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.
References8
- github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621d…
- github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200…
- github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7…
- github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c…
- github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f…
- github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca…
- github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-34…
- github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-34…
Metrics
- CVSS 3.1
-
9.8
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - EPSS — exploit probability
- 1% percentile: 66 · as of 8 November 2026
- CWE
- CWE-121
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.