Local privilege escalation through crafted CLFS log
Published Sep 15, 2021 · Updated Aug 10, 2026
Use-after-free in the Microsoft Windows CLFS driver allows local users to elevate privileges to SYSTEM through a crafted Base Log File. Public research associates this CVE with metadata handling that repopulates an entry with a shadow pointer to freed memory, enabling a double free when the log handle closes. A low-privileged local session is required; successful exploitation can replace a process token and execute code with SYSTEM privileges.
Summary
What happened
Use-after-free in the Microsoft Windows CLFS driver allows local users to elevate privileges to SYSTEM through a crafted Base Log File. Public research associates this CVE with metadata handling that repopulates an entry with a shadow pointer to freed memory, enabling a double free when the log handle closes. A low-privileged local session is required; successful exploitation can replace a process token and execute code with SYSTEM privileges.
The record
- CVE
- CVE-2021-36955
- Published
- Sep 15, 2021
- Updated
- Aug 10, 2026
- Vendor
- Microsoft
- Product
- Windows 10 Version 1507
- Classifications
- CWE-269, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 15, 2021CVE publishedPublication date reported by the CVE source.
- Aug 10, 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=10.0.10240.0 <10.0.10240.19060
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
- Exploiting a use-after-free in Windows Common Logging File Systemfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Reported exploitation
- CISA Known Exploited Vulnerabilities Catalog listingknown exploited catalog
- CISA ransomware-campaign associationransomware
Technologies
Your stack
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Your stack
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