dbcve.org
Windows 10 21h2Operating system · Microsoft

CVE-2026-42915

MEDIUM · 5.5 CVSS v3.1 Published 2026-06-09
Fix available
A fix is available. Upgrade to 10.0.19044.7417 / 10.0.19045.7417 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click

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
Incorrect calculation of buffer size in Windows VMSwitch allows an authorized attacker to deny service locally.

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

Incorrect buffer size calculation in Windows VMSwitch (the virtual switch component for Hyper-V) allows a locally positioned authorized attacker to cause a denial of service via the buffer sizing flaw.

MitigationApply the Microsoft security update for this vulnerability through Windows Update or enterprise patch management once released. Prioritize patching Windows Server systems running the Hyper-V role.

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 21h2Operating system
Affected:< 10.0.19044.7417
Windows 10 22h2Operating system
Affected:< 10.0.19045.7417
Windows 11 23h2Operating system
Affected:< 10.0.22631.7219
Windows 11 24h2Operating system
Affected:< 10.0.26100.8655
Windows 11 25h2Operating system
Affected:< 10.0.26200.8655
Windows 11 26h1Operating system
Affected:< 10.0.28000.2269
Windows Server 2022Operating system
Affected:< 10.0.20348.5256
Windows Server 2025Operating system
Affected:< 10.0.26100.32995

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
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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. Check Windows version against affected ranges
    Run 'winver' or 'systeminfo | findstr /B /C:"OS Version"' and compare the build number to the vulnerable versions: 19044.7417 (Win10 21h2), 19045.7417 (Win10 22h2), 22631.7219 (Win11 23h2), 26100.8655 (Win11 24h2/Server2025), 26200.8655 (Win11 25h2), 28000.2269 (Win11 26h1), 20348.5256 (Server2022)
    Affected if The installed build number is LOWER than the threshold for your Windows version
  2. Verify Hyper-V is installed
    Run 'Get-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V' in PowerShell, or check 'systeminfo' for Hyper-V requirements
    Affected if Hyper-V is installed and the Windows version check shows a vulnerable build
  3. Confirm VMSwitch is present
    Run 'Get-VMSwitch -ErrorAction SilentlyContinue' in PowerShell (requires Hyper-V PowerShell module)
    Affected if VMSwitch exists and the system is on a vulnerable Windows version
  4. Check Hyper-V Virtual Switch extension status
    Run 'Get-VMSwitchExtension -VMSwitchName (Get-VMSwitch).Name' to list extensions including VMSwitch
    Affected if VMSwitch extension is loaded and the host OS is vulnerable

You are affected if your Windows build is below the threshold for your version AND Hyper-V with VMSwitch is enabled on the system.

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 10.0.19044.7417 / 10.0.19045.7417 / 10.0.20348.5256 or later
Fixed in 10.0.19044.741710.0.19045.741710.0.20348.5256
Interim mitigation

Apply the Microsoft security update for this vulnerability through Windows Update or enterprise patch management once released. Prioritize patching Windows Server systems running the Hyper-V role.

Recommended fix Moderate confidence

Windows 10 21h2: 10.0.19044.7417 or later | Windows 10 22h2: 10.0.19045.7417 or later | Windows 11 23h2: 10.0.22631.7219 or later | Windows 11 24h2: 10.0.26100.8655 or later | Windows 11 25h2: 10.0.26200.8655 or later | Windows 11 26h1: 10.0.28000.2269 or later | Windows Server 2022: 10.0.20348.5256

  1. Identify the current Windows version by running 'winver' or 'systeminfo' to confirm which build number is installed
  2. Determine the applicable upgrade path from the affected versions list based on your current Windows edition (Windows 10 21h2, Windows 10 22h2, Windows 11 23h2/24h2/25h2/26h1, Windows Server 2022, or Windows Server 2025)
  3. Apply the latest Windows Security Update that addresses this vulnerability by checking Windows Update or Microsoft's Update Catalog
  4. Verify the installation was successful by running 'winver' and confirming the build number matches or exceeds the fixed version (e.g., 10.0.19044.7417 for Windows 10 21h2)
  5. Restart the system if prompted to complete the update installation
Caveat Standard Windows update risks apply - ensure backups and compatibility testing for critical systems before deployment

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

Fix this in Windows 10 21h2 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
Get the upgrade done

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Scan for this in your stack

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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-2026-42915 in production — separate from our analysis above.

No notes yet

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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