dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-20831

HIGH · 7.0 CVSS v3.1 Published 2026-01-13
Fix available
A fix is available. Upgrade to 10.0.14393.8783 / 10.0.17763.8276 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
Time-of-check time-of-use (toctou) race condition in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

In the news

Third-party coverage
Trending covered by 1 outlet this week · latest 7mo ago

Surfaced from public web coverage — external links open in a new tab.

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

A time-of-check time-of-use (TOCTOU) race condition in the Windows Ancillary Function Driver for WinSock (AFD.sys) allows a locally authorized attacker to exploit the timing gap between security state validation and resource usage, enabling local privilege escalation.

MitigationApply Microsoft security updates for this vulnerability immediately; as an interim control, limit local system access to trusted administrators only.

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:< 10.0.14393.8783
Windows 10 1809Operating system
Affected:< 10.0.17763.8276
Windows 10 21h2Operating system
Affected:< 10.0.19044.6809
Windows 10 22h2Operating system
Affected:< 10.0.19045.6809
Windows 11 23h2Operating system
Affected:< 10.0.22631.6491
Windows 11 24h2Operating system
Affected:< 10.0.26100.7623
Windows 11 25h2Operating system
Affected:< 10.0.26200.7623
Windows Server 2008Operating 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
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. Identify Windows version and build number
    Run 'winver' or 'systeminfo' from command prompt, or query registry at HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion
    Affected if The build number falls within the affected ranges: < 10.0.14393.8783 (1607), < 10.0.17763.8276 (1809), < 10.0.19044.6809 (21h2), < 10.0.19045.6809 (22h2), < 10.0.22631.6491 (23h2), < 10.0.26100.7623 (24h2), < 10.0.26200.7623 (25h2), or Windows Server 2008 R2 any version
  2. Confirm AFD.sys driver is present
    Verify file exists at C:\Windows\System32\drivers\afd.sys or run 'wmic path Win32_PnPSignedDriver where "DeviceName like "%afd%"" get DeviceName,DriverVersion'
    Affected if The AFD.sys driver is loaded on the system (this is default for Windows systems with networking)
  3. Check AFD.sys file version
    Right-click afd.sys, select Properties > Details, or run 'powershell (Get-Item C:\Windows\System32\drivers\afd.sys).VersionInfo.FileVersion'
    Affected if The driver version is below the security patch level for your Windows version (compare your build to the fixed versions listed in the affected products)

The system is affected if running any Windows 10 version 1607 through 22h2, Windows 11 23h2 through 25h2, or Windows Server 2008 R2 with a build number lower than the fixed versions AND the AFD.sys driver is present.

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 10.0.14393.8783 / 10.0.17763.8276 / 10.0.19044.6809 or later
Fixed in 10.0.14393.878310.0.17763.827610.0.19044.6809
Interim mitigation

Apply Microsoft security updates for this vulnerability immediately; as an interim control, limit local system access to trusted administrators only.

Recommended fix High confidence

Install Windows Security Update containing CVE-2026-20831 fix (KB patch from Microsoft Update Catalog)

  1. Identify the current Windows version by running 'winver' or 'systeminfo' in Command Prompt
  2. Open Windows Update by navigating to Settings > Update & Security > Windows Update
  3. Click 'Check for updates' to download and install all available security updates
  4. For Windows Server 2008 which is end-of-life, manually download and install the specific KB patch from Microsoft Update Catalog corresponding to the CVE fix
  5. After installation, restart the system when prompted
  6. Verify the installed version matches or exceeds the fixed version: Windows 10 1607 should be 10.0.14393.8783 or later; Windows 10 1809 should be 10.0.17763.8276 or later; Windows 10 21h2 should be 10.0.19044.6809 or later; Windows 10 22h2 should be 10.0.19045.6809 or later; Windows 11 23h2 should be 10.0.22631.6491 or later; Windows 11 24h2 should be 10.0.26100.7623 or later; Windows 11 25h2 shoul
  7. Confirm successful patch installation by checking installed updates via Control Panel > Programs > View installed updates
Caveat Standard Windows cumulative security updates typically have minimal compatibility impact; verify application compatibility before deploying in enterprise environments

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

Fix this in Windows 10 1607 Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA6.0 h
30.0 hours of engineering $5,120
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,192.

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-2026-20831 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