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Windows 10 1809Operating system · Microsoft

CVE-2026-20810

HIGH · 7.8 CVSS v3.1 Published 2026-01-13
Fix available
A fix is available. Upgrade to 10.0.17763.8276 / 10.0.19044.6809 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
Free of memory not on the heap 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 confidence

A memory corruption vulnerability exists in the Windows Ancillary Function Driver (AFD.sys) for WinSock where the driver improperly frees memory that was not allocated on the heap. This allows a locally authorized attacker to escalate privileges to SYSTEM level.

MitigationApply Microsoft security updates for Windows once available. Until patch release, restrict local access to trusted users only and monitor for indicators of compromise targeting AFD.sys.

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 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 Server 2019Operating system
Affected:< 10.0.17763.8276

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. Verify AFD.sys driver is loaded
    Open Command Prompt and run: driverquery /v | findstr AFD.sys to confirm the Ancillary Function Driver is loaded in the system
    Affected if The driver must be running for this vulnerability to be exploitable - if AFD.sys is not loaded, the system is not vulnerable to this specific flaw
  2. Check Windows 10 1809 build number
    Run 'winver' or 'systeminfo | findstr /C:"Build"' and note the build number (e.g., 10.0.17763.xxxx)
    Affected if If the OS is Windows 10 version 1809 and the build number is less than 17763.8276, the system is affected
  3. Check Windows 10 21h2 build number
    Run 'winver' or 'systeminfo | findstr /C:"Build"' and note the build number (e.g., 10.0.19044.xxxx)
    Affected if If the OS is Windows 10 version 21h2 and the build number is less than 19044.6809, the system is affected
  4. Check Windows 10 22h2 build number
    Run 'winver' or 'systeminfo | findstr /C:"Build"' and note the build number (e.g., 10.0.19045.xxxx)
    Affected if If the OS is Windows 10 version 22h2 and the build number is less than 19045.6809, the system is affected
  5. Check Windows Server 2019 build number
    Run 'winver' or 'systeminfo | findstr /C:"Build"' and note the build number (e.g., 10.0.17763.xxxx)
    Affected if If the OS is Windows Server 2019 and the build number is less than 17763.8276, the system is affected

The system is affected if AFD.sys is loaded and the Windows build number falls below the specified thresholds for the respective version (17763.8276 for 1809/Server 2019, 19044.6809 for 21h2, or 19045.6809 for 22h2).

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 10.0.17763.8276 / 10.0.19044.6809 / 10.0.19045.6809 or later
Fixed in 10.0.17763.827610.0.19044.680910.0.19045.6809
Interim mitigation

Apply Microsoft security updates for Windows once available. Until patch release, restrict local access to trusted users only and monitor for indicators of compromise targeting AFD.sys.

Recommended fix High confidence

Windows 10 1809/Server 2019: build 10.0.17763.8276 or later | Windows 10 21h2: build 10.0.19044.6809 or later | Windows 10 22h2: build 10.0.19045.6809 or later

  1. Check current Windows version by running `winver` or `systeminfo` in Command Prompt
  2. Open Settings > Update & Security > Windows Update
  3. Click 'Check for updates' to download and install the latest security updates
  4. Ensure the installed build number meets or exceeds: Windows 10 1809/Server 2019: 10.0.17763.8276, Windows 10 21h2: 10.0.19044.6809, Windows 10 22h2: 10.0.19045.6809
  5. Restart the system if prompted to complete the update installation
  6. Verify the update was successfully installed by checking the installed updates in Settings > Update & Security > Windows Update > View update history
Caveat Standard Windows update; no breaking changes expected for typical end users

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

Fix this in Windows 10 1809 Scoped from the published advisory
  • Consultation4.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,600
Get the upgrade done

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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-2026-20810 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