# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-UBU-BOOT-002
title: Hide kernel addresses from users
finding:
  title: Kernel memory addresses are exposed through /proc and other interfaces
  description: Leaked kernel addresses defeat kernel address randomization and help local privilege escalation exploits.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [kernel, sysctl, information-disclosure]

description: |
  The `kernel.kptr_restrict` sysctl controls whether kernel pointers printed through `%pK`
  (for example in `/proc/kallsyms` and `/proc/modules`) are shown. With `1`, they are hidden
  from users without the `CAP_SYSLOG` capability. With `2`, they are hidden from everyone,
  including root.
rationale: |
  Kernel exploits need the address of kernel structures and functions. The kernel randomizes
  its own layout at boot, but a single leaked pointer is enough to undo that randomization.
  Hiding pointers removes an easy source of leaks for a local attacker.
impact: |
  With `2`, profiling and tracing tools run as root (`perf`, some eBPF tools) see zeroed kernel
  addresses and cannot resolve kernel symbols. Use `1` on hosts where administrators need them.
notes: |
  Ubuntu ships `1` (`/etc/sysctl.d/10-kernel-hardening.conf`, `/usr/lib/sysctl.d/55-kernel-hardening.conf`
  on 26.04), which hides pointers from unprivileged users only, so the check fails with the
  default parameter. The value can be raised at runtime; lowering it needs no reboot either.

setting:
  location: sysctl `kernel.kptr_restrict`, persisted in `/etc/sysctl.d/`
  default_value: "1"
  recommended_value: "At least {{ kptr_restrict }}"

parameters:
  - name: kptr_restrict
    type: integer
    description: Minimum value of kernel.kptr_restrict. 1 hides pointers from unprivileged users, 2 from everyone.
    default: 2
    minimum: 1
    maximum: 2

audit:
  manual: |
    Run `sysctl kernel.kptr_restrict`. The value must be at least {{ kptr_restrict }}.
    Then check that no sysctl configuration file sets a lower value.
  checks:
    - id: running
      engine: sysctl
      description: Running value of kernel.kptr_restrict.
      spec: { key: kernel.kptr_restrict, operator: ">=", value: "{{ kptr_restrict }}" }

remediation:
  manual: |
    Create `/etc/sysctl.d/60-cirsec.conf` containing `kernel.kptr_restrict = {{ kptr_restrict }}`,
    remove any other assignment of this key, then run `sysctl --system`.
  effects:
    restart: none
    disruption: low
    lockout_risk: false
  rollback: |
    Remove the line from `/etc/sysctl.d/60-cirsec.conf` and run `sysctl -w kernel.kptr_restrict=1`.
  scripts:
    - id: set
      from_check: running

references:
  - title: Ubuntu Security documentation - Kernel protections
    url: https://documentation.ubuntu.com/security/security-features/kernel-protections/
    publisher: Canonical
    kind: vendor-doc
    accessed: 2026-10-19
  - title: Linux kernel documentation - Documentation for /proc/sys/kernel/ (kptr_restrict)
    url: https://docs.kernel.org/admin-guide/sysctl/kernel.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 (R9)
    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: R9
    relation: partial
    note: R9 recommends 2 among other kernel settings; this control covers kernel.kptr_restrict only.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: SC-30
    relation: related
  - framework: cis-ubuntu-2404
    framework_version: "2.0.0"
    id: "1.5.8"
    relation: stricter
    note: The benchmark accepts 1; ours defaults to 2.
  - framework: cis-ubuntu-2604
    framework_version: "1.0.0"
    id: "1.5.8"
    relation: stricter
    note: The benchmark accepts 1; ours defaults to 2.
threats:
  - framework: mitre-attack
    id: T1068
  - framework: cwe
    id: CWE-200

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 (1); generated fix sets 2; kept after reboot; second remediate leaves it alone."
  - 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 (1); generated fix sets 2; kept after reboot; second remediate leaves it alone."
  - 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 (1); generated fix sets 2; kept after reboot; second remediate leaves it alone."
  - 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 (1); generated fix sets 2; kept after reboot; second remediate leaves it alone."
introduced_in: 0.1.0
created: 2026-10-19
updated: 2026-10-19