CVE-2021-40450
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 · uneditedWin32k 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 confidenceThis is an elevation of privilege vulnerability in the Win32k kernel mode driver (win32k.sys). Win32k handles window management and graphics rendering for Windows applications. The vulnerability allows a local authenticated attacker to execute arbitrary code in kernel mode, escalating their privileges from a low-privileged user account to SYSTEM.
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< 10.0.17763.2237< 10.0.18363.1854< 10.0.19041.1288< 10.0.19042.1288< 10.0.19043.1288< 10.0.22000.258< 10.0.19041.1288< 10.0.17763.2237CVSS 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 checksWork through these to decide whether this CVE applies to you.
-
Check Windows build numberRun 'winver' or 'systeminfo | findstr /B /C:"OS Version"' to obtain the full build numberAffected if The build number is below the threshold for your Windows version (17763.2237 for 1809/Server 2019, 18363.1854 for 1909, 19041.1288 for 2004/Server 2004, 19042.1288 for 20H2, 19043.1288 for 21H1, 22000.258 for Windows 11)
-
Verify win32k.sys versionOpen File Explorer, navigate to C:\Windows\System32\drivers\win32k.sys, right-click and select Properties, then check the File version on the Details tabAffected if The file version is lower than the patched version corresponding to your Windows build
-
Check for security update installationRun 'wmic qfe list' or 'Get-HotFix | Sort-Object InstalledOn' to list installed Windows updatesAffected if No September 2021 security update (KB5005565 or subsequent monthly rollup) is installed for your Windows version
-
Confirm Win32k subsystem is activeVerify the target system is a Windows desktop or server with GUI (Win32k.sys loads automatically on systems with graphical shell)Affected if The system has a graphical desktop environment (vulnerability applies to all Windows systems with GUI, no special feature toggle needed)
The system is affected if it runs a Windows 10/11 or Windows Server version within the affected build ranges AND lacks the September 2021 security updates.
Generated from the published advisory. Verify against your own configuration.
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 · scoped10.0.17763.223710.0.18363.185410.0.19041.1288
Apply the Microsoft security updates for CVE-2021-40450. This vulnerability was addressed in the September 2021 Windows security updates. Organizations should prioritize patching affected Windows systems, particularly domain controllers and servers, as this EoP flaw could be combined with other vulnerabilities for more severe attacks.
Apply the appropriate Windows security update for your version (build numbers >= 10.0.17763.2237 for 1809/Server 2019, >= 10.0.18363.1854 for 1909, >= 10.0.19041.1288 for 2004/Server 2004, >= 10.0.19042.1288 for 20h2, >= 10.0.19043.1288 for 21h1, >= 10.0.22000.258 for Win11 21h2)
- Identify the current Windows version by running 'winver' or checking System Information
- Navigate to Windows Update settings (Settings > Update & Security > Windows Update)
- Check for and install the latest Windows security updates
- Alternatively, download the specific security update from the Microsoft Update Catalog for this CVE (CVE-2021-40450)
- Restart the system after applying the update
- Verify the update was installed successfully by checking Windows Update history
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,808.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-40450 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-40450 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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.
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.
- 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