{"apiVersion":"1.0","identifier":"CVE-2026-80585","description":"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-.","publishedAt":"2026-08-26T15:17:14","lastModifiedAt":"2026-08-27T06:17:45","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-80585","cvssScore":9.4,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H","epssProbability":0.00317,"riskScore":0.97,"affectedProduct":"Linux kernel","affectedVersions":"unknown","vulnerabilityType":"Kernel","operatingSystems":[],"links":{"self":"https://www.redsauce.net/api/cves/CVE-2026-80585","webPages":{"es":"https://www.redsauce.net/es/cves/CVE-2026-80585","en":"https://www.redsauce.net/en/cves/CVE-2026-80585","fr":"https://www.redsauce.net/fr/cves/CVE-2026-80585","pt":"https://www.redsauce.net/pt/cves/CVE-2026-80585","de":"https://www.redsauce.net/de/cves/CVE-2026-80585","sk":"https://www.redsauce.net/sk/cves/CVE-2026-80585","el":"https://www.redsauce.net/el/cves/CVE-2026-80585"},"source":"https://nvd.nist.gov/vuln/detail/CVE-2026-80585"}}