{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2026-80840", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2026-80840", "idYear": 2026, "status": "PUBLISHED", "publishedAt": "2026-09-04T15:54:50.403Z", "updatedAt": "2026-10-19T08:44:33.475Z", "importedAt": "2026-10-24T01:58:30.346Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "ipv6: seg6: clear IPv4 control block on IPIP decapsulation", "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: seg6: clear IPv4 control block on IPIP decapsulation\n\nEnd.DX4 and End.DT4 decapsulate an IPv4 packet through\ndecap_and_validate() and send it directly to IPv4 routing. The inner\npacket therefore bypasses ip_rcv_core(), which normally clears IPCB\nbefore IPv4 interprets skb->cb.\n\nThe skb instead retains IP6CB data from the outer packet. IP6CB and\nIPCB use the same skb->cb storage, so IP6CB(skb)->lastopt overlaps\nIPCB(skb)->opt.optlen and srr, while IP6CB(skb)->nhoff overlaps rr and\nts.\n\nThe sender can make the stale optlen byte nonzero with a valid outer\nextension-header chain. The reproducers put an eight-byte Destination\nOptions header immediately after the 40-byte IPv6 header and before the\nSegment Routing Header. ipv6_destopt_rcv() records the sender-controlled\nDestination Options offset in both lastopt and nhoff, setting them to\n40. On the reproduced little-endian x86-64 kernel, IPv4 therefore sees\noptlen = 40 and rr = 40.\n\nBoth tcp_v4_save_options() and __ip_options_echo() skip option copying\nwhen optlen is zero. Here optlen is 40, so the TCP SYN path allocates\nroom for 40 bytes of option data and calls __ip_options_echo(). The\nstale rr value makes that function read inner packet byte 41 as the\nRecord Route option length. The reproducers set that sender-controlled\nbyte to 255, so __ip_options_echo() copies 255 bytes into the 40-byte\noption-data area.\n\nSeparate End.DX4 and End.DT4 reproducers on the unpatched v7.2-rc5\nkernel both produced:\n\n BUG: KASAN: slab-out-of-bounds in __ip_options_echo()\n Write of size 255\n\nThe relevant End.DX4 call path is:\n\n __ip_options_echo\n tcp_v4_route_req\n tcp_conn_request\n tcp_v4_conn_request\n tcp_rcv_state_process\n tcp_v4_do_rcv\n tcp_v4_rcv\n ip_protocol_deliver_rcu\n ip_local_deliver_finish\n ip_local_deliver\n input_action_end_dx4_finish\n input_action_end_dx4\n\nThe relevant End.DT4 call path is:\n\n __ip_options_echo\n tcp_v4_route_req\n tcp_conn_request\n tcp_v4_conn_request\n tcp_rcv_state_process\n tcp_v4_do_rcv\n tcp_v4_rcv\n ip_protocol_deliver_rcu\n ip_local_deliver_finish\n ip_local_deliver\n input_action_end_dt4\n\ntcp_v4_save_options() is inlined into the tcp_v4_route_req() path, so\nit does not appear as a separate frame.\n\nWhen decap_and_validate() handles IPPROTO_IPIP, save the ingress\ninterface from IP6CB, clear IPCB, and restore the saved value. Doing\nthis in the common decapsulation path covers End.DX4, End.DT4, and\nEnd.DT46's IPv4 arm.\n\nUse IP6CB(skb)->iif rather than skb->skb_iif. These actions run after\nl3mdev processing, which can replace skb_iif with the L3 master;\nIP6CB iif still records the receiving interface set at IPv6 ingress.", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "eb0f422487228e140f3d609b032ac61aedcab8fa" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "f52f1e75716d2ee49e013edf204ac92337c72fd8" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "0e3f01fe2e704e76af4385b8a1742641885a191c" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "3e4476e58343fb8f2fffced9e22d935376b17aaf" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "bf1c1151560d11036a144d917fa4c131831342d7" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "f4be3b391265e24c7720fc867c50062b436acf33" }, { "version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556", "status": "affected", "versionType": "git", "lessThan": "44930446dde45a7a90fe1446fa38eb0e2c561646" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "4.14", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "4.14" }, { "version": "5.10.269", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.15.220", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.15.*" }, { "version": "6.1.187", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.1.*" }, { "version": "6.6.156", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.6.*" }, { "version": "6.12.108", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.12.*" }, { "version": "6.18.49", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.18.*" }, { "version": "7.1.13", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "7.1.*" }, { "version": "7.2.3", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "7.2.*" }, { "version": "7.3", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }