# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-BOOT-005
title: Disable core dumps of setuid programs
finding:
  title: Privileged programs can write their memory to core dump files
  description: A crashing setuid program can leave secrets such as password hashes in a core file.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [kernel, sysctl, core-dump, credentials]

description: |
  The `fs.suid_dumpable` sysctl decides whether a process that changed privileges (setuid or
  setgid programs, or programs that dropped privileges) can produce a core dump when it crashes.
  With `0`, such processes never dump core.
rationale: |
  Setuid programs such as `passwd` or `su` handle secrets while running with root privileges.
  A core dump of their memory can expose password hashes, keys or tokens, and an attacker who
  can make one crash may be able to read the dump.
impact: |
  Crashes of setuid programs cannot be analysed from a core dump. Debug them on a test system.
notes: |
  `1` dumps them like any process and `2` dumps them readable by root only. Both are unsafe
  on production systems. Core dumps of regular processes are a separate topic.

  On Ubuntu, apport writes `2` to `fs.suid_dumpable` when it starts, after `/etc/sysctl.d/` has
  been applied, and `0` when it stops. The value set by this fix only survives a reboot when
  apport is disabled (CB-UBU-BOOT-015).

setting:
  location: sysctl `fs.suid_dumpable`, persisted in `/etc/sysctl.d/`
  default_value: "2 while apport runs, 0 otherwise"
  recommended_value: "0"

audit:
  manual: |
    Run `sysctl fs.suid_dumpable`. The value must be `0`.
    Then check that no sysctl configuration file sets another value.
  checks:
    - id: running
      engine: sysctl
      description: Running value of fs.suid_dumpable.
      spec: { key: fs.suid_dumpable, value: 0 }

remediation:
  manual: |
    Create `/etc/sysctl.d/60-cirsec.conf` containing `fs.suid_dumpable = 0`,
    remove any other assignment of this key, then run `sysctl --system`.
  effects:
    restart: none
    disruption: none
    lockout_risk: false
  rollback: |
    Remove the line from `/etc/sysctl.d/60-cirsec.conf` and run `sysctl --system`.
  scripts:
    - id: set
      from_check: running

references:
  - title: Ubuntu Security documentation - Dangerous sysctls
    url: https://documentation.ubuntu.com/security/common-mistakes/dangerous-sysctls/
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
  - title: Linux kernel documentation - Documentation for /proc/sys/fs/ (suid_dumpable)
    url: https://docs.kernel.org/admin-guide/sysctl/fs.html
    publisher: The Linux Kernel Organization
    kind: vendor-doc
    accessed: 2026-10-19
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R14)
    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: R14
    relation: partial
    note: R14 lists several filesystem settings; this control covers fs.suid_dumpable.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: SI-11
    relation: related
  - framework: cis-ubuntu-2004
    framework_version: "3.0.0"
    id: "1.5.3"
    relation: partial
    note: The benchmark item also limits the core file size, which is CB-UBU-BOOT-013.
  - framework: cis-ubuntu-2204
    framework_version: "3.0.0"
    id: "1.5.3"
    relation: equivalent
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "1.5.4"
    relation: equivalent
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "1.5.4"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1003
  - framework: cwe
    id: CWE-528
related_controls:
  - id: CB-UBU-BOOT-015
    type: requires
  - id: CB-UBU-BOOT-013
    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, BIOS boot
    notes: "Fails on a fresh install (2, set by apport); passes once CB-UBU-BOOT-015 stops apport; 0 kept after reboot."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["22.04"]
    environment: Proxmox VM, Ubuntu 22.04 cloud image, kernel 5.15.0-198-generic, BIOS boot
    notes: "Fails on a fresh install (2, set by apport); passes once CB-UBU-BOOT-015 stops apport; 0 kept after reboot."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["24.04"]
    environment: Proxmox VM, Ubuntu 24.04 cloud image, kernel 6.8.0-147-generic, BIOS boot
    notes: "Fails on a fresh install (2, set by apport); passes once CB-UBU-BOOT-015 stops apport; 0 kept after reboot."
  - date: 2026-10-19
    by: Sn0wAlice
    versions: ["26.04"]
    environment: Proxmox VM, Ubuntu 26.04 cloud image, kernel 7.0.0-38-generic, BIOS boot
    notes: "Fails on a fresh install (2, set by apport); passes once CB-UBU-BOOT-015 stops apport; 0 kept after reboot."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19