Vulnerability · Published Feb 25, 2026 · Assigned by Fortra
CVE-2026-2636Denial of Service in Microsoft OS
Medium 5.5
In plain English
A medium-severity security flaw in Windows OS from Microsoft. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code.
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Windows OS | 0 – before 25H20 – through 1123h2 |
Weakness: CWE-159 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H