CVE-2026-2636 Denial of Service in Microsoft OS
An unprivileged user can trigger a system crash in the CLFS.sys driver, causing a denial of service on affected Windows systems.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-2636?
CVE-2026-2636 is a medium-severity denial of service vulnerability in Microsoft Windows OS, published on 25 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
This vulnerability is caused by a CWE‑159: "Improper Handling of Invalid Use of Special Elements" weakness, which leads to an unrecoverable inconsistency in the CLFS.sys driver. This condition forces a call to the KeBugCheckEx function, allowing an unprivileged user to trigger a system crash. Microsoft silently fixed this vulnerability in the September 2025 cumulative update for Windows 11 2024 LTSC and Windows Server 2025. Windows 25H2 (released in September) was released with the patch. Windows 1123h2 and earlier versions remain vulnerable.
Weakness: CWE-159
Which versions are affected by CVE-2026-2636?
How do I fix CVE-2026-2636?
No fix has been published for CVE-2026-2636 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-2636 being exploited?
There is no known exploitation of CVE-2026-2636 in the wild and no public exploit code.
Public exploit code: 2 proofs of concept on GitHub.
Sources
Also known as GHSA-fww6-3c6x-rf7p.