{"id":"CVE-2026-80840","revision":"ddc4449465584d8bb40db8b04b1c2a45","records":[{"revision":"ddc4449465584d8bb40db8b04b1c2a45","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-80840","aliases":[],"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":0,"publishedAt":"2026-09-04T15:54:50.403+00:00","modifiedAt":"2026-10-19T08:44:33.475+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"net/ipv6/seg6_local.c\"\n ],\n \"versions\": [\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"eb0f422487228e140f3d609b032ac61aedcab8fa\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"f52f1e75716d2ee49e013edf204ac92337c72fd8\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"0e3f01fe2e704e76af4385b8a1742641885a191c\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"3e4476e58343fb8f2fffced9e22d935376b17aaf\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"bf1c1151560d11036a144d917fa4c131831342d7\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"f4be3b391265e24c7720fc867c50062b436acf33\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"891ef8dd2a8d14e4e73a81dcdb135b574c57f556\",\n \"lessThan\": \"44930446dde45a7a90fe1446fa38eb0e2c561646\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"net/ipv6/seg6_local.c\"\n ],\n \"versions\": [\n {\n \"version\": \"4.14\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"4.14\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.10.269\",\n \"lessThanOrEqual\": \"5.10.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.220\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.187\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.156\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.108\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.49\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.1.13\",\n \"lessThanOrEqual\": \"7.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2.3\",\n \"lessThanOrEqual\": \"7.2.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.3\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667","https://git.kernel.org/stable/c/eb0f422487228e140f3d609b032ac61aedcab8fa","https://git.kernel.org/stable/c/9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c","https://git.kernel.org/stable/c/f52f1e75716d2ee49e013edf204ac92337c72fd8","https://git.kernel.org/stable/c/0e3f01fe2e704e76af4385b8a1742641885a191c","https://git.kernel.org/stable/c/3e4476e58343fb8f2fffced9e22d935376b17aaf","https://git.kernel.org/stable/c/bf1c1151560d11036a144d917fa4c131831342d7","https://git.kernel.org/stable/c/f4be3b391265e24c7720fc867c50062b436acf33","https://git.kernel.org/stable/c/44930446dde45a7a90fe1446fa38eb0e2c561646"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-80840","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-80840","identifiers":["CVE-2026-80840"]},"retained":false,"historicalAffected":[]}],"coverage":[]}