Buffer overflow in Openwrt Odhcpd
CVE-2026-53921
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Openwrt Odhcpd — versions < 25.12
Weakness classification (CWE)
References
- github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496
- github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03
- github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3
- github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9
- github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a
- github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7
- github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328
Frequently asked questions
- What is CVE-2026-53921?
- CVE-2026-53921 is a critical-severity vulnerability in Openwrt Odhcpd, classified under Stack-based Buffer Overflow. CVSS score: 9.8/10. Published 2026-10-23.
- How severe is CVE-2026-53921?
- Critical severity. CVSS v3 base score is 9.8 out of 10.