# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-AUTH-026
title: Store every password hash in shadow and leave no account without a password
finding:
  title: An account has its password hash in /etc/passwd, or an empty password
  description: /etc/passwd is readable by every user; an empty password field opens the account to anyone.
status: active
profiles: [core]
risk:
  severity: high
assessment: automated
tags: [accounts, password, shadow]

description: |
  `/etc/passwd` is world-readable and must only contain `x` in the password field; the hashes
  belong in `/etc/shadow`, readable by root and the `shadow` group only. In `/etc/shadow`, each
  password field holds a hash, or `!`/`*` for locked accounts, but is never empty.
rationale: |
  A hash left in `/etc/passwd` can be copied and cracked by any local user. An empty password
  field lets anyone log in to the account where empty passwords are accepted.
impact: |
  None for a standard system.

audit:
  manual: |
    1. `awk -F: '$2 != "x"' /etc/passwd` prints nothing.
    2. `awk -F: '$2 == ""' /etc/shadow` prints nothing.
  checks:
    - id: shadowed
      engine: shell
      spec:
        script: |
          u=$(awk -F: '$2 != "x" {print $1}' /etc/passwd | tr '\n' ' ')
          echo "not shadowed: ${u:-none}"
          [ -z "$u" ]
    - id: not-empty
      engine: shell
      spec:
        script: |
          u=$(awk -F: '$2 == "" {print $1}' /etc/shadow | tr '\n' ' ')
          echo "empty password: ${u:-none}"
          [ -z "$u" ]

remediation:
  manual: |
    1. Run `pwconv` to move any hash from `/etc/passwd` to `/etc/shadow`.
    2. Lock each account with an empty password (`passwd -l <user>`) or give it one (`passwd <user>`).
  effects:
    restart: none
    disruption: low
    lockout_risk: false
  rollback: |
    Restore `/etc/passwd` and `/etc/shadow` from the backup.
  scripts:
    - id: fix
      engine: shell
      content: |
        cb_backup /etc/passwd
        cb_backup /etc/shadow
        pwconv
        for u in $(awk -F: '$2 == "" {print $1}' /etc/shadow); do passwd -l "$u" >/dev/null; done

references:
  - title: shadow(5), Ubuntu manual pages
    url: https://manpages.ubuntu.com/manpages/noble/man5/shadow.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 (R68)
    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: R68
    relation: partial
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: IA-5(1)
    relation: related
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "7.2.1"
    relation: equivalent
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "7.2.2"
    relation: equivalent
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "7.2.1"
    relation: equivalent
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "7.2.2"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "7.2.1"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "7.2.2"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "7.2.1"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "7.2.2"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1003.008

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: "Passes on a fresh install; profiles core and server-hardened."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["22.04"]
    environment: Proxmox VM, Ubuntu 22.04 cloud image, kernel 5.15.0-198-generic
    notes: "Passes on a fresh install; profiles core and server-hardened."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["24.04"]
    environment: Proxmox VM, Ubuntu 24.04 cloud image, kernel 6.8.0-147-generic
    notes: "Passes on a fresh install; profiles core and server-hardened."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["26.04"]
    environment: Proxmox VM, Ubuntu 26.04 cloud image, kernel 7.0.0-38-generic
    notes: "Passes on a fresh install; profiles core and server-hardened."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19