High

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

IdentifiersCVE-2026-21238CWE-284· Improper Access Control

CVE-2026-21238 is an elevation of privilege vulnerability in the Windows Ancillary Function Driver for WinSock (AFD.sys). The provided content states that the issue is caused by improper access control, allowing an authorized attacker to elevate privileges locally. No further technical detail about the specific vulnerable function, code path, or triggering IOCTL/operation is provided in the supplied material.

For your environment

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows a local authorized attacker to elevate privileges on the affected Windows system. The supplied context indicates this can result in SYSTEM-level privileges, enabling full control over the host, including execution of code with highest local privileges, tampering with protected resources, disabling defenses, credential theft, and persistence.

Mitigation

If you can’t patch tonight, do this now.

No specific workaround or mitigation for CVE-2026-21238 is provided in the supplied content. In the absence of a vendor workaround, reduce exposure by limiting local access, restricting the ability of untrusted users to log on interactively or execute code locally, enforcing least privilege, and prioritizing patch deployment.

Remediation

Patch, then assume compromise.

Apply Microsoft's February 2026 security update for CVE-2026-21238 on all supported affected Windows versions, including the Windows 10 builds referenced in the provided context. Microsoft has released patches for supported product versions, and installation should be verified through Windows Update, Update History, or the Microsoft Update Catalog if standalone packages are required.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

Microsoft CorporationWindows 10 1607operating_system

Microsoft CorporationWindows 10 1809operating_system

Microsoft CorporationWindows 10 21h2operating_system

Microsoft CorporationWindows 10 22h2operating_system

Microsoft CorporationWindows 11 23h2operating_system

Microsoft CorporationWindows 11 24h2operating_system

Microsoft CorporationWindows 11 25h2operating_system

Microsoft CorporationWindows 11 26h1operating_system

Microsoft CorporationWindows Ancillary Function Driver For Winsockoperating_system

Microsoft CorporationWindows Server 2012operating_system

Microsoft CorporationWindows Server 2012 R2operating_system

Microsoft CorporationWindows Server 2016operating_system

Microsoft CorporationWindows Server 2019operating_system

Microsoft CorporationWindows Server 2022operating_system

Microsoft CorporationWindows Server 2022 23h2operating_system

Microsoft CorporationWindows Server 2025operating_system

Microsoft CorporationWindows Server 23h2operating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

9 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

9 SOURCESView more in app

flareio blogNews

Mar 13, 2026

Cybercrime Intelligence After February 2026 Patch Tuesday - Flare

A local privilege escalation vulnerability in the Windows Ancillary Function Driver for WinSock that can provide SYSTEM privileges and is likely useful as part of an attack chain.

nsfocus globalNews

Mar 4, 2026

Microsoft’s February Security Update of High-Risk Vulnerability Notice for Multiple Products - NSFOCUS, Inc., a global network and cyber security leader, protects enterprises and carriers from advanced cyber attacks.

A privilege escalation vulnerability affecting the Windows Ancillary Function Driver for WinSock (spelled WinSoc in the source).

bleeping computerNews

Feb 10, 2026

Microsoft February 2026 Patch Tuesday fixes 6 zero-days, 58 flaws

An elevation of privilege vulnerability in Windows Ancillary Function Driver for WinSock (no additional details provided in the content).

zerodayinitiative blogNews

Feb 10, 2026

Zero Day Initiative - The February 2026 Security Update Review

An elevation of privilege vulnerability in the Windows Ancillary Function Driver for WinSock (AFD).

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures1

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity3

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-21238

NVD

nvd.nist.gov/vuln/detail/CVE-2026-21238

MITRE CWE · CWE-284

Improper Access Control

Vendor Advisory

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21238