# yaml-language-server: $schema=../../../../schema/control.schema.json
id: CB-DEB-NET-001
title: Decide whether IPv6 is used, and disable or secure it accordingly
finding:
  title: IPv6 is active without a decision to use it
  description: An IPv6 stack nobody planned for is often left unfiltered and unmonitored, next to a hardened IPv4 configuration.
status: active
profiles: [core]
risk:
  severity: low
assessment: manual
tags: [ipv6, network]

description: |
  Debian enables IPv6 by default: every interface gets a link-local address, and a global address
  as soon as a router advertises a prefix. Each system must have a recorded decision: either IPv6
  is used, and it is configured and filtered like IPv4, or it is not, and the stack is disabled.
rationale: |
  Firewall rules, monitoring and hardening are often written for IPv4 only. An IPv6 stack left on
  by default gives an attacker on the local network a second, less watched path to the system
  (router advertisements, link-local services).
impact: |
  Disabling IPv6 breaks software that expects `::1` or IPv6 sockets. Check local services after the
  change.
notes: |
  The IPv6 sysctl controls of this standard only apply when the IPv6 stack is present, through the
  `ipv6` fact.

audit:
  manual: |
    1. Find whether IPv6 is enabled: `test -d /proc/sys/net/ipv6 && sysctl net.ipv6.conf.all.disable_ipv6`
       (`0` means enabled), and list addresses with `ip -6 address`.
    2. Check the system documentation for a decision on IPv6 for this host.
    3. If IPv6 is used, check that the firewall also filters IPv6 (`ufw status verbose` with
       `IPV6=yes` in `/etc/default/ufw`, or an `inet`/`ip6` table in `nft list ruleset`).

remediation:
  manual: |
    - If IPv6 is not used, add `ipv6.disable=1` to `GRUB_CMDLINE_LINUX` in `/etc/default/grub`,
      run `update-grub` and reboot. Without access to the boot loader, set
      `net.ipv6.conf.all.disable_ipv6 = 1` and `net.ipv6.conf.default.disable_ipv6 = 1` in
      `/etc/sysctl.d/60-cirsec.conf` instead.
    - If IPv6 is used, apply the IPv6 controls of this standard and filter IPv6 in the firewall.
    - Record the decision in the system documentation.
  rollback: |
    Remove `ipv6.disable=1` or the `disable_ipv6` lines, then reboot.

references:
  - title: Linux kernel documentation - IP Sysctl (disable_ipv6)
    url: https://docs.kernel.org/networking/ip-sysctl.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 (R13)
    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: R13
    relation: equivalent
  - framework: nist-800-53r5
    framework_version: "5.1.1"
    id: CM-7
    relation: related
  - framework: cis-debian-12
    framework_version: "2.0.0"
    id: "3.1.1"
    relation: equivalent
  - framework: cis-debian-13
    framework_version: "1.1.0"
    id: "3.1.1"
    relation: equivalent
threats:
  - framework: mitre-attack
    id: T1557
related_controls:
  - id: CB-DEB-NET-014
    type: related

authors:
  - name: Alice
    github: Sn0wAlice
introduced_in: 0.1.0
created: 2026-10-18
updated: 2026-10-18