CISA has issued an pressing safety advisory, including Microsoft Home windows privilege escalation vulnerability CVE-2021-43226 to its Identified Exploited Vulnerabilities (KEV) catalog on October 6, 2025.
The vulnerability impacts the Microsoft Home windows Widespread Log File System (CLFS) Driver and poses important safety dangers to enterprise environments.
The CVE-2021-43226 vulnerability resides inside Microsoft’s Widespread Log File System Driver, a core Home windows element answerable for managing transaction logging operations.
Microsoft Home windows Privilege Escalation Flaw (CVE-2021-43226)
This privilege escalation flaw permits native, authenticated attackers with present system entry to bypass essential safety mechanisms and elevate their privileges to SYSTEM degree entry.
In line with Microsoft’s Safety Response Middle, the vulnerability stems from improper validation of user-supplied knowledge inside the CLFS driver’s reminiscence administration routines.
Attackers can exploit this weak spot by crafting malicious CLFS log information that set off buffer overflow situations, resulting in arbitrary code execution with elevated privileges.
The exploit requires native entry and normal person privileges as stipulations, making it notably harmful in enterprise environments the place attackers have already gained an preliminary foothold by means of phishing or social engineering assaults.
The vulnerability impacts a number of Home windows variations, together with Home windows 10, Home windows 11, Home windows Server 2016, Home windows Server 2019, and Home windows Server 2022.
Safety researchers have recognized proof-of-concept exploit code circulating in underground boards, growing the chance of lively exploitation campaigns.
Threat FactorsDetailsAffected ProductsMicrosoft Home windows 10 (all variations)Microsoft Home windows 11 (all variations)Home windows Server 2016Windows Server 2019Windows Server 2022Windows Server 2008 R2 SP1Windows 7 SP1ImpactPrivilege EscalationExploit PrerequisitesLocal entry to focus on system, Authenticated person account, Potential to execute code regionally, Normal person privileges minimumCVSS 3.1 Score7.8 (Excessive)
Mitigations
CISA has established a compulsory remediation deadline of October 27, 2025, requiring federal companies and demanding infrastructure organizations to implement safety patches instantly.
The directive follows Binding Operational Directive (BOD) 22-01 tips, which mandate swift motion in opposition to vulnerabilities with proof of lively exploitation.
Organizations should apply Microsoft’s safety updates by means of the usual Home windows Replace mechanism or Home windows Server Replace Companies (WSUS) for enterprise deployments.
System directors ought to prioritize patching area controllers, file servers, and different essential infrastructure parts first.
For methods unable to obtain instant updates, Microsoft recommends implementing Software Management insurance policies and Home windows Defender Exploit Guard as non permanent mitigations.
The vulnerability’s addition to CISA’s KEV catalog signifies confirmed exploitation in real-world assault eventualities, although particular ransomware marketing campaign attribution stays unknown.
Safety groups ought to monitor for suspicious Occasion ID 4656 and 4658 logs indicating unauthorized file system entry makes an attempt, notably involving CLFS-related processes like clfs.sys and clfsw32.dll.
Organizations ought to conduct instant vulnerability assessments utilizing instruments like Microsoft Baseline Safety Analyzer or third-party scanners to establish susceptible methods throughout their infrastructure.
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