CVE-2026-80585 - mptcp: fastopen: only mark MPTFO subflows with SYN data

CVE-2026-80585 - mptcp: fastopen: only mark MPTFO subflows with SYN data

https://cvefeed.io/rssfeed/latest.atom / Wed, 08/26/2026 - 19:28
CVE ID :CVE-2026-80585
Published : Aug. 26, 2026, 3:17 p.m. | 1 hour, 12 minutes ago
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".
Severity: 0.0 | NA
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