# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-DESK-004
title: Never run software automatically from inserted media in GNOME
finding:
  title: GNOME can start programs from inserted media
  description: When a disc or USB device is inserted, GNOME may offer or start the program the medium declares, which a crafted medium can abuse.
status: active
profiles: [desktop]
risk:
  severity: medium
assessment: automated
tags: [gnome, dconf, removable-media]

applicability:
  facts: [desktop-gnome]

description: |
  `org.gnome.desktop.media-handling autorun-never` set to `true` stops GNOME from prompting
  for or launching programs when media are inserted. The key is set in the system dconf
  database `local` and locked.
rationale: |
  Autorun turns the insertion of a medium into code execution with one click, or none if the
  user chose "always". It is a classic infection path for removable media.
impact: |
  Users open media content themselves from the file manager.
notes: |
  Ubuntu 24.04 and 26.04 (GNOME 46 and 50) already default to `true`; 20.04 and 22.04 (GNOME
  3.36 and 42) default to `false`. In every version, users can change
  it unless the key is locked.

setting:
  location: /etc/dconf/db/local.d/, key /org/gnome/desktop/media-handling/autorun-never
  default_value: false (20.04, 22.04), true (24.04, 26.04), not locked
  recommended_value: true, locked

audit:
  manual: |
    1. `dconf read /org/gnome/desktop/media-handling/autorun-never` must print `true`.
    2. The key must be listed in a file of `/etc/dconf/db/local.d/locks/`.
  checks:
    - id: autorun-never
      engine: dconf
      description: GNOME never runs software from inserted media.
      facts: [desktop-gnome]
      spec:
        key: /org/gnome/desktop/media-handling/autorun-never
        value: "true"

remediation:
  manual: |
    1. Make sure `/etc/dconf/profile/user` contains `user-db:user` and `system-db:local`.
    2. Create `/etc/dconf/db/local.d/00-media-autorun`:
       ```
       [org/gnome/desktop/media-handling]
       autorun-never=true
       ```
    3. List `/org/gnome/desktop/media-handling/autorun-never` in
       `/etc/dconf/db/local.d/locks/00-media-autorun`.
    4. Run `dconf update`.
  effects:
    restart: session
    disruption: none
    lockout_risk: false
  rollback: |
    Delete the files written in `/etc/dconf/db/local.d/` and its `locks/` directory, then run
    `dconf update`.
  scripts:
    - id: autorun-never
      from_check: autorun-never

references:
  - title: gsettings-desktop-schemas - org.gnome.desktop.media-handling schema
    url: https://gitlab.gnome.org/GNOME/gsettings-desktop-schemas/-/blob/master/schemas/org.gnome.desktop.media-handling.gschema.xml.in
    publisher: The GNOME Project
    kind: vendor-doc
    accessed: 2026-10-19
  - title: GNOME System Administration Guide - Lock down specific settings
    url: https://help.gnome.org/admin/system-admin-guide/stable/dconf-lockdown.html.en
    publisher: The GNOME Project
    kind: vendor-doc
    accessed: 2026-10-19
mappings:
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "1.7.8"
    relation: equivalent
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "1.7.9"
    relation: equivalent
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "1.7.8"
    relation: equivalent
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "1.7.9"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "1.7.5"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "1.7.5"
    relation: equivalent
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: CM-7
    relation: related
threats:
  - framework: mitre-attack
    id: T1091
related_controls:
  - id: CB-UBU-DESK-001
    type: related

authors:
  - name: Alice
    github: Sn0wAlice
verified:
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["20.04"]
    environment: Proxmox VM with Ubuntu Desktop (GNOME 3.36, gdm3), Ubuntu 20.04.6, kernel 5.4.0-216-generic
    notes: "Generated dconf check and fix (desktop-hardened); value and lock confirmed with gsettings get/writable as a user under dbus-run-session (write refused); second remediation reported compliant; state kept after reboot."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["22.04"]
    environment: Proxmox VM with Ubuntu Desktop (GNOME 42, gdm3), Ubuntu 22.04.5, kernel 5.15.0-198-generic
    notes: "Generated dconf check and fix (desktop-hardened); value and lock confirmed with gsettings get/writable as a user under dbus-run-session (write refused); second remediation reported compliant; state kept after reboot."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["24.04"]
    environment: Proxmox VM with Ubuntu Desktop (GNOME 46, gdm3), Ubuntu 24.04.5, kernel 6.8.0-147-generic
    notes: "Generated dconf check and fix (desktop-hardened); value and lock confirmed with gsettings get/writable as a user under dbus-run-session (write refused); second remediation reported compliant; state kept after reboot."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["26.04"]
    environment: Proxmox VM with Ubuntu Desktop (GNOME 50, gdm3), Ubuntu 26.04.1, kernel 7.0.0-38-generic
    notes: "Generated dconf check and fix (desktop-hardened); value and lock confirmed with gsettings get/writable as a user under dbus-run-session (write refused); second remediation reported compliant; state kept after reboot."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19