CVE-2026-40402
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 · uneditedUse after free in Windows Hyper-V allows an unauthorized 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 confidenceA use-after-free vulnerability exists in Windows Hyper-V that allows a local attacker to achieve privilege escalation. The flaw involves improper memory management where memory is accessed after being freed, potentially enabling an attacker to gain elevated SYSTEM or hypervisor-level privileges.
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< 10.0.22631.7079< 10.0.20348.5074CVSS 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
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:N/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 if Hyper-V is enabledRun 'Get-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V | Select-Object State' in PowerShell, or check services listing for Hyper-V Virtual Machine Management service (vmms)Affected if Hyper-V is installed and enabled on the system
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Determine Windows build versionRun 'winver' or execute 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to display the installed Windows version and build numberAffected if The build version falls below 10.0.22631.7079 for Windows 11 23h2, or below 10.0.20348.5074 for Windows Server 2022
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Confirm Windows edition matches affected productsRun 'systeminfo' and verify the OS is either Windows 11 version 23h2 or Windows Server 2022Affected if The system is running Windows 11 23h2 or Windows Server 2022 and the version is below the thresholds in step 2
The environment is affected if Hyper-V is enabled and the installed Windows build number is lower than 10.0.22631.7079 (Windows 11 23h2) or 10.0.20348.5074 (Windows Server 2022).
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 · scoped10.0.20348.507410.0.22631.7079
Apply Microsoft security updates for Windows Hyper-V as soon as patches become available; prioritize patching given the critical 9.3 CVSS score and local privilege escalation vector.
Windows 11 23h2: build 10.0.22631.7079 or later | Windows Server 2022: build 10.0.20348.5074 or later
- Check current Windows build version by running 'winver' or 'systeminfo' in Command Prompt
- For Windows 11 23h2: Verify build is below 10.0.22631.7079
- For Windows Server 2022: Verify build is below 10.0.20348.5074
- Open Settings > Windows Update (or use WSUS/Intune for enterprise deployments)
- Check for updates and install all available security updates
- Restart the system when prompted to complete the update installation
- Verify the fix by checking the build version matches or exceeds the fixed release
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 h
- Testing8.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,472.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40402 — 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-2026-40402 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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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
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