{"id":"CVE-2026-53921","state":"PUBLISHED","title":"odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)","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.","publishedAt":"2026-10-23T13:20:30.249Z","updatedAt":"2026-10-29T13:28:11.455Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["openwrt odhcpd"],"affected":[{"vendor":"openwrt","product":"odhcpd","versions":[{"version":"< 25.12","status":"affected"}]}],"references":["https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496","https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03","https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3","https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9","https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a","https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7","https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328"],"weaknesses":["CWE-121"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/53xxx/CVE-2026-53921.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-53921","state":"PUBLISHED","datePublished":"2026-10-23T13:20:30.249Z","dateUpdated":"2026-10-29T13:28:11.455Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-11T15:46:12.316Z"},"containers":{"cna":{"title":"odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"openwrt","product":"odhcpd","versions":[{"version":"< 25.12","status":"affected"}]}],"references":[{"url":"https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496","name":"https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03","name":"https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03","tags":["x_refsource_MISC"]},{"url":"https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3","name":"https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3","tags":["x_refsource_MISC"]},{"url":"https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9","name":"https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9","tags":["x_refsource_MISC"]},{"url":"https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a","name":"https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a","tags":["x_refsource_MISC"]},{"url":"https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7","name":"https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7","tags":["x_refsource_MISC"]},{"url":"https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328","name":"https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":9.8,"baseSeverity":"CRITICAL","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-121","lang":"en","description":"CWE-121: Stack-based Buffer Overflow","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-10-23T13:20:30.249Z"},"source":{"advisory":"GHSA-7fwx-hhrg-3496","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-29T13:27:12.914498Z","id":"CVE-2026-53921","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-29T13:28:11.455Z"}}]}}}