FKIE_CVE-2026-80585

Vulnerability from fkie_nvd - Published: 2026-08-26 15:17 - Updated: 2026-08-26 15:17
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: mptcp: fastopen: only mark MPTFO subflows with SYN data Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty. mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established(). Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty. Note that mptcp_subflow_context's is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really "doing TFO".
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/mptcp/fastopen.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f75f174edc865738522e514d042cf5627f084859",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
              "lessThan": "fca7e444c04689fe4cc6b56f2725f804a4bb1ef9",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
              "lessThan": "75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
              "lessThan": "72b4a0c51a4b550d40301d60a366b429b8c8e78d",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
              "lessThan": "e00b63056fb4f261455b3e5df5268a1f8ce47a87",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/mptcp/fastopen.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.2"
            },
            {
              "lessThan": "6.2",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.153",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.105",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.46",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fastopen: only mark MPTFO subflows with SYN data\n\nPassive TCP Fast Open accepts a valid-cookie SYN even when it carries\nno data. In that case the child socket\u0027s receive queue is intentionally\nleft empty.\n\nmptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking\nfor queued SYN data. That made data-less TFO SYNs hit a WARN and, if\nthe warning was non-fatal, left stale MPTFO state behind. The stale\nflag could later trigger a state-confusion bug in\ncheck_fully_established().\n\nOnly mark the subflow as MPTFO after confirming that an SKB was queued.\nReturn quietly when the receive queue is empty.\n\nNote that mptcp_subflow_context\u0027s is_mptfo field is now not just about\nsubflows where the TFO was present, but about MPTFO subflow that\nconsumed SYN data. Only having a valid cookie but not carrying data is\nnot really \"doing TFO\"."
    }
  ],
  "id": "CVE-2026-80585",
  "lastModified": "2026-08-26T15:17:14.750",
  "metrics": {},
  "published": "2026-08-26T15:17:14.750",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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