---
id: "CVE-2026-53921"
kind: "vulnerability"
aliases: ["CVE-2026-53921"]
title: "OpenWrt odhcpd: DHCPv6 packet overflows stack, enables root code execution"
severity: "critical"
cvss: 9.8
epss: 0.0088
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["dhcpv6", "embedded-routers", "odhcpd", "openwrt", "runtime"]
not_affected_if: ["odhcpd-not-installed", "patched-25.12-or-later"]
published_at: "2026-10-23T14:17:53+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-25T12:38:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53921", "first_seen_at": "2026-10-23T21:57:34+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-53921", "first_seen_at": "2026-10-25T12:38:49+00:00"}]
---

# OpenWrt odhcpd: DHCPv6 packet overflows stack, enables root code execution

odhcpd, the DHCP and router-advertisement server on OpenWrt, has a stack buffer overflow in its DHCPv6 handler triggered by one crafted REQUEST packet. A remote attacker with no login can run code as root on the router.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

Run 'odhcpd -v' or check the installed OpenWrt package version (for example 'opkg list-installed | grep odhcpd') and compare it against 25.12.

## Fix

Upgrade odhcpd to version 25.12 or later, which contains the patch.

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-53921
- 2026-10-25T12:38:49+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-53921

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_