# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-PKG-007
title: Install security updates automatically
finding:
  title: Security updates are not installed automatically
  description: Fixes wait for a human to apply them, often for weeks, while the vulnerabilities they close are public.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [apt, updates, unattended-upgrades]

description: |
  `unattended-upgrades` installs available updates without human action. Two systemd timers drive
  it: `apt-daily.timer` refreshes the package lists and `apt-daily-upgrade.timer` installs the
  updates, when `APT::Periodic::Update-Package-Lists` and `APT::Periodic::Unattended-Upgrade` are
  not `0`. Which updates are installed is set by `Unattended-Upgrade::Origins-Pattern`; Debian's
  default includes the security suite.
rationale: |
  Most compromises exploit vulnerabilities for which a fix already exists. Installing security
  fixes daily and automatically closes that window without depending on a manual process. Debian
  security updates are minimal backported fixes, designed to be installed without review.
impact: |
  Services are restarted by their package when updated, which can cause a short interruption. The
  system is not rebooted (`Unattended-Upgrade::Automatic-Reboot` is false by default), so kernel
  and libc fixes still need a planned reboot. Organisations that deploy updates with a central
  patch management tool can exclude this control in their tailoring file and document it.
notes: |
  Installed and enabled by default on the Debian 12 and 13 cloud images. A Debian installer setup
  installs it only when chosen during installation.

setting:
  location: /etc/apt/apt.conf.d/20auto-upgrades, /etc/apt/apt.conf.d/50unattended-upgrades
  default_value: Enabled on cloud images, depends on the installer choice otherwise
  recommended_value: unattended-upgrades installed, both APT::Periodic options set to 1, security origin allowed, timers enabled

audit:
  manual: |
    1. `dpkg -s unattended-upgrades` shows `Status: install ok installed`.
    2. `apt-config dump APT::Periodic` shows `Update-Package-Lists` and `Unattended-Upgrade` set
       to `1` (or another non-zero value).
    3. `apt-config dump Unattended-Upgrade::Origins-Pattern` contains `label=Debian-Security` or
       a `-security` codename.
    4. `systemctl is-enabled apt-daily.timer apt-daily-upgrade.timer` prints `enabled` twice.
    5. `unattended-upgrade --dry-run --debug` lists the security origin among the allowed ones.
  checks:
    - id: package
      engine: package
      description: unattended-upgrades package.
      spec: { name: unattended-upgrades, state: installed }
    - id: periodic
      engine: shell
      description: APT::Periodic options, as merged by apt-config.
      spec:
        script: |
          eval "$(apt-config shell L APT::Periodic::Update-Package-Lists U APT::Periodic::Unattended-Upgrade)" || exit 3
          echo "Update-Package-Lists=${L:-unset} Unattended-Upgrade=${U:-unset}"
          case ${L:-0}:${U:-0} in 0:* | *:0 | false:* | *:false | no:* | *:no) exit 1 ;; esac
    - id: origins
      engine: shell
      description: Origins allowed to unattended-upgrades.
      spec:
        script: |
          o=$(apt-config dump Unattended-Upgrade::Origins-Pattern Unattended-Upgrade::Allowed-Origins 2>/dev/null | grep -E '::(Origins-Pattern|Allowed-Origins):: ')
          printf '%s\n' "$o" | grep -Ei 'Debian-Security|-security' || { echo "no security origin allowed"; exit 1; }
    - id: lists-timer
      engine: systemd-unit
      description: Timer that refreshes the package lists.
      spec: { unit: apt-daily.timer, state: enabled }
    - id: upgrade-timer
      engine: systemd-unit
      description: Timer that installs the updates.
      spec: { unit: apt-daily-upgrade.timer, state: enabled }

remediation:
  manual: |
    1. `apt-get install unattended-upgrades`.
    2. Write `/etc/apt/apt.conf.d/20auto-upgrades` with
       `APT::Periodic::Update-Package-Lists "1";` and `APT::Periodic::Unattended-Upgrade "1";`
       (this is what `dpkg-reconfigure -plow unattended-upgrades` does), and remove any later
       setting to `0`.
    3. If `Unattended-Upgrade::Origins-Pattern` was customised, add back
       `"origin=Debian,codename=${distro_codename}-security,label=Debian-Security";` in
       `/etc/apt/apt.conf.d/50unattended-upgrades`.
    4. `systemctl enable --now apt-daily.timer apt-daily-upgrade.timer`.
  effects:
    restart: none
    disruption: low
    lockout_risk: false
  rollback: |
    Set both `APT::Periodic` options to `0` in `/etc/apt/apt.conf.d/20auto-upgrades`, or purge
    `unattended-upgrades`.
  scripts:
    - id: package
      from_check: package
    - id: periodic
      engine: shell
      content: |
        f=/etc/apt/apt.conf.d/20auto-upgrades
        cb_backup "$f"
        printf '%s\n' 'APT::Periodic::Update-Package-Lists "1";' 'APT::Periodic::Unattended-Upgrade "1";' >"$f"
    - id: lists-timer
      from_check: lists-timer
    - id: upgrade-timer
      from_check: upgrade-timer

references:
  - title: unattended-upgrade(8), Debian manual pages
    url: https://manpages.debian.org/trixie/unattended-upgrades/unattended-upgrade.8.en.html
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: Debian Wiki - UnattendedUpgrades
    url: https://wiki.debian.org/UnattendedUpgrades
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: The Debian Administrator's Handbook - Automatic upgrades
    url: https://www.debian.org/doc/manuals/debian-handbook/sect.regular-upgrades.en.html
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R61)
    url: https://messervices.cyber.gouv.fr/documents-guides/fr_np_linux_configuration-v2.0.pdf
    publisher: ANSSI
    kind: guide
    accessed: 2026-10-18
mappings:
  - framework: anssi-linux
    framework_version: "2.0"
    id: R61
    relation: partial
    note: R61 asks for a regular and reactive security update process; this control automates the Debian part of it.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: SI-2(5)
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1190
  - framework: mitre-attack
    id: T1068
  - framework: cwe
    id: CWE-1395
related_controls:
  - id: CB-DEB-PKG-006
    type: requires
  - id: CB-DEB-PKG-008
    type: related

authors:
  - name: Alice
    github: Sn0wAlice
verified:
  - date: 2026-10-18
    by: Sn0wAlice
    versions: ["12"]
    environment: Proxmox VM, Debian 12 genericcloud image, kernel 6.1.0-54-cloud-amd64
    notes: "Passes on stock; purged package, missing 20auto-upgrades and disabled upgrade timer detected; fix reinstalls, rewrites 20auto-upgrades and enables the timer; kept after reboot."
  - date: 2026-10-18
    by: Sn0wAlice
    versions: ["13"]
    environment: Proxmox VM, Debian 13 genericcloud image, kernel 6.12.113+deb13-cloud-amd64
    notes: "Passes on stock; purged package, missing 20auto-upgrades and disabled upgrade timer detected; fix reinstalls, rewrites 20auto-upgrades and enables the timer; kept after reboot."
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18