cis-ubuntu1804-v220-5-2-3-8

name	cis-ubuntu1804-v220-5-2-3-8
version	2.2.0
date_published	"2024-01-01T00:00:00.000Z"
category	cis-logging
description	Ensure events that modify user/group information are collected
author	CIS Benchmarks
tags	["cis","ubuntu","linux","ubuntu-18.04","auditing","auditd"]
target	{"platform":"linux","version":"18.04"}
severity_boost	{}

5.2.3.8 Ensure events that modify user/group information are collected

Profile Applicability

• 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

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

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/ ) \
&&/ +-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

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/ ) \
&&(/ 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

Remediation

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: