{"api_version":"1","generated_at":"2026-09-12T20:52:29+00:00","cve":"CVE-2026-80840","urls":{"html":"https://cve.report/CVE-2026-80840","api":"https://cve.report/api/cve/CVE-2026-80840.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-80840","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-80840"},"summary":{"title":"ipv6: seg6: clear IPv4 control block on IPIP decapsulation","description":"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.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-09-04 16:18:12","updated_at":"2026-09-04 16:18:12"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/3e4476e58343fb8f2fffced9e22d935376b17aaf","name":"https://git.kernel.org/stable/c/3e4476e58343fb8f2fffced9e22d935376b17aaf","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/f4be3b391265e24c7720fc867c50062b436acf33","name":"https://git.kernel.org/stable/c/f4be3b391265e24c7720fc867c50062b436acf33","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667","name":"https://git.kernel.org/stable/c/10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/0e3f01fe2e704e76af4385b8a1742641885a191c","name":"https://git.kernel.org/stable/c/0e3f01fe2e704e76af4385b8a1742641885a191c","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/44930446dde45a7a90fe1446fa38eb0e2c561646","name":"https://git.kernel.org/stable/c/44930446dde45a7a90fe1446fa38eb0e2c561646","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/bf1c1151560d11036a144d917fa4c131831342d7","name":"https://git.kernel.org/stable/c/bf1c1151560d11036a144d917fa4c131831342d7","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/f52f1e75716d2ee49e013edf204ac92337c72fd8","name":"https://git.kernel.org/stable/c/f52f1e75716d2ee49e013edf204ac92337c72fd8","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/eb0f422487228e140f3d609b032ac61aedcab8fa","name":"https://git.kernel.org/stable/c/eb0f422487228e140f3d609b032ac61aedcab8fa","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c","name":"https://git.kernel.org/stable/c/9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-80840","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80840","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 eb0f422487228e140f3d609b032ac61aedcab8fa git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 891ef8dd2a8d14e4e73a81dcdb135b574c57f556 f52f1e75716d2ee49e013edf204ac92337c72fd8 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"80840","cve":"CVE-2026-80840","epss":"0.002050000","percentile":"0.104890000","score_date":"2026-09-07","updated_at":"2026-09-08 00:05:27"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["net/ipv6/seg6_local.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"eb0f422487228e140f3d609b032ac61aedcab8fa","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"f52f1e75716d2ee49e013edf204ac92337c72fd8","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"0e3f01fe2e704e76af4385b8a1742641885a191c","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"3e4476e58343fb8f2fffced9e22d935376b17aaf","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"bf1c1151560d11036a144d917fa4c131831342d7","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"f4be3b391265e24c7720fc867c50062b436acf33","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"},{"lessThan":"44930446dde45a7a90fe1446fa38eb0e2c561646","status":"affected","version":"891ef8dd2a8d14e4e73a81dcdb135b574c57f556","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["net/ipv6/seg6_local.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"4.14"},{"lessThan":"4.14","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.269","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.220","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.187","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.156","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.108","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.49","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.13","versionType":"semver"},{"lessThanOrEqual":"7.2.*","status":"unaffected","version":"7.2.3","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.3-rc1","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.269","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.220","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.187","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.156","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.108","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.49","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.13","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.3","versionStartIncluding":"4.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3-rc1","versionStartIncluding":"4.14","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"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."}],"providerMetadata":{"dateUpdated":"2026-09-04T15:54:50.403Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667"},{"url":"https://git.kernel.org/stable/c/eb0f422487228e140f3d609b032ac61aedcab8fa"},{"url":"https://git.kernel.org/stable/c/9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c"},{"url":"https://git.kernel.org/stable/c/f52f1e75716d2ee49e013edf204ac92337c72fd8"},{"url":"https://git.kernel.org/stable/c/0e3f01fe2e704e76af4385b8a1742641885a191c"},{"url":"https://git.kernel.org/stable/c/3e4476e58343fb8f2fffced9e22d935376b17aaf"},{"url":"https://git.kernel.org/stable/c/bf1c1151560d11036a144d917fa4c131831342d7"},{"url":"https://git.kernel.org/stable/c/f4be3b391265e24c7720fc867c50062b436acf33"},{"url":"https://git.kernel.org/stable/c/44930446dde45a7a90fe1446fa38eb0e2c561646"}],"title":"ipv6: seg6: clear IPv4 control block on IPIP decapsulation","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-80840","datePublished":"2026-09-04T15:54:50.403Z","dateReserved":"2026-08-26T14:34:25.796Z","dateUpdated":"2026-09-04T15:54:50.403Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-04 16:18:12","lastModifiedDate":"2026-09-04 16:18:12","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"80840","Ordinal":"1","Title":"ipv6: seg6: clear IPv4 control block on IPIP decapsulation","CVE":"CVE-2026-80840","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"80840","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"ipv6: seg6: clear IPv4 control block on IPIP decapsulation"}]}}}