{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "36b122baf6a8bd46b4a591f12f4ed17b22257408"
            },
            {
              "fixed": "f75f174edc865738522e514d042cf5627f084859"
            },
            {
              "fixed": "fca7e444c04689fe4cc6b56f2725f804a4bb1ef9"
            },
            {
              "fixed": "75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5"
            },
            {
              "fixed": "72b4a0c51a4b550d40301d60a366b429b8c8e78d"
            },
            {
              "fixed": "e00b63056fb4f261455b3e5df5268a1f8ce47a87"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "6.2.0"
            },
            {
              "fixed": "6.6.153"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.7.0"
            },
            {
              "fixed": "6.12.105"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.46"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "7.1.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80585.json"
  },
  "details": "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's 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's 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",
  "modified": "2026-08-28T03:30:20.531807812Z",
  "published": "2026-08-26T14:37:40.901Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80585.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80585"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "mptcp: fastopen: only mark MPTFO subflows with SYN data"
}