Bug 2502304 (CVE-2026-63867) - CVE-2026-63867 kernel: mptcp: close TOCTOU race while computing rcv_wnd
Summary: CVE-2026-63867 kernel: mptcp: close TOCTOU race while computing rcv_wnd
Keywords:
Status: NEW
Alias: CVE-2026-63867
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-07-19 15:02 UTC by OSIDB Bzimport
Modified: 2026-07-21 19:23 UTC (History)
2 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-07-19 15:02:54 UTC 
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.
Comment 1 Keith Grant 2026-07-21 19:22:28 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026071912-CVE-2026-63867-eac1@gregkh/T
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