# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-SVC-004
title: Disable LDAP and NIS directory server services the system does not provide
finding:
  title: An LDAP or NIS directory server can run on a system that does not provide one
  description: A forgotten directory server can leak account data or let an attacker publish accounts.
status: active
profiles: [core]
risk:
  severity: medium
assessment: automated
tags: [services, ldap, nis, attack-surface]

description: |
  Directory servers packaged by Debian:

  - OpenLDAP: `slapd`;
  - NIS: `ypserv`, with its companions `yppasswdd` (password changes) and `ypxfrd` (map
    transfers).

  The control passes when each unit is masked or not installed at all.
rationale: |
  A directory server holds account and group data that other systems trust. NIS sends password
  hashes to any client that asks and has no real authentication; an unattended OpenLDAP server
  can expose or accept changes to that data.
impact: |
  Masking a unit stops it and prevents it from starting again. LDAP and NIS clients are not
  affected. Directory servers must exclude this control in their tailoring file.
notes: |
  A unit that does not exist counts as compliant. On Debian 12, `slapd` only ships a System V init
  script; systemd still masks the generated `slapd.service`.

audit:
  manual: |
    For each unit, run `systemctl is-enabled <unit>`. It must print `masked`, or fail because the
    unit does not exist: `slapd.service`, `ypserv.service`, `yppasswdd.service`, `ypxfrd.service`.
  logic: all
  checks:
    - id: slapd
      engine: systemd-unit
      description: OpenLDAP server.
      spec: { unit: slapd.service, state: masked }
    - id: ypserv
      engine: systemd-unit
      description: NIS server.
      spec: { unit: ypserv.service, state: masked }
    - id: yppasswdd
      engine: systemd-unit
      description: NIS password update server.
      spec: { unit: yppasswdd.service, state: masked }
    - id: ypxfrd
      engine: systemd-unit
      description: NIS map transfer server.
      spec: { unit: ypxfrd.service, state: masked }

remediation:
  manual: |
    Stop and mask each unit that is installed: `systemctl mask --now <unit>`. If the package is not
    needed at all, remove it instead: `apt purge slapd ypserv`.
  effects:
    restart: none
    disruption: low
    lockout_risk: false
  rollback: |
    Run `systemctl unmask <unit>` then `systemctl enable --now <unit>`.
  scripts:
    - id: slapd
      from_check: slapd
    - id: ypserv
      from_check: ypserv
    - id: yppasswdd
      from_check: yppasswdd
    - id: ypxfrd
      from_check: ypxfrd

references:
  - title: slapd(8), Debian manual pages
    url: https://manpages.debian.org/trixie/slapd/slapd.8.en.html
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: ypserv(8), Debian manual pages
    url: https://manpages.debian.org/trixie/ypserv/ypserv.8.en.html
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: systemctl(1), Debian manual pages
    url: https://manpages.debian.org/trixie/systemd/systemctl.1.en.html
    publisher: Debian
    kind: vendor-doc
    accessed: 2026-10-18
  - title: ANSSI-BP-028 v2.0 - Recommandations de configuration d'un système GNU/Linux (R62)
    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: R62
    relation: partial
    note: R62 asks to disable every unneeded service and names NIS; this control covers directory servers.
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: CM-7
    relation: partial
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "2.1.10"
    relation: equivalent
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "2.1.13"
    relation: equivalent
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "2.1.7"
    relation: equivalent
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "2.1.10"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1210
  - framework: mitre-attack
    id: T1087.002

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: "Fresh image passes; with slapd and ypserv installed the checks fail (ypserv disabled still fails), fix masks, audit passes after reboot; packages still purge cleanly."
  - date: 2026-10-18
    by: Sn0wAlice
    versions: ["13"]
    environment: Proxmox VM, Debian 13 genericcloud image, kernel 6.12.113+deb13-cloud-amd64
    notes: "Fresh image passes; with slapd and ypserv installed the checks fail (ypserv disabled still fails), fix masks, audit passes after reboot; packages still purge cleanly."
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18