CVE-2021-43226MicrosoftOperating systemsOctober 6, 2025

Microsoft Windows Privilege Escalation Vulnerability

High 7.8Actively exploitedUsed by ransomware

Description

Microsoft Windows Common Log File System Driver contains a privilege escalation vulnerability that could allow a local, privileged attacker to bypass certain security mechanisms.

What to do

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

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Details

Vendor
Microsoft
Product
Windows
CVE
CVE-2021-43226
Affected versions
Windows 10 Version 1809 10.0: from 10.0.0 to 10.0.17763.2366 (excluded) — fixed in 10.0.17763.2366
Windows Server 2019 10.0: from 10.0.0 to 10.0.17763.2366 (excluded) — fixed in 10.0.17763.2366
Windows Server 2019 (Server Core installation) 10.0: from 10.0.0 to 10.0.17763.2366 (excluded) — fixed in 10.0.17763.2366
Windows 10 Version 1909 10.0: from 10.0.0 to 10.0.18363.1977 (excluded) — fixed in 10.0.18363.1977
Windows 10 Version 21H1 10.0: from 10.0.0 to 10.0.19043.1415 (excluded) — fixed in 10.0.19043.1415
Windows Server 2022 10.0: from 10.0.0 to 10.0.20348.405 (excluded) — fixed in 10.0.20348.405
Windows 10 Version 2004 10.0: from 10.0.0 to 10.0.19041.1415 (excluded) — fixed in 10.0.19041.1415
Windows Server version 2004 10.0: from 10.0.0 to 10.0.19041.1415 (excluded) — fixed in 10.0.19041.1415
Windows 10 Version 20H2 10.0: from 10.0.0 to 10.0.19042.1415 (excluded) — fixed in 10.0.19042.1415
Windows Server version 20H2 10.0: from 10.0.0 to 10.0.19042.1415 (excluded) — fixed in 10.0.19042.1415
Windows 11 version 21H2 10.0: from 10.0.0 to 10.0.22000.376 (excluded) — fixed in 10.0.22000.376
Windows 10 Version 21H2 10.0: from 10.0.0 to 10.0.19044.1415 (excluded) — fixed in 10.0.19044.1415
Windows 10 Version 1507 10.0: from 10.0.0 to 10.0.10240.19145 (excluded) — fixed in 10.0.10240.19145
Windows 10 Version 1607 10.0: from 10.0.0 to 10.0.14393.4825 (excluded) — fixed in 10.0.14393.4825
Windows Server 2016 10.0: from 10.0.0 to 10.0.14393.4825 (excluded) — fixed in 10.0.14393.4825
Windows Server 2016 (Server Core installation) 10.0: from 10.0.0 to 10.0.14393.4825 (excluded) — fixed in 10.0.14393.4825
Windows 7 6.1: from 6.1.0 to 6.1.7601.25796 (excluded) — fixed in 6.1.7601.25796
Windows 7 Service Pack 1 6.1: from 6.1.0 to 6.1.7601.25796 (excluded) — fixed in 6.1.7601.25796
Windows 8.1 6.3: from 6.3.0 to 6.3.9600.20207 (excluded) — fixed in 6.3.9600.20207
Windows Server 2008 Service Pack 2 6.0: from 6.0.0 to 6.0.6003.21309 (excluded) — fixed in 6.0.6003.21309
Windows Server 2008 Service Pack 2 (Server Core installation 6.0: from 6.0.0 to 6.0.6003.21309 (excluded) — fixed in 6.0.6003.21309
Windows Server 2008 Service Pack 2 6.0: from 6.0.0 to 6.0.6003.21309 (excluded) — fixed in 6.0.6003.21309
Windows Server 2008 R2 Service Pack 1 6.1: from 6.1.0 to 6.1.7601.25796 (excluded) — fixed in 6.1.7601.25796
Windows Server 2008 R2 Service Pack 1 (Server Core installat 6: from 6.0.0 to 6.1.7601.25796 (excluded) — fixed in 6.1.7601.25796
Windows Server 2012 6.2: from 6.2.0 to 6.2.9200.23545 (excluded); from 6.2.0 to 6.2.9200.23540 (excluded) — fixed in 6.2.9200.23545, 6.2.9200.23540
Windows Server 2012 (Server Core installation) 6.2: from 6.2.0 to 6.2.9200.23545 (excluded); from 6.2.0 to 6.2.9200.23540 (excluded) — fixed in 6.2.9200.23545, 6.2.9200.23540
Windows Server 2012 R2 6.3: from 6.3.0 to 6.3.9600.20207 (excluded) — fixed in 6.3.9600.20207
Windows Server 2012 R2 (Server Core installation) 6.3: from 6.3.0 to 6.3.9600.20207 (excluded) — fixed in 6.3.9600.20207 (from the advisory and NVD; check the exact builds in the official advisory)
CVSS score
7.8
Actively exploited
Yes, listed in the CISA Known Exploited Vulnerabilities catalog
CISA due date
October 27, 2025 (deadline for US federal agencies: a good benchmark for you too)
Source
CISA KEV – original advisory
Published
October 6, 2025

The description and the recommended action are quoted from the public advisory; severity, exploitation status and affected versions are compiled automatically from public sources and may contain errors. The vendor's original advisory prevails: check it before taking action. This information is provided without warranty and does not replace a professional assessment.

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