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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 1 Dec 2021. Known ransomware use
Windows 10 1507Operating system · Microsoft

CVE-2021-40449

HIGH · 7.8 CVSS v3.1 Published 2021-10-13
Fix available
A fix is available. Upgrade to 10.0.10240.19086 / 10.0.14393.4704 or later.
See remediation →
96/100
Remediation priority · Urgent
In the wild Ransomware High EPSS Public exploit 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
Win32k 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

CVE-2021-40449 is a Win32k (win32k.sys) Elevation of Privilege vulnerability. Win32k is the Windows kernel-mode driver that manages the Windows GUI subsystem (windows, menus, etc.). This local privilege escalation vulnerability allows a low-privileged attacker to gain SYSTEM-level code execution, typically through a specially crafted exploit targeting the kernel driver.

MitigationApply the Microsoft security update for CVE-2021-40449. This is a kernel-level vulnerability requiring a vendor patch; there are no effective workarounds. Prioritize patching systems with user-facing exposure.

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:< 10.0.10240.19086
Windows 10 1607Operating system
Affected:< 10.0.14393.4704
Windows 10 1809Operating system
Affected:< 10.0.17763.2237
Windows 10 1909Operating system
Affected:< 10.0.18363.1854
Windows 10 2004Operating system
Affected:< 10.0.19041.1288
Windows 10 20h2Operating system
Affected:< 10.0.19041.1288
Windows 10 21h1Operating system
Affected:< 10.0.19041.1288
Windows 11Operating system
Affected:all versions

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 version and build number
    Run 'winver' from command prompt or check 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to get the exact Windows version and build number
    Affected if The system is Windows 10 version 1507 through 21h1 with a build number below the fixed versions, or Windows 11 of any version
  2. Check win32k.sys file version
    Right-click C:\Windows\System32\win32k.sys, select Properties, then view the Details tab to see the File version; alternatively run 'powershell (Get-Item C:\Windows\System32\win32k.sys).VersionInfo'
    Affected if The file version is older than the patched builds for the corresponding Windows 10 release
  3. Verify current OS build against CVE thresholds
    Run 'winver' and compare the displayed build (for example 19043.1234) against the affected ranges: 1507 < 10240.19086, 1607 < 14393.4704, 1809 < 17763.2237, 1909 < 18363.1854, 2004/20h2/21h1 < 19041.1288
    Affected if The installed build number falls below the minimum fixed version for that Windows 10 release, or the system is any version of Windows 11
  4. Confirm Windows 11 is in scope
    Check if the system is Windows 11 by running 'systeminfo' and looking for 'Windows 11' in the OS Name or running 'winver' which displays the Windows version
    Affected if The system is running Windows 11 (all versions are affected per the CVE advisory)

You are affected if your Windows 10 build is below the specified threshold for your version, or if you are running any version of Windows 11.

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 10.0.10240.19086 / 10.0.14393.4704 / 10.0.17763.2237 or later
Fixed in 10.0.10240.1908610.0.14393.470410.0.17763.2237
Vendor patch portal.msrc.microsoft.com →
Interim mitigation

Apply the Microsoft security update for CVE-2021-40449. This is a kernel-level vulnerability requiring a vendor patch; there are no effective workarounds. Prioritize patching systems with user-facing exposure.

Recommended fix High confidence

Windows 10 build 10.0.19041.1288 (for 2004/20h2/21h1) or respective build numbers for other versions; Windows 11 latest cumulative update

  1. Check the current Windows build version by running 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"'
  2. Identify the specific Windows 10 version (1507, 1607, 1809, 1909, 2004, 20h2, or 21h1) from the build number
  3. For Windows 10 1507: Upgrade to Windows 10 build 10.0.10240.19086 or later
  4. For Windows 10 1607: Upgrade to Windows 10 build 10.0.14393.4704 or later
  5. For Windows 10 1809: Upgrade to Windows 10 build 10.0.17763.2237 or later
  6. For Windows 10 1909: Upgrade to Windows 10 build 10.0.18363.1854 or later
  7. For Windows 10 2004, 20h2, or 21h1: Upgrade to Windows 10 build 10.0.19041.1288 or later
  8. For Windows 11: Apply the cumulative Windows Update KB5007186 (or later) or upgrade to the latest Windows 11 version
Caveat Standard Windows cumulative update - no expected breaking changes for this security patch; ensure standard backup and testing procedures are followed before production deployment

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

Fix this in Windows 10 1507 Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,970
Get it fixed fast

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,152.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-40449 — 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-2021-40449 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