CVE-2026-63867 (CVSS 8.2)

Description

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.

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CVSS v3.1 Score

8.2

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

EPSS — Exploit Prediction

0.0033

Probability of exploitation

0.25%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://git.kernel.org/stable/c/301a33fd590c408a05c5df800e0cc1e6a8a2f8f8 https://git.kernel.org/stable/c/3b8cbba7c0ed31189c89f90be247b8973ffa79ef https://git.kernel.org/stable/c/68364963e5baf03f16b4420292291f75c8f66497 https://git.kernel.org/stable/c/8ab24fdebc369c0dfb90f82c1650b1e66662bb45 https://git.kernel.org/stable/c/8f4f0a157e8436a05bf8c3670b24dbc258911c43 https://git.kernel.org/stable/c/907ac6b1658e0277f979fcdfae2a753b495c1510 https://git.kernel.org/stable/c/c4f4cf60797974873dbc8e100144682a6f2f861f

Frequently Asked Questions

What is CVE-2026-63867? +

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. It has a CVSS v3.1 base score of 8.2 (HIGH).

How severe is CVE-2026-63867? +

CVE-2026-63867 has a CVSS v3.1 score of 8.2 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0033, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-63867? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

CVE-2026-63867