{"id":"CVE-2026-53921","title":"odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)","summary":"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 …","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-121"],"vendor":"openwrt","product":"odhcpd","affected":["odhcpd < 25.12"],"exploitAvailable":true,"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T13:20:30.249Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-53921","references":[{"url":"https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496","label":"https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496"},{"url":"https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03","label":"https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03"},{"url":"https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3","label":"https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3"},{"url":"https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9","label":"https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9"},{"url":"https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a","label":"https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a"},{"url":"https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7","label":"https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7"},{"url":"https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328","label":"https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328"}],"tags":["cve.org","exploit-available"],"exploits":{"github":2,"githubRepos":["https://github.com/tc4dy/CVE-2026-53921-PoC-Exploit","https://github.com/0xBlackash/CVE-2026-53921"],"checkedAt":"2026-10-23T14:28:42.423Z"},"ingestedAt":"2026-10-23T14:28:08.714Z","slug":"CVE-2026-53921","body":"## Overview\n\nodhcpd 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.\n\n## Affected\n\n- `odhcpd < 25.12`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"abyssal","depthScore":66,"depthScoreParts":{"impact":53.9,"likelihood":0,"exploitation":12,"ransomware":0},"changes":[]}