Exploited vulnerability · CISA KEV
Yes. CVE-2021-43226, Microsoft Windows Privilege Escalation Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 6 Oct 2025, 1391 days after it was published. It is known to be used in ransomware campaigns. It affects Microsoft Windows. If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Microsoft Windows Common Log File System Driver contains a privilege escalation vulnerability that could allow a local, privileged attacker to bypass certain security mechanisms.
| Vendor | Microsoft (391 exploited CVEs in KEV) |
| Product | Windows |
| Vulnerability | Microsoft Windows Privilege Escalation Vulnerability |
| Weakness | not specified |
| Published | 15 Dec 2021 |
| Added to KEV | 6 Oct 2025 |
| Reported by (CNA) | microsoft |
Yes. CISA added CVE-2021-43226 to the Known Exploited Vulnerabilities catalog on 6 Oct 2025, which means there is reliable evidence of exploitation in the wild.
Yes, CISA lists it as known to be used in ransomware campaigns.
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Check Microsoft's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Windows and watch it for signs of compromise.
Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in October 2025 · Microsoft scorecard · act-now radar.
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