CVE-2026-53921 odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-53921?
CVE-2026-53921 is a critical vulnerability in openwrt odhcpd, published on 23 Oct 2026.
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.
Weakness: CWE-121
Which versions are affected by CVE-2026-53921?
How do I fix CVE-2026-53921?
No fix has been published for CVE-2026-53921 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-53921 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53921 exists.
Public exploit code: 3 proofs of concept on GitHub.
Sources
Also known as GHSA-7fwx-hhrg-3496.