---
id: CVE-2026-123603
title: Hickory DNS Missing IPv4-Mapped IPv6 Canonicalization Access Control Bypass
summary: >-
  hickory-proto and hickory-resolver 0.26.0 before 0.26.2, hickory-server
  0.25.0-alpha.1 before 0.26.2, and hickory-recursor 0.25.0-alpha.3 through
  0.26.0-alpha.1 fail to canonicalize IPv4-mapped IPv6 addresses when checking
  deny_answers, …
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-284
vendor: hickory-dns
product: hickory-dns
affected:
  - hickory-dns >= 0.25.0-alpha.3 <= 0.26.0-alpha.1
  - hickory-dns >= 0.26.0 < 0.26.2
  - hickory-dns >= 0.26.0 < 0.26.2
  - hickory-dns >= 0.25.0-alpha.1 < 0.26.2
published: '2026-11-08'
updated: '2026-11-08'
sourceUpdated: '2026-11-08T01:38:30.679Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-123603'
references:
  - url: >-
      https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-4jwp-xjwm-333g
    label: GitHub Security Advisory (GHSA-4jwp-xjwm-333g)
  - url: >-
      https://www.vulncheck.com/advisories/hickory-dns-missing-ipv4-mapped-ipv6-canonicalization-access-control-bypass
    label: >-
      VulnCheck Advisory: Hickory DNS Missing IPv4-Mapped IPv6 Canonicalization
      Access Control Bypass
tags:
  - cve.org
ingestedAt: '2026-11-08T02:43:18.641Z'
---

## Overview

hickory-proto and hickory-resolver 0.26.0 before 0.26.2, hickory-server 0.25.0-alpha.1 before 0.26.2, and hickory-recursor 0.25.0-alpha.3 through 0.26.0-alpha.1 fail to canonicalize IPv4-mapped IPv6 addresses when checking deny_answers, deny_server, or AccessControlSet rules. Attackers can use IPv4-mapped addresses to evade answer filtering, trigger queries to denied nameservers, or reach hickory-server library deployments on dual-stack IPv6 sockets from denied clients.

## Affected

- `hickory-dns >= 0.25.0-alpha.3 <= 0.26.0-alpha.1`
- `hickory-dns >= 0.26.0 < 0.26.2`
- `hickory-dns >= 0.26.0 < 0.26.2`
- `hickory-dns >= 0.25.0-alpha.1 < 0.26.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.