---
id: "CVE-2026-53920"
kind: "vulnerability"
aliases: ["CVE-2026-53920"]
title: "OpenWrt odhcpd: DHCPv6 IA parser leaks stack memory to network clients"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["dhcpv6", "infrastructure", "openwrt", "routers"]
not_affected_if: ["dhcpv6-server-disabled", "patched-25.12.3-or-later"]
published_at: "2026-10-23T14:17:53+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-23T22:35:03+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53920", "first_seen_at": "2026-10-23T21:57:34+00:00"}]
---

# OpenWrt odhcpd: DHCPv6 IA parser leaks stack memory to network clients

odhcpd, the DHCPv6 and router-advertisement server on OpenWrt, reads past a receive buffer when handling a short IA option from a client. The leaked bytes are returned in the DHCPv6 reply, exposing stack contents including the stack canary, which helps an attacker bypass memory protections.

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

## How to check

Check the installed odhcpd version; the affected range is 17.01.0 up to but not including 25.12.3.

## Fix

Upgrade odhcpd to 25.12.3 or later.

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-53920

## From the sources

odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. From version 17.01.0 to before version 25.12.3, odhcpd's DHCPv6 IA parser accepts an IA_NA or IA_PD option whose body is shorter than struct dhcpv6_ia_hdr, casts the option header to that full structure, and reads ia->iaid before proving that the IA body contains the IAID field. If an unauthenticated network-adjacent client places a zero-length or otherwise short IA option at the end of odhcpd's 8192-byte receive stack buffer, the IAID read crosses from data_buf into adjacent stack memory. The disclosed bytes are then reflected in the DHCPv6 reply IAID; prior ARM validation showed data_buf[8192:8196] disclosing the saved stack canary, and wider stack scans can leak ASLR-useful stack/process contents. This issue has been patched in version 25.12.3.

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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_