CVE-2026-20866
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 · uneditedConcurrent execution using shared resource with improper synchronization ('race condition') in Windows Management Services allows an authorized attacker to elevate privileges locally.
In the news
Third-party coverage- Microsoft CVE Summary - Bleeping Computer
- Microsoft January 2026 Patch Tuesday fixes 3 zero-days, 114 flaws
Surfaced from public web coverage — external links open in a new tab.
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 a race condition vulnerability in Windows Management Services where improper synchronization of shared resources allows an authorized local attacker to elevate privileges. The vulnerability stems from concurrent execution issues that can be exploited by timing operations to access privileged resources.
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< 10.0.17763.8276< 10.0.19044.6809< 10.0.19045.6809< 10.0.22631.6491< 10.0.26100.7623< 10.0.26200.7623< 10.0.17763.8276< 10.0.20348.4648CVSS 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
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/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.
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Check Windows versionRun 'winver' from command prompt, or execute 'Get-ComputerInfo | Select-Object WindowsVersion,OsVersion,OsBuildNumber' in PowerShell to obtain the full OS build numberAffected if The displayed build number is lower than any of these thresholds: 17763.8276 (Windows 10 1809/Server 2019), 19044.6809 (Windows 10 21h2), 19045.6809 (Windows 10 22h2), 22631.6491 (Windows 11 23h2), 26100.7623 (Windows 11 24h2), 26200.7623 (Windows 11 25h2), or 20348.4648 (Windows Server 2022)
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Confirm Windows Management Services is installedRun 'Get-Service -Name WinMgmt' in PowerShell or check Services.msc for the Windows Management Instrumentation serviceAffected if The service exists and shows a status of Running, Stopped, or any other state - the component is present on the system regardless of state
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Check for installed security updatesRun 'Get-HotFix | Where-Object {$_.Description -eq "Security Update"} | Sort-Object InstalledOn -Descending | Select-Object -First 10' in PowerShell to list recent security patchesAffected if No security update matching CVE-2026-20866 or the specific build numbers above appears in the installed updates list
You are affected if your Windows build number falls below the thresholds listed AND the Windows Management Instrumentation (WinMgmt) service is present on your system.
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 · scoped10.0.17763.827610.0.19044.680910.0.19045.6809
Apply the Microsoft security patch for CVE-2026-20866 once available through Windows Update or the Microsoft Security Response Center. Verify the Windows Management Services component is patched and monitor for any service disruptions.
Minimum fixed builds: Windows 10 1809 (10.0.17763.8276), Windows 10 21h2 (10.0.19044.6809), Windows 10 22h2 (10.0.19045.6809), Windows 11 23h2 (10.0.22631.6491), Windows 11 24h2 (10.0.26100.7623), Windows 11 25h2 (10.0.26200.7623), Windows Server 2019 (10.0.17763.8276), Windows Server 2022 (10.0.203
- 1. Identify the current Windows build number by running 'winver' or 'systeminfo | findstr /B /C:"OS Version"' in Command Prompt
- 2. Compare your current build number against the fixed versions: Windows 10 1809 requires 10.0.17763.8276 or higher; Windows 10 21h2 requires 10.0.19044.6809 or higher; Windows 10 22h2 requires 10.0.19045.6809 or higher; Windows 11 23h2 requires 10.0.22631.6491 or higher; Windows 11 24h2 requires 10.0.26100.7623 or higher; Windows 11 25h2 requires 10.0.26200.7623 or higher; Windows Server 2019 req
- 3. Open Settings > Windows Update (or WSUS for enterprise) and check for available updates
- 4. Install all pending Windows updates, ensuring the update containing the CVE-2026-20866 patch is applied
- 5. Restart the system when prompted to complete the installation
- 6. After reboot, verify the fix by running 'winver' again and confirming the build number meets or exceeds the required fixed version
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-20866 — 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-2026-20866 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
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- 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