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Review reviewHigh

CVE-2026-63867

Linux

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.

CVSS
8.2
EPSS
-
- percentile
CISA KEV
Not listed
Published
2026.07.20
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability-
Technical severityCVSS 8.2

Vulnerability overview

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.

Affected product and versions

Product
Linux
Affected versions
>= fa3fe2b150316b294f2c662653501273ff25bba8 < 301a33fd590c408a05c5df800e0cc1e6a8a2f8f8, >= fa3fe2b150316b294f2c662653501273ff25bba8 < 68364963e5baf03f16b4420292291f75c8f66497, >= fa3fe2b150316b294f2c662653501273ff25bba8 < 907ac6b1658e0277f979fcdfae2a753b495c1510, >= fa3fe2b150316b294f2c662653501273ff25bba8 < c4f4cf60797974873dbc8e100144682a6f2f861f, >= fa3fe2b150316b294f2c662653501273ff25bba8 < 3b8cbba7c0ed31189c89f90be247b8973ffa79ef, >= fa3fe2b150316b294f2c662653501273ff25bba8 < 8f4f0a157e8436a05bf8c3670b24dbc258911c43, >= fa3fe2b150316b294f2c662653501273ff25bba8 < 8ab24fdebc369c0dfb90f82c1650b1e66662bb45, >= 5.11
Fixed versions
No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Linux and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
CWE
Not available