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netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.259, 5.15.210, 6.1.176, 6.12.93, 6.18.35, 6.6.143, 7.0.12
CVEs
CVE-2026-63913
Confirmed fixed CVEs
Not specified
Updated in this feed
5 Nov 2026, 04:08 UTC · Revision 1

Source evidence

netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check

core-osv · Original source

Published 19 Jul 2026, 14:55 UTC

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.

osv:CVE-2026-63913

Kernel

Fixed versions: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35, 7.0.12

Complete source record
{
  "id": "2c13cbec622d13eee1162e5cb79f246ce7a896ded8d81cc8b7dccc3001bc8567",
  "url": "https://osv.dev/vulnerability/CVE-2026-63913",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.",
    "evidence": "osv:CVE-2026-63913",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "5.10.259",
            "evidence": "/affected/1/ranges"
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          {
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            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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          {
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            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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          {
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            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.12",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-63913",
      "aliases": [
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H"
        }
      ],
      "affected": [
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              "type": "GIT",
              "events": [
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                },
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                {
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63913.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "2.6.15"
                },
                {
                  "fixed": "5.10.259"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
                },
                {
                  "fixed": "5.15.210"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
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                {
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            },
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                  "introduced": "6.2.0"
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            {
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              "events": [
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                  "introduced": "6.7.0"
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                {
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
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                {
                  "fixed": "6.18.35"
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              ]
            },
            {
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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          "database_specific": {
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          }
        }
      ],
      "modified": "2026-11-01T02:30:42.047690899Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656",
        "https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77",
        "https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238",
        "https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f",
        "https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a",
        "https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8",
        "https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58",
        "https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63913.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-63913",
        "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/2026/63xxx/CVE-2026-63913.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-63913",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 510117,
  "published_at": "2026-07-19T14:55:17.917+00:00"
}