{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-80585", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-08-26T14:34:25.769Z", "datePublished": "2026-08-26T14:37:40.901Z", "dateUpdated": "2026-10-16T19:26:28.485Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-27T05:02:06.112Z" }, "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": { "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" }, "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." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/mptcp/fastopen.c" ], "versions": [ { "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408", "lessThan": "f75f174edc865738522e514d042cf5627f084859", "status": "affected", "versionType": "git" }, { "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408", "lessThan": "fca7e444c04689fe4cc6b56f2725f804a4bb1ef9", "status": "affected", "versionType": "git" }, { "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408", "lessThan": "75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5", "status": "affected", "versionType": "git" }, { "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408", "lessThan": "72b4a0c51a4b550d40301d60a366b429b8c8e78d", "status": "affected", "versionType": "git" }, { "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408", "lessThan": "e00b63056fb4f261455b3e5df5268a1f8ce47a87", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/mptcp/fastopen.c" ], "versions": [ { "version": "6.2", "status": "affected" }, { "version": "0", "lessThan": "6.2", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.153", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.105", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.46", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.10", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.153" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.12.105" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.18.46" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "7.1.10" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "7.2" } ] } ] } ], "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" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-80585", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:17:56.710913Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:28.485Z" } } ] } }