Known exploited vulnerability
CVE-2021-43226
The short answer
CVE-2021-43226 affects Microsoft Windows 10 Version 1809 and is rated high (CVSS 7.8). CISA added it to the Known Exploited Vulnerabilities catalog on 2025-10-06: attackers are using it, so patch it first. The vendor has linked a patch.
What it is
Windows Common Log File System Driver Elevation of Privilege Vulnerability
Severity
7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Oct 6, 2025
Federal due date Oct 27, 2025
EPSS, next 30 days
3.3%
Higher than 89% of scored CVEs
How it can be exploited
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says 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.
Affected products
Windows 10 Version 1809, Windows Server 2019, Windows Server 2019 (Server Core installation), Windows 10 Version 1909, Windows 10 Version 21H1, Windows Server 2022, Windows 10 Version 2004, Windows Server version 2004, Windows 10 Version 20H2, Windows Server version 20H2, Windows 11 version 21H2, Windows 10 Version 21H2. NVD's record lists the exact affected versions.
References
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43226 PatchVendor Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43226 PatchVendor Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-43226 US Government Resource
Questions
Is CVE-2021-43226 being exploited?
Yes. CISA added CVE-2021-43226 to its Known Exploited Vulnerabilities catalog on 2025-10-06, with a federal remediation due date of 2025-10-27. CISA lists it as used in ransomware campaigns.
How do I fix CVE-2021-43226?
CISA's required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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