CVE-2026-98374 (GCVE-0-2026-98374)
Vulnerability from cvelistv5
Published
2026-10-07 13:01
Modified
2026-10-24 14:08
Severity ?
8.8 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
Version: c31b70c9968fe9c4194d1b5d06d07596a3b680de
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/tcp_output.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
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          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "5.15.222",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.1.189",
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              "version": "6.6.158",
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              "status": "unaffected",
              "version": "6.12.112",
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            },
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.55",
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            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.222",
                  "versionStartIncluding": "5.11",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.189",
                  "versionStartIncluding": "5.11",
                  "vulnerable": true
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                  "versionEndExcluding": "6.12.112",
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                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.55",
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                  "vulnerable": true
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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-\u003ehighest_sack.\ntp-\u003eretransmit_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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - A malicious IPv4 peer supplies fragmentation-needed ICMP messages quoting the client\u0027s 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\u0027s 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-\u003esyn_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": {
        "dateUpdated": "2026-10-24T14:08:34.914Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
        }
      ],
      "title": "tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98374",
    "datePublished": "2026-10-07T13:01:48.600Z",
    "dateReserved": "2026-09-25T10:25:14.345Z",
    "dateUpdated": "2026-10-24T14:08:34.914Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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