# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-AUTH-003
title: Protect the login banner files from modification
finding:
  title: Login banner files can be changed by non-root users
  description: Someone who can rewrite the banners can remove the legal notice or plant misleading instructions for users.
status: active
profiles: [core]
risk:
  severity: low
assessment: automated
tags: [banner, login, permissions]

description: |
  `/etc/issue`, `/etc/issue.net` and `/etc/motd` are shown to users before or after login. They
  must be owned by root and writable only by root.
rationale: |
  A writable banner lets an attacker remove the legal warning, or display fake instructions that
  trick users into running commands or giving out credentials.
impact: |
  None known. These are the Debian defaults.

setting:
  location: /etc/issue, /etc/issue.net, /etc/motd
  default_value: "root:root 0644"
  recommended_value: "root:root, mode 0644 or stricter"

audit:
  manual: |
    Run `stat -c '%n %U:%G %a' /etc/issue /etc/issue.net /etc/motd`.
    Each file must be `root:root` with mode `644` or stricter.
  checks:
    - id: issue
      engine: file-perms
      spec: { path: /etc/issue, owner: root, group: root, mode: "0644" }
    - id: issue-net
      engine: file-perms
      spec: { path: /etc/issue.net, owner: root, group: root, mode: "0644" }
    - id: motd
      engine: file-perms
      spec: { path: /etc/motd, owner: root, group: root, mode: "0644" }

remediation:
  manual: |
    Run `chown root:root /etc/issue /etc/issue.net /etc/motd` and
    `chmod 644 /etc/issue /etc/issue.net /etc/motd`.
  effects:
    restart: none
    disruption: none
    lockout_risk: false
  scripts:
    - id: issue
      from_check: issue
    - id: issue-net
      from_check: issue-net
    - id: motd
      from_check: motd

references:
  - title: issue(5), Debian manual pages
    url: https://manpages.debian.org/trixie/manpages/issue.5.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 (R50)
    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: R50
    relation: partial
    note: R50 covers every sensitive file; this control covers the login banners.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: AC-3
    relation: related
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "1.6.6"
    relation: partial
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "1.6.7"
    relation: partial
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "1.6.8"
    relation: partial
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "1.6.6"
    relation: partial
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "1.6.7"
    relation: partial
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "1.6.8"
    relation: partial
threats:
  - framework: cwe
    id: CWE-732

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: Generated check, fix and check again for profiles core and server-hardened; state 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: Generated check, fix and check again for profiles core and server-hardened; state kept after reboot.
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18