CVE-2021-43226: Microsoft Windows privilege escalation in Common Log File System Driver

CVE-2021-43226 · Severity: critical · CVSS 7.8 · Exploited in the wild · Published 2025-10-06

A security vulnerability exists in the Windows component responsible for managing system logs. An attacker who already has basic access to a computer could exploit this flaw to gain full administrative control over the system. This could allow them to install programs, view or delete sensitive data, or create new accounts with full user rights.

Technologies: Microsoft Windows. Vendors: Microsoft.

Quick answers

Is CVE-2021-43226 exploited in the wild?
Yes. CVE-2021-43226 is known to be exploited in the wild, first recorded on 6 October 2025. Treat it as urgent.
How severe is CVE-2021-43226?
Critical severity, with a CVSS score of 7.8, published 6 October 2025.
Which products and versions are affected?
Microsoft Windows 7, 8.1, 10, 11, Server 2008, 2012, 2016, 2019, 2022.
Is there a fix for CVE-2021-43226?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2021-43226 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2021-43226?
Check whether you run Microsoft Windows. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An elevation of privilege vulnerability exists in the Microsoft Windows Common Log File System (CLFS) driver. The flaw allows a local attacker with low-privileged access to execute code with SYSTEM privileges by exploiting improper memory handling or validation within the driver. This is a local attack vector requiring no user interaction. The vulnerability has been observed being exploited in the wild, and Microsoft has released patches for affected versions of Windows and Windows Server.

Affected products

  • Microsoft Windows 7, 8.1, 10, 11, Server 2008, 2012, 2016, 2019, 2022

Timeline

  • 2021-11-21: disclosed: Initial MSRC advisory publication
  • 2025-10-06: kev added: Added to CISA Known Exploited Vulnerabilities catalog

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