CVE-2021-38633

Local privilege escalation to SYSTEM

Published Sep 15, 2021 · Updated Aug 10, 2026

Privilege escalation in the Windows Common Log File System driver allows local users with low privileges to execute code as SYSTEM. Microsoft has not disclosed the exact defective operation, and public CLFS analysis cannot distinguish this issue from two related September 2021 CVEs. Exploitation requires local code execution and can give the attacking process complete control of the affected host.

CVSS severity7.8
High
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege escalation in the Windows Common Log File System driver allows local users with low privileges to execute code as SYSTEM. Microsoft has not disclosed the exact defective operation, and public CLFS analysis cannot distinguish this issue from two related September 2021 CVEs. Exploitation requires local code execution and can give the attacking process complete control of the affected host.

The record

CVE
CVE-2021-38633
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

  1. Sep 15, 2021CVE publishedPublication date reported by the CVE source.
  2. 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.

  1. Affected versionversion=10.0.10240.0 <10.0.10240.19060

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.10240.0 <10.0.10240.19060
Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows 7version=6.1.0 <6.1.7601.25712
Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1237
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1801
Microsoft · Windows 8.1version=6.3.0 <6.3.9600.20120
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2012 (Server Core installation)version=6.2.9200.0 <6.2.9200.23462
Microsoft · Windows Server 2012version=6.2.9200.0 <6.2.9200.23462
Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19041.1237
Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2008 R2 Service Pack 1version=6.1.7601.0 <6.1.7601.25712
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1237
Microsoft · Windows Server 2008 R2 Service Pack 1 (Server Core installation)version=6.1.7601.0 <6.1.7601.25712
Microsoft · Windows Server 2012 R2 (Server Core installation)version=6.3.9600.0 <6.3.9600.20120
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows 7 Service Pack 1version=6.1.0 <6.1.7601.25712
Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19042.1237
Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2008 Service Pack 2version=6.0.6003.0 <6.0.6003.21218
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.230
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1237
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.2183; version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows Server 2012 R2version=6.3.9600.0 <6.3.9600.20120
Microsoft · Windows Server 2008 Service Pack 2 (Server Core installation)version=6.0.6003.0 <6.0.6003.21218

Published CVSS scores

4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
7.8Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-269Improper Privilege Management
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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