cis-ubuntu1804-v220-5-2-3-14

name	cis-ubuntu1804-v220-5-2-3-14
description	Ensure events that modify the system's Mandatory Access Controls are collected
version	2.2.0
category	cis-logging
tags	["cis","ubuntu","linux","ubuntu-18.04","auditing","auditd"]
author	CIS Benchmarks
target	{"platform":"linux","version":"18.04"}
severity_boost	{}

CIS Ubuntu 18.04 - Ensure events that modify the system's Mandatory Access Controls are collected (5.2.3.14)

Metadata

• ID: cis-ubuntu1804-v220-5-2-3-14
• Title: Ensure events that modify the system's Mandatory Access Controls are collected
• CIS Control: 5.2.3.14
• Profile Applicability: Level 2 - Server, Level 2 - Workstation
• Benchmark: CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
• Category: cis-logging
• Tags: cis, ubuntu, linux, ubuntu-18.04, auditing, auditd
• Severity: medium
• Version: 2.2.0

Description

Monitor AppArmor, an implementation of mandatory access controls. The parameters below monitor any write access (potential additional, deletion or modification of files in the directory) or attribute changes to the /etc/apparmor/ and /etc/apparmor.d/ directories.

Note: If a different Mandatory Access Control method is used, changes to the corresponding directories should be audited.

Rationale

Changes to files in the /etc/apparmor/ and /etc/apparmor.d/ directories could indicate that an unauthorized user is attempting to modify access controls and change security contexts, leading to a compromise of the system.

Impact

None

Audit

On Disk Configuration

UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && awk "/^ *-w/ \
&&(/\/etc\/apparmor/ \
||/\/etc\/apparmor.d/) \
&&/ -p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/" /etc/audit/rules.d/*.rules

Expected Output:

-w /etc/apparmor/ -p wa -k MAC-policy
-w /etc/apparmor.d/ -p wa -k MAC-policy

Running Configuration

auditctl -l | awk "/^ *-w/ \
&&(/\/etc\/apparmor/ \
||/\/etc\/apparmor.d/) \
&&/ -p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/"

Expected Output:

-w /etc/apparmor/ -p wa -k MAC-policy
-w /etc/apparmor.d/ -p wa -k MAC-policy

Remediation

Create Audit Rules

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 the system's Mandatory Access Controls.

Example:

printf "
-w /etc/apparmor/ -p wa -k MAC-policy
-w /etc/apparmor.d/ -p wa -k MAC-policy
" >> /etc/audit/rules.d/50-MAC-policy.rules

Load Audit 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

• NIST SP 800-53 Rev. 5: AU-3, CM-6

CIS Controls

• v8: 8.5 Collect Detailed Audit Logs
• v7: 5.5 Implement Automated Configuration Monitoring Systems

MITRE ATT&CK Mappings

• Techniques: T1562, T1562.006
• Tactics: TA0004
• Mitigations: M1022

Additional Information

Potential Reboot Required

If the auditing configuration is locked (-e 2), then augenrules will not warn in any way that rules could not be loaded into the running configuration. A system reboot will be required to load the rules into the running configuration.

System Call Structure

For performance (man 7 audit.rules) reasons it is preferable to have all the system calls on one line. However, your configuration may have them on one line each or some other combination. This is important to understand for both the auditing and remediation sections as the examples given are optimized for performance as per the man page.