CVE-2026-21241
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 Ancillary Function Driver for WinSock 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 use-after-free vulnerability exists in the Windows Ancillary Function Driver (AFD) for WinSock, which handles network communications. The flaw allows a locally authenticated attacker to manipulate memory after it has been freed, potentially achieving elevated privileges by executing arbitrary code in kernel context.
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< 10.0.22631.6649< 10.0.26100.7781< 10.0.26200.7781< 10.0.20348.4711< 10.0.25398.2149< 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
- 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 checksWork through these to decide whether this CVE applies to you.
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Check Windows build versionRun 'winver' from command prompt or execute 'systeminfo | findstr /C:"Build"' to retrieve the current OS build numberAffected if The build number falls below the fixed version for your specific Windows edition (23h2: <10.0.22631.6649, 24h2: <10.0.26100.7781, 25h2: <10.0.26200.7781, Server 2022: <10.0.20348.4711, Server 2022 23h2: <10.0.25398.2149, Server 2025: <10.0.26100.32313)
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Identify Windows edition and versionRun 'winver' or check 'System Information' (msinfo32) to determine whether you are running Windows 11 23h2, 24h2, 25h2, Server 2022, Server 2022 23h2, or Server 2025Affected if The edition matches any of the affected products listed in the CVE and the build is below the corresponding threshold
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Locate and verify AFD driver versionOpen File Explorer, navigate to C:\Windows\System32\drivers\afd.sys, right-click the file, select Properties, and check the File version on the Details tabAffected if The driver version is earlier than the version bundled with the patched build for your Windows edition (typically aligns with the build numbers above)
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Check if running as local authenticated userVerify that user accounts exist on the system (run 'net user' to list local users). The vulnerability is exploitable by any locally authenticated user, not just administratorsAffected if Local user accounts are present on the system, meaning an attacker with any local credentials could potentially attempt exploitation
Your system is affected if it runs any of the listed Windows editions with a build number lower than the specified fixed version, and local user authentication is enabled.
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 · scoped10.0.20348.471110.0.22631.664910.0.25398.2149
Apply the Microsoft security update for CVE-2026-21241 through Windows Update or manual patch deployment. As a compensating control, limit local user privileges and monitor for suspicious processes attempting to interact with the AFD driver.
Windows 11 23h2: 10.0.22631.6649 | Windows 11 24h2: 10.0.26100.7781 | Windows 11 25h2: 10.0.26200.7781 | Windows Server 2022: 10.0.20348.4711 | Windows Server 2022 23h2: 10.0.25398.2149 | Windows Server 2025: 10.0.26100.32313
- Identify the current Windows build version by running 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"'
- For Windows 11 23h2: Install KB5055523 (or subsequent security update) to reach build 10.0.22631.6649 or later
- For Windows 11 24h2: Install KB5056678 (or subsequent security update) to reach build 10.0.26100.7781 or later
- For Windows 11 25h2: Install KB5060116 (or subsequent security update) to reach build 10.0.26200.7781 or later
- For Windows Server 2022: Install KB5055520 (or subsequent security update) to reach build 10.0.20348.4711 or later
- For Windows Server 2022 23h2: Install KB5056679 (or subsequent security update) to reach build 10.0.25398.2149 or later
- For Windows Server 2025: Install KB5056657 (or subsequent security update) to reach build 10.0.26100.32313 or later
- Verify the installed build matches or exceeds the fixed version using 'winver' or 'systeminfo'
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-21241 — 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-2026-21241 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
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