CVE-2026-21245
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 · uneditedHeap-based buffer overflow in Windows Kernel 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 confidenceA heap-based buffer overflow vulnerability in the Windows Kernel that enables a local authenticated attacker to escalate privileges, likely gaining SYSTEM-level access. The vulnerability exists in kernel-mode memory handling and can be exploited by an authorized user with local access to the 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< 10.0.26100.7781< 10.0.26200.7781< 10.0.26100.32313CVSS 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.
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Check Windows version and build numberOpen Command Prompt or PowerShell and run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to display the installed Windows version and build numberAffected if The build number is lower than 10.0.26100.7781 for Windows 11 24h2, lower than 10.0.26200.7781 for Windows 11 25h2, or lower than 10.0.26100.32313 for Windows Server 2025
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Confirm exact build revisionRun 'winver' and note the full build number displayed (including the revision number after the build, for example 26100.7781)Affected if The displayed revision number is lower than the thresholds listed above for the corresponding Windows edition
A user is affected if they are running Windows 11 24h2, Windows 11 25h2, or Windows Server 2025 with a build number below the specified fixed revisions.
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 · scoped10.0.26100.778110.0.26100.3231310.0.26200.7781
Apply Microsoft security updates for this vulnerability once released. Until a patch is available, minimize the attack surface by restricting user privileges to the minimum required and monitoring for indicators of compromise.
KB5055523 (Windows 11 24h2), KB5055523 (Windows 11 25h2), or corresponding Windows Server 2025 security update containing build 10.0.26100.32313
- Open Settings on the Windows system
- Navigate to Windows Update (Settings > Update & Security > Windows Update)
- Click 'Check for updates' to download and install all available security updates
- After installation, verify the build number matches or exceeds: 10.0.26100.7781 for Windows 11 24h2, 10.0.26200.7781 for Windows 11 25h2, or 10.0.26100.32313 for Windows Server 2025
- Restart the system if prompted to complete the update installation
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-21245 — 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-2026-21245 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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