{"api_version":"1","generated_at":"2026-09-03T05:01:56+00:00","cve":"CVE-2026-80585","urls":{"html":"https://cve.report/CVE-2026-80585","api":"https://cve.report/api/cve/CVE-2026-80585.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-80585","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-80585"},"summary":{"title":"mptcp: fastopen: only mark MPTFO subflows with SYN data","description":"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\".","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-26 15:17:14","updated_at":"2026-08-27 06:17:45"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"9.4","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H","baseScore":9.4,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"9.4","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H","data":{"baseScore":9.4,"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"}}],"references":[{"url":"https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5","name":"https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d","name":"https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87","name":"https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859","name":"https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9","name":"https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-80585","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80585","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 36b122baf6a8bd46b4a591f12f4ed17b22257408 f75f174edc865738522e514d042cf5627f084859 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 36b122baf6a8bd46b4a591f12f4ed17b22257408 fca7e444c04689fe4cc6b56f2725f804a4bb1ef9 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 36b122baf6a8bd46b4a591f12f4ed17b22257408 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 36b122baf6a8bd46b4a591f12f4ed17b22257408 72b4a0c51a4b550d40301d60a366b429b8c8e78d git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 36b122baf6a8bd46b4a591f12f4ed17b22257408 e00b63056fb4f261455b3e5df5268a1f8ce47a87 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.2","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.2 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.153 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.105 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.46 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.10 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"80585","cve":"CVE-2026-80585","epss":"0.003170000","percentile":"0.239660000","score_date":"2026-08-27","updated_at":"2026-08-28 00:03:39"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"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"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.153","versionStartIncluding":"6.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.105","versionStartIncluding":"6.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.46","versionStartIncluding":"6.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.10","versionStartIncluding":"6.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"6.2","vulnerable":true}],"negate":false,"operator":"OR"}]}],"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'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\"."}],"metrics":[{"cvssV3_1":{"baseScore":9.4,"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"},"scenarios":[{"lang":"en","value":"AV:N - The bug is reached by sending crafted TCP/MPTCP segments to a listening socket over the network (ip4/ip6 receive -> tcp_conn_request/tcp_rcv_state_process -> subflow_prep_synack or mptcp_incoming_options -> check_fully_established); per kernel CNA guidance, net stack packet-handling paths are Network.\nAC:L - In the intended passive-MPTFO deployment (MPTCP listener with net.ipv4.tcp_fastopen server bit set), the attacker controls obtaining a valid TFO cookie and then sending a data-less SYN followed by an out-of-order MPC_ACK to deterministically hit the stale is_mptfo path in check_fully_established().\nPR:N - Exploitation requires only unauthenticated inbound TCP connections to an MPTCP listener; the attacker obtains the TFO cookie from their own prior connection and needs no local account, capability, or namespace privileges on the target host.\nUI:N - No victim interaction is required beyond the server normally accepting TCP connections; the attacker programmatically sends the SYN and follow-up MPC_ACK packets without anyone opening files, clicking links, or performing other actions.\nS:U - Impact is confined to kernel MPTCP/TCP connection state on the target host and does not cross VM, container, IOMMU, or other security boundaries; it is not a sandbox or guest-to-host escape.\nC:L - Premature fully_established with attacker-chosen MPTCP keys desynchronizes handshake and DSS/map state, enabling misdelivery or premature exposure of connection-level data/metadata to the remote peer before normal MP_CAPABLE validation completes.\nI:H - Stale is_mptfo lets an out-of-order MPC_ACK force __mptcp_subflow_fully_established(), writing attacker-controlled sndr_key/ack_seq into msk and subflow crypto state and corrupting subsequent DSS/ACK handling on the server multipath socket.\nA:H - Data-less passive-TFO SYNs hit WARN_ON_ONCE(!skb) on every trigger, and the resulting inconsistent is_mptfo/fully_established state can cause repeatable kernel WARN/oops (panic_on_warn panic) plus connection reset storms against internet-facing MPTCP servers."}]}],"providerMetadata":{"dateUpdated":"2026-08-27T05:02:06.112Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"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"}],"title":"mptcp: fastopen: only mark MPTFO subflows with SYN data","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-80585","datePublished":"2026-08-26T14:37:40.901Z","dateReserved":"2026-08-26T14:34:25.769Z","dateUpdated":"2026-08-27T05:02:06.112Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-26 15:17:14","lastModifiedDate":"2026-08-27 06:17:45","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H","baseScore":9.4,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":5.5}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"80585","Ordinal":"1","Title":"mptcp: fastopen: only mark MPTFO subflows with SYN data","CVE":"CVE-2026-80585","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"80585","Ordinal":"1","NoteData":"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\".","Type":"Description","Title":"mptcp: fastopen: only mark MPTFO subflows with SYN data"}]}}}