---
id: CVE-2026-53921
title: >-
  odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent
  sites)
summary: >-
  odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt.
  Prior to version 25.12, odhcpd's DHCPv6 IA response handler writes past the
  end of a fixed 512-byte stack buffer (pdbuf) when a single DHCPv6 REQUEST
  carries …
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-121
vendor: openwrt
product: odhcpd
affected:
  - odhcpd < 25.12
exploitAvailable: true
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T13:20:30.249Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-53921'
references:
  - url: 'https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496'
    label: 'https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496'
  - url: >-
      https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03
    label: >-
      https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03
  - url: >-
      https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3
    label: >-
      https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3
  - url: >-
      https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9
    label: >-
      https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9
  - url: >-
      https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a
    label: >-
      https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a
  - url: >-
      https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7
    label: >-
      https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7
  - url: >-
      https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328
    label: >-
      https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328
tags:
  - cve.org
  - exploit-available
exploits:
  github: 2
  githubRepos:
    - 'https://github.com/tc4dy/CVE-2026-53921-PoC-Exploit'
    - 'https://github.com/0xBlackash/CVE-2026-53921'
  checkedAt: '2026-10-23T14:28:42.423Z'
ingestedAt: '2026-10-23T14:28:08.714Z'
---

## Overview

odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. Prior to version 25.12, odhcpd's DHCPv6 IA response handler writes past the end of a fixed 512-byte stack buffer (pdbuf) when a single DHCPv6 REQUEST carries enough IA options to nearly exhaust the reply space. Two independent overflow sites exist in the same call chain, both reachable from the network via a single unauthenticated UDP packet. odhcpd runs as root on OpenWrt; embedded targets often lack stack canaries and ASLR, making code execution realistic. This issue has been patched in version 25.12.

## Affected

- `odhcpd < 25.12`

## Remediation

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