dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-21238

HIGH · 7.8 CVSS v3.1 Published 2026-02-10
Fix available
A fix is available. Upgrade to 10.0.14393.8868 / 10.0.17763.8389 or later.
See remediation →
80/100
Remediation priority · High
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
Improper access control 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 · high confidence

This is a local privilege escalation vulnerability in the Windows Ancillary Function Driver (AFD.sys), which handles WinSock network communications. The vulnerability involves improper access control that allows an authenticated local attacker to elevate their privileges to SYSTEM or administrative levels.

MitigationApply the relevant Microsoft security update for CVE-2026-21238 through Windows Update or manual patch deployment, as this is a driver-level vulnerability fixed by Microsoft.

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 1607Operating system
Affected:< 10.0.14393.8868
Windows 10 1809Operating system
Affected:< 10.0.17763.8389
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 2012Operating system
Affected:all versions= r2

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Check Windows version and build number
    Open Command Prompt or PowerShell and run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to obtain the exact Windows version and build number
    Affected if The installed build number falls below any of these thresholds: 14393.8868 (Win10 1607), 17763.8389 (Win10 1809), 19044.6937 (Win10 21h2), 19045.6937 (Win10 22h2), 22631.6649 (Win11 23h2), 26100.7781 (Win11 24h2), 26200.7781 (Win11 25h2), or any Windows Server 2012 R2 version
  2. Verify AFD.sys driver presence
    Check that AFD.sys exists on the system by running 'dir C:\Windows\System32\drivers\AFD.sys' in an elevated Command Prompt
    Affected if The driver file exists (which is true on all standard Windows installations with networking) and the Windows version is in the affected range from step 1
  3. Confirm user context for exploitation
    Recognize this is a local privilege escalation requiring an authenticated local user account. Check current user context with 'whoami' in Command Prompt
    Affected if The system runs an affected Windows version AND accepts local user connections (standard configuration). The vulnerability is exploitable by any authenticated local user on the system.

The system is affected if it runs any Windows version with a build number lower than the fixed versions listed, as the vulnerable AFD.sys driver is present by default on affected Windows installations.

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 10.0.14393.8868 / 10.0.17763.8389 / 10.0.19044.6937 or later
Fixed in 10.0.14393.886810.0.17763.838910.0.19044.6937
Interim mitigation

Apply the relevant Microsoft security update for CVE-2026-21238 through Windows Update or manual patch deployment, as this is a driver-level vulnerability fixed by Microsoft.

Recommended fix High confidence

Upgrade to the appropriate fixed build for your Windows version (e.g., Windows 10 22h2 build >= 10.0.19045.6937, Windows 11 24h2 >= 10.0.26100.7781)

  1. Identify the current Windows version by running 'winver' or 'systeminfo' in Command Prompt
  2. Determine which version branch you're on (e.g., 1607, 1809, 21h2, 22h2, 23h2, 24h2, 25h2, or Windows Server 2012 R2)
  3. For Windows 10 1607: Upgrade to build 10.0.14393.8868 or later
  4. For Windows 10 1809: Upgrade to build 10.0.17763.8389 or later
  5. For Windows 10 21h2: Upgrade to build 10.0.19044.6937 or later
  6. For Windows 10 22h2: Upgrade to build 10.0.19045.6937 or later
  7. For Windows 11 23h2: Upgrade to build 10.0.22631.6649 or later
  8. For Windows 11 24h2: Upgrade to build 10.0.26100.7781 or later
Caveat Windows Server 2012 R2 has no patch; migration to a supported Windows Server version is required

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

Fix this in Windows 10 1607 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,210
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,936.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

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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-2026-21238 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