SB20260720408 - Time-of-check Time-of-use (TOCTOU) Race Condition in Linux kernel mptcp

CSH
CYBERSECURITY HELP
Sign In REGISTER

Main Vulnerability Database SB20260720408

SB20260720408 - Time-of-check Time-of-use (TOCTOU) Race Condition in Linux kernel mptcp

Published: July 20, 2026

Security Bulletin ID SB20260720408
CSH Severity
Medium
Patch available
YES
Number of vulnerabilities 1
Exploitation vector Remote access
Highest impact Data manipulation

Breakdown by Severity

Medium 100%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 1 vulnerability.


1) Time-of-check Time-of-use (TOCTOU) Race Condition (CVE-ID: CVE-2026-63867)

CWE-ID: CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition

CVSSv4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to cause inconsistent MPTCP receiver window signaling.

The vulnerability exists due to a time-of-check time-of-use race in the MPTCP DSS option handling in net/mptcp/options.c when processing and emitting MPTCP acknowledgments on outgoing packets. A remote attacker can trigger packet processing that causes inconsistent ack_seq values to be used to confuse the peer.

The issue arises because the MPTCP-level ack_seq was accessed locklessly multiple times, allowing different values to be used for the DSS data acknowledgment and the announced receive window within the same packet.


Remediation

Install update from vendor's website.

References