CVE-2021-43226 - PatchNow

📋 Vulnerability Details

Data Source: CIRCL

Confidence: HIGH

Exploitation Method: OTHER

CVE Published: 2021-12-15

Added to CISA KEV: 2025-10-06 1391 DAYS BETWEEN CVE AND KEV

🎯 Recommendations:

CRITICAL: Check for indicators of compromise - this vulnerability is in CISA KEV indicating active exploitation in the wild. Review logs, check for unauthorized access, verify system integrity
Apply December 2021 Windows security updates immediately across all affected systems
Monitor for unusual privilege escalation activities and unauthorized administrative access
Implement endpoint detection and response (EDR) solutions to detect exploitation attempts
Review access controls and limit local logon rights where possible
Patch priority: HIGH - due to active exploitation despite requiring local access

🔍 Web Intelligence (Kagi · 2026-06-04)

CVE-2021-43226 is a privilege escalation vulnerability residing in the Microsoft Windows Common Log File System (CLFS) driver ^[1]. It gained significant attention in October 2025 when it was added to the Cybersecurity and Infrastructure Security Agency (CISA) Known Exploited Vulnerabilities (KEV) catalog due to active exploitation in the wild ^[1] ^[5].

Exploitation and Threat Actor Usage

Active Exploitation: The vulnerability is actively exploited in the wild ^[2].
Ransomware and Targeted Attacks: It has been observed in targeted campaigns, specifically within ransomware operations ^[2]. Attackers leverage this flaw to escalate privileges after gaining initial access to a system, which allows them to disable security defenses, deploy malware, and achieve full system compromise ^[2].
Threat Actors: While specific threat actor groups have not been publicly identified, the nature of its use in ransomware campaigns indicates it is being utilized by sophisticated cybercriminal entities ^[4].

Attack Method and Requirements

Access Level: Exploitation requires the attacker to be a local, authenticated user with existing system access ^[1].
Method: The vulnerability is triggered via buffer overflows caused by malicious CLFS log files ^[5].
User Interaction: No specific user interaction is typically required once the attacker has established initial local access.

Impact

Privilege Escalation: Successful exploitation allows an attacker to bypass critical security mechanisms and elevate their privileges to SYSTEM level access ^[1].

Affected Products and Mitigation

Affected Versions: The flaw affects multiple versions of Microsoft Windows, including Windows 10, Windows 11, and various Windows Server editions ^[2] ^[5].
Mitigation: Organizations are strongly advised to apply the latest security updates provided by Microsoft to patch the CLFS driver vulnerability. Because it is listed in the CISA KEV catalog, federal agencies and organizations following CISA guidelines are required to remediate this vulnerability within specified timeframes ^[3].

Sources

CISA Warns of Windows Privilege Escalation Vulnerability Exploited...
The CVE-2021-43226 vulnerability resides within Microsoft’s Common Log File System Driver, a core Windows component responsible for managing transaction logging operations. Microsoft Windows Privilege Escalation Flaw (CVE-2021-43226). This privilege escalation flaw allows local, authenticated attack…
CVE-2021-43226 Windows Vulnerability Actively Exploited
The flaw affects multiple Windows versions, including Windows 10, 11, and Server editions. Recently added to CISA's Known Exploited ... Vulnerability Details.The flaw affects multiple Windows versions, including Windows 10, 11, and Server editions. Recently added to CISA’s Known Exploited Vulnerabil…
CVE-2021-43226 Detail - NVD
This CVE is in CISA's Known Exploited Vulnerabilities Catalog. Reference CISA's BOD 22-01 and Known Exploited Vulnerabilities Catalog for further guidance and ... Official websites use .gov A .gov website belongs to an official government organization in the United States. ... CVE-2021-43226 Detail.
CISA Warns of Active Exploitation of Windows Privilege Escalation ...
Active Exploitation and Impact While the specific threat actors exploiting CVE-2021-43226 have not been publicly identified, CISA’s sudden addition of this issue to its Known Exploited Vulnerabilities catalog on October 6, 2025, underscores the heightened risk.
Cybersecurity Newsletter Weekly - Discord, Red Hat Data Breach...
CISA added CVE-2021-43226, a privilege escalation vulnerability in the Microsoft Windows Common Log File System (CLFS) Driver, to its Known Exploited Vulnerabilities catalog on October 6, 2025. This flaw allows local authenticated attackers to elevate privileges to SYSTEM level through buffer overfl…

🟢 CVE-2021-43226