High

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

IdentifiersCVE-2026-21236CWE-122· Heap-based Buffer Overflow

CVE-2026-21236 is a heap-based buffer overflow in the Windows Ancillary Function Driver for WinSock (AFD.sys). Microsoft describes it as an elevation of privilege vulnerability affecting the Windows networking driver stack. The available supporting content identifies the flaw class as a heap overflow in AFD.sys and indicates that public research has performed patch diffing, vulnerability analysis, and proof-of-concept generation, but the specific vulnerable function and exact triggering code path are not provided in the supplied material. Successful exploitation allows a local attacker with authorization on the target system to corrupt heap memory in kernel context and elevate privileges.

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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 results in local elevation of privilege on the affected Windows system. Because the flaw is in AFD.sys, exploitation likely crosses a trust boundary into kernel-mode code, enabling an attacker who already has local code execution as a low-privileged user to obtain higher privileges, potentially up to SYSTEM. This can enable full compromise of the host, including disabling security controls, credential theft, persistence, and follow-on lateral movement.

Mitigation

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

If immediate patching is not possible, reduce exposure by limiting local access to trusted users only, restricting the ability to execute untrusted code on endpoints, and enforcing application control to prevent low-privileged code execution that could be used to trigger the vulnerability. Because this is a local authorized-attacker privilege escalation in a core Windows driver, there is no specific robust workaround provided in the supplied content; patching is the primary mitigation.

Remediation

Patch, then assume compromise.

Apply Microsoft's February 11, 2026 security updates for all affected Windows versions. The supplied content indicates Microsoft released patches for supported product versions and recommends verifying successful installation through Windows Update, Update History, or by using standalone packages from the Microsoft Update Catalog if necessary.

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 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

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

12 SOURCESView more in app

ncc group researchNews

Mar 16, 2026

Vulnerability Analysis of CVE-2026-21236 | NCC Group

A heap-based buffer overflow vulnerability in the Windows Ancillary Function Driver for WinSock (AFD.sys). The content highlights patch diffing, vulnerability analysis, and proof-of-concept generation.

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.

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 signatures

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 activity7

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

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-21236

NVD

nvd.nist.gov/vuln/detail/CVE-2026-21236

MITRE CWE · CWE-122

Heap-based Buffer Overflow

Vendor Advisory

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21236