CVE-2026-80585 (GCVE-0-2026-80585)
Vulnerability from cvelistv5
Published
2026-08-26 14:37
Modified
2026-10-16 19:26
Severity ?
9.4 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
Summary
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".
References
Impacted products
Vendor Product Version
Linux Linux Version: 36b122baf6a8bd46b4a591f12f4ed17b22257408
Version: 36b122baf6a8bd46b4a591f12f4ed17b22257408
Version: 36b122baf6a8bd46b4a591f12f4ed17b22257408
Version: 36b122baf6a8bd46b4a591f12f4ed17b22257408
Version: 36b122baf6a8bd46b4a591f12f4ed17b22257408
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