# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-BOOT-012
title: Restrict access to the boot loader configuration
finding:
  title: Users can read the boot loader configuration
  description: The GRUB configuration can hold the boot password hash and reveals the boot parameters of the system.
status: active
profiles: [core]
risk:
  severity: low
assessment: automated
tags: [grub, boot, permissions]

applicability:
  facts: [grub]

description: |
  `/boot/grub/grub.cfg` is the configuration GRUB reads at boot. It is generated by `update-grub`
  and contains every boot entry, the kernel command lines and, when one is set, the PBKDF2 hash
  of the boot password.
rationale: |
  A readable password hash can be attacked offline. Restricting the file to root also hides the
  boot parameters from local users and stops them from learning which protections are enabled.
impact: |
  None known. GRUB reads the file before the operating system starts, and `update-grub` keeps
  the restricted mode when it regenerates the file.

setting:
  location: /boot/grub/grub.cfg
  default_value: "root:root 0644"
  recommended_value: "root:root, mode 0600 or stricter"

audit:
  manual: |
    Run `stat -c '%U:%G %a' /boot/grub/grub.cfg`. It must print `root:root` and a mode of `600` or stricter.
  checks:
    - id: perms
      engine: file-perms
      description: Owner, group and mode of /boot/grub/grub.cfg.
      spec: { path: /boot/grub/grub.cfg, owner: root, group: root, mode: "0600" }

remediation:
  manual: |
    Run `chown root:root /boot/grub/grub.cfg` and `chmod 600 /boot/grub/grub.cfg`.
  effects:
    restart: none
    disruption: none
    lockout_risk: false
  rollback: |
    Run `chmod 644 /boot/grub/grub.cfg`.
  scripts:
    - id: perms
      from_check: perms

references:
  - 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 (R29)
    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: R29
    relation: partial
    note: R29 restricts the whole /boot directory; this control covers the GRUB configuration.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: AC-3
    relation: related
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "1.4.2"
    relation: equivalent
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "1.4.2"
    relation: equivalent
threats:
  - framework: cwe
    id: CWE-732
related_controls:
  - id: CB-DEB-BOOT-011
    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, BIOS boot
    notes: Fails on fresh install (0644); fix sets 0600; mode kept by update-grub and after reboot.
  - 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: Fails on fresh install (0644); fix sets 0600; mode kept by update-grub and after reboot.
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18