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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 27 Oct 2025.
Windows 10 1507Operating system · Microsoft

CVE-2021-43226

HIGH · 7.8 CVSS v3.1 Published 2021-12-15
Fix available
A fix is available. Upgrade to 10.0.10240.19145 / 10.0.14393.4825 or later.
See remediation →
96/100
Remediation priority · Urgent
In the wild Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Windows Common Log File System Driver Elevation of Privilege Vulnerability

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A vulnerability in the Windows Common Log File System (CLFS) driver allows a local attacker to elevate privileges to kernel/system level. The CLFS is a general-purpose logging subsystem used by various Windows components.

MitigationApply the Microsoft security update for CVE-2021-43226, available through Windows Update or the Microsoft Security Update Catalog.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Windows 10 1507Operating system
Affected:< 10.0.10240.19145
Windows 10 1607Operating system
Affected:< 10.0.14393.4825
Windows 10 1809Operating system
Affected:< 10.0.17763.2366
Windows 10 1909Operating system
Affected:< 10.0.18363.1977
Windows 10 2004Operating system
Affected:< 10.0.19041.1415
Windows 10 20h2Operating system
Affected:< 10.0.19042.1415
Windows 10 21h1Operating system
Affected:< 10.0.19043.1415
Windows 10 21h2Operating system
Affected:< 10.0.19044.1415

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Windows 10 build version
    Open Command Prompt or PowerShell and run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to display the installed Windows 10 version and build number
    Affected if The build number displayed is lower than any of the following: 10240.19145 (1507), 14393.4825 (1607), 17763.2366 (1809), 18363.1977 (1909), 19041.1415 (2004), 19042.1415 (20h2), 19043.1415 (21h1), or 19044.1415 (21h2)
  2. Confirm exact build number via PowerShell
    Run 'Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion" | Select-Object CurrentBuild, DisplayVersion, UBR' in PowerShell to retrieve precise build and revision numbers
    Affected if The CurrentBuild and UBR values combined fall below the vulnerable version thresholds listed in the CVE affecting your specific Windows 10 release branch

You are affected if your Windows 10 build number is lower than the specified version for your particular Windows 10 release (1507, 1607, 1809, 1909, 2004, 20h2, 21h1, or 21h2) as listed in the CVE.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.0.10240.19145 / 10.0.14393.4825 / 10.0.17763.2366 or later
Fixed in 10.0.10240.1914510.0.14393.482510.0.17763.2366
Vendor patch portal.msrc.microsoft.com →
Interim mitigation

Apply the Microsoft security update for CVE-2021-43226, available through Windows Update or the Microsoft Security Update Catalog.

Recommended fix High confidence

Windows 10 version-specific cumulative update reaching build 10.0.10240.19145 (1507), 10.0.14393.4825 (1607), 10.0.17763.2366 (1809), 10.0.18363.1977 (1909), 10.0.19041.1415 (2004), 10.0.19042.1415 (20h2), 10.0.19043.1415 (21h1), or 10.0.19044.1415 (21h2)

  1. Identify the current Windows 10 version by running 'winver' or 'systeminfo'
  2. Determine which version range applies (1507, 1607, 1809, 1909, 2004, 20h2, 21h1, or 21h2)
  3. Apply the appropriate Windows cumulative update for your version to reach the fixed build number: For 1507: 10.0.10240.19145, For 1607: 10.0.14393.4825, For 1809: 10.0.17763.2366, For 1909: 10.0.18363.1977, For 2004: 10.0.19041.1415, For 20h2: 10.0.19042.1415, For 21h1: 10.0.19043.1415, For 21h2: 10.0.19044.1415
  4. Restart the system after applying the update
  5. Verify the installed version matches or exceeds the fixed build for your version using 'winver'
Caveat Standard Windows update risks - ensure backups and compatibility testing for business-critical applications

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Windows 10 1507 Exploited in the wild — priority engagement
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get it fixed fast

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-43226 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-43226 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data