CVE-2026-53921criticalCWE-121

CVE-2026-53921: critical vulnerability in openwrt odhcpd

odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)

Published

48Vexday Risk Score

No sign of exploitation. It has a public proof of concept.

ssvc Attendcvss 9.8epss 1.1%
from disclosure to weapon0 days
Published on NVDOct 23
1st PoCJul 28
exploitation probability
1.1%top 34% of all CVEs
observed exploitation
nono source reports it
2 public exploit(s)
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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected products
openwrt · odhcpd
public PoCs found — 2
githubgithub.com/tc4dy/CVE-2026-53921-PoC-Exploit★ 6githubgithub.com/0xBlackash/CVE-2026-53921★ 2
⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.
Related CVEs — openwrt odhcpd

In the same product, most dangerous first.

CVE-2026-53922MEDIUModhcpd: pre-auth remote DoS via size_t underflow in dhcpv6_ia_handle_IAs (stack BOF, canary-terminated)EPSS 0.6%CVE-2026-53918HIGHodhcpd DHCPv6 IA dangling first pointer use-after-freeEPSS 0.5%CVE-2026-53920HIGHodhcpd DHCPv6 Short IA_NA/IA_PD Body Stack DisclosureEPSS 0.4%CVE-2026-55606MEDIUModhcpd: Stack buffer overread via DUID length endianness mismatch in memcmp()EPSS 0.4%
References
https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5ahttps://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496