SYSTEM privilege escalation via uninitialized query size
Published Dec 15, 2021 · Updated Aug 22, 2026
Privilege escalation in the Windows CLFS driver allows local users to execute code with SYSTEM privileges through a crafted log query. CClfsLogFcbVirtual::QueryLogFileInfo passes an uninitialized Size value to an operation that writes into a 120-byte stack buffer, causing an overflow. Exploitation requires low-privileged local code execution and a crafted virtual CLFS log; the resulting kernel-memory corruption grants full SYSTEM control.
Summary
What happened
Privilege escalation in the Windows CLFS driver allows local users to execute code with SYSTEM privileges through a crafted log query. CClfsLogFcbVirtual::QueryLogFileInfo passes an uninitialized Size value to an operation that writes into a 120-byte stack buffer, causing an overflow. Exploitation requires low-privileged local code execution and a crafted virtual CLFS log; the resulting kernel-memory corruption grants full SYSTEM control.
The record
- CVE
- CVE-2021-43226
- Published
- Dec 15, 2021
- Updated
- Aug 22, 2026
- Vendor
- Microsoft
- Product
- Windows 10 Version 1507
- Classifications
- T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Dec 15, 2021CVE publishedPublication date reported by the CVE source.
- Aug 22, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0.0 <10.0.10240.19145
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Rosayxy cve-2021-43226PoCproof of concept · demonstrated
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Reported exploitation
- CISA Known Exploited Vulnerabilities catalog entryknown exploited catalog
- DPRK cyber-group use of Windows log-file vulnerabilitiesthreat actor
Technologies
Your stack
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Your stack
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