# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-BOOT-011
title: Protect the boot loader configuration with a password
finding:
  title: Anyone at the console can edit the boot entries
  description: Editing the kernel command line at boot (for example adding init=/bin/sh) gives a root shell without any password.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [grub, boot, physical-access]

applicability:
  facts: [grub]

description: |
  GRUB can require a superuser name and password before anyone edits a boot entry or opens the
  GRUB command line. The password is stored as a PBKDF2 hash in the GRUB configuration.
  Marking the normal boot entries `--unrestricted` keeps unattended boots working: the password
  is only asked to change them.
rationale: |
  Whoever reaches the console (physically, through a hypervisor console or a remote management
  card) can otherwise edit the kernel command line, boot into single-user mode or a shell, and
  bypass every account and audit control of the system.
impact: |
  Editing boot entries or using the GRUB shell during an incident needs the GRUB password. Store
  it with the other break-glass secrets. Boots without changes are not affected.
notes: |
  Full disk encryption is the stronger protection against offline attacks. The GRUB password
  does not protect against booting another medium; restrict that in the firmware settings.

setting:
  location: "`/etc/grub.d/40_custom` (or another file in `/etc/grub.d/`), compiled into `/boot/grub/grub.cfg`"
  default_value: No password
  recommended_value: A superuser and a PBKDF2 password hash

audit:
  manual: |
    In `/boot/grub/grub.cfg`, check that a `set superusers=` line and a `password_pbkdf2` line exist.
  checks:
    - id: superusers
      engine: file-content
      description: A GRUB superuser is declared.
      spec: { path: /boot/grub/grub.cfg, pattern: "^\\s*set\\s+superusers=" }
    - id: password
      engine: file-content
      description: The superuser has a PBKDF2 password.
      spec: { path: /boot/grub/grub.cfg, pattern: "^\\s*password_pbkdf2\\s+" }

remediation:
  manual: |
    1. Generate a hash: `grub-mkpasswd-pbkdf2`.
    2. Append to `/etc/grub.d/40_custom`:
       ```
       set superusers="root"
       password_pbkdf2 root grub.pbkdf2.sha512.10000.<hash>
       ```
    3. To keep normal boots unattended, add `--unrestricted` to the `CLASS=` line of
       `/etc/grub.d/10_linux`, or to each `menuentry` you want bootable without a password.
    4. Run `update-grub`, then reboot once from the console to confirm the default entry still boots.
  rollback: |
    Remove the two lines from `/etc/grub.d/40_custom` and run `update-grub`.

references:
  - title: grub-mkpasswd-pbkdf2(1), Debian manual pages
    url: https://manpages.debian.org/trixie/grub-common/grub-mkpasswd-pbkdf2.1.en.html
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: GNU GRUB Manual - Authentication and authorisation
    url: https://www.gnu.org/software/grub/manual/grub/html_node/Authentication-and-authorisation.html
    publisher: GNU Project
    kind: vendor-doc
    accessed: 2026-10-18
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R5)
    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: R5
    relation: equivalent
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: AC-3
    relation: related
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "1.4.1"
    relation: equivalent
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "1.4.1"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1542

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, BIOS boot
    notes: Manual procedure applied (pbkdf2 hash, --unrestricted); check passes; unattended reboot works.
  - date: 2026-10-18
    by: Sn0wAlice
    versions: ["13"]
    environment: Proxmox VM, Debian 13 genericcloud image, kernel 6.12.113+deb13-cloud-amd64, BIOS boot
    notes: Manual procedure applied (pbkdf2 hash, --unrestricted); check passes; unattended reboot works.
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18