CISA Warns of Windows Privilege Escalation Vulnerability Exploited in Attacks
The Cybersecurity and Infrastructure Security Agency (CISA) has issued a security advisory regarding the Microsoft Windows privilege escalation vulnerability CVE-2021-43226, which was added to its Known Exploited Vulnerabilities (KEV) catalog on Fri, Oct…
The Cybersecurity and Infrastructure Security Agency (CISA) has issued a security advisory regarding the Microsoft Windows privilege escalation vulnerability CVE-2021-43226, which was added to its Known Exploited Vulnerabilities (KEV) catalog on Fri, Oct 6, 2025.
This vulnerability affects the Microsoft Windows Common Log File System (CLFS) Driver, introducing significant security risks to enterprise environments. It enables local, authenticated attackers with existing system access to bypass critical security mechanisms and elevate their privileges to SYSTEM level access.
The flaw arises from improper validation of user-supplied data within the CLFS driver’s memory management routines, which attackers can exploit by crafting malicious CLFS log files to trigger buffer overflow conditions, potentially leading to arbitrary code execution with elevated privileges.
Microsoft Windows 10 (all versions) Microsoft Windows 11 (all versions) Windows Server 2016 Windows Server 2019 Windows Server 2022 Windows Server 2008 R2 SP1 Windows 7 SP1
The vulnerability requires local access and standard user privileges, posing a significant threat in environments where attackers have gained a foothold through methods such as phishing or social engineering attacks.
The vulnerability has been exploited in real-world attack scenarios, with proof-of-concept exploit code detected in underground forums.
Risk Factors Details
This vulnerability affects the Microsoft Windows Common Log File System (CLFS) Driver, introducing significant security risks to enterprise environments.
Affected Products Microsoft Windows 10, 11, Server 2016, 2019, 2022, Server 2008 R2 SP1, Windows 7 SP1
Impact Privilege Escalation
Exploit Prerequisites Local access, Authenticated user account, Ability to execute code locally, Standard user privileges minimum
CVSS 3.1 Score 7.8 (High)
CISA has set a mandatory remediation deadline of Mon, Oct 27, 2025, for federal agencies and critical infrastructure organizations to implement necessary security patches. This directive is in accordance with Binding Operational Directive (BOD) 22-01, which mandates swift action against actively exploited vulnerabilities.
Organizations are advised to apply Microsoft’s security updates via the Windows Update mechanism or Windows Server Update Services (WSUS) for enterprise deployments. Priority should be given to patching domain controllers, file servers, and other critical infrastructure components.
For systems unable to receive immediate updates, Microsoft suggests implementing Application Control policies and Windows Defender Exploit Guard as interim measures.
Security teams should monitor Event ID 4656 and 4658 logs for unauthorized file system access attempts, particularly those involving CLFS-related processes such as clfs.sys and clfsw32.dll.
It is recommended that organizations conduct vulnerability assessments utilizing tools like Microsoft Baseline Security Analyzer or third-party scanners to identify susceptible systems within their infrastructure.
Based on reporting by Cyber Security News.