# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-AUDIT-026
title: Audit every use of setuid and setgid programs
finding:
  title: Use of privileged programs is not recorded
  description: Programs that run with more rights than their caller are the main path to privilege escalation and are used without a record.
status: active
profiles: [server-hardened, desktop-hardened]
risk:
  severity: medium
assessment: automated
tags: [auditd, setuid]

description: |
  One auditd rule per setuid or setgid program found on the local file systems that allow
  them (not mounted `nosuid` or `noexec`), key `privileged`, in
  `/etc/audit/rules.d/60-cirsec-privileged.rules`. Each rule records every run of the program by a
  user who logged in. The list is rebuilt from the file system each time the check or the fix runs.
rationale: |
  `passwd`, `su`, `sudo`, `mount`, `chsh` and similar programs run as root on behalf of a user.
  Recording each use shows who used them and is the first place to look after a privilege escalation.
impact: |
  Installing or removing a package that ships a setuid program makes the check fail until the fix
  runs again. Once the audit configuration is locked (CB-UBU-AUDIT-029), the new rule only loads at
  the next reboot.
notes: |
  The scan covers local file systems listed by `findmnt --real`. Programs on network file systems are not covered.
  Snap images (`squashfs` mounts under `/snap/`) are skipped: they are read-only, replaced at each
  snap refresh (which would make the check fail every time), and their setuid copies are not used
  by the host. `/usr/lib/snapd/snap-confine` itself is on the root file system and is covered.

setting:
  location: /etc/audit/rules.d/60-cirsec-privileged.rules
  default_value: No audit rules
  recommended_value: "Rules loaded (auditctl -l) and present in /etc/audit/rules.d/60-cirsec-privileged.rules"

audit:
  manual: |
    1. Run `auditctl -l` as root. It must list the rules shown below (keys `privileged`).
    2. Run `grep -h . /etc/audit/rules.d/*.rules`. The same rules must be present, so they load at boot.

    Expected rules, as `auditctl -l` prints them:
    ```
    -a always,exit -S all -F path=<program> -F perm=x -F auid>=1000 -F auid!=-1 -F key=privileged
    ```
  checks:
    - id: rules
      engine: shell
      description: Rules loaded in the kernel and present in /etc/audit/rules.d.
      spec:
        script: |
          command -v auditctl >/dev/null 2>&1 || { echo "auditctl not found: auditd is not installed"; exit 1; }
          want() {
          # every setuid or setgid file on local file systems mounted without nosuid or noexec, snaps excluded
          for m in $(findmnt -rn --real -t nosquashfs -O nonosuid,nonoexec -o TARGET); do
            find "$m" -xdev -type f \( -perm -4000 -o -perm -2000 \) 2>/dev/null
          done | sort -u | while IFS= read -r p; do
            echo "-a always,exit -S all -F path=$p -F perm=x -F auid>=1000 -F auid!=-1 -F key=privileged"
          done
          }
          loaded=$(auditctl -l 2>&1) || { echo "$loaded"; exit 3; }
          disk=$(cat /etc/audit/rules.d/*.rules 2>/dev/null)
          n=0 rc=0
          while IFS= read -r r; do
            [ -n "$r" ] || continue
            n=$((n + 1))
            printf '%s\n' "$loaded" | grep -Fxq -- "$r" || { echo "not loaded: $r"; rc=1; }
            printf '%s\n' "$disk" | grep -Fxq -- "$r" || { echo "not in /etc/audit/rules.d: $r"; rc=1; }
          done <<EOF
          $(want)
          EOF
          [ "$rc" = 1 ] || echo "$n rules loaded and present in /etc/audit/rules.d"
          exit "$rc"

remediation:
  manual: |
    1. Write the expected rules to `/etc/audit/rules.d/60-cirsec-privileged.rules` (mode 0640).
    2. Run `augenrules --load`. If `auditctl -s` shows `enabled 2`, the configuration is locked:
       reboot to load the new rules.
  effects:
    restart: none
    disruption: none
    lockout_risk: false
  rollback: |
    Delete `/etc/audit/rules.d/60-cirsec-privileged.rules` and run `augenrules --load` (or reboot if the configuration is locked).
  scripts:
    - id: rules-file
      engine: shell
      content: |
        command -v augenrules >/dev/null 2>&1 || { echo "auditd is not installed" >&2; exit 1; }
        want() {
        # every setuid or setgid file on local file systems mounted without nosuid or noexec, snaps excluded
        for m in $(findmnt -rn --real -t nosquashfs -O nonosuid,nonoexec -o TARGET); do
          find "$m" -xdev -type f \( -perm -4000 -o -perm -2000 \) 2>/dev/null
        done | sort -u | while IFS= read -r p; do
          echo "-a always,exit -S all -F path=$p -F perm=x -F auid>=1000 -F auid!=-1 -F key=privileged"
        done
        }
        f=/etc/audit/rules.d/60-cirsec-privileged.rules
        t=$(mktemp)
        { echo '# Written by CIRSEC Baselines CB-UBU-AUDIT-026'; want; } >"$t"
        if ! cmp -s "$t" "$f"; then
          cb_backup "$f"
          cat "$t" >"$f"
        fi
        rm -f "$t"
        chmod 640 "$f"
        if auditctl -s | grep -q '^enabled 2'; then
          echo "audit rules are locked (-e 2): reboot to load $f"
        else
          augenrules --load >/dev/null
        fi

references:
  - title: audit.rules(7), Ubuntu manual pages
    url: https://manpages.ubuntu.com/manpages/noble/man7/audit.rules.7.html
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
  - title: auditctl(8), Ubuntu manual pages
    url: https://manpages.ubuntu.com/manpages/noble/man8/auditctl.8.html
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R73)
    url: https://messervices.cyber.gouv.fr/documents-guides/fr_np_linux_configuration-v2.0.pdf
    publisher: ANSSI
    kind: guide
    accessed: 2026-10-19
mappings:
  - framework: anssi-linux
    framework_version: "2.0"
    id: "R33"
    relation: partial
  - framework: anssi-linux
    framework_version: "2.0"
    id: "R73"
    relation: partial
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: "AU-12"
    relation: related
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: "AC-6(9)"
    relation: related
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "6.3.3.6"
    relation: equivalent
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "6.2.3.6"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "6.2.3.10"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "6.2.3.10"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1548.001
related_controls:
  - id: CB-UBU-AUDIT-011
    type: requires
  - id: CB-UBU-AUDIT-029
    type: related

authors:
  - name: Alice
    github: Sn0wAlice
verified:
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["20.04"]
    environment: Proxmox VM, Ubuntu 20.04 cloud image, kernel 5.4.0-216-generic
    notes: "Fails after auditd install; rules written and loaded (augenrules), all present in auditctl -l with auditd 2.8.5; passes after reboot with enabled 2. Snap squashfs mounts skipped."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["22.04"]
    environment: Proxmox VM, Ubuntu 22.04 cloud image, kernel 5.15.0-198-generic
    notes: "Fails after auditd install; rules written and loaded (augenrules), all present in auditctl -l with auditd 3.0.7; passes after reboot with enabled 2. Snap squashfs mounts skipped."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["24.04"]
    environment: Proxmox VM, Ubuntu 24.04 cloud image, kernel 6.8.0-147-generic
    notes: "Fails after auditd install; rules written and loaded (augenrules), all present in auditctl -l with auditd 3.1.2; passes after reboot with enabled 2. Snap squashfs mounts skipped."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["26.04"]
    environment: Proxmox VM, Ubuntu 26.04 cloud image, kernel 7.0.0-38-generic
    notes: "Fails after auditd install; rules written and loaded (augenrules), all present in auditctl -l with auditd 4.1.2; passes after reboot with enabled 2. Snap squashfs mounts skipped."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19