Add nosuid Option to /var/log/audit
Mounts /var/log/audit with the nosuid option so the kernel ignores set-UID/set-GID bits on binaries there.
Checked against the resolved running state (e.g. sshd -T, sysctl, systemctl show), catches drop-ins and Includes a file read would miss. Caveat: runtime ≠ persistence; a value correct now may not survive a reboot.
Pavois asserts the effective configuration, the live, resolved state, not a file. File-based scanners (OVAL/SCAP, Lynis) miss Includes, drop-ins and runtime defaults; this check sees what is actually applied.
A mapping is a cross-reference to where each standard places this requirement, anchored and cross-validated, not a claim of equivalence. A passing check is evidence toward these references, how to read it.
Why this rule matters
SUID and SGID executables run with their owner's privileges (often root) instead of the caller's, so their presence must be tightly controlled. The audit log partition /var/log/audit has no reason to host such binaries. The nosuid option makes the kernel ignore the set-user-ID and set-group-ID bits on anything stored there, removing a potential privilege-escalation vector if an attacker manages to write to the partition.
What Pavois checks
Pavois inspects the effective mount with mount('/var/log/audit') and asserts its resolved options include nosuid. It reads the live kernel mount table, what is actually enforced, rather than /etc/fstab, so it catches a partition remounted without the flag, a systemd mount-unit override, or an fstab entry that never applied, which a file-based scanner would wrongly pass.
describe mount('/var/log/audit') do
its('options') { should include 'nosuid' }
end
describe command("{ findmnt --fstab -no OPTIONS /var/log/audit 2>/dev/null; grep -hsE '[[:space:]]/var/log/audit[[:space:]]' /etc/fstab 2>/dev/null; systemctl show -p Options -- $(systemd-escape -p --suffix=mount /var/log/audit 2>/dev/null) 2>/dev/null; } | grep -ow 'nosuid'") do
its('stdout') { should match(/\S/) }
endHow to verify it is applied
Run findmnt /var/log/audit (or findmnt -no OPTIONS /var/log/audit) and confirm nosuid is in the option list. Expected output contains nosuid, e.g. /var/log/audit ... rw,nosuid,nodev,noexec,relatime.
Inspect & investigate
Mount state is queried live with findmnt /var/log/audit or cat /proc/mounts, not from a log. Boot-time and remount events appear via journalctl -b | grep -i audit. The audit daemon writes its records to /var/log/audit/audit.log.
Remediation
No automated harden plan ships for this rule yet, so it must be applied manually: this requires /var/log/audit to be a separate partition. Add nosuid to its /etc/fstab entry, then mount -o remount /var/log/audit, or reboot, and re-scan to confirm.
Pavois applies this with its own harden engine, the plan below, not a shell script:
| command | awk -v m=/var/log/audit -v o=nosuid '$0!~/^[[:space:]]*#/&&$2==m{n=split($4,a,",");h=0;for(i=1;i<=n;i++)if(a[i]==o)h=1;if(!h)$4=$4","o}{print}' /etc/fstab >/etc/.fstab.pav && cat /etc/.fstab.pav >/etc/fstab && rm -f /etc/.fstab.pav; mountpoint -q /var/log/audit && mount -o remount,nosuid /var/log/audit || true |
|---|---|
| name | mount-var-log-audit-nosuid |
| not_if | awk -v m=/var/log/audit '$2==m&&$0!~/^[[:space:]]*#/{print $4}' /etc/fstab | tr , '\n' | grep -qx nosuid |
| resource | exec |
pavois harden plan localwhere the target is local, a user@host SSH alias, or a container , Docs
Impact & precautions
Functional impact is essentially nil, no legitimate SUID/SGID binary belongs under the audit log directory. Precautions: the option can only be set if /var/log/audit is a dedicated partition; on a default layout you must first create it (a disruptive change requiring planning, migration of existing audit logs, and a reboot). Stop auditd before migrating data to avoid corrupting the active log.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| CIS | 1.1.2.7.3 | direct | per OS, see the benchmark table | high |
| NIST | AC-6, AC-6(1), CM-6(a), CM-7(a), CM-7(b), MP-7 | supporting | 800-53 Rev 5 · 800-171 Rev 2 (pinned) | medium |
Each reference is a cross-reference anchored in the upstream benchmark and cross-validated against the SCAP Security Guide and ansible-lockdown, not a claim of equivalence. Direct = a prescriptive, line-level requirement; supporting = an abstract control family (NIST) the check provides evidence toward. How to read a mapping.