Guide to the Secure Configuration of Red Hat Enterprise Linux 7

with profile Red Hat Corporate Profile for Certified Cloud Providers (RH CCP)
This is a *draft* SCAP profile for Red Hat Certified Cloud Providers

This guide presents a catalog of security-relevant configuration settings for Red Hat Enterprise Linux 7 formatted in the eXtensible Configuration Checklist Description Format (XCCDF).

Providing system administrators with such guidance informs them how to securely configure systems under their control in a variety of network roles. Policy makers and baseline creators can use this catalog of settings, with its associated references to higher-level security control catalogs, in order to assist them in security baseline creation. This guide is a catalog, not a checklist, and satisfaction of every item is not likely to be possible or sensible in many operational scenarios. However, the XCCDF format enables granular selection and adjustment of settings, and their association with OVAL and OCIL content provides an automated checking capability. Transformations of this document, and its associated automated checking content, are capable of providing baselines that meet a diverse set of policy objectives. Some example XCCDF Profiles, which are selections of items that form checklists and can be used as baselines, are available with this guide. They can be processed, in an automated fashion, with tools that support the Security Content Automation Protocol (SCAP). The DISA STIG for Red Hat Enterprise Linux 7 is one example of a baseline created from this guidance.
Do not attempt to implement any of the settings in this guide without first testing them in a non-operational environment. The creators of this guidance assume no responsibility whatsoever for its use by other parties, and makes no guarantees, expressed or implied, about its quality, reliability, or any other characteristic.
Profile TitleRed Hat Corporate Profile for Certified Cloud Providers (RH CCP)
Profile IDxccdf_org.ssgproject.content_profile_rht-ccp

Revision History

Current version: 0.1.26

  • draft (as of 2015-11-25)

Platforms

  • cpe:/o:redhat:enterprise_linux:7
  • cpe:/o:redhat:enterprise_linux:7::client

Table of Contents

  1. System Settings
    1. Installing and Maintaining Software
    2. File Permissions and Masks
    3. SELinux
    4. Account and Access Control
    5. Network Configuration and Firewalls
    6. System Accounting with auditd
  2. Services
    1. Obsolete Services
    2. Base Services
    3. SSH Server

Checklist

contains 67 rules

System Settingsgroup

contains 55 rules

Installing and Maintaining Softwaregroup

The following sections contain information on security-relevant choices during the initial operating system installation process and the setup of software updates.

contains 9 rules

Disk Partitioninggroup

To ensure separation and protection of data, there are top-level system directories which should be placed on their own physical partition or logical volume. The installer's default partitioning scheme creates separate logical volumes for /, /boot, and swap.

  • If starting with any of the default layouts, check the box to "Review and modify partitioning." This allows for the easy creation of additional logical volumes inside the volume group already created, though it may require making /'s logical volume smaller to create space. In general, using logical volumes is preferable to using partitions because they can be more easily adjusted later.
  • If creating a custom layout, create the partitions mentioned in the previous paragraph (which the installer will require anyway), as well as separate ones described in the following sections.
If a system has already been installed, and the default partitioning scheme was used, it is possible but nontrivial to modify it to create separate logical volumes for the directories listed above. The Logical Volume Manager (LVM) makes this possible. See the LVM HOWTO at http://tldp.org/HOWTO/LVM-HOWTO/ for more detailed information on LVM.

contains 4 rules

Ensure /tmp Located On Separate Partitionrule

The /tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

The /tmp partition is used as temporary storage by many programs. Placing /tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.

identifiers:  CCE-27173-4

references:  SC-32, Test attestation on 20120928 by MM

Ensure /var Located On Separate Partitionrule

The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages.

identifiers:  CCE-26404-4

references:  SC-32, Test attestation on 20120928 by MM

Ensure /var/log Located On Separate Partitionrule

System logs are stored in the /var/log directory. Ensure that it has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Placing /var/log in its own partition enables better separation between log files and other files in /var/.

identifiers:  CCE-26967-0

references:  AU-9, SC-32, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20120928 by MM

Ensure /var/log/audit Located On Separate Partitionrule

Audit logs are stored in the /var/log/audit directory. Ensure that it has its own partition or logical volume at installation time, or migrate it later using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon.

Rationale:

Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.

identifiers:  CCE-26971-2

references:  AU-4, AU-9, SC-32, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20120928 by MM

Updating Softwaregroup

The yum command line tool is used to install and update software packages. The system also provides a graphical software update tool in the System menu, in the Administration submenu, called Software Update.

Red Hat Enterprise Linux systems contain an installed software catalog called the RPM database, which records metadata of installed packages. Consistently using yum or the graphical Software Update for all software installation allows for insight into the current inventory of installed software on the system.

contains 4 rules

Ensure Red Hat GPG Key Installedrule

To ensure the system can cryptographically verify base software packages come from Red Hat (and to connect to the Red Hat Network to receive them), the Red Hat GPG key must properly be installed. To install the Red Hat GPG key, run: 

$ sudo rhn_register
If the system is not connected to the Internet or an RHN Satellite, then install the Red Hat GPG key from trusted media such as the Red Hat installation CD-ROM or DVD. Assuming the disc is mounted in /media/cdrom, use the following command as the root user to import it into the keyring: 
$ sudo rpm --import /media/cdrom/RPM-GPG-KEY

Rationale:

Changes to software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor. The Red Hat GPG key is necessary to cryptographically verify packages are from Red Hat.

identifiers:  CCE-26957-1

references:  CM-5(3), SI-7, MA-1(b), 1749, 366, Req-5, Test attestation on 20150407 by sdw

Remediation script:
# The two fingerprints below are retrieved from https://access.redhat.com/security/team/key
readonly REDHAT_RELEASE_2_FINGERPRINT="567E 347A D004 4ADE 55BA 8A5F 199E 2F91 FD43 1D51"
readonly REDHAT_AUXILIARY_FINGERPRINT="43A6 E49C 4A38 F4BE 9ABF 2A53 4568 9C88 2FA6 58E0"
# Location of the key we would like to import (once it's integrity verified)
readonly REDHAT_RELEASE_KEY="/etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release"

RPM_GPG_DIR_PERMS=$(stat -c %a "$(dirname "$REDHAT_RELEASE_KEY")")

# Verify /etc/pki/rpm-gpg directory permissions are safe
if [ "${RPM_GPG_DIR_PERMS}" -le "755" ]
then
  # If they are safe, try to obtain fingerprints from the key file
  # (to ensure there won't be e.g. CRC error)
  IFS=$'\n' GPG_OUT=($(gpg --with-fingerprint "${REDHAT_RELEASE_KEY}"))
  GPG_RESULT=$?
  # No CRC error, safe to proceed
  if [ "${GPG_RESULT}" -eq "0" ]
  then
    for ITEM in "${GPG_OUT[@]}"
    do
      # Filter just hexadecimal fingerprints from gpg's output from
      # processing of a key file
      RESULT=$(echo ${ITEM} | sed -n "s/[[:space:]]*Key fingerprint = \(.*\)/\1/p" | tr -s '[:space:]')
      # If fingerprint matches Red Hat's release 2 or auxiliary key import the key
      if [[ ${RESULT} ]] && ([[ ${RESULT} = "${REDHAT_RELEASE_2_FINGERPRINT}" ]] || \
                             [[ ${RESULT} = "${REDHAT_AUXILIARY_FINGERPRINT}" ]])
      then
        rpm --import "${REDHAT_RELEASE_KEY}"
      fi
    done
  fi
fi

Ensure gpgcheck Enabled In Main Yum Configurationrule

The gpgcheck option controls whether RPM packages' signatures are always checked prior to installation. To configure yum to check package signatures before installing them, ensure the following line appears in /etc/yum.conf in the [main] section: 

gpgcheck=1

Rationale:

Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).

identifiers:  CCE-26989-4

references:  CM-5(3), SI-7, MA-1(b), 1749, 366, Req-5, Test attestation on 20150407 by sdw

Remediation script:
sed -i 's/gpgcheck=.*/gpgcheck=1/g' /etc/yum.conf

Ensure gpgcheck Enabled For All Yum Package Repositoriesrule

To ensure signature checking is not disabled for any repos, remove any lines from files in /etc/yum.repos.d of the form: 

gpgcheck=0

Rationale:

Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).

identifiers:  CCE-26876-3

references:  CM-5(3), SI-7, MA-1(b), 1749, 366, Req-5, Test attestation on 20150407 by sdw

Remediation script:
sed -i 's/gpgcheck=.*/gpgcheck=1/g' /etc/yum.repos.d/*

Ensure Software Patches Installedrule

If the system is joined to the Red Hat Network, a Red Hat Satellite Server, or a yum server, run the following command to install updates: 

$ sudo yum update
If the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from the Red Hat Network and installed using rpm.

Rationale:

Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities.

identifiers:  CCE-26895-3

references:  SI-2, MA-1(b), http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-6, Test attestation on 20120928 by MM

Software Integrity Checkinggroup

Both the AIDE (Advanced Intrusion Detection Environment) software and the RPM package management system provide mechanisms for verifying the integrity of installed software. AIDE uses snapshots of file metadata (such as hashes) and compares these to current system files in order to detect changes. The RPM package management system can conduct integrity checks by comparing information in its metadata database with files installed on the system.

Integrity checking cannot prevent intrusions, but can detect that they have occurred. Requirements for software integrity checking may be highly dependent on the environment in which the system will be used. Snapshot-based approaches such as AIDE may induce considerable overhead in the presence of frequent software updates.

contains 1 rule

Verify Integrity with AIDEgroup

AIDE conducts integrity checks by comparing information about files with previously-gathered information. Ideally, the AIDE database is created immediately after initial system configuration, and then again after any software update. AIDE is highly configurable, with further configuration information located in /usr/share/doc/aide-VERSION.

contains 1 rule

Install AIDErule

Install the AIDE package with the command: 

$ sudo yum install aide

Rationale:

The AIDE package must be installed if it is to be available for integrity checking.

identifiers:  CCE-27096-7

references:  CM-3(d), CM-3(e), CM-6(d), CM-6(3), SC-28, SI-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-11, Test attestation on 20121024 by DS

Remediation script:
yum -y install aide

File Permissions and Masksgroup

Traditional Unix security relies heavily on file and directory permissions to prevent unauthorized users from reading or modifying files to which they should not have access.

Several of the commands in this section search filesystems for files or directories with certain characteristics, and are intended to be run on every local partition on a given system. When the variable PART appears in one of the commands below, it means that the command is intended to be run repeatedly, with the name of each local partition substituted for PART in turn.

The following command prints a list of all xfs partitions on the local system, which is the default filesystem for Red Hat Enterprise Linux 7 installations: 

$ mount -t xfs | awk '{print $3}'
For any systems that use a different local filesystem type, modify this command as appropriate.

contains 16 rules

Verify Permissions on Important Files and Directoriesgroup

Permissions for many files on a system must be set restrictively to ensure sensitive information is properly protected. This section discusses important permission restrictions which can be verified to ensure that no harmful discrepancies have arisen.

contains 16 rules
contains 12 rules

Verify User Who Owns shadow Filerule

To properly set the owner of /etc/shadow, run the command: 

$ sudo chown root /etc/shadow

Rationale:

The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.

identifiers:  CCE-26795-5

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chown root /etc/shadow

Verify Group Who Owns shadow Filerule

To properly set the group owner of /etc/shadow, run the command: 

$ sudo chgrp root xsl:value-of select="@file"/>

Rationale:

The /etc/shadow file stores password hashes. Protection of this file is critical for system security.

identifiers:  CCE-27125-4

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chgrp root /etc/shadow

Verify Permissions on shadow Filerule

To properly set the permissions of /etc/shadow, run the command: 

$ sudo chmod 0000 /etc/shadow

Rationale:

The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.

identifiers:  CCE-27100-7

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chmod 0000 /etc/shadow

Verify User Who Owns group Filerule

To properly set the owner of /etc/group, run the command: 

$ sudo chown root /etc/group

Rationale:

The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

identifiers:  CCE-26933-2

references:  AC-6, Req-8, Test attestation on 20121026 by DS

Remediation script:
chown root /etc/group

Verify Group Who Owns group Filerule

To properly set the group owner of /etc/group, run the command: 

$ sudo chgrp root xsl:value-of select="@file"/>

Rationale:

The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

identifiers:  CCE-27037-1

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chgrp root /etc/group

Verify Permissions on group Filerule

To properly set the permissions of /etc/group, run the command: 

$ sudo chmod 644 /etc/group

Rationale:

The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

identifiers:  CCE-26949-8

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chmod 644 /etc/group

Verify User Who Owns gshadow Filerule

To properly set the owner of /etc/gshadow, run the command: 

$ sudo chown root /etc/gshadow

Rationale:

The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.

identifiers:  CCE-27161-9

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121026 by DS

Remediation script:
chown root /etc/gshadow

Verify Group Who Owns gshadow Filerule

To properly set the group owner of /etc/gshadow, run the command: 

$ sudo chgrp root xsl:value-of select="@file"/>

Rationale:

The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.

identifiers:  CCE-26840-9

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121026 by DS

Remediation script:
chgrp root /etc/gshadow

Verify Permissions on gshadow Filerule

To properly set the permissions of /etc/gshadow, run the command: 

$ sudo chmod 0000 /etc/gshadow

Rationale:

The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.

identifiers:  CCE-27162-7

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121026 by DS

Remediation script:
chmod 0000 /etc/gshadow

Verify User Who Owns passwd Filerule

To properly set the owner of /etc/passwd, run the command: 

$ sudo chown root /etc/passwd

Rationale:

The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security.

identifiers:  CCE-27138-7

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chown root /etc/passwd

Verify Group Who Owns passwd Filerule

To properly set the group owner of /etc/passwd, run the command: 

$ sudo chgrp root xsl:value-of select="@file"/>

Rationale:

The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security.

identifiers:  CCE-26639-5

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chgrp root /etc/passwd

Verify Permissions on passwd Filerule

To properly set the permissions of /etc/passwd, run the command: 

$ sudo chmod 0644 /etc/passwd

Rationale:

If the /etc/passwd file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security.

identifiers:  CCE-26887-0

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Remediation script:
chmod 0644 /etc/passwd

Verify File Permissions Within Some Important Directoriesgroup

Some directories contain files whose confidentiality or integrity is notably important and may also be susceptible to misconfiguration over time, particularly if unpackaged software is installed. As such, an argument exists to verify that files' permissions within these directories remain configured correctly and restrictively.

contains 4 rules

Verify that Shared Library Files Have Restrictive Permissionsrule

System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: 

/lib
/lib64
/usr/lib
/usr/lib64
Kernel modules, which can be added to the kernel during runtime, are stored in /lib/modules. All files in these directories should not be group-writable or world-writable. If any file in these directories is found to be group-writable or world-writable, correct its permission with the following command: 
$ sudo chmod go-w FILE

Rationale:

Files from shared library directories are loaded into the address space of processes (including privileged ones) or of the kernel itself at runtime. Restrictive permissions are necessary to protect the integrity of the system.

identifiers:  CCE-26966-2

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121026 by DS

Remediation script:
DIRS="/lib /lib64 /usr/lib /usr/lib64"
for dirPath in $DIRS; do
	find "$dirPath" -perm /022 -type f -exec chmod go-w '{}' \;
done

Verify that Shared Library Files Have Root Ownershiprule

System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: 

/lib
/lib64
/usr/lib
/usr/lib64
Kernel modules, which can be added to the kernel during runtime, are also stored in /lib/modules. All files in these directories should be owned by the root user. If the directory, or any file in these directories, is found to be owned by a user other than root correct its ownership with the following command: 
$ sudo chown root FILE

Rationale:

Files from shared library directories are loaded into the address space of processes (including privileged ones) or of the kernel itself at runtime. Proper ownership is necessary to protect the integrity of the system.

identifiers:  CCE-26648-6

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20130914 by swells

Remediation script:
for LIBDIR in /usr/lib /usr/lib64 /lib /lib64
do
  if [ -d $LIBDIR ]
  then
    find -L $LIBDIR \! -user root -exec chown root {} \; 
  fi
done

Verify that System Executables Have Restrictive Permissionsrule

System executables are stored in the following directories by default: 

/bin
/sbin
/usr/bin
/usr/libexec
/usr/local/bin
/usr/local/sbin
/usr/sbin
All files in these directories should not be group-writable or world-writable. If any file FILE in these directories is found to be group-writable or world-writable, correct its permission with the following command: 
$ sudo chmod go-w FILE

Rationale:

System binaries are executed by privileged users, as well as system services, and restrictive permissions are necessary to ensure execution of these programs cannot be co-opted.

identifiers:  CCE-27075-1

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx

Remediation script:
DIRS="/bin /usr/bin /usr/local/bin /sbin /usr/sbin /usr/local/sbin /usr/libexec"
for dirPath in $DIRS; do
	find "$dirPath" -perm /022 -exec chmod go-w '{}' \;
done

Verify that System Executables Have Root Ownershiprule

System executables are stored in the following directories by default: 

/bin
/sbin
/usr/bin
/usr/libexec
/usr/local/bin
/usr/local/sbin
/usr/sbin
All files in these directories should be owned by the root user. If any file FILE in these directories is found to be owned by a user other than root, correct its ownership with the following command: 
$ sudo chown root FILE

Rationale:

System binaries are executed by privileged users as well as system services, and restrictive permissions are necessary to ensure that their execution of these programs cannot be co-opted.

identifiers:  CCE-27119-7

references:  AC-6, http://iase.disa.mil/stigs/cci/Pages/index.aspx

Remediation script:
find /bin/ \
/usr/bin/ \
/usr/local/bin/ \
/sbin/ \
/usr/sbin/ \
/usr/local/sbin/ \
/usr/libexec \
\! -user root -execdir chown root {} \;

SELinuxgroup

SELinux is a feature of the Linux kernel which can be used to guard against misconfigured or compromised programs. SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take.

The default SELinux policy, as configured on Red Hat Enterprise Linux 7, has been sufficiently developed and debugged that it should be usable on almost any Red Hat machine with minimal configuration and a small amount of system administrator training. This policy prevents system services - including most of the common network-visible services such as mail servers, FTP servers, and DNS servers - from accessing files which those services have no valid reason to access. This action alone prevents a huge amount of possible damage from network attacks against services, from trojaned software, and so forth.

This guide recommends that SELinux be enabled using the default (targeted) policy on every Red Hat system, unless that system has unusual requirements which make a stronger policy appropriate.

contains 2 rules

Ensure SELinux State is Enforcingrule

The SELinux state should be set to enforcing at system boot time. In the file /etc/selinux/config, add or correct the following line to configure the system to boot into enforcing mode: 

SELINUX=enforcing

Rationale:

Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.

identifiers:  CCE-27334-2

references:  AC-3, AC-3(3), AC-4, AC-6, AU-9, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
var_selinux_state="enforcing"
grep -q ^SELINUX= /etc/selinux/config && \
  sed -i "s/SELINUX=.*/SELINUX=$var_selinux_state/g" /etc/selinux/config
if ! [ $? -eq 0 ]; then
    echo "SELINUX=$var_selinux_state" >> /etc/selinux/config
fi

Configure SELinux Policyrule

The SELinux targeted policy is appropriate for general-purpose desktops and servers, as well as systems in many other roles. To configure the system to use this policy, add or correct the following line in /etc/selinux/config: 

SELINUXTYPE=targeted
Other policies, such as mls, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases.

Rationale:

Setting the SELinux policy to targeted or a more specialized policy ensures the system will confine processes that are likely to be targeted for exploitation, such as network or system services. Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in permissive mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to targeted.

identifiers:  CCE-27279-9

references:  AC-3, AC-3(3), AC-4, AC-6, AU-9, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
var_selinux_policy_name="targeted"
grep -q ^SELINUXTYPE /etc/selinux/config && \
  sed -i "s/SELINUXTYPE=.*/SELINUXTYPE=$var_selinux_policy_name/g" /etc/selinux/config
if ! [ $? -eq 0 ]; then
    echo "SELINUXTYPE=$var_selinux_policy_name" >> /etc/selinux/config
fi

Account and Access Controlgroup

In traditional Unix security, if an attacker gains shell access to a certain login account, they can perform any action or access any file to which that account has access. Therefore, making it more difficult for unauthorized people to gain shell access to accounts, particularly to privileged accounts, is a necessary part of securing a system. This section introduces mechanisms for restricting access to accounts under Red Hat Enterprise Linux 7.

contains 23 rules

Protect Accounts by Restricting Password-Based Logingroup

Conventionally, Unix shell accounts are accessed by providing a username and password to a login program, which tests these values for correctness using the /etc/passwd and /etc/shadow files. Password-based login is vulnerable to guessing of weak passwords, and to sniffing and man-in-the-middle attacks against passwords entered over a network or at an insecure console. Therefore, mechanisms for accessing accounts by entering usernames and passwords should be restricted to those which are operationally necessary.

contains 7 rules

Restrict Root Loginsgroup

Direct root logins should be allowed only for emergency use. In normal situations, the administrator should access the system via a unique unprivileged account, and then use su or sudo to execute privileged commands. Discouraging administrators from accessing the root account directly ensures an audit trail in organizations with multiple administrators. Locking down the channels through which root can connect directly also reduces opportunities for password-guessing against the root account. The login program uses the file /etc/securetty to determine which interfaces should allow root logins. The virtual devices /dev/console and /dev/tty* represent the system consoles (accessible via the Ctrl-Alt-F1 through Ctrl-Alt-F6 keyboard sequences on a default installation). The default securetty file also contains /dev/vc/*. These are likely to be deprecated in most environments, but may be retained for compatibility. Root should also be prohibited from connecting via network protocols. Other sections of this document include guidance describing how to prevent root from logging in via SSH.

contains 2 rules

Ensure that System Accounts Do Not Run a Shell Upon Loginrule

Some accounts are not associated with a human user of the system, and exist to perform some administrative function. Should an attacker be able to log into these accounts, they should not be granted access to a shell.

The login shell for each local account is stored in the last field of each line in /etc/passwd. System accounts are those user accounts with a user ID less than 1000. The user ID is stored in the third field. If any system account SYSACCT (other than root) has a login shell, disable it with the command: 

$ sudo usermod -s /sbin/nologin SYSACCT

warning  Do not perform the steps in this section on the root account. Doing so might cause the system to become inaccessible.
Rationale:

Ensuring shells are not given to system accounts upon login makes it more difficult for attackers to make use of system accounts.

identifiers:  CCE-26448-1

references:  AC-2, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Verify Only Root Has UID 0rule

If any account other than root has a UID of 0, this misconfiguration should be investigated and the accounts other than root should be removed or have their UID changed.

Rationale:

An account has root authority if it has a UID of 0. Multiple accounts with a UID of 0 afford more opportunity for potential intruders to guess a password for a privileged account. Proper configuration of sudo is recommended to afford multiple system administrators access to root privileges in an accountable manner.

identifiers:  CCE-27175-9

references:  AC-6, IA-2(1), http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
awk -F: '$3 == 0 && $1 != "root" { print $1 }' /etc/passwd | xargs passwd -l

Verify Proper Storage and Existence of Password Hashesgroup

By default, password hashes for local accounts are stored in the second field (colon-separated) in /etc/shadow. This file should be readable only by processes running with root credentials, preventing users from casually accessing others' password hashes and attempting to crack them. However, it remains possible to misconfigure the system and store password hashes in world-readable files such as /etc/passwd, or to even store passwords themselves in plaintext on the system. Using system-provided tools for password change/creation should allow administrators to avoid such misconfiguration.

contains 2 rules

Prevent Log In to Accounts With Empty Passwordrule

If an account is configured for password authentication but does not have an assigned password, it may be possible to log into the account without authentication. Remove any instances of the nullok option in /etc/pam.d/system-auth to prevent logins with empty passwords.

Rationale:

If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.

identifiers:  CCE-27286-4

references:  IA-5(b), IA-5(c), IA-5(1)(a), Req-8, Test attestation on 20121024 by DS

Remediation script:
sed -i 's/\<nullok\>//g' /etc/pam.d/system-auth

Verify All Account Password Hashes are Shadowedrule

If any password hashes are stored in /etc/passwd (in the second field, instead of an x), the cause of this misconfiguration should be investigated. The account should have its password reset and the hash should be properly stored, or the account should be deleted entirely.

Rationale:

The hashes for all user account passwords should be stored in the file /etc/shadow and never in /etc/passwd, which is readable by all users.

identifiers:  CCE-27352-4

references:  IA-5(h), http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121024 by DS

Set Password Expiration Parametersgroup

The file /etc/login.defs controls several password-related settings. Programs such as passwd, su, and login consult /etc/login.defs to determine behavior with regard to password aging, expiration warnings, and length. See the man page login.defs(5) for more information.

Users should be forced to change their passwords, in order to decrease the utility of compromised passwords. However, the need to change passwords often should be balanced against the risk that users will reuse or write down passwords if forced to change them too often. Forcing password changes every 90-360 days, depending on the environment, is recommended. Set the appropriate value as PASS_MAX_DAYS and apply it to existing accounts with the -M flag.

The PASS_MIN_DAYS (-m) setting prevents password changes for 7 days after the first change, to discourage password cycling. If you use this setting, train users to contact an administrator for an emergency password change in case a new password becomes compromised. The PASS_WARN_AGE (-W) setting gives users 7 days of warnings at login time that their passwords are about to expire.

For example, for each existing human user USER, expiration parameters could be adjusted to a 180 day maximum password age, 7 day minimum password age, and 7 day warning period with the following command: 

$ sudo chage -M 180 -m 7 -W 7 USER

contains 3 rules

Protect Accounts by Configuring PAMgroup

PAM, or Pluggable Authentication Modules, is a system which implements modular authentication for Linux programs. PAM provides a flexible and configurable architecture for authentication, and it should be configured to minimize exposure to unnecessary risk. This section contains guidance on how to accomplish that.

PAM is implemented as a set of shared objects which are loaded and invoked whenever an application wishes to authenticate a user. Typically, the application must be running as root in order to take advantage of PAM, because PAM's modules often need to be able to access sensitive stores of account information, such as /etc/shadow. Traditional privileged network listeners (e.g. sshd) or SUID programs (e.g. sudo) already meet this requirement. An SUID root application, userhelper, is provided so that programs which are not SUID or privileged themselves can still take advantage of PAM.

PAM looks in the directory /etc/pam.d for application-specific configuration information. For instance, if the program login attempts to authenticate a user, then PAM's libraries follow the instructions in the file /etc/pam.d/login to determine what actions should be taken.

One very important file in /etc/pam.d is /etc/pam.d/system-auth. This file, which is included by many other PAM configuration files, defines 'default' system authentication measures. Modifying this file is a good way to make far-reaching authentication changes, for instance when implementing a centralized authentication service.

warning  Be careful when making changes to PAM's configuration files. The syntax for these files is complex, and modifications can have unexpected consequences. The default configurations shipped with applications should be sufficient for most users.
warning  Running authconfig or system-config-authentication will re-write the PAM configuration files, destroying any manually made changes and replacing them with a series of system defaults. One reference to the configuration file syntax can be found at http://www.kernel.org/pub/linux/libs/pam/Linux-PAM-html/sag-configuration-file.html.
contains 11 rules

Set Password Quality Requirementsgroup

The default pam_pwquality PAM module provides strength checking for passwords. It performs a number of checks, such as making sure passwords are not similar to dictionary words, are of at least a certain length, are not the previous password reversed, and are not simply a change of case from the previous password. It can also require passwords to be in certain character classes. The pam_pwquality module is the preferred way of configuring password requirements.

The pam_cracklib PAM module can also provide strength checking for passwords as the pam_pwquality module. It performs a number of checks, such as making sure passwords are not similar to dictionary words, are of at least a certain length, are not the previous password reversed, and are not simply a change of case from the previous password. It can also require passwords to be in certain character classes.

The man pages pam_pwquality(8) and pam_cracklib(8) provide information on the capabilities and configuration of each.

contains 6 rules

Set Password Quality Requirements with pam_pwqualitygroup

The pam_pwquality PAM module can be configured to meet requirements for a variety of policies.

For example, to configure pam_pwquality to require at least one uppercase character, lowercase character, digit, and other (special) character, make sure that pam_pwquality exists in /etc/pam.d/system-auth: 

password    requisite     pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type=
If no such line exists, add one as the first line of the password section in /etc/pam.d/system-auth. Next, modify the settings in /etc/security/pwquality.conf to match the following: 
difok = 4
minlen = 14
dcredit = -1
ucredit = -1
lcredit = -1
ocredit = -1
maxrepeat = 3
The arguments can be modified to ensure compliance with your organization's security policy. Discussion of each parameter follows.

warning  Note that the password quality requirements are not enforced for the root account for some reason.
contains 6 rules

Set Password Retry Prompts Permitted Per-Sessionrule

To configure the number of retry prompts that are permitted per-session:

Edit the pam_pwquality.so statement in /etc/pam.d/system-auth to show retry=3, or a lower value if site policy is more restrictive.

The DoD requirement is a maximum of 3 prompts per session.

Rationale:

Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks. Note that this is different from account lockout, which is provided by the pam_faillock module.

identifiers:  CCE-27160-1

references:  IA-5(c), http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20140925 by swells

Remediation script:
var_password_pam_retry="3"
if grep -q "retry=" /etc/pam.d/system-auth; then   
	sed -i --follow-symlink "s/\(retry *= *\).*/\1$var_password_pam_retry/" /etc/pam.d/system-auth
else
	sed -i --follow-symlink "/pam_pwquality.so/ s/$/ retry=$var_password_pam_retry/" /etc/pam.d/system-auth
fi

Set Password Strength Minimum Digit Charactersrule

The pam_pwquality module's dcredit parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_pwquality will grant +1 additional length credit for each digit. Modify the dcredit setting in /etc/security/pwquality.conf to require the use of a digit in passwords.

Rationale:

Requiring digits makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27214-6

references:  IA-5(b), IA-5(c), 194, 194, 71, Req-8, Test attestation on 20121024 by DS

Remediation script:
var_password_pam_dcredit="1"
if egrep -q ^dcredit[[:space:]]*=[[:space:]]*[-]?[[:digit:]]+ /etc/security/pwquality.conf; then
	sed -i "s/^\(dcredit *= *\).*/\1$var_password_pam_dcredit/" /etc/security/pwquality.conf
else
	sed -i "/\(dcredit *= *\).*/a dcredit = $var_password_pam_dcredit" /etc/security/pwquality.conf
fi

Set Password Strength Minimum Uppercase Charactersrule

The pam_pwquality module's ucredit= parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each uppercase character. Modify the ucredit setting in /etc/security/pwquality.conf to require the use of an uppercase character in passwords.

Rationale:

Requiring a minimum number of uppercase characters makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27200-5

references:  IA-5(b), IA-5(c), IA-5(1)(a), 192, 69, Req-8, Test attestation on 20121024 by DS

Remediation script:
var_password_pam_ucredit="2"
if egrep -q ^ucredit[[:space:]]*=[[:space:]]*[-]?[[:digit:]]+ /etc/security/pwquality.conf; then
	sed -i "s/^\(ucredit *= *\).*/\1$var_password_pam_ucredit/" /etc/security/pwquality.conf
else
	sed -i "/\(ucredit *= *\).*/a ucredit = $var_password_pam_ucredit" /etc/security/pwquality.conf
fi

Set Password Strength Minimum Special Charactersrule

The pam_pwquality module's ocredit= parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each special character. Modify the ocredit setting in /etc/security/pwquality.conf to equal 2 to require use of a special character in passwords.

Rationale:

Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27360-7

references:  IA-5(b), IA-5(c), IA-5(1)(a), 1619, 266, Test attestation on 20121024 by DS

Remediation script:
var_password_pam_ocredit="2"
if egrep -q ^ocredit[[:space:]]*=[[:space:]]*[-]?[[:digit:]]+ /etc/security/pwquality.conf; then
	sed -i "s/^\(ocredit *= *\).*/\1$var_password_pam_ocredit/" /etc/security/pwquality.conf
else
	sed -i "/\(ocredit *= *\).*/a ocredit = $var_password_pam_ocredit" /etc/security/pwquality.conf
fi

Set Password Strength Minimum Lowercase Charactersrule

The pam_pwquality module's lcredit parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each lowercase character. Modify the lcredit setting in /etc/security/pwquality.conf to require the use of a lowercase character in passwords.

Rationale:

Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27345-8

references:  IA-5(b), IA-5(c), IA-5(1)(a), 193, 70, Req-8, Test attestation on 20121024 by DS

Remediation script:
var_password_pam_lcredit="2"
if egrep -q ^lcredit[[:space:]]*=[[:space:]]*[-]?[[:digit:]]+ /etc/security/pwquality.conf; then
	sed -i "s/^\(lcredit *= *\).*/\1$var_password_pam_lcredit/" /etc/security/pwquality.conf
else
	sed -i "/\(lcredit *= *\).*/a lcredit = $var_password_pam_lcredit" /etc/security/pwquality.conf
fi

Set Password Strength Minimum Different Charactersrule

The pam_pwquality module's difok parameter controls requirements for usage of different characters during a password change. Modify the difok setting in /etc/security/pwquality.conf to equal 3 to require differing characters when changing passwords. The DoD requirement is 4.

Rationale:

Requiring a minimum number of different characters during password changes ensures that newly changed passwords should not resemble previously compromised ones. Note that passwords which are changed on compromised systems will still be compromised, however.

identifiers:  CCE-26631-2

references:  IA-5(b), IA-5(c), IA-5(1)(b), 195, 72, Test attestation on 20121024 by DS

Remediation script:
var_password_pam_difok="3"
if egrep -q ^difok[[:space:]]*=[[:space:]]*[-]?[[:digit:]]+ /etc/security/pwquality.conf; then
	sed -i "s/^\(difok *= *\).*/\1$var_password_pam_difok/" /etc/security/pwquality.conf
else
	sed -i "/\(difok *= *\).*/a difok = $var_password_pam_difok" /etc/security/pwquality.conf
fi

Set Lockouts for Failed Password Attemptsgroup

The pam_faillock PAM module provides the capability to lock out user accounts after a number of failed login attempts. Its documentation is available in /usr/share/doc/pam-VERSION/txts/README.pam_faillock.

warning  Locking out user accounts presents the risk of a denial-of-service attack. The lockout policy must weigh whether the risk of such a denial-of-service attack outweighs the benefits of thwarting password guessing attacks.
contains 2 rules

Set Deny For Failed Password Attemptsrule

To configure the system to lock out accounts after a number of incorrect login attempts using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • add the following line immediately before the pam_unix.so statement in the AUTH section: 
    auth required pam_faillock.so preauth silent deny=5 unlock_time=604800 fail_interval=900
  • add the following line immediately after the pam_unix.so statement in the AUTH section: 
    auth [default=die] pam_faillock.so authfail deny=5 unlock_time=604800 fail_interval=900
  • add the following line immediately before the pam_unix.so statement in the ACCOUNT section: 
    account required pam_faillock.so

Rationale:

Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks.

identifiers:  CCE-27350-8

references:  AC-7(a), 44, 21, Req-8

Remediation script:
var_accounts_passwords_pam_faillock_deny="5"
AUTH_FILES[0]="/etc/pam.d/system-auth"
AUTH_FILES[1]="/etc/pam.d/password-auth"

for pamFile in "${AUTH_FILES[@]}"
do
	
	# pam_faillock.so already present?
	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

		# pam_faillock.so present, deny directive present?
		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*deny=" $pamFile; then

			# both pam_faillock.so & deny present, just correct deny directive value
			sed -i --follow-symlink "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(deny *= *\).*/\1\2$var_accounts_passwords_pam_faillock_deny/" $pamFile
			sed -i --follow-symlink "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(deny *= *\).*/\1\2$var_accounts_passwords_pam_faillock_deny/" $pamFile

		# pam_faillock.so present, but deny directive not yet
		else

			# append correct deny value to appropriate places
			sed -i --follow-symlink "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ deny=$var_accounts_passwords_pam_faillock_deny/" $pamFile
			sed -i --follow-symlink "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ deny=$var_accounts_passwords_pam_faillock_deny/" $pamFile
		fi

	# pam_faillock.so not present yet
	else

		# insert pam_faillock.so preauth & authfail rows with proper value of the 'deny' option
		sed -i --follow-symlink "/^auth.*sufficient.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent deny=$var_accounts_passwords_pam_faillock_deny" $pamFile
		sed -i --follow-symlink "/^auth.*sufficient.*pam_unix.so.*/a auth        [default=die] pam_faillock.so authfail deny=$var_accounts_passwords_pam_faillock_deny" $pamFile
		sed -i --follow-symlink "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
	fi
done

Limit Password Reuserule

Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_unix or pam_pwhistory PAM modules. In the file /etc/pam.d/system-auth, append remember=5 to the line which refers to the pam_unix.so or pam_pwhistory.somodule, as shown below:

  • for the pam_unix.so case: 
    password sufficient pam_unix.so existing_options remember=5
  • for the pam_pwhistory.so case: 
    password requisite pam_pwhistory.so existing_options remember=5
The DoD STIG requirement is 5 passwords.

Rationale:

Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user.

identifiers:  CCE-26923-3

references:  IA-5(f), IA-5(1)(e), 200, 77, Req-8, Test attestation on 20121024 by DS

Remediation script:
var_password_pam_unix_remember="5"
if grep -q "remember=" /etc/pam.d/system-auth; then   
	sed -i --follow-symlink "s/\(remember *= *\).*/\1$var_password_pam_unix_remember/" /etc/pam.d/system-auth
else
	sed -i --follow-symlink "/^password[[:space:]]\+sufficient[[:space:]]\+pam_unix.so/ s/$/ remember=$var_password_pam_unix_remember/" /etc/pam.d/system-auth
fi

Set Password Hashing Algorithmgroup

The system's default algorithm for storing password hashes in /etc/shadow is SHA-512. This can be configured in several locations.

contains 3 rules

Set Password Hashing Algorithm in /etc/pam.d/system-authrule

In /etc/pam.d/system-auth, the password section of the file controls which PAM modules execute during a password change. Set the pam_unix.so module in the password section to include the argument sha512, as shown below: 

password    sufficient    pam_unix.so sha512 other arguments...
This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default.

Rationale:

Using a stronger hashing algorithm makes password cracking attacks more difficult.

identifiers:  CCE-27104-9

references:  IA-5(b), IA-5(c), IA-5(1)(c), IA-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121024 by DS

Remediation script:
if ! grep -q "^password.*sufficient.*pam_unix.so.*sha512" /etc/pam.d/system-auth; then   
	sed -i --follow-symlink "/^password.*sufficient.*pam_unix.so/ s/$/ sha512/" /etc/pam.d/system-auth
fi

Set Password Hashing Algorithm in /etc/login.defsrule

In /etc/login.defs, add or correct the following line to ensure the system will use SHA-512 as the hashing algorithm: 

ENCRYPT_METHOD SHA512

Rationale:

Using a stronger hashing algorithm makes password cracking attacks more difficult.

identifiers:  CCE-27124-7

references:  IA-5(b), IA-5(c), IA-5(1)(c), IA-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121024 by DS

Remediation script:
if grep --silent ^ENCRYPT_METHOD /etc/login.defs ; then
	sed -i 's/^ENCRYPT_METHOD.*/ENCRYPT_METHOD SHA512/g' /etc/login.defs
else
	echo "" >> /etc/login.defs
	echo "ENCRYPT_METHOD SHA512" >> /etc/login.defs
fi

Set Password Hashing Algorithm in /etc/libuser.confrule

In /etc/libuser.conf, add or correct the following line in its [defaults] section to ensure the system will use the SHA-512 algorithm for password hashing: 

crypt_style = sha512

Rationale:

Using a stronger hashing algorithm makes password cracking attacks more difficult.

identifiers:  CCE-27053-8

references:  IA-5(b), IA-5(c), IA-5(1)(c), IA-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121026 by DS

Protect Physical Console Accessgroup

It is impossible to fully protect a system from an attacker with physical access, so securing the space in which the system is located should be considered a necessary step. However, there are some steps which, if taken, make it more difficult for an attacker to quickly or undetectably modify a system from its console.

contains 5 rules

Set Boot Loader Passwordgroup

During the boot process, the boot loader is responsible for starting the execution of the kernel and passing options to it. The boot loader allows for the selection of different kernels - possibly on different partitions or media. The default Red Hat Enterprise Linux boot loader for x86 systems is called GRUB2. Options it can pass to the kernel include single-user mode, which provides root access without any authentication, and the ability to disable SELinux. To prevent local users from modifying the boot parameters and endangering security, protect the boot loader configuration with a password and ensure its configuration file's permissions are set properly.

contains 4 rules

Verify /boot/grub2/grub.cfg User Ownershiprule

The file /boot/grub2/grub.cfg should be owned by the root user to prevent destruction or modification of the file. To properly set the owner of /boot/grub2/grub.cfg, run the command: 

$ sudo chown root /boot/grub2/grub.cfg

Rationale:

Only root should be able to modify important boot parameters.

identifiers:  CCE-26860-7

references:  AC-6(7), 225, Req-7, Test attestation on 20121026 by DS

Remediation script:
chown root /boot/grub2/grub.cfg

Verify /boot/grub2/grub.cfg Group Ownershiprule

The file /boot/grub2/grub.cfg should be group-owned by the root group to prevent destruction or modification of the file. To properly set the group owner of /boot/grub2/grub.cfg, run the command: 

$ sudo chgrp root xsl:value-of select="@file"/>

Rationale:

The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway.

identifiers:  CCE-26812-8

references:  AC-6(7), 225, Req-7, Test attestation on 20121026 by DS

Remediation script:
chgrp root /boot/grub2/grub.cfg

Verify /boot/grub2/grub.cfg Permissionsrule

File permissions for /boot/grub2/grub.cfg should be set to 600. To properly set the permissions of /boot/grub2/grub.cfg, run the command: 

$ sudo chmod 600 /boot/grub2/grub.cfg

Rationale:

Proper permissions ensure that only the root user can modify important boot parameters.

identifiers:  CCE-27054-6

references:  AC-6(7), 225, Test attestation on 20121026 by DS

Remediation script:
chmod 600 /boot/grub2/grub.cfg

Set Boot Loader Passwordrule

The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

To do so, select a superuser account and password and add them into the appropriate grub2 configuration file(s) under /etc/grub.d. Since plaintext passwords are a security risk, generate a hash for the pasword by running the following command: 

$ grub2-mkpasswd-pbkdf2
When prompted, enter the password that was selected and insert the returned password hash into the appropriate grub2 configuration file(s) under /etc/grub.d immediately after the superuser account. (Use the output from grub2-mkpasswd-pbkdf2 as the value of password-hash): 
password_pbkdf2 superusers-account password-hash
NOTE: It is recommended not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.
To meet FISMA Moderate, the bootloader superuser account and password MUST differ from the root account and password. Once the superuser account and password have been added, update the grub.cfg file by running: 
grub2-mkconfig -o /boot/grub2/grub.cfg
NOTE: Do NOT manually add the superuser account and password to the grub.cfg file as the grub2-mkconfig command overwrites this file.

Rationale:

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. For more information on how to configure the grub2 superuser account and password, please refer to

  • https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/sec-GRUB_2_Password_Protection.html
    • .

identifiers:  CCE-27309-4

references:  IA-2(1), IA-5(e), AC-3, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121026 by DS

Require Authentication for Single User Moderule

Single-user mode is intended as a system recovery method, providing a single user root access to the system by providing a boot option at startup. By default, no authentication is performed if single-user mode is selected.

By default, single-user mode is protected by requiring a password and is set in /usr/lib/systemd/system/rescue.service.

Rationale:

This prevents attackers with physical access from trivially bypassing security on the machine and gaining root access. Such accesses are further prevented by configuring the bootloader password.

identifiers:  CCE-27287-2

references:  IA-2(1), AC-3, 213, Test attestation on 20121024 by DS

Remediation script:
grep -q sulogin /usr/lib/systemd/system/rescue.service 
if ! [ $? -eq 0 ]; then
    sed -i "s/-c \"/-c \"\/sbin\/sulogin; /g" /usr/lib/systemd/system/rescue.service
fi

Network Configuration and Firewallsgroup

Most machines must be connected to a network of some sort, and this brings with it the substantial risk of network attack. This section discusses the security impact of decisions about networking which must be made when configuring a system.

This section also discusses firewalls, network access controls, and other network security frameworks, which allow system-level rules to be written that can limit an attackers' ability to connect to your system. These rules can specify that network traffic should be allowed or denied from certain IP addresses, hosts, and networks. The rules can also specify which of the system's network services are available to particular hosts or networks.

contains 4 rules

firewalldgroup

The dynamic firewall daemon firewalld provides a dynamically managed firewall with support for network “zones” to assign a level of trust to a network and its associated connections and interfaces. It has support for IPv4 and IPv6 firewall settings. It supports Ethernet bridges and has a separation of runtime and permanent configuration options. It also has an interface for services or applications to add firewall rules directly.
A graphical configuration tool, firewall-config, is used to configure firewalld, which in turn uses iptables tool to communicate with Netfilter in the kernel which implements packet filtering.
The firewall service provided by firewalld is dynamic rather than static because changes to the configuration can be made at anytime and are immediately implemented. There is no need to save or apply the changes. No unintended disruption of existing network connections occurs as no part of the firewall has to be reloaded.

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Inspect and Activate Default firewalld Rulesgroup

Firewalls can be used to separate networks into different zones based on the level of trust the user has decided to place on the devices and traffic within that network. NetworkManager informs firewalld to which zone an interface belongs. An interface's assigned zone can be changed by NetworkManager or via the firewall-config tool.
The zone settings in /etc/firewalld/ are a range of preset settings which can be quickly applied to a network interface. These are the zones provided by firewalld sorted according to the default trust level of the zones from untrusted to trusted:

  • drop

    Any incoming network packets are dropped, there is no reply. Only outgoing network connections are possible.

  • block

    Any incoming network connections are rejected with an icmp-host-prohibited message for IPv4 and icmp6-adm-prohibited for IPv6. Only network connections initiated from within the system are possible.

  • public

    For use in public areas. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.

  • external

    For use on external networks with masquerading enabled especially for routers. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.

  • dmz

    For computers in your demilitarized zone that are publicly-accessible with limited access to your internal network. Only selected incoming connections are accepted.

  • work

    For use in work areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.

  • home

    For use in home areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.

  • internal

    For use on internal networks. You mostly trust the other computers on the networks to not harm your computer. Only selected incoming connections are accepted.

  • trusted

    All network connections are accepted.


It is possible to designate one of these zones to be the default zone. When interface connections are added to NetworkManager, they are assigned to the default zone. On installation, the default zone in firewalld is set to be the public zone.
To find out all the settings of a zone, for example the public zone, enter the following command as root: 
# firewall-cmd --zone=public --list-all
Example output of this command might look like the following: 
# firewall-cmd --zone=public --list-all
public
  interfaces:
  services: mdns dhcpv6-client ssh
  ports:
  forward-ports:
  icmp-blocks: source-quench
To view the network zones currently active, enter the following command as root: 
# firewall-cmd --get-service
The following listing displays the result of this command on common Red Hat Enterprise Linux 7 Server system: 
# firewall-cmd --get-service
amanda-client bacula bacula-client dhcp dhcpv6 dhcpv6-client dns ftp
high-availability http https imaps ipp ipp-client ipsec kerberos kpasswd
ldap ldaps libvirt libvirt-tls mdns mountd ms-wbt mysql nfs ntp openvpn
pmcd pmproxy pmwebapi pmwebapis pop3s postgresql proxy-dhcp radius rpc-bind
samba samba-client smtp ssh telnet tftp tftp-client transmission-client
vnc-server wbem-https
Finally to view the network zones that will be active after the next firewalld service reload, enter the following command as root: 
# firewall-cmd --get-service --permanent

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Verify firewalld Enabledrule

The firewalld service can be enabled with the following command: 

$ sudo systemctl enable firewalld.service

Rationale:

The dynamic firewall daemon firewalld provides a dynamically managed firewall with support for network “zones”, Ethernet bridges, and has a separation of runtime and permanent configuration options. It has support for both IPv4 and IPv6 firewall settings.

identifiers:  CCE-27361-5

Remediation script:
#
# Enable firewalld.service for all systemd targets
#
systemctl enable firewalld.service

#
# Start firewalld.service if not currently running
#
systemctl start firewalld.service

Strengthen the Default Rulesetgroup

The default rules can be strengthened. The system scripts that activate the firewall rules expect them to be defined in configuration files under the /etc/firewalld/services and /etc/firewalld/zones directories.

The following recommendations describe how to strengthen the default ruleset configuration file. An alternative to editing this configuration file is to create a shell script that makes calls to the firewall-cmd program to load in rules under the /etc/firewalld/services and /etc/firewalld/zones directories.

Instructions apply to both unless otherwise noted. Language and address conventions for regular firewalld rules are used throughout this section.

warning  The program firewall-config allows additional services to penetrate the default firewall rules and automatically adjusts the firewalld ruleset(s).
contains 1 rule

Set Default firewalld Zone for Incoming Packetsrule

To set the default zone to drop for the built-in default zone which processes incoming IPv4 and IPv6 packets, modify the following line in /etc/firewalld/firewalld.conf to be: 

DefaultZone=drop

Rationale:

In firewalld the default zone is applied only after all the applicable rules in the table are examined for a match. Setting the default zone to drop implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted.

identifiers:  CCE-27349-0

references:  CM-7, 66, 1109, 1154, 1414

Remediation script:
grep -q ^DefaultZone= /etc/firewalld/firewalld.conf && \
  sed -i "s/DefaultZone=.*/DefaultZone=drop/g" /etc/firewalld/firewalld.conf
if ! [ $? -eq 0 ]; then
    echo "DefaultZone=drop" >> /etc/firewalld/firewalld.conf
fi

Uncommon Network Protocolsgroup

The system includes support for several network protocols which are not commonly used. Although security vulnerabilities in kernel networking code are not frequently discovered, the consequences can be dramatic. Ensuring uncommon network protocols are disabled reduces the system's risk to attacks targeted at its implementation of those protocols.

warning  Although these protocols are not commonly used, avoid disruption in your network environment by ensuring they are not needed prior to disabling them.
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Disable DCCP Supportrule

The Datagram Congestion Control Protocol (DCCP) is a relatively new transport layer protocol, designed to support streaming media and telephony. To configure the system to prevent the dccp kernel module from being loaded, add the following line to a file in the directory /etc/modprobe.d: 

install dccp /bin/true

Rationale:

Disabling DCCP protects the system against exploitation of any flaws in its implementation.

identifiers:  CCE-26828-4

references:  CM-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
echo "install dccp /bin/true" > /etc/modprobe.d/dccp.conf

Disable SCTP Supportrule

The Stream Control Transmission Protocol (SCTP) is a transport layer protocol, designed to support the idea of message-oriented communication, with several streams of messages within one connection. To configure the system to prevent the sctp kernel module from being loaded, add the following line to a file in the directory /etc/modprobe.d: 

install sctp /bin/true

Rationale:

Disabling SCTP protects the system against exploitation of any flaws in its implementation.

identifiers:  CCE-27106-4

references:  CM-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
echo "install sctp /bin/true" > /etc/modprobe.d/sctp.conf

System Accounting with auditdgroup

The audit service provides substantial capabilities for recording system activities. By default, the service audits about SELinux AVC denials and certain types of security-relevant events such as system logins, account modifications, and authentication events performed by programs such as sudo. Under its default configuration, auditd has modest disk space requirements, and should not noticeably impact system performance.
NOTE: The Linux Audit daemon auditd can be configured to use the augenrules program to read audit rules files (*.rules) located in /etc/audit/rules.d location and compile them to create the resulting form of the /etc/audit/audit.rules configuration file during the daemon startup (default configuration). Alternatively, the auditd daemon can use the auditctl utility to read audit rules from the /etc/audit/audit.rules configuration file during daemon startup, and load them into the kernel. The expected behavior is configured via the appropriate ExecStartPost directive setting in the /usr/lib/systemd/system/auditd.service configuration file. To instruct the auditd daemon to use the augenrules program to read audit rules (default configuration), use the following setting: 

ExecStartPost=-/sbin/augenrules --load
in the /usr/lib/systemd/system/auditd.service configuration file. In order to instruct the auditd daemon to use the auditctl utility to read audit rules, use the following setting: 
ExecStartPost=-/sbin/auditctl -R /etc/audit/audit.rules
in the /usr/lib/systemd/system/auditd.service configuration file. Refer to [Service] section of the /usr/lib/systemd/system/auditd.service configuration file for further details.
Government networks often have substantial auditing requirements and auditd can be configured to meet these requirements. Examining some example audit records demonstrates how the Linux audit system satisfies common requirements. The following example from Fedora Documentation available at https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/SELinux_Users_and_Administrators_Guide/sect-Security-Enhanced_Linux-Troubleshooting-Fixing_Problems.html#sect-Security-Enhanced_Linux-Fixing_Problems-Raw_Audit_Messages shows the substantial amount of information captured in a two typical "raw" audit messages, followed by a breakdown of the most important fields. In this example the message is SELinux-related and reports an AVC denial (and the associated system call) that occurred when the Apache HTTP Server attempted to access the /var/www/html/file1 file (labeled with the samba_share_t type): 
type=AVC msg=audit(1226874073.147:96): avc:  denied  { getattr } for pid=2465 comm="httpd"
path="/var/www/html/file1" dev=dm-0 ino=284133 scontext=unconfined_u:system_r:httpd_t:s0
tcontext=unconfined_u:object_r:samba_share_t:s0 tclass=file

type=SYSCALL msg=audit(1226874073.147:96): arch=40000003 syscall=196 success=no exit=-13
a0=b98df198 a1=bfec85dc a2=54dff4 a3=2008171 items=0 ppid=2463 pid=2465 auid=502 uid=48
gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=6 comm="httpd"
exe="/usr/sbin/httpd" subj=unconfined_u:system_r:httpd_t:s0 key=(null)
  • msg=audit(1226874073.147:96)
    • The number in parentheses is the unformatted time stamp (Epoch time) for the event, which can be converted to standard time by using the date command.
  • { getattr }
    • The item in braces indicates the permission that was denied. getattr indicates the source process was trying to read the target file's status information. This occurs before reading files. This action is denied due to the file being accessed having the wrong label. Commonly seen permissions include getattr, read, and write.
  • comm="httpd"
    • The executable that launched the process. The full path of the executable is found in the exe= section of the system call (SYSCALL) message, which in this case, is exe="/usr/sbin/httpd".
  • path="/var/www/html/file1"
    • The path to the object (target) the process attempted to access.
  • scontext="unconfined_u:system_r:httpd_t:s0"
    • The SELinux context of the process that attempted the denied action. In this case, it is the SELinux context of the Apache HTTP Server, which is running in the httpd_t domain.
  • tcontext="unconfined_u:object_r:samba_share_t:s0"
    • The SELinux context of the object (target) the process attempted to access. In this case, it is the SELinux context of file1. Note: the samba_share_t type is not accessible to processes running in the httpd_t domain.
  • From the system call (SYSCALL) message, two items are of interest:
    • success=no: indicates whether the denial (AVC) was enforced or not. success=no indicates the system call was not successful (SELinux denied access). success=yes indicates the system call was successful - this can be seen for permissive domains or unconfined domains, such as initrc_t and kernel_t.
    • exe="/usr/sbin/httpd": the full path to the executable that launched the process, which in this case, is exe="/usr/sbin/httpd".

contains 1 rule

Configure auditd Rules for Comprehensive Auditinggroup

The auditd program can perform comprehensive monitoring of system activity. This section describes recommended configuration settings for comprehensive auditing, but a full description of the auditing system's capabilities is beyond the scope of this guide. The mailing list linux-audit@redhat.com exists to facilitate community discussion of the auditing system.

The audit subsystem supports extensive collection of events, including:

  • Tracing of arbitrary system calls (identified by name or number) on entry or exit.
  • Filtering by PID, UID, call success, system call argument (with some limitations), etc.
  • Monitoring of specific files for modifications to the file's contents or metadata.

Auditing rules at startup are controlled by the file /etc/audit/audit.rules. Add rules to it to meet the auditing requirements for your organization. Each line in /etc/audit/audit.rules represents a series of arguments that can be passed to auditctl and can be individually tested during runtime. See documentation in /usr/share/doc/audit-VERSION and in the related man pages for more details.

If copying any example audit rulesets from /usr/share/doc/audit-VERSION, be sure to comment out the lines containing arch= which are not appropriate for your system's architecture. Then review and understand the following rules, ensuring rules are activated as needed for the appropriate architecture.

After reviewing all the rules, reading the following sections, and editing as needed, the new rules can be activated as follows: 
$ sudo service auditd restart

contains 1 rule

System Audit Logs Must Have Mode 0640 or Less Permissiverule

If log_group in /etc/audit/auditd.conf is set to a group other than the root group account, change the mode of the audit log files with the following command: 

$ sudo chmod 0640 audit_file

Otherwise, change the mode of the audit log files with the following command: 
$ sudo chmod 0600 audit_file

Rationale:

If users can write to audit logs, audit trails can be modified or destroyed.

identifiers:  CCE-27205-4

references:  AC-6, AU-1(b), AU-9, IR-5, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-10, Test attestation on 20121024 by DS

Remediation script:

if `grep -q ^log_group /etc/audit/auditd.conf` ; then
  GROUP=$(awk -F "=" '/log_group/ {print $2}' /etc/audit/auditd.conf | tr -d ' ')
  if ! [ "${GROUP}" == 'root' ] ; then
    chmod 0640 /var/log/audit/audit.log
    chmod 0440 /var/log/audit/audit.log.*
  else
    chmod 0600 /var/log/audit/audit.log
    chmod 0400 /var/log/audit/audit.log.*
  fi

  chmod 0640 /etc/audit/audit*
  chmod 0640 /etc/audit/rules.d/*
else
  chmod 0600 /var/log/audit/audit.log
  chmod 0400 /var/log/audit/audit.log.*
  chmod 0640 /etc/audit/audit*
  chmod 0640 /etc/audit/rules.d/*
fi

Servicesgroup

The best protection against vulnerable software is running less software. This section describes how to review the software which Red Hat Enterprise Linux 7 installs on a system and disable software which is not needed. It then enumerates the software packages installed on a default Red Hat Enterprise Linux 7 system and provides guidance about which ones can be safely disabled.

Red Hat Enterprise Linux 7 provides a convenient minimal install option that essentially installs the bare necessities for a functional system. When building Red Hat Enterprise Linux 7 servers, it is highly recommended to select the minimal packages and then build up the system from there.

contains 12 rules

Obsolete Servicesgroup

This section discusses a number of network-visible services which have historically caused problems for system security, and for which disabling or severely limiting the service has been the best available guidance for some time. As a result of this, many of these services are not installed as part of Red Hat Enterprise Linux 7 by default.

Organizations which are running these services should switch to more secure equivalents as soon as possible. If it remains absolutely necessary to run one of these services for legacy reasons, care should be taken to restrict the service as much as possible, for instance by configuring host firewall software such as firewalld to restrict access to the vulnerable service to only those remote hosts which have a known need to use it.

contains 1 rule

Telnetgroup

The telnet protocol does not provide confidentiality or integrity for information transmitted on the network. This includes authentication information such as passwords. Organizations which use telnet should be actively working to migrate to a more secure protocol.

contains 1 rule

Remove telnet Clientsrule

The telnet client 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 Red Hat Enterprise Linux.

identifiers:  CCE-27305-2

Remediation script:
yum -y remove telnet

Base Servicesgroup

This section addresses the base services that are installed on a Red Hat Enterprise Linux 7 default installation which are not covered in other sections. Some of these services listen on the network and should be treated with particular discretion. Other services are local system utilities that may or may not be extraneous. In general, system services should be disabled if not required.

contains 1 rule

Disable Automatic Bug Reporting Tool (abrtd)rule

The Automatic Bug Reporting Tool (abrtd) daemon collects and reports crash data when an application crash is detected. Using a variety of plugins, abrtd can email crash reports to system administrators, log crash reports to files, or forward crash reports to a centralized issue tracking system such as RHTSupport. The abrtd service can be disabled with the following command: 

$ sudo systemctl disable abrtd.service

Rationale:

Mishandling crash data could expose sensitive information about vulnerabilities in software executing on the local machine, as well as sensitive information from within a process's address space or registers.

identifiers:  CCE-26872-2

references:  AC-17(8), CM-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20140921 by JL

Remediation script:
#
# Disable abrtd.service for all systemd targets
#
systemctl disable abrtd.service

#
# Stop abrtd.service if currently running
#
systemctl stop abrtd.service

SSH Servergroup

The SSH protocol is recommended for remote login and remote file transfer. SSH provides confidentiality and integrity for data exchanged between two systems, as well as server authentication, through the use of public key cryptography. The implementation included with the system is called OpenSSH, and more detailed documentation is available from its website, http://www.openssh.org. Its server program is called sshd and provided by the RPM package openssh-server.

contains 10 rules

Configure OpenSSH Server if Necessarygroup

If the system needs to act as an SSH server, then certain changes should be made to the OpenSSH daemon configuration file /etc/ssh/sshd_config. The following recommendations can be applied to this file. See the sshd_config(5) man page for more detailed information.

contains 10 rules

Allow Only SSH Protocol 2rule

Only SSH protocol version 2 connections should be permitted. The default setting in /etc/ssh/sshd_config is correct, and can be verified by ensuring that the following line appears: 

Protocol 2

Rationale:

SSH protocol version 1 suffers from design flaws that result in security vulnerabilities and should not be used.

identifiers:  CCE-27320-1

references:  AC-17(7), IA-5(1)(c), http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
grep -qi ^Protocol /etc/ssh/sshd_config && \
  sed -i "s/Protocol.*/Protocol 2/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "Protocol 2" >> /etc/ssh/sshd_config
fi

Set SSH Idle Timeout Intervalrule

SSH allows administrators to set an idle timeout interval. After this interval has passed, the idle user will be automatically logged out.

To set an idle timeout interval, edit the following line in /etc/ssh/sshd_config as follows: 

ClientAliveInterval interval
The timeout interval is given in seconds. To have a timeout of 15 minutes, set interval to 900.

If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made here. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle.

Rationale:

Causing idle users to be automatically logged out guards against compromises one system leading trivially to compromises on another.

identifiers:  CCE-27433-2

references:  AC-2(5), SA-8, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8, Test attestation on 20121024 by DS

Remediation script:
sshd_idle_timeout_value="300"
grep -qi ^ClientAliveInterval /etc/ssh/sshd_config && \
  sed -i "s/ClientAliveInterval.*/ClientAliveInterval $sshd_idle_timeout_value/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "ClientAliveInterval $sshd_idle_timeout_value" >> /etc/ssh/sshd_config
fi

Set SSH Client Alive Countrule

To ensure the SSH idle timeout occurs precisely when the ClientAliveCountMax is set, edit /etc/ssh/sshd_config as follows: 

ClientAliveCountMax 0

Rationale:

This ensures a user login will be terminated as soon as the ClientAliveCountMax is reached.

identifiers:  CCE-27082-7

references:  AC-2(5), SA-8, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
grep -qi ^ClientAliveCountMax /etc/ssh/sshd_config && \
  sed -i "s/ClientAliveCountMax.*/ClientAliveCountMax 0/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "ClientAliveCountMax 0" >> /etc/ssh/sshd_config
fi

Disable SSH Support for .rhosts Filesrule

SSH can emulate the behavior of the obsolete rsh command in allowing users to enable insecure access to their accounts via .rhosts files.

To ensure this behavior is disabled, add or correct the following line in /etc/ssh/sshd_config: 

IgnoreRhosts yes

Rationale:

SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.

identifiers:  CCE-27377-1

references:  AC-3, http://iase.disa.mil/stigs/cci/Pages/index.aspx

Remediation script:
grep -qi ^IgnoreRhosts /etc/ssh/sshd_config && \
  sed -i "s/IgnoreRhosts.*/IgnoreRhosts yes/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "IgnoreRhosts yes" >> /etc/ssh/sshd_config
fi

Disable Host-Based Authenticationrule

SSH's cryptographic host-based authentication is more secure than .rhosts authentication. However, it is not recommended that hosts unilaterally trust one another, even within an organization.

To disable host-based authentication, add or correct the following line in /etc/ssh/sshd_config: 

HostbasedAuthentication no

Rationale:

SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.

identifiers:  CCE-27413-4

references:  AC-3, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
grep -q ^HostbasedAuthentication /etc/ssh/sshd_config && \
  sed -i "s/HostbasedAuthentication.*/HostbasedAuthentication no/g" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "HostbasedAuthentication no" >> /etc/ssh/sshd_config
fi

Disable SSH Access via Empty Passwordsrule

To explicitly disallow remote login from accounts with empty passwords, add or correct the following line in /etc/ssh/sshd_config: 

PermitEmptyPasswords no
Any accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords.

Rationale:

Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.

identifiers:  CCE-27471-2

references:  AC-3, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
grep -qi ^PermitEmptyPasswords /etc/ssh/sshd_config && \
  sed -i "s/PermitEmptyPasswords.*/PermitEmptyPasswords no/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "PermitEmptyPasswords no" >> /etc/ssh/sshd_config
fi

Enable SSH Warning Bannerrule

To enable the warning banner and ensure it is consistent across the system, add or correct the following line in /etc/ssh/sshd_config: 

Banner /etc/issue
Another section contains information on how to create an appropriate system-wide warning banner.

Rationale:

The warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers. Alternatively, systems whose ownership should not be obvious should ensure usage of a banner that does not provide easy attribution.

identifiers:  CCE-27314-4

references:  AC-8(a), AC-8(c)(1), AC-8(c)(2), AC-8(c)(3), 1384, 1385, 1386, 1387, 1388, 228, Test attestation on 20121024 by DS

Remediation script:
grep -qi ^Banner /etc/ssh/sshd_config && \
  sed -i "s/Banner.*/Banner \/etc\/issue/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "" >> /etc/ssh/sshd_config
    echo "Banner /etc/issue" >> /etc/ssh/sshd_config
fi

Do Not Allow SSH Environment Optionsrule

To ensure users are not able to present environment options to the SSH daemon, add or correct the following line in /etc/ssh/sshd_config: 

PermitUserEnvironment no

Rationale:

SSH environment options potentially allow users to bypass access restriction in some configurations.

identifiers:  CCE-27363-1

references:  http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
grep -qi ^PermitUserEnvironment /etc/ssh/sshd_config && \
  sed -i "s/PermitUserEnvironment.*/PermitUserEnvironment no/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "PermitUserEnvironment no" >> /etc/ssh/sshd_config
fi

Use Only Approved Ciphersrule

Limit the ciphers to those algorithms which are FIPS-approved. Counter (CTR) mode is also preferred over cipher-block chaining (CBC) mode. The following line in /etc/ssh/sshd_config demonstrates use of FIPS-approved ciphers: 

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc
The man page sshd_config(5) contains a list of supported ciphers.

Rationale:

Approved algorithms should impart some level of confidence in their implementation. These are also required for compliance.

identifiers:  CCE-27295-5

references:  AC-3, AC-17(2), AU-10(5), IA-5(1)(c), IA-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Test attestation on 20121024 by DS

Remediation script:
grep -qi ^Ciphers /etc/ssh/sshd_config && \
  sed -i "s/Ciphers.*/Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc/gI" /etc/ssh/sshd_config
if ! [ $? -eq 0 ]; then
    echo "Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc" >> /etc/ssh/sshd_config
fi
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