openwrt odhcpd up to 25.11 Response buffer overflow

Summaryinfo

A vulnerability was found in openwrt odhcpd up to 25.11. It has been classified as very critical. This issue affects some unknown processing of the component Response Handler. Performing a manipulation results in buffer overflow. This vulnerability was named CVE-2026-53921. The attack may be initiated remotely. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in openwrt odhcpd up to 25.11. It has been classified as very critical. This affects an unknown code block of the component Response Handler. The manipulation with an unknown input leads to a buffer overflow vulnerability. CWE is classifying the issue as CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-53921 since 06/11/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/23/2026).

Upgrading to version 25.12 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• openwrt

Name

• odhcpd

Version

• 25.0
• 25.1
• 25.2
• 25.3
• 25.4
• 25.5
• 25.6
• 25.7
• 25.8
• 25.9
• 25.10
• 25.11

Website

• Product: https://github.com/openwrt/odhcpd/

CPE 2.3info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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