tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()

{
  "id": "93967d83a5dc2e256ef7437d6e207155b697f486b1747062b7e9d4dc928a785e",
  "url": "https://osv.dev/vulnerability/CVE-2026-98374",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack() When tcp_send_synack() replaces the cloned SYN skb at the head of the retransmit queue with a copy, it frees the original with tcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack. tp->retransmit_skb_hint keeps pointing at the freed skbuff_fclone_cache object. The dangling hint is read in tcp_verify_retransmit_hint() and used as the root of the rbtree walk in tcp_xmit_retransmit_queue(). An unprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with an attacker-supplied ICMP fragmentation-needed message, after which a simultaneous open frees the armed SYN skb: BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) Read of size 4 at addr ffff88800604d928 by task swapper/1/0 Call Trace: tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) tcp_simple_retransmit (net/ipv4/tcp_input.c:3158) tcp_v4_err (net/ipv4/tcp_ipv4.c:587) Sync the hint to the copy.",
    "evidence": "osv:CVE-2026-98374",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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        "affected_versions": []
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    "severity": "high",
    "structured": {
      "id": "CVE-2026-98374",
      "aliases": [
        "CVE-2026-98374"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
        }
      ],
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            "ecosystem": "Linux"
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      "modified": "2026-10-28T02:30:30.035730960Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0f87720c7e4bcab07c24888b3cf12bfe857bb90e",
        "https://git.kernel.org/stable/c/631aa4cb45099f09e9385dd786bd291c6270bfc4",
        "https://git.kernel.org/stable/c/71d45049b0d631dfdbf3c65305f7fca676de023b",
        "https://git.kernel.org/stable/c/c5b4da1f403a658c1c19766be2b426003ada419f",
        "https://git.kernel.org/stable/c/e3ea71cb1408a013ed4e8a757b815f1a919324bd",
        "https://git.kernel.org/stable/c/fad6d429651e748365e93ca54645accc212f0018",
        "https://git.kernel.org/stable/c/fe99bbeee5c5dbd3abc30721a8079ced59649d97",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98374.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98374",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98374.json"
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    "related_cves": [
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        "value": "CVE-2026-98374",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496895,
  "published_at": "2026-10-07T13:01:48.6+00:00"
}