MEDIUM RHCOS (Node) M3: Audit Rules - DAC Modifications P3

Verified CNF-23513 (In Progress) Compare Branch Synced: 2026-05-04

Overview

This remediation configures audit rules to monitor Discretionary Access Control (DAC) modifications, specifically file permission and ownership changes.

Settings

Rule	Description
`chmod`	Audit file permission changes via chmod
`chown`	Audit file ownership changes via chown

Implementation

The remediation applies audit rules via MachineConfig:

apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  name: 75-audit-dac-medium
  labels:
    machineconfiguration.openshift.io/role: master
spec:
  config:
    ignition:
      version: 3.2.0
    storage:
      files:
        - path: /etc/audit/rules.d/75-dac-modification.rules
          mode: 0644
          overwrite: true
          contents:
            inline: |
              ## DAC modification monitoring
              -a always,exit -F arch=b64 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=unset -k perm_mod
              -a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=unset -k perm_mod
              -a always,exit -F arch=b64 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=unset -k perm_mod
              -a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=unset -k perm_mod

Compliance Checks Remediated

Check	Profile	Description	Docs
`rhcos4-e8-worker-audit-rules-dac-modification-chmod`	E8	Audit chmod syscalls	📖
`rhcos4-e8-worker-audit-rules-dac-modification-chown`	E8	Audit chown syscalls	📖

Source Remediation Files

medium/rhcos4-e8-worker-audit-rules-dac-modification-chmod.yaml
medium/rhcos4-e8-worker-audit-rules-dac-modification-chown.yaml

Verification

After applying, verify audit rules are loaded:

oc debug node/<node-name> -- chroot /host auditctl -l | grep perm_mod

Security Impact

Monitoring DAC modifications helps detect:

Unauthorized permission escalations
Attempts to modify critical file permissions
Potential privilege escalation attempts

Upstream Proposal

The following changes could eliminate the need for MachineConfig remediation. Items are categorized by recommended scope:

chmod/chown DAC audit rules RAN Low

openshift/os /etc/audit/rules.d/50-dac-modification.rules

Standard CIS/STIG audit requirement. Tracks permission changes for forensic analysis.
Scope: Audit rules add overhead. Not all clusters need DAC modification forensic logging.

PR History

chmod/chown DAC audit rules Not Filed blocked

coreos/rhel-coreos-config

Audit rules are compliance monitoring policies, not security defaults. RHCOS ships no audit rules in rules.d by default — only samples in /usr/share/audit/sample-rules/ that Red Hat explicitly warns are 'not exhaustive nor up to date.' CoreOS maintainers debated whether to include the audit RPM at all (fedora-coreos-tracker#461) and called it 'an odd fit' (coreos/bugs#140). Audit messages already flood console on fresh boot (fedora-coreos-tracker#220). Deploying rules in the base image would substantially increase audit volume for all RHCOS deployments. The Compliance Operator's MachineConfig remediation model is the intended deployment path.

coreos/fedora-coreos-tracker/issues/461 coreos/fedora-coreos-tracker/issues/220 coreos/bugs/issues/140 docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/security_hardening/auditing-the-system_security-hardening

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