CVE-2026-80585

Name of the Vulnerable Software and Affected Versions Linux kernel (affected versions not specified)

Description An issue exists in the Multipath TCP (MPTCP) implementation regarding TCP Fast Open (TFO). The function mptcp fastopen subflow synack set params() incorrectly sets the is mptfo flag before verifying if the SYN packet contains queued data. When a passive TFO accepts a valid cookie SYN without data, the receive queue remains empty, which can trigger a warning and leave a stale MPTFO state. This stale state may subsequently lead to a state-confusion bug within the check fully established() function.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.