{"id":"CVE-2026-98374","state":"PUBLISHED","title":"tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()\n\nWhen tcp_send_synack() replaces the cloned SYN skb at the head of the\nretransmit queue with a copy, it frees the original with\ntcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack.\ntp->retransmit_skb_hint keeps pointing at the freed\nskbuff_fclone_cache object.\n\nThe dangling hint is read in tcp_verify_retransmit_hint() and used as\nthe root of the rbtree walk in tcp_xmit_retransmit_queue().  An\nunprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with\nan attacker-supplied ICMP fragmentation-needed message, after which a\nsimultaneous open frees the armed SYN skb:\n\n  BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)\n  Read of size 4 at addr ffff88800604d928 by task swapper/1/0\n  Call Trace:\n   tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)\n   tcp_simple_retransmit (net/ipv4/tcp_input.c:3158)\n   tcp_v4_err (net/ipv4/tcp_ipv4.c:587)\n\nSync the hint to the copy.","publishedAt":"2026-10-07T13:01:48.600Z","updatedAt":"2026-10-24T14:08:34.914Z","severity":{"score":8.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"fad6d429651e748365e93ca54645accc212f0018","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"c5b4da1f403a658c1c19766be2b426003ada419f","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"71d45049b0d631dfdbf3c65305f7fca676de023b","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"e3ea71cb1408a013ed4e8a757b815f1a919324bd","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"631aa4cb45099f09e9385dd786bd291c6270bfc4","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"0f87720c7e4bcab07c24888b3cf12bfe857bb90e","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"fe99bbeee5c5dbd3abc30721a8079ced59649d97","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/tcp_output.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.11","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.55","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.9","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/tcp_output.c"]}],"references":["https://git.kernel.org/stable/c/fad6d429651e748365e93ca54645accc212f0018","https://git.kernel.org/stable/c/c5b4da1f403a658c1c19766be2b426003ada419f","https://git.kernel.org/stable/c/71d45049b0d631dfdbf3c65305f7fca676de023b","https://git.kernel.org/stable/c/e3ea71cb1408a013ed4e8a757b815f1a919324bd","https://git.kernel.org/stable/c/631aa4cb45099f09e9385dd786bd291c6270bfc4","https://git.kernel.org/stable/c/0f87720c7e4bcab07c24888b3cf12bfe857bb90e","https://git.kernel.org/stable/c/fe99bbeee5c5dbd3abc30721a8079ced59649d97"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98374.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98374","state":"PUBLISHED","datePublished":"2026-10-07T13:01:48.600Z","dateUpdated":"2026-10-24T14:08:34.914Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.345Z"},"containers":{"cna":{"title":"tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()\n\nWhen tcp_send_synack() replaces the cloned SYN skb at the head of the\nretransmit queue with a copy, it frees the original with\ntcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack.\ntp->retransmit_skb_hint keeps pointing at the freed\nskbuff_fclone_cache object.\n\nThe dangling hint is read in tcp_verify_retransmit_hint() and used as\nthe root of the rbtree walk in tcp_xmit_retransmit_queue().  An\nunprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with\nan attacker-supplied ICMP fragmentation-needed message, after which a\nsimultaneous open frees the armed SYN skb:\n\n  BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)\n  Read of size 4 at addr ffff88800604d928 by task swapper/1/0\n  Call Trace:\n   tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316)\n   tcp_simple_retransmit (net/ipv4/tcp_input.c:3158)\n   tcp_v4_err (net/ipv4/tcp_ipv4.c:587)\n\nSync the hint to the copy."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"fad6d429651e748365e93ca54645accc212f0018","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"c5b4da1f403a658c1c19766be2b426003ada419f","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"71d45049b0d631dfdbf3c65305f7fca676de023b","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"e3ea71cb1408a013ed4e8a757b815f1a919324bd","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"631aa4cb45099f09e9385dd786bd291c6270bfc4","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"0f87720c7e4bcab07c24888b3cf12bfe857bb90e","versionType":"git"},{"version":"c31b70c9968fe9c4194d1b5d06d07596a3b680de","status":"affected","lessThan":"fe99bbeee5c5dbd3abc30721a8079ced59649d97","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/tcp_output.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.11","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.55","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.9","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/tcp_output.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/fad6d429651e748365e93ca54645accc212f0018"},{"url":"https://git.kernel.org/stable/c/c5b4da1f403a658c1c19766be2b426003ada419f"},{"url":"https://git.kernel.org/stable/c/71d45049b0d631dfdbf3c65305f7fca676de023b"},{"url":"https://git.kernel.org/stable/c/e3ea71cb1408a013ed4e8a757b815f1a919324bd"},{"url":"https://git.kernel.org/stable/c/631aa4cb45099f09e9385dd786bd291c6270bfc4"},{"url":"https://git.kernel.org/stable/c/0f87720c7e4bcab07c24888b3cf12bfe857bb90e"},{"url":"https://git.kernel.org/stable/c/fe99bbeee5c5dbd3abc30721a8079ced59649d97"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","baseScore":8.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - A malicious IPv4 peer supplies fragmentation-needed ICMP messages quoting the client's TFO SYN and an ACK-less crossed TCP SYN; ip_rcv() dispatches these through tcp_v4_err() and tcp_rcv_state_process() to the patched tcp_send_synack().\nAC:L - After the victim's TFO send, the peer controls packet ordering: ICMP makes tcp_simple_retransmit() cache and clone the SYN, then the crossed SYN makes tcp_send_synack() free it; a later PMTU event dereferences the stale hint without requiring a race or external failure.\nPR:N - The ordinary TCP and ICMP paths require only a matching tuple and quoted sequence, not authentication or target privileges; a peer that received the TFO SYN knows the values checked by tcp_v4_err() and the TCP socket lookup.\nUI:R - A victim-side process must issue sendmsg(MSG_FASTOPEN) with data and a usable cookie or no-cookie mode to establish tp->syn_data in TCP_SYN_SENT; remote packets alone cannot construct this vulnerable retransmit queue state.\nS:U - The freed skb, retransmit tree, and subsequent stale accesses all belong to the same host kernel TCP security authority; tcp_send_synack() does not cross a VM, IOMMU, or sandbox boundary.\nC:H - retransmit_skb_hint retains a freed skbuff_fclone_cache address, and tcp_verify_retransmit_hint() reads its TCP control block while tcp_xmit_retransmit_queue() follows its rbnode links, permitting attacker-influenced stale-object reads after slab reuse.\nI:H - tcp_xmit_retransmit_queue() can treat the reclaimed object as a live skb and pass it into retransmission code that modifies skb control and header state; attacker-shaped reuse of the stale rbnode and skb fields makes this UAF exploitable for kernel memory corruption.\nA:H - The demonstrated stale TCP_SKB_CB read already triggers KASAN in tcp_mark_skb_lost(), while using the freed object as an rbtree-walk root can dereference invalid links and cause a kernel oops or panic."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-24T14:08:34.914Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"5.15.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.12.112"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.18.55"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"7.2.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}