CVE Catalog

CVE-2026-63867

HighCVSS 8.2
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.32%

24th percentile - higher than 24% of all known CVEs

Summary

In the Linux kernel MPTCP subsystem, a TOCTOU (time-of-check time-of-use) race condition was found while computing the receive window (rcv_wnd). The MPTCP output path reads the acknowledgment sequence (ack_seq) without locking, which may cause inconsistencies between the data_ack value in the DSS option and the calculated receive window in the same packet.

Risk Assessment

Inconsistencies in MPTCP communication may confuse the remote peer, potentially leading to flow control errors, packet loss, or degraded network performance.

Recommendation

Immediately update the Linux kernel to a version containing the fix that eliminates the TOCTOU race and ensures the MPTCP receive window is updated only when the egress packet actually carries a DSS acknowledgment.

Other vulnerabilities in Linux kernel

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Original NVD description (English source)

In the Linux kernel, the following vulnerability has been resolved: mptcp: close TOCTOU race while computing rcv_wnd The MPTCP output path access locklessly the MPTCP-level ack_seq in multiple times, using possibly different values for the data_ack in the DSS option and to compute the announced rcv wnd for the same packet. Refactor the cote to avoid inconsistencies which may confuse the peer. Also ensure that the MPTCP level rcv wnd is updated only when the egress packet actually contains a DSS ack.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS