
279 | P a g e
6.2.10 Ensure users' dot files are not group or world writable (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
While the system administrator can establish secure permissions for users' "dot" files, the
users can easily override these.
Rationale:
Group or world-writable user configuration files may enable malicious users to steal or
modify other users' data or to gain another user's system privileges.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for dir in `cat /etc/passwd | egrep -v '(root|sync|halt|shutdown)' | awk -F: '($7 !=
"/sbin/nologin") { print $6 }'`; do
for file in $dir/.[A-Za-z0-9]*; do
if [ ! -h "$file" -a -f "$file" ]; then
fileperm=`ls -ld $file | cut -f1 -d" "`
if [ `echo $fileperm | cut -c6
echo "Group Write permission
fi
if [ `echo $fileperm | cut -c9
echo "Other Write permission
fi
fi
done
done
` != "-" ]; then
set on file $file"
` != "-" ]; then
set on file $file"
Remediation:
Making global modifications to users' files without alerting the user community can result
in unexpected outages and unhappy users. Therefore, it is recommended that a monitoring
policy be established to report user dot file permissions and determine the action to be
taken in accordance with site policy.
280 | P a g e
6.2.11 Ensure no users have .forward files (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The .forward file specifies an email address to forward the user's mail to.
Rationale:
Use of the .forward file poses a security risk in that sensitive data may be inadvertently
transferred outside the organization. The .forward file also poses a risk as it can be used
to execute commands that may perform unintended actions.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for dir in `cat /etc/passwd |\
awk -F: '{ print $6 }'`; do
if [ ! -h "$dir/.forward" -a -f "$dir/.forward" ]; then
echo ".forward file $dir/.forward exists"
fi
done
Remediation:
Making global modifications to users' files without alerting the user community can result
in unexpected outages and unhappy users. Therefore, it is recommended that a monitoring
policy be established to report user .forward files and determine the action to be taken in
accordance with site policy.
281 | P a g e
6.2.12 Ensure no users have .netrc files (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
The .netrc file contains data for logging into a remote host for file transfers via FTP.
Rationale:
The .netrc file presents a significant security risk since it stores passwords in
unencrypted form. Even if FTP is disabled, user accounts may have brought over .netrc
files from other systems which could pose a risk to those systems.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for dir in `cat /etc/passwd |\
awk -F: '{ print $6 }'`; do
if [ ! -h "$dir/.netrc" -a -f "$dir/.netrc" ]; then
echo ".netrc file $dir/.netrc exists"
fi
done
Remediation:
Making global modifications to users' files without alerting the user community can result
in unexpected outages and unhappy users. Therefore, it is recommended that a monitoring
policy be established to report user .netrc files and determine the action to be taken in
accordance with site policy.
282 | P a g e
6.2.13 Ensure users' .netrc Files are not group or world accessible
(Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
While the system administrator can establish secure permissions for users' .netrc files,
the users can easily override these.
Rationale:
files may contain unencrypted passwords that may be used to attack other
systems.
.netrc
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for dir in `cat /etc/passwd | egrep -v '(root|sync|halt|shutdown)' | awk -F: '($7 !=
"/sbin/nologin") { print $6 }'`; do
for file in $dir/.netrc; do
if [ ! -h "$file" -a -f "$file" ]; then
fileperm=`ls -ld $file | cut -f1 -d" "`
if [ `echo $fileperm | cut -c5 ` != "-" ]; then
echo "Group Read set on $file"
fi
if [ `echo $fileperm | cut -c6 ` != "-" ]; then
echo "Group Write set on $file"
fi
if [ `echo $fileperm | cut -c7 ` != "-" ]; then
echo "Group Execute set on $file"
fi
if [ `echo $fileperm | cut -c8 ` != "-" ]; then
echo "Other Read set on $file"
fi
if [ `echo $fileperm | cut -c9 ` != "-" ]; then
echo "Other Write set on $file"
fi
if [ `echo $fileperm | cut -c10 ` != "-" ]; then
echo "Other Execute set on $file"
fi
fi
done
done
Remediation:
283 | P a g e
Making global modifications to users' files without alerting the user community can result
in unexpected outages and unhappy users. Therefore, it is recommended that a monitoring
policy be established to report user .netrc file permissions and determine the action to be
taken in accordance with site policy.
Notes:
While the complete removal of .netrc files is recommended if any are required on the
system secure permissions must be applied.
284 | P a g e
6.2.14 Ensure no users have .rhosts files (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
While no .rhosts files are shipped by default, users can easily create them.
Rationale:
This action is only meaningful if .rhosts support is permitted in the file /etc/pam.conf.
Even though the .rhosts files are ineffective if support is disabled in /etc/pam.conf, they
may have been brought over from other systems and could contain information useful to
an attacker for those other systems.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for dir in `cat /etc/passwd
"/sbin/nologin") { print $6
for file in $dir/.rhosts;
if [ ! -h "$file" -a -f
echo ".rhosts file in
fi
done
done
| egrep -v '(root|halt|sync|shutdown)' | awk -F: '($7 !=
}'`; do
do
"$file" ]; then
$dir"
Remediation:
Making global modifications to users' files without alerting the user community can result
in unexpected outages and unhappy users. Therefore, it is recommended that a monitoring
policy be established to report user .rhosts files and determine the action to be taken in
accordance with site policy.
285 | P a g e
6.2.15 Ensure all groups in /etc/passwd exist in /etc/group (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Over time, system administration errors and changes can lead to groups being defined in
/etc/passwd but not in /etc/group.
Rationale:
Groups defined in the /etc/passwd file but not in the /etc/group file pose a threat to
system security since group permissions are not properly managed.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
for i in $(cut -s -d: -f4 /etc/passwd | sort -u ); do
grep -q -P "^.*?:[^:]*:$i:" /etc/group
if [ $? -ne 0 ]; then
echo "Group $i is referenced by /etc/passwd but does not exist in /etc/group"
fi
done
Remediation:
Analyze the output of the Audit step above and perform the appropriate action to correct
any discrepancies found.
286 | P a g e
6.2.16 Ensure no duplicate UIDs exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Although the useradd program will not let you create a duplicate User ID (UID), it is
possible for an administrator to manually edit the /etc/passwd file and change the UID
field.
Rationale:
Users must be assigned unique UIDs for accountability and to ensure appropriate access
protections.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
cat /etc/passwd | cut -f3 -d":" | sort -n | uniq -c | while read x ; do
[ -z "${x}" ] && break
set - $x
if [ $1 -gt 1 ]; then
users=`awk -F: '($3 == n) { print $1 }' n=$2 /etc/passwd | xargs`
echo "Duplicate UID ($2): ${users}"
fi
done
Remediation:
Based on the results of the audit script, establish unique UIDs and review all files owned by
the shared UIDs to determine which UID they are supposed to belong to.
287 | P a g e
6.2.17 Ensure no duplicate GIDs exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Although the groupadd program will not let you create a duplicate Group ID (GID), it is
possible for an administrator to manually edit the /etc/group file and change the GID
field.
Rationale:
User groups must be assigned unique GIDs for accountability and to ensure appropriate
access protections.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
cat /etc/group | cut -f3 -d":" | sort -n | uniq -c | while read x ; do
[ -z "${x}" ] && break
set - $x
if [ $1 -gt 1 ]; then
groups=`awk -F: '($3 == n) { print $1 }' n=$2 /etc/group | xargs`
echo "Duplicate GID ($2): ${groups}"
fi
done
Remediation:
Based on the results of the audit script, establish unique GIDs and review all files owned by
the shared GID to determine which group they are supposed to belong to.
Notes:
You can also use the grpck command to check for other inconsistencies in the /etc/group
file.
288 | P a g e
6.2.18 Ensure no duplicate user names exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Although the useradd program will not let you create a duplicate user name, it is possible
for an administrator to manually edit the /etc/passwd file and change the user name.
Rationale:
If a user is assigned a duplicate user name, it will create and have access to files with the
first UID for that username in /etc/passwd. For example, if "test4" has a UID of 1000 and a
subsequent "test4" entry has a UID of 2000, logging in as "test4" will use UID 1000.
Effectively, the UID is shared, which is a security problem.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
cat /etc/passwd | cut -f1 -d":" | sort -n | uniq -c | while read x ; do
[ -z "${x}" ] && break
set - $x
if [ $1 -gt 1 ]; then
uids=`awk -F: '($1 == n) { print $3 }' n=$2 /etc/passwd | xargs`
echo "Duplicate User Name ($2): ${uids}"
fi
done
Remediation:
Based on the results of the audit script, establish unique user names for the users. File
ownerships will automatically reflect the change as long as the users have unique UIDs.
289 | P a g e
6.2.19 Ensure no duplicate group names exist (Scored)
Profile Applicability:
 Level 1 - Server
 Level 1 - Workstation
Description:
Although the groupadd program will not let you create a duplicate group name, it is
possible for an administrator to manually edit the /etc/group file and change the group
name.
Rationale:
If a group is assigned a duplicate group name, it will create and have access to files with the
first GID for that group in /etc/group. Effectively, the GID is shared, which is a security
problem.
Audit:
Run the following script and verify no results are returned:
#!/bin/bash
cat /etc/group | cut -f1 -d":" | sort -n | uniq -c | while read x ; do
[ -z "${x}" ] && break
set - $x
if [ $1 -gt 1 ]; then
gids=`gawk -F: '($1 == n) { print $3 }' n=$2 /etc/group | xargs`
echo "Duplicate Group Name ($2): ${gids}"
fi
done
Remediation:
Based on the results of the audit script, establish unique names for the user groups. File
group ownerships will automatically reflect the change as long as the groups have unique
GIDs.
290 | P a g e
Control
1
1.1
1.1.1
1.1.1.1
1.1.1.2
1.1.1.3
1.1.1.4
1.1.1.5
1.1.1.6
1.1.1.7
1.1.1.8
1.1.2
1.1.3
1.1.4
1.1.5
1.1.6
1.1.7
1.1.8
1.1.9
1.1.10
1.1.11
1.1.12
1.1.13
1.1.14
1.1.15
1.1.16
1.1.17
1.1.18
1.1.19
1.1.20
1.1.21
1.1.22
1.2
1.2.1
1.2.2
Initial Setup
Filesystem Configuration
Disable unused filesystems
Ensure mounting of cramfs filesystems is disabled (Scored)
Ensure mounting of freevxfs filesystems is disabled (Scored)
Ensure mounting of jffs2 filesystems is disabled (Scored)
Ensure mounting of hfs filesystems is disabled (Scored)
Ensure mounting of hfsplus filesystems is disabled (Scored)
Ensure mounting of squashfs filesystems is disabled (Scored)
Ensure mounting of udf filesystems is disabled (Scored)
Ensure mounting of FAT filesystems is disabled (Scored)
Ensure separate partition exists for /tmp (Scored)
Ensure nodev option set on /tmp partition (Scored)
Ensure nosuid option set on /tmp partition (Scored)
Ensure noexec option set on /tmp partition (Scored)
Ensure separate partition exists for /var (Scored)
Ensure separate partition exists for /var/tmp (Scored)
Ensure nodev option set on /var/tmp partition (Scored)
Ensure nosuid option set on /var/tmp partition (Scored)
Ensure noexec option set on /var/tmp partition (Scored)
Ensure separate partition exists for /var/log (Scored)
Ensure separate partition exists for /var/log/audit (Scored)
Ensure separate partition exists for /home (Scored)
Ensure nodev option set on /home partition (Scored)
Ensure nodev option set on /dev/shm partition (Scored)
Ensure nosuid option set on /dev/shm partition (Scored)
Ensure noexec option set on /dev/shm partition (Scored)
Ensure nodev option set on removable media partitions (Not
Scored)
Ensure nosuid option set on removable media partitions (Not
Scored)
Ensure noexec option set on removable media partitions (Not
Scored)
Ensure sticky bit is set on all world-writable directories
(Scored)
Disable Automounting (Scored)
Configure Software Updates
Ensure package manager repositories are configured (Not
Scored)
Ensure GPG keys are configured (Not Scored)
Set
Correctly
Yes No






























































291 | P a g e
1.2.3
1.3
1.3.1
1.3.2
1.4
1.4.1
1.4.2
1.4.3
1.4.4
1.5
1.5.1
1.5.2
1.5.3
1.5.4
1.6
1.6.1
1.6.1.1
1.6.1.2
1.6.1.3
1.6.1.4
1.6.1.5
1.6.1.6
1.6.2
1.7
1.7.1
1.7.1.1
1.7.1.2
1.7.1.3
1.7.1.4
1.7.1.5
1.7.1.6
1.7.2
1.8
2
Ensure gpgcheck is globally activated (Scored)
Filesystem Integrity Checking
Ensure AIDE is installed (Scored)
Ensure filesystem integrity is regularly checked (Scored)
Secure Boot Settings
Ensure permissions on bootloader config are configured
(Scored)
Ensure bootloader password is set (Scored)
Ensure authentication required for single user mode (Scored)
Ensure interactive boot is not enabled (Scored)
Additional Process Hardening
Ensure core dumps are restricted (Scored)
Ensure XD/NX support is enabled (Not Scored)
Ensure address space layout randomization (ASLR) is enabled
(Scored)
Ensure prelink is disabled (Scored)
Mandatory Access Control
Configure SELinux
Ensure SELinux is not disabled in bootloader configuration
(Scored)
Ensure the SELinux state is enforcing (Scored)
Ensure SELinux policy is configured (Scored)
Ensure SETroubleshoot is not installed (Scored)
Ensure the MCS Translation Service (mcstrans) is not
installed (Scored)
Ensure no unconfined daemons exist (Scored)
Ensure SELinux is installed (Scored)
Warning Banners
Command Line Warning Banners
Ensure message of the day is configured properly (Scored)
Ensure local login warning banner is configured properly
(Not Scored)
Ensure remote login warning banner is configured properly
(Not Scored)
Ensure permissions on /etc/motd are configured (Not
Scored)
Ensure permissions on /etc/issue are configured (Scored)
Ensure permissions on /etc/issue.net are configured (Not
Scored)
Ensure GDM login banner is configured (Scored)
Ensure updates, patches, and additional security software are
installed (Not Scored)
Services
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2.1
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
2.1.7
2.1.8
2.1.9
2.1.10
2.1.11
2.2
2.2.1
2.2.1.1
2.2.1.2
2.2.1.3
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.2.8
2.2.9
2.2.10
2.2.11
2.2.12
2.2.13
2.2.14
2.2.15
2.2.16
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
3
3.1
3.1.1
3.1.2
inetd Services
Ensure chargen services are not enabled (Scored)
Ensure daytime services are not enabled (Scored)
Ensure discard services are not enabled (Scored)
Ensure echo services are not enabled (Scored)
Ensure time services are not enabled (Scored)
Ensure rsh server is not enabled (Scored)
Ensure talk server is not enabled (Scored)
Ensure telnet server is not enabled (Scored)
Ensure tftp server is not enabled (Scored)
Ensure rsync service is not enabled (Scored)
Ensure xinetd is not enabled (Scored)
Special Purpose Services
Time Synchronization
Ensure time synchronization is in use (Not Scored)
Ensure ntp is configured (Scored)
Ensure chrony is configured (Scored)
Ensure X Window System is not installed (Scored)
Ensure Avahi Server is not enabled (Scored)
Ensure CUPS is not enabled (Scored)
Ensure DHCP Server is not enabled (Scored)
Ensure LDAP server is not enabled (Scored)
Ensure NFS and RPC are not enabled (Scored)
Ensure DNS Server is not enabled (Scored)
Ensure FTP Server is not enabled (Scored)
Ensure HTTP server is not enabled (Scored)
Ensure IMAP and POP3 server is not enabled (Scored)
Ensure Samba is not enabled (Scored)
Ensure HTTP Proxy Server is not enabled (Scored)
Ensure SNMP Server is not enabled (Scored)
Ensure mail transfer agent is configured for local-only mode
(Scored)
Ensure NIS Server is not enabled (Scored)
Service Clients
Ensure NIS Client is not installed (Scored)
Ensure rsh client is not installed (Scored)
Ensure talk client is not installed (Scored)
Ensure telnet client is not installed (Scored)
Ensure LDAP client is not installed (Scored)
Network Configuration
Network Parameters (Host Only)
Ensure IP forwarding is disabled (Scored)
Ensure packet redirect sending is disabled (Scored)
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3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.3
3.3.1
3.3.2
3.3.3
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
3.5
3.5.1
3.5.2
3.5.3
3.5.4
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.7
4
4.1
4.1.1
4.1.1.1
4.1.1.2
4.1.1.3
4.1.2
4.1.3
Network Parameters (Host and Router)
Ensure source routed packets are not accepted (Scored)
Ensure ICMP redirects are not accepted (Scored)
Ensure secure ICMP redirects are not accepted (Scored)
Ensure suspicious packets are logged (Scored)
Ensure broadcast ICMP requests are ignored (Scored)
Ensure bogus ICMP responses are ignored (Scored)
Ensure Reverse Path Filtering is enabled (Scored)
Ensure TCP SYN Cookies is enabled (Scored)
IPv6
Ensure IPv6 router advertisements are not accepted (Scored)
Ensure IPv6 redirects are not accepted (Scored)
Ensure IPv6 is disabled (Not Scored)
TCP Wrappers
Ensure TCP Wrappers is installed (Scored)
Ensure /etc/hosts.allow is configured (Scored)
Ensure /etc/hosts.deny is configured (Scored)
Ensure permissions on /etc/hosts.allow are configured
(Scored)
Ensure permissions on /etc/hosts.deny are configured
(Scored)
Uncommon Network Protocols
Ensure DCCP is disabled (Not Scored)
Ensure SCTP is disabled (Not Scored)
Ensure RDS is disabled (Not Scored)
Ensure TIPC is disabled (Not Scored)
Firewall Configuration
Ensure iptables is installed (Scored)
Ensure default deny firewall policy (Scored)
Ensure loopback traffic is configured (Scored)
Ensure outbound and established connections are configured
(Not Scored)
Ensure firewall rules exist for all open ports (Scored)
Ensure wireless interfaces are disabled (Not Scored)
Logging and Auditing
Configure System Accounting (auditd)
Configure Data Retention
Ensure audit log storage size is configured (Not Scored)
Ensure system is disabled when audit logs are full (Scored)
Ensure audit logs are not automatically deleted (Scored)
Ensure auditd service is enabled (Scored)
Ensure auditing for processes that start prior to auditd is
enabled (Scored)
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4.1.4
4.1.5
4.1.6
4.1.7
4.1.8
4.1.9
4.1.10
4.1.11
4.1.12
4.1.13
4.1.14
4.1.15
4.1.16
4.1.17
4.1.18
4.2
4.2.1
4.2.1.1
4.2.1.2
4.2.1.3
4.2.1.4
4.2.1.5
4.2.2
4.2.2.1
4.2.2.2
4.2.2.3
4.2.2.4
4.2.2.5
4.2.3
4.2.4
Ensure events that modify date and time information are
collected (Scored)
Ensure events that modify user/group information are
collected (Scored)
Ensure events that modify the system's network environment
are collected (Scored)
Ensure events that modify the system's Mandatory Access
Controls are collected (Scored)
Ensure login and logout events are collected (Scored)
Ensure session initiation information is collected (Scored)
Ensure discretionary access control permission modification
events are collected (Scored)
Ensure unsuccessful unauthorized file access attempts are
collected (Scored)
Ensure use of privileged commands is collected (Scored)
Ensure successful file system mounts are collected (Scored)
Ensure file deletion events by users are collected (Scored)
Ensure changes to system administration scope (sudoers) is
collected (Scored)
Ensure system administrator actions (sudolog) are collected
(Scored)
Ensure kernel module loading and unloading is collected
(Scored)
Ensure the audit configuration is immutable (Scored)
Configure Logging
Configure rsyslog
Ensure rsyslog Service is enabled (Scored)
Ensure logging is configured (Not Scored)
Ensure rsyslog default file permissions configured (Scored)
Ensure rsyslog is configured to send logs to a remote log host
(Scored)
Ensure remote rsyslog messages are only accepted on
designated log hosts. (Not Scored)
Configure syslog-ng
Ensure syslog-ng service is enabled (Scored)
Ensure logging is configured (Not Scored)
Ensure syslog-ng default file permissions configured (Scored)
Ensure syslog-ng is configured to send logs to a remote log
host (Not Scored)
Ensure remote syslog-ng messages are only accepted on
designated log hosts (Not Scored)
Ensure rsyslog or syslog-ng is installed (Scored)
Ensure permissions on all logfiles are configured (Scored)
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4.3
5
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.6
5.1.7
5.1.8
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
5.2.8
5.2.9
5.2.10
5.2.11
5.2.12
5.2.13
5.2.14
5.2.15
5.2.16
5.3
5.3.1
5.3.2
5.3.3
5.3.4
5.4
5.4.1
Ensure logrotate is configured (Not Scored)
Access, Authentication and Authorization
Configure cron
Ensure cron daemon is enabled (Scored)
Ensure permissions on /etc/crontab are configured (Scored)
Ensure permissions on /etc/cron.hourly are configured
(Scored)
Ensure permissions on /etc/cron.daily are configured
(Scored)
Ensure permissions on /etc/cron.weekly are configured
(Scored)
Ensure permissions on /etc/cron.monthly are configured
(Scored)
Ensure permissions on /etc/cron.d are configured (Scored)
Ensure at/cron is restricted to authorized users (Scored)
SSH Server Configuration
Ensure permissions on /etc/ssh/sshd_config are configured
(Scored)
Ensure SSH Protocol is set to 2 (Scored)
Ensure SSH LogLevel is set to INFO (Scored)
Ensure SSH X11 forwarding is disabled (Scored)
Ensure SSH MaxAuthTries is set to 4 or less (Scored)
Ensure SSH IgnoreRhosts is enabled (Scored)
Ensure SSH HostbasedAuthentication is disabled (Scored)
Ensure SSH root login is disabled (Scored)
Ensure SSH PermitEmptyPasswords is disabled (Scored)
Ensure SSH PermitUserEnvironment is disabled (Scored)
Ensure only approved ciphers are used (Scored)
Ensure only approved MAC algorithms are used (Scored)
Ensure SSH Idle Timeout Interval is configured (Scored)
Ensure SSH LoginGraceTime is set to one minute or less
(Scored)
Ensure SSH access is limited (Scored)
Ensure SSH warning banner is configured (Scored)
Configure PAM
Ensure password creation requirements are configured
(Scored)
Ensure lockout for failed password attempts is configured
(Scored)
Ensure password reuse is limited (Scored)
Ensure password hashing algorithm is SHA-512 (Scored)
User Accounts and Environment
Set Shadow Password Suite Parameters
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5.4.1.1
5.4.1.2
5.4.1.3
5.4.1.4
5.4.2
5.4.3
5.4.4
5.5
5.6
6
6.1
6.1.1
6.1.2
6.1.3
6.1.4
6.1.5
6.1.6
6.1.7
6.1.8
6.1.9
6.1.10
6.1.11
6.1.12
6.1.13
6.1.14
6.2
6.2.1
6.2.2
6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.2.9
6.2.10
6.2.11
6.2.12
Ensure password expiration is 90 days or less (Scored)
Ensure minimum days between password changes is 7 or
more (Scored)
Ensure password expiration warning days is 7 or more
(Scored)
Ensure inactive password lock is 30 days or less (Scored)
Ensure system accounts are non-login (Scored)
Ensure default group for the root account is GID 0 (Scored)
Ensure default user umask is 027 or more restrictive (Scored)
Ensure root login is restricted to system console (Not Scored)
Ensure access to the su command is restricted (Scored)
System Maintenance
System File Permissions
Audit system file permissions (Not Scored)
Ensure permissions on /etc/passwd are configured (Scored)
Ensure permissions on /etc/shadow are configured (Scored)
Ensure permissions on /etc/group are configured (Scored)
Ensure permissions on /etc/gshadow are configured (Scored)
Ensure permissions on /etc/passwd- are configured (Scored)
Ensure permissions on /etc/shadow- are configured (Scored)
Ensure permissions on /etc/group- are configured (Scored)
Ensure permissions on /etc/gshadow- are configured
(Scored)
Ensure no world writable files exist (Scored)
Ensure no unowned files or directories exist (Scored)
Ensure no ungrouped files or directories exist (Scored)
Audit SUID executables (Not Scored)
Audit SGID executables (Not Scored)
User and Group Settings
Ensure password fields are not empty (Scored)
Ensure no legacy "+" entries exist in /etc/passwd (Scored)
Ensure no legacy "+" entries exist in /etc/shadow (Scored)
Ensure no legacy "+" entries exist in /etc/group (Scored)
Ensure root is the only UID 0 account (Scored)
Ensure root PATH Integrity (Scored)
Ensure all users' home directories exist (Scored)
Ensure users' home directories permissions are 750 or more
restrictive (Scored)
Ensure users own their home directories (Scored)
Ensure users' dot files are not group or world writable
(Scored)
Ensure no users have .forward files (Scored)
Ensure no users have .netrc files (Scored)
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6.2.13
6.2.14
6.2.15
6.2.16
6.2.17
6.2.18
6.2.19
Ensure users' .netrc Files are not group or world accessible
(Scored)
Ensure no users have .rhosts files (Scored)
Ensure all groups in /etc/passwd exist in /etc/group (Scored)
Ensure no duplicate UIDs exist (Scored)
Ensure no duplicate GIDs exist (Scored)
Ensure no duplicate user names exist (Scored)
Ensure no duplicate group names exist (Scored)
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Appendix: Change History
Date
Version
Changes for this version
05-03-2016
2.0.0
Initial Release
06-02-2016
2.0.1
2.2.3-14, 2.2.16 - Fixed typos in audit
examples (Tickets #63, #64)
06-02-2016
2.0.1
1.1.21 - Small update to remediation
command (Ticket #55)
06-02-2016
2.0.1
1.5.1 - Fixed typo in remediation
(Ticket #61)
06-02-2016
2.0.1
2.2.3 - Fixed typo in rationale (Ticket
#77)
06-02-2016
2.0.1
3.3.1, 3.3.2 - Fixed typo in audit
examples (Ticket #74)
06-02-2016
2.0.1
2.2.5, 2.2.8-13 - Fixed typo in
remediation (Red Hat Ticket #586)
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