dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-21236

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
Heap-based buffer overflow 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 heap-based buffer overflow vulnerability exists in the Windows Ancillary Function Driver (afd.sys), which handles Windows Sockets communications. An authorized local attacker can exploit this to elevate privileges to SYSTEM level, potentially gaining full control of the affected system.

MitigationApply the Microsoft security update for CVE-2026-21236 via Windows Update or enterprise patch management systems. Prioritize patching systems with interactive user access.

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
    Run 'winver' or 'systeminfo' from command prompt to obtain the exact OS version and build number (for example, 10.0.19045.6937 for Windows 10 22h2)
    Affected if The build number is lower than the version listed in the affected ranges for your Windows release (for example, below 10.0.19045.6937 for Windows 10 22h2, or any build for Windows Server 2012/R2)
  2. Identify Windows release name
    Run 'winver' to see the release name (such as 'Version 22h2' or '23H2') or check 'systeminfo' for the OS Name field to map to the affected product list
    Affected if The identified release matches any of the affected products listed in the CVE (Windows 10 1607, 1809, 21h2, 22h2, Windows 11 23h2, 24h2, 25h2, or Windows Server 2012/R2) and the build is below the threshold
  3. Verify afd.sys driver presence
    Check that the file C:\Windows\System32\drivers\afd.sys exists on the system; this is the Ancillary Function Driver component vulnerable to the buffer overflow
    Affected if The afd.sys file exists (this driver is present by default on all affected Windows systems with network capabilities)
  4. Confirm local authorized access
    Determine whether you have an authorized local user account on the target system; this vulnerability requires a local attacker with the ability to execute code
    Affected if You are running on an affected Windows version with local user access, as the flaw is exploitable by a local authorized attacker to escalate to SYSTEM privileges

A system is affected if it runs any Windows version within the specified build ranges or is Windows Server 2012/R2 (all builds), and the attacker has local authorized access to trigger the afd.sys buffer overflow.

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 Microsoft security update for CVE-2026-21236 via Windows Update or enterprise patch management systems. Prioritize patching systems with interactive user access.

Recommended fix High confidence

Windows 10 1607: build 10.0.14393.8868 or later | Windows 10 1809: build 10.0.17763.8389 or later | Windows 10 21h2: build 10.0.19044.6937 or later | Windows 10 22h2: build 10.0.19045.6937 or later | Windows 11 23h2: build 10.0.22631.6649 or later | Windows 11 24h2: build 10.0.26100.7781 or later |

  1. Open Settings on the Windows system and navigate to Windows Update
  2. Click 'Check for updates' to download and install the latest security updates
  3. Alternatively, manually check the Microsoft Update Catalog (catalog.update.microsoft.com) for KB articles corresponding to this CVE (CVE-2026-21236)
  4. After installation, restart the system to complete the patch
  5. For Windows Server 2012 R2 which has reached end of support: migrate to a supported Windows Server version (e.g., Windows Server 2019, 2022, or 2025)
Caveat Windows Server 2012 R2 has reached end of support with no patch available; 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
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2026-21236 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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