Vulnerability · Published Oct 23, 2026 · Assigned by GitHub_M
CVE-2026-53921odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)
Critical 9.8
In plain English
A critical-severity stack buffer overflow in odhcpd from openwrt. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.1% (higher than 66% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code.
Official 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.
Affected products (as reported)
Weakness: CWE-121 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496 x_refsource_CONFIRM
- https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03 x_refsource_MISC
- https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3 x_refsource_MISC
- https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9 x_refsource_MISC
- https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a x_refsource_MISC
- https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7 x_refsource_MISC
- https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328 x_refsource_MISC