{ "affected": [ { "ranges": [ { "events": [ { "introduced": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556" }, { "fixed": "10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667" }, { "fixed": "eb0f422487228e140f3d609b032ac61aedcab8fa" }, { "fixed": "9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c" }, { "fixed": "f52f1e75716d2ee49e013edf204ac92337c72fd8" }, { "fixed": "0e3f01fe2e704e76af4385b8a1742641885a191c" }, { "fixed": "3e4476e58343fb8f2fffced9e22d935376b17aaf" }, { "fixed": "bf1c1151560d11036a144d917fa4c131831342d7" }, { "fixed": "f4be3b391265e24c7720fc867c50062b436acf33" }, { "fixed": "44930446dde45a7a90fe1446fa38eb0e2c561646" } ], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "type": "GIT" } ] }, { "package": { "ecosystem": "Linux", "name": "Kernel" }, "ranges": [ { "events": [ { "introduced": "4.14.0" }, { "fixed": "5.10.269" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "5.11.0" }, { "fixed": "5.15.220" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "5.16.0" }, { "fixed": "6.1.187" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.2.0" }, { "fixed": "6.6.156" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.7.0" }, { "fixed": "6.12.108" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.13.0" }, { "fixed": "6.18.49" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.19.0" }, { "fixed": "7.1.13" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "7.2.0" }, { "fixed": "7.2.3" } ], "type": "ECOSYSTEM" } ] } ], "database_specific": { "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80840.json" }, "details": "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-\u003ecb.\n\nThe skb instead retains IP6CB data from the outer packet. IP6CB and\nIPCB use the same skb-\u003ecb storage, so IP6CB(skb)-\u003elastopt overlaps\nIPCB(skb)-\u003eopt.optlen and srr, while IP6CB(skb)-\u003enhoff 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)-\u003eiif rather than skb-\u003eskb_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.", "id": "CVE-2026-80840", "modified": "2026-09-06T03:30:30.928707341Z", "published": "2026-09-04T15:54:50.403Z", "references": [ { "type": "WEB", "url": "https://git.kernel.org/stable/c/0e3f01fe2e704e76af4385b8a1742641885a191c" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/3e4476e58343fb8f2fffced9e22d935376b17aaf" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/44930446dde45a7a90fe1446fa38eb0e2c561646" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/bf1c1151560d11036a144d917fa4c131831342d7" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/eb0f422487228e140f3d609b032ac61aedcab8fa" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/f4be3b391265e24c7720fc867c50062b436acf33" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/f52f1e75716d2ee49e013edf204ac92337c72fd8" }, { "type": "ADVISORY", "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80840.json" }, { "type": "ADVISORY", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80840" }, { "type": "PACKAGE", "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git" } ], "schema_version": "1.9.0", "summary": "ipv6: seg6: clear IPv4 control block on IPIP decapsulation" }