# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-AUDIT-034
title: Build the AIDE database and check file integrity every day
finding:
  title: File integrity is never checked
  description: Without a reference database and a regular check, AIDE cannot report modified system files.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [aide, integrity, systemd]

description: |
  AIDE needs a reference database, `/var/lib/aide/aide.db`, built with `aideinit` from the
  current state of the system. `aide-common` then runs a daily check, which compares the files
  with the database and writes a report to `/var/log/aide/` (and mails it when a mail transport
  is installed):

  - from Ubuntu 24.04 (AIDE 0.18 and later), with `dailyaidecheck.timer`;
  - on Ubuntu 20.04 and 22.04 (AIDE 0.16 and 0.17), with the cron job `/etc/cron.daily/aide`,
    which `CRON_DAILY_RUN=no` in `/etc/default/aide` turns off.

  This control requires the database to exist and the daily check to be enabled.
rationale: |
  The database is the trusted reference; the daily check turns it into detection. Without either,
  an installed AIDE gives a false sense of protection.
impact: |
  Building the database reads every covered file: a few minutes and a short burst of disk
  activity. The daily check does the same. After legitimate changes (upgrades, configuration),
  review the report and update the database (`aide --update`, then replace `aide.db` with
  `aide.db.new`).
notes: |
  Build the database once the system is in its intended state: run this fix after the other
  hardening fixes, or rebuild the database afterwards with `aideinit -y -f`, otherwise the first
  reports list every change made by the hardening.

setting:
  location: /var/lib/aide/aide.db, dailyaidecheck.timer (20.04 and 22.04 - /etc/cron.daily/aide)
  default_value: No database; daily check enabled when aide-common is installed
  recommended_value: Database present, daily check enabled

audit:
  manual: |
    1. Run `ls -l /var/lib/aide/aide.db`. The file must exist and not be empty.
    2. Ubuntu 24.04 and later: run `systemctl is-enabled dailyaidecheck.timer`. It must print
       `enabled`. Ubuntu 20.04 and 22.04: `/etc/cron.daily/aide` must be executable and
       `/etc/default/aide` must not set `CRON_DAILY_RUN=no`.
    3. Read the last report in `/var/log/aide/` and check that differences are explained.
  checks:
    - id: database
      engine: shell
      description: The AIDE reference database exists.
      spec:
        script: |
          if [ -s /var/lib/aide/aide.db ]; then
            ls -l /var/lib/aide/aide.db
          else
            echo "/var/lib/aide/aide.db missing or empty"
            exit 1
          fi
    - id: timer
      engine: systemd-unit
      description: dailyaidecheck.timer is enabled.
      versions: ["24.04", "26.04"]
      spec: { unit: dailyaidecheck.timer, state: enabled }
    - id: cron
      engine: shell
      description: The daily AIDE cron job is present and not turned off (AIDE 0.16 and 0.17).
      versions: ["20.04", "22.04"]
      spec:
        script: |
          [ -x /etc/cron.daily/aide ] || { echo "/etc/cron.daily/aide missing or not executable"; exit 1; }
          v=$(sed -n 's/^[[:space:]]*CRON_DAILY_RUN=//p' /etc/default/aide 2>/dev/null | tail -n 1 | tr -d "\"'")
          echo "/etc/cron.daily/aide present, CRON_DAILY_RUN=${v:-yes (default)}"
          [ "${v:-yes}" = yes ]

remediation:
  manual: |
    1. Run `aideinit -y -f` and wait for it to finish (a few minutes).
    2. Ubuntu 24.04 and later: run `systemctl enable --now dailyaidecheck.timer`. Ubuntu 20.04 and
       22.04: run `chmod 755 /etc/cron.daily/aide` and set `CRON_DAILY_RUN=yes` (or remove the line)
       in `/etc/default/aide`.
  effects:
    restart: none
    disruption: low
    lockout_risk: false
  rollback: |
    Run `systemctl disable --now dailyaidecheck.timer` (20.04 and 22.04: set `CRON_DAILY_RUN=no` in `/etc/default/aide`) and delete `/var/lib/aide/aide.db`.
  scripts:
    - id: database
      engine: shell
      content: |
        command -v aideinit >/dev/null 2>&1 || { echo "AIDE is not installed" >&2; exit 1; }
        # umask 027: aideinit would otherwise create its logs readable by everyone
        [ -s /var/lib/aide/aide.db ] || (umask 027; aideinit -y -f)
    - id: timer
      from_check: timer
    - id: cron
      engine: shell
      versions: ["20.04", "22.04"]
      content: |
        [ -f /etc/cron.daily/aide ] || { echo "AIDE is not installed" >&2; exit 1; }
        chmod 755 /etc/cron.daily/aide
        if grep -Eq '^[[:space:]]*CRON_DAILY_RUN=' /etc/default/aide 2>/dev/null; then
          cb_backup /etc/default/aide
          sed -i 's/^[[:space:]]*CRON_DAILY_RUN=.*/CRON_DAILY_RUN=yes/' /etc/default/aide
        fi

references:
  - title: aideinit(8), Ubuntu manual pages
    url: https://manpages.ubuntu.com/manpages/noble/man8/aideinit.8.html
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
  - title: systemd.timer(5), Ubuntu manual pages
    url: https://manpages.ubuntu.com/manpages/noble/man5/systemd.timer.5.html
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R76)
    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: R76
    relation: equivalent
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: SI-7(1)
    relation: related
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "6.1.1"
    relation: partial
    note: The package installation is in CB-UBU-AUDIT-032.
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "6.1.2"
    relation: equivalent
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "6.3.1"
    relation: partial
    note: The package installation is in CB-UBU-AUDIT-032.
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "6.3.2"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "6.3.1"
    relation: partial
    note: The package installation is in CB-UBU-AUDIT-032.
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "6.3.2"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "6.3.1"
    relation: partial
    note: The package installation is in CB-UBU-AUDIT-032.
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "6.3.2"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1036.005
  - framework: cwe
    id: CWE-353
related_controls:
  - id: CB-UBU-AUDIT-032
    type: requires
  - id: CB-UBU-AUDIT-033
    type: requires
  - id: CB-UBU-AUDIT-035
    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 on stock image; aideinit builds aide.db (about 10 min on 1 vCPU), cron.daily/aide present; passes after reboot."
  - 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 on stock image; aideinit builds aide.db (about 10 min on 1 vCPU), cron.daily/aide present; passes after reboot."
  - 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 on stock image; aideinit builds aide.db, dailyaidecheck.timer enabled; passes after reboot."
  - 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 on stock image; aideinit builds aide.db, dailyaidecheck.timer enabled; passes after reboot."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19