CVE-2026-50349: Windows WinSock Race Condition Vulnerability

CVE-2026-50349 Overview

CVE-2026-50349 is a race condition vulnerability in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw involves concurrent execution using a shared resource with improper synchronization [CWE-362]. An authorized local attacker can exploit the race window to elevate privileges on an affected Windows system. The vulnerability affects a kernel-mode driver responsible for user-mode WinSock API operations, making successful exploitation a direct path from a low-privileged process to SYSTEM-level control.

Critical Impact
Successful exploitation grants an authenticated local attacker elevated privileges on the host, enabling full compromise of confidentiality, integrity, and availability at the kernel level.

Affected Products

Windows Ancillary Function Driver for WinSock (afd.sys)
Microsoft Windows (versions listed in the Microsoft Security Update Guide)
Windows Server (versions listed in the Microsoft Security Update Guide)

Discovery Timeline

2026-09-08 - CVE-2026-50349 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-50349

Vulnerability Analysis

The Ancillary Function Driver for WinSock (afd.sys) is a kernel-mode driver that services user-mode socket operations for the Windows networking stack. This vulnerability arises when multiple threads access a shared resource inside the driver without adequate synchronization. An attacker who races operations across threads can force the driver into an inconsistent state.

Because afd.sys runs in kernel mode, corrupting its internal state gives the attacker an opportunity to manipulate kernel memory or hijack privileged execution flow. The result is local privilege escalation from a standard user context to SYSTEM.

Root Cause

The root cause is improper synchronization on a shared resource during concurrent execution, classified as [CWE-362]. The affected code path likely fails to hold a lock, acquire a reference, or validate object state between a check and a subsequent use. This creates a Time-of-Check to Time-of-Use (TOCTOU) window that a second thread can exploit by mutating the shared object.

Attack Vector

Exploitation requires local access and low privileges but no user interaction. Attack complexity is high because the attacker must reliably win a narrow timing window in kernel code. An attacker typically spawns two or more threads that repeatedly invoke crafted WinSock I/O control requests to the AFD device, seeking to interleave operations at the precise moment that triggers the unsynchronized access.

Once the race is won, the attacker leverages the resulting memory corruption or dangling reference to overwrite kernel structures and pivot to SYSTEM. Refer to the Microsoft Security Update Guide for authoritative technical guidance.

No public proof-of-concept exploit code has been released. No verified exploitation details are available for reproduction here.

Detection Methods for CVE-2026-50349

Indicators of Compromise

Unexpected SYSTEM-level processes spawned from user sessions or non-service parent processes.
Kernel bug checks or crashes referencing afd.sys on hosts where unprivileged users are active.
Anomalous token elevation events shortly after high-frequency socket or I/O control activity from a standard user process.

Detection Strategies

Monitor for tight loops of DeviceIoControl calls targeting the AFD device from low-privileged processes, especially with multi-threaded patterns.
Correlate process creation events where a child process runs as SYSTEM but the parent runs as a standard user without a legitimate elevation mechanism.
Baseline expected behavior of applications that use raw WinSock APIs and flag deviations that involve concurrent thread patterns targeting kernel I/O.

Monitoring Recommendations

Enable Windows kernel and driver telemetry, including audit process creation with command line logging, and forward events to a centralized analytics platform.
Track EPSS trend data (currently 0.193%) and reprioritize detection engineering if exploit availability changes.
Review endpoint detection and response telemetry for behavioral indicators of local privilege escalation chains rather than signature-based artifacts.

How to Mitigate CVE-2026-50349

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update Guide to all affected Windows and Windows Server systems.
Prioritize patching on multi-user hosts, terminal servers, virtual desktop infrastructure, and developer workstations where local attackers are more likely to gain a foothold.
Audit accounts with interactive logon rights and remove unnecessary local access.

Patch Information

Microsoft has published guidance and updates through the Security Update Guide. Administrators should consult the Microsoft Security Update Guide entry for CVE-2026-50349 to identify the specific KB articles and cumulative updates applicable to each Windows build in the environment.

Workarounds

No official vendor workaround has been published; applying the security update is the recommended remediation.
Reduce exposure by enforcing least privilege, restricting local logon rights, and blocking execution of untrusted binaries on affected endpoints.
Use application control policies such as Windows Defender Application Control or AppLocker to limit which processes standard users can execute.

bash

# Verify installed Windows updates on an affected host
wmic qfe list brief /format:table

# PowerShell alternative to enumerate installed hotfixes
Get-HotFix | Sort-Object -Property InstalledOn -Descending