CVE-2026-63867
Published Jul 19, 2026
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.
Is your site exposed to CVE-2026-63867?
Run a free security scan — no signup, results in seconds.
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.
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.