{"id":"CVE-2026-80585","title":"mptcp: fastopen: only mark MPTFO subflows with SYN data","summary":"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 …","severity":"critical","cvss":9.4,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < f75f174edc865738522e514d042cf5627f084859","Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < fca7e444c04689fe4cc6b56f2725f804a4bb1ef9","Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5","Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < 72b4a0c51a4b550d40301d60a366b429b8c8e78d","Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < e00b63056fb4f261455b3e5df5268a1f8ce47a87","Linux 6.2"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-16T19:17:56.710913Z"},"published":"2026-08-26","updated":"2026-10-16","sourceUpdated":"2026-10-16T19:26:28.485Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-80585","references":[{"url":"https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859"},{"url":"https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9"},{"url":"https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5"},{"url":"https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d"},{"url":"https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87"}],"tags":["cve.org"],"epss":0.00313,"epssPercentile":0.22647,"ingestedAt":"2026-10-16T19:46:24.316Z","slug":"CVE-2026-80585","body":"## Overview\n\nIn 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\".\n\n## Affected\n\n- `Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < f75f174edc865738522e514d042cf5627f084859`\n- `Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < fca7e444c04689fe4cc6b56f2725f804a4bb1ef9`\n- `Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5`\n- `Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < 72b4a0c51a4b550d40301d60a366b429b8c8e78d`\n- `Linux >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < e00b63056fb4f261455b3e5df5268a1f8ce47a87`\n- `Linux 6.2`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":52,"depthScoreParts":{"impact":51.7,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}