# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-BOOT-004
title: Restrict ptrace to descendant processes
finding:
  title: Any process can trace and read the memory of other processes of the same user
  description: A compromised process can read secrets (SSH agent keys, browser sessions) from every other process the user runs.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [kernel, sysctl, yama, credentials]

description: |
  The Yama security module adds the `kernel.yama.ptrace_scope` sysctl, which restricts the
  `ptrace` system call used by debuggers to inspect and modify other processes:

  - `0`: a process can trace any process with the same user ID.
  - `1`: a process can only trace its own descendants, unless the target allows it explicitly.
  - `2`: only processes with the `CAP_SYS_PTRACE` capability can use `ptrace`.
  - `3`: nobody can use `ptrace`, and the value cannot be changed until the next reboot.
rationale: |
  With the default `0`, malware running as a user can attach to the user's SSH agent, password
  manager or browser and read keys and session tokens from their memory. Limiting `ptrace` to
  descendants keeps normal debugging (`gdb ./program`, `strace command`) working while blocking
  attachment to unrelated running processes.
impact: |
  With `1`, attaching a debugger to an already running process (`gdb -p`, `strace -p`) needs
  root or `CAP_SYS_PTRACE`. With `2`, every use of `ptrace` needs privileges, which breaks
  debugging by regular users. `3` cannot be undone without a reboot.

setting:
  location: sysctl `kernel.yama.ptrace_scope`, persisted in `/etc/sysctl.d/`
  default_value: "0"
  recommended_value: "At least {{ ptrace_scope }}"

parameters:
  - name: ptrace_scope
    type: integer
    description: Minimum value of kernel.yama.ptrace_scope.
    default: 1
    profile_defaults:
      server-hardened: 2
      desktop-hardened: 2
    minimum: 1
    maximum: 3

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

remediation:
  manual: |
    Create `/etc/sysctl.d/60-cirsec.conf` containing `kernel.yama.ptrace_scope = {{ ptrace_scope }}`,
    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.yama.ptrace_scope=0`.
    A value of 3 can only be lowered by rebooting after removing the line.
  scripts:
    - id: set
      from_check: running

references:
  - title: Linux kernel documentation - Yama
    url: https://docs.kernel.org/admin-guide/LSM/Yama.html
    publisher: The Linux Kernel Organization
    kind: vendor-doc
    accessed: 2026-10-18
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R11)
    url: https://messervices.cyber.gouv.fr/documents-guides/fr_np_linux_configuration-v2.0.pdf
    publisher: ANSSI
    kind: guide
    accessed: 2026-10-18
mappings:
  - framework: anssi-linux
    framework_version: "2.0"
    id: R11
    relation: equivalent
    note: Both require a value of at least 1.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: SC-39
    relation: related
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "1.5.3"
    relation: equivalent
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "1.5.3"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1055.008
  - framework: mitre-attack
    id: T1003

authors:
  - name: Alice
    github: Sn0wAlice
verified:
  - date: 2026-10-18
    by: Sn0wAlice
    versions: ["12"]
    environment: Proxmox VM, Debian 12 genericcloud image, kernel 6.1.0-54-cloud-amd64
    notes: Generated check, fix and check again for profiles core and server-hardened; values kept after reboot; fix idempotent.
  - date: 2026-10-18
    by: Sn0wAlice
    versions: ["13"]
    environment: Proxmox VM, Debian 13 genericcloud image, kernel 6.12.113+deb13-cloud-amd64
    notes: Generated check, fix and check again for profiles core and server-hardened; values kept after reboot; fix idempotent.
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18