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Windows 10 21h2Operating system · Microsoft

CVE-2026-21242

HIGH · 7.0 CVSS v3.1 Published 2026-02-10
Fix available
A fix is available. Upgrade to 10.0.19044.6937 / 10.0.19045.6937 or later.
See remediation →
72/100
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
Use after free in Windows Subsystem for Linux allows an authorized attacker to elevate privileges 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

Use-after-free vulnerability in Windows Subsystem for Linux enables a locally authorized attacker to escalate privileges to a higher integrity level. The vulnerability involves improper memory management where memory is accessed after being freed, leading to arbitrary code execution in kernel context.

MitigationApply Microsoft security patches for Windows Subsystem for Linux when released. Until then, limit local access to trusted users and monitor for unusual WSL process activity.

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:< 10.0.19044.6937
Windows 10 22h2Operating system
Affected:< 10.0.19045.6937
Windows 11 23h2Operating system
Affected:< 10.0.22631.6649
Windows 11 24h2Operating system
Affected:< 10.0.26100.7781
Windows 11 25h2Operating system
Affected:< 10.0.26200.7781
Windows Server 2022Operating system
Affected:< 10.0.20348.4711
Windows Server 2022 23h2Operating system
Affected:< 10.0.25398.2149
Windows Server 2025Operating system
Affected:< 10.0.26100.32313

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
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/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. Verify Windows Subsystem for Linux is installed
    Open Command Prompt or PowerShell and run 'wsl --status' or check 'Get-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux' in PowerShell. If the command fails or shows WSL is disabled, the vulnerability does not apply.
    Affected if WSL is installed and enabled on the system
  2. Determine the installed Windows build number
    Open Command Prompt and run 'winver' to display the OS version and build, or run 'systeminfo | findstr /B /C:"OS Version"' for a text-based output. Note the full build number (e.g., 10.0.19045.xxxx).
    Affected if The build number is visible and can be compared to the affected ranges
  3. Compare your build against the affected version ranges
    For Windows 10 21h2: ensure build is 10.0.19044.6937 or higher. For Windows 10 22h2: ensure build is 10.0.19045.6937 or higher. For Windows 11 23h2: ensure build is 10.0.22631.6649 or higher. For Windows 11 24h2: ensure build is 10.0.26100.7781 or higher. For Windows 11 25h2: ensure build is 10.0.26200.7781 or higher. For Windows Server 2022: ensure build is 10.0.20348.4711 or higher. For Windows Server 2022 23h2: ensure build is 10.0.25398.2149 or higher. For Windows Server 2025: ensure build is 10.0.26100.32313 or higher.
    Affected if Your Windows build number is lower than the fixed version for your specific Windows release

You are affected if WSL is installed and enabled and your Windows build number falls below the minimum fixed version for your Windows release.

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 10.0.19044.6937 / 10.0.19045.6937 / 10.0.20348.4711 or later
Fixed in 10.0.19044.693710.0.19045.693710.0.20348.4711
Interim mitigation

Apply Microsoft security patches for Windows Subsystem for Linux when released. Until then, limit local access to trusted users and monitor for unusual WSL process activity.

Recommended fix High confidence

Upgrade to the specific build numbers: Windows 10 21h2 to 10.0.19044.6937, Windows 10 22h2 to 10.0.19045.6937, Windows 11 23h2 to 10.0.22631.6649, Windows 11 24h2 to 10.0.26100.7781, Windows 11 25h2 to 10.0.26200.7781, Windows Server 2022 to 10.0.20348.4711, Windows Server 2022 23h2 to 10.0.25398.21

  1. 1. Open Settings on the Windows system
  2. 2. Navigate to Windows Update (Settings > Windows Update)
  3. 3. Click 'Check for updates' to download and install the latest security updates
  4. 4. Ensure the update includes the specific build number for your Windows version (10.0.19044.6937 for 21h2, 10.0.19045.6937 for 22h2, 10.0.22631.6649 for 23h2, 10.0.26100.7781 for 24h2, 10.0.26200.7781 for 25h2, 10.0.20348.4711 for Server 2022, 10.0.25398.2149 for Server 2022 23h2, or 10.0.26100.32313 for Server 2025)
  5. 5. Restart the system when prompted to complete the update installation
  6. 6. Verify the installed version by running 'winver' or 'systeminfo' to confirm the build number matches or exceeds the fixed version
Caveat Standard Windows update risks apply: potential for temporary service disruption during update installation and restart

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
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
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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-2026-21242 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