CVE-2026-64024 (GCVE-0-2026-64024)

Vulnerability from cvelistv5 – Published: 2026-07-19 15:39 – Updated: 2026-07-20 13:42
VLAI
Title
tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction
Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming the value would always be consumed by tcp_conn_request() for the same packet that wrote it. That assumption is violated by multiple drop paths between the producer (__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer (tcp_conn_request()): - min_ttl / min_hopcount check - xfrm policy check - tcp_inbound_hash() MD5/AO mismatch - tcp_filter() eBPF/SO_ATTACH_FILTER drop - th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv() - tcp_checksum_complete() in tcp_v{4,6}_do_rcv() - tcp_v{4,6}_cookie_check() returning NULL When a packet is dropped on any of these paths, tcp_tw_isn is left set. The next SYN processed on the same CPU then consumes the non zero value in tcp_conn_request(), receiving a potentially predictable ISN. This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu variable. Note that tcp_v{4,6}_fill_cb() do not set it. Very litle impact on overall code size/complexity: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7) Function old new delta tcp_v6_rcv 3038 3042 +4 tcp_v4_rcv 3035 3039 +4 tcp_conn_request 2938 2923 -15 Total: Before=24436060, After=24436053, chg -0.00%
Severity
9.4 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 , < e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd (git)
Affected: 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 , < 4affe063fa56c880cbea8d0bfded0bb80751579d (git)
Affected: 41eecbd712b73f0d5dcf1152b9a1c27b1f238028 , < 1bbf0ced1d9db73ac7893c2187f3459288603e0d (git)
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Linux Linux Affected: 6.10
Unaffected: 0 , < 6.10 (semver)
Unaffected: 6.18.34 , ≤ 6.18.* (semver)
Unaffected: 7.0.11 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/tcp.h",
            "net/ipv4/tcp.c",
            "net/ipv4/tcp_input.c",
            "net/ipv4/tcp_ipv4.c",
            "net/ipv6/tcp_ipv6.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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          "programFiles": [
            "include/net/tcp.h",
            "net/ipv4/tcp.c",
            "net/ipv4/tcp_input.c",
            "net/ipv4/tcp_ipv4.c",
            "net/ipv6/tcp_ipv6.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "6.10"
            },
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              "status": "unaffected",
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              "version": "6.18.34",
              "versionType": "semver"
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              "version": "7.0.11",
              "versionType": "semver"
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              "version": "7.1",
              "versionType": "original_commit_for_fix"
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      ],
      "cpeApplicability": [
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          "nodes": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.10",
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                  "versionEndExcluding": "7.0.11",
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction\n\nBlamed commit moved the TIME_WAIT-derived ISN from the skb control\nblock to a per-CPU variable, assuming the value would always be consumed\nby tcp_conn_request() for the same packet that wrote it. That assumption\nis violated by multiple drop paths between the producer\n(__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer\n(tcp_conn_request()):\n\n - min_ttl / min_hopcount check\n - xfrm policy check\n - tcp_inbound_hash() MD5/AO mismatch\n - tcp_filter() eBPF/SO_ATTACH_FILTER drop\n - th-\u003esyn \u0026\u0026 th-\u003efin discard in tcp_rcv_state_process() TCP_LISTEN\n - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv()\n - tcp_checksum_complete() in tcp_v{4,6}_do_rcv()\n - tcp_v{4,6}_cookie_check() returning NULL\n\nWhen a packet is dropped on any of these paths, tcp_tw_isn is left set.\n\nThe next SYN processed on the same CPU then consumes the non zero value in\ntcp_conn_request(), receiving a potentially predictable ISN.\n\nThis patch moves back tcp_tw_isn to skb-\u003ecb[], getting rid of the per-cpu\nvariable.\n\nNote that tcp_v{4,6}_fill_cb() do not set it.\n\nVery litle impact on overall code size/complexity:\n\n$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new\nadd/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7)\nFunction                                     old     new   delta\ntcp_v6_rcv                                  3038    3042      +4\ntcp_v4_rcv                                  3035    3039      +4\ntcp_conn_request                            2938    2923     -15\nTotal: Before=24436060, After=24436053, chg -0.00%"
        }
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            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H",
            "version": "3.1"
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      "providerMetadata": {
        "dateUpdated": "2026-07-20T13:42:28.932Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd"
        },
        {
          "url": "https://git.kernel.org/stable/c/4affe063fa56c880cbea8d0bfded0bb80751579d"
        },
        {
          "url": "https://git.kernel.org/stable/c/1bbf0ced1d9db73ac7893c2187f3459288603e0d"
        }
      ],
      "title": "tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64024",
    "datePublished": "2026-07-19T15:39:16.598Z",
    "dateReserved": "2026-07-19T07:54:57.027Z",
    "dateUpdated": "2026-07-20T13:42:28.932Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-64024",
      "date": "2026-07-21",
      "epss": "0.0039",
      "percentile": "0.31415"
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  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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