cis-ubuntu2004-v300-6-3-3-8

6.3.3.8 Ensure events that modify user/group information are collected (Automated)

Profile

• Level 2 - Server
• Level 2 - Workstation

Description

Record events affecting the modification of user or group information, including that of passwords and old passwords if in use.

• /etc/group - system groups
• /etc/passwd - system users
• /etc/gshadow - encrypted password for each group
• /etc/shadow - system user passwords
• /etc/security/opasswd - storage of old passwords if the relevant PAM module is in use
• /etc/nsswitch.conf - file configures how the system uses various databases and name resolution mechanisms
• /etc/pam.conf - file determines the authentication services to be used, and the order in which the services are used.
• /etc/pam.d - directory contains the PAM configuration files for each PAM-aware application.

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 Procedure

Command Line

On disk configuration - Run the following command to check the on disk rules:

# awk '/^ *-w/ \
&&(/\/etc\/group/ \
  ||/\/etc\/passwd/ \
  ||/\/etc\/gshadow/ \
  ||/\/etc\/shadow/ \
  ||/\/etc\/security\/opasswd/ \
  ||/\/etc\/nsswitch.conf/ \
  ||/\/etc\/pam.conf/ \
  ||/\/etc\/pam.d/) \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)' /etc/audit/rules.d/*.rules

Verify the output matches:

-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
-w /etc/nsswitch.conf -p wa -k identity
-w /etc/pam.conf -p wa -k identity
-w /etc/pam.d -p wa -k identity

Running configuration - Run the following command to check loaded rules:

# auditctl -l | awk '/^ *-w/ \
&&(/\/etc\/group/ \
  ||/\/etc\/passwd/ \
  ||/\/etc\/gshadow/ \
  ||/\/etc\/shadow/ \
  ||/\/etc\/security\/opasswd/ \
  ||/\/etc\/nsswitch.conf/ \
  ||/\/etc\/pam.conf/ \
  ||/\/etc\/pam.d/) \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)'

Verify the output matches:

-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
-w /etc/nsswitch.conf -p wa -k identity
-w /etc/pam.conf -p wa -k identity
-w /etc/pam.d -p wa -k identity

Expected Result

Both on disk and running configuration should show identity audit rules for user/group information files.

Remediation

Command Line

Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor events that modify user/group information.

Example:

# printf "
-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
-w /etc/nsswitch.conf -p wa -k identity
-w /etc/pam.conf -p wa -k identity
-w /etc/pam.d -p wa -k identity
" >> /etc/audit/rules.d/50-identity.rules

Merge and load the rules into active configuration:

# augenrules --load

Check if reboot is required:

# if [[ $(auditctl -s | grep "enabled") =~ "2" ]]; then printf "Reboot required to load rules\n"; fi

References

1. NIST SP 800-53 Rev. 5: AU-3
2. https://manpages.debian.org/bookworm/manpages/nsswitch.conf.5.en.html
3. https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/managing_smart_cards/pam_configuration_files

CIS Controls

MITRE ATT&CK Mappings: T1562, T1562.006 / TA0004 / M1047