Cis Ubuntu1804 V220 5 2 3 21

CIS Ubuntu 18.04 - Ensure the running and on disk configuration is the same (5.2.3.21)

Metadata

• ID: cis-ubuntu1804-v220-5-2-3-21
• Title: Ensure the running and on disk configuration is the same
• CIS Control: 5.2.3.21
• 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

Verify that the running configuration matches what is defined in the on-disk audit configuration files.

The audit system can operate in several modes:

• Enabled (1): Audit rules can be loaded and changed
• Immutable (2): Audit rules cannot be changed until reboot

It is important to verify that the running audit configuration matches the on-disk configuration to ensure that all required audit rules are actively monitoring system events.

Rationale

If the running audit configuration differs from the on-disk configuration, critical audit rules may not be active, leading to gaps in security monitoring and compliance violations. This could allow unauthorized activities to go undetected.

Impact

None. This is a verification check to ensure consistency between running and on-disk configurations.

Audit

Compare Running vs On-Disk Configuration

# Check if audit is enabled
auditctl -s | grep enabled

# Check running rule count
auditctl -l | wc -l

# Check on-disk rule count (excluding comments and blank lines)
cat /etc/audit/rules.d/*.rules | grep -v '^#' | grep -v '^$' | wc -l

# Detailed comparison (optional)
diff <(auditctl -l | sort) <(cat /etc/audit/rules.d/*.rules | augenrules --check | sort)

Expected Behavior:

• Audit should be enabled (enabled 1 or enabled 2)
• Running rule count should match or be close to on-disk rule count
• No significant differences between running and on-disk rules

Check if Reboot is Required

if [[ $(auditctl -s | grep "enabled") =~ "2" ]]; then
    printf "Audit is in immutable mode - reboot required to load new rules\n"
fi

Remediation

Load On-Disk Configuration into Running Configuration

If the running configuration differs from the on-disk configuration, load the rules:

# Merge and load all rules from /etc/audit/rules.d/
augenrules --load

Verify Rules Were Loaded

auditctl -l

If Audit is in Immutable Mode

If audit is configured in immutable mode (-e 2), you must reboot the system to apply any changes:

# Check if immutable mode is enabled
if [[ $(auditctl -s | grep "enabled") =~ "2" ]]; then
    printf "Reboot required to load rules\n"
    # Schedule reboot (optional)
    # shutdown -r +5 "Rebooting to apply audit configuration changes"
fi

Best Practices

1. Always verify running configuration after making changes to audit rules
2. Test audit rules in enabled mode (-e 1) before setting to immutable mode (-e 2)
3. Document all changes to audit configuration
4. Maintain version control of audit rule files

References

• NIST SP 800-53 Rev. 5: AU-9, CM-6

CIS Controls

• v8: 8.5 Collect Detailed Audit Logs
• v7: 6.2 Activate audit logging, 6.3 Enable Detailed Logging

MITRE ATT&CK Mappings

• Techniques: T1562, T1562.006
• Tactics: TA0005
• 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.

Common Discrepancies

Running and on-disk configurations may differ due to:

1. Manual changes made with auditctl (not persisted to disk)
2. Changes made to /etc/audit/rules.d/*.rules files without running augenrules --load
3. System in immutable mode preventing rule updates
4. Service restart issues

Troubleshooting

If rules fail to load:

1. Check audit daemon status: systemctl status auditd
2. Review audit logs: journalctl -u auditd
3. Validate rule syntax: augenrules --check
4. Ensure no conflicting rules exist
5. Verify sufficient permissions to modify audit configuration