CVE-2026-63867: In the Linux kernel, the following vulnerability has been resolved: mptcp: close TOCTOU race while computing

Q: How do I fix CVE-2026-63867?

linux kernel: upgrade to 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13. Exact commands for each OS are on this page.

Q: Is CVE-2026-63867 being exploited?

CVE-2026-63867 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-63867 affect?

CVE-2026-63867 affects linux kernel. Severity is high (CVSS 8.2). 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 th

Q: How urgent is CVE-2026-63867?

Priority 44/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

This month

HIGH 8.2REMOTEWATCHLISTUPGRADE

CVE-2026-63867 is a high-severity flaw (CVSS 8.2) affecting linux kernel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-367, CWE-362
Published	2026-07-19
Last modified	2026-10-26

Publisher (CNA): kernel.org · Vendor: linux

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-19 15:16 UTCPublished CVE record published
2026-10-26 16:49 UTCUpdated Record last modified

linux linux kernel UPGRADE

Affected: >= 5.11 and < 5.15.210 · >= 5.16 and < 6.1.176 · >= 6.2 and < 6.6.143 · >= 6.7 and < 6.12.94 · >= 6.13 and < 6.18.36 · >= 6.19 and < 7.0.13 · 7.1 rc1 · 7.1 rc2

Fixed in: 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-63867?

linux kernel: upgrade to 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13. Exact commands for each OS are on this page.

Is CVE-2026-63867 being exploited?

CVE-2026-63867 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-63867 affect?

CVE-2026-63867 affects linux kernel. Severity is high (CVSS 8.2). 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 th

How urgent is CVE-2026-63867?

Priority 44/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Linux kernel vulnerabilities

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References

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