# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-PKG-005
title: Restrict access to APT repository credentials
finding:
  title: APT repository credentials are readable or writable by other users
  description: Local users can read the logins and passwords used to reach private repositories or proxies, or replace them.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [apt, credentials, permissions]

description: |
  `/etc/apt/auth.conf` and the `.conf` files of `/etc/apt/auth.conf.d/` hold logins and passwords
  for private repositories and proxies, in a netrc-like format. APT reads them as root before it
  drops privileges, so they can be `root:root` mode `0600`. The directory itself should be
  `root:root` mode `0755` or stricter.
rationale: |
  These credentials often give access to commercial or internal repositories, sometimes shared by
  a whole fleet. A readable file leaks them to every local user; a writable directory lets a user
  add or change them.
impact: |
  None known. The directory is empty on a default installation; the file checks apply only when
  files exist.

setting:
  location: /etc/apt/auth.conf, /etc/apt/auth.conf.d
  default_value: "Directory root:root 0755, no file"
  recommended_value: "Directory root:root 0755 or stricter, files root:root 0600 or stricter"

audit:
  manual: |
    1. `stat -c '%U:%G %a' /etc/apt/auth.conf.d` shows `root:root` and `755` or stricter.
    2. `stat -c '%U:%G %a %n' /etc/apt/auth.conf /etc/apt/auth.conf.d/*` shows `root:root` and
       `600` or stricter for every existing file.
  checks:
    - id: auth-conf-d
      engine: file-perms
      description: The /etc/apt/auth.conf.d directory.
      spec: { path: /etc/apt/auth.conf.d, owner: root, group: root, mode: "0755" }
    - id: auth-conf-d-files
      engine: file-perms
      description: Files in /etc/apt/auth.conf.d (not applicable when empty).
      spec: { path: "/etc/apt/auth.conf.d/*", owner: root, group: root, mode: "0600" }
    - id: auth-conf
      engine: file-perms
      description: The legacy /etc/apt/auth.conf file (not applicable when absent).
      spec: { path: /etc/apt/auth.conf, owner: root, group: root, mode: "0600" }

remediation:
  manual: |
    Run `chown root:root /etc/apt/auth.conf.d`, `chmod 755 /etc/apt/auth.conf.d`, then for each
    credential file `chown root:root <file>` and `chmod 600 <file>`. Change the passwords if the
    files were readable by other users.
  effects:
    restart: none
    disruption: none
    lockout_risk: false
  rollback: |
    Restore the previous owner and mode with `chown` and `chmod`.
  scripts:
    - id: auth-conf-d
      from_check: auth-conf-d
    - id: auth-conf-d-files
      from_check: auth-conf-d-files
    - id: auth-conf
      from_check: auth-conf

references:
  - title: apt_auth.conf(5), Ubuntu manual pages
    url: https://manpages.ubuntu.com/manpages/noble/man5/apt_auth.conf.5.html
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
mappings:
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: IA-5
    relation: related
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "1.2.1.5"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "1.2.1.6"
    relation: stricter
    note: Files must not be readable by their group either (0600).
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "1.2.1.5"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "1.2.1.6"
    relation: stricter
    note: Files must not be readable by their group either (0600).
threats:
  - framework: mitre-attack
    id: T1552.001
  - framework: cwe
    id: CWE-522
related_controls:
  - id: CB-UBU-PKG-004
    type: related

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 stock (empty auth.conf.d); 0644 credential file detected and fixed."
  - 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 stock (empty auth.conf.d); 0644 credential file detected and fixed."
  - 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 stock (empty auth.conf.d); 0644 credential file detected and fixed."
  - 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 stock (empty auth.conf.d); 0644 credential file detected and fixed."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19