Vulnerability Description
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.
CVSS Score
CRITICAL
Related Weaknesses (CWE)
References
- https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc0
- https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f
- https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a
- https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5
- https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b
- https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade2832
- https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496
- https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496
FAQ
What is CVE-2026-53921?
CVE-2026-53921 is a vulnerability with a CVSS score of 9.8 (CRITICAL). 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) ...
How severe is CVE-2026-53921?
CVE-2026-53921 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-53921?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.