CVE-2026-27922: Windows WinSock Use After Free Vulnerability

CVE-2026-27922 Overview

CVE-2026-27922 is a Use After Free vulnerability in the Windows Ancillary Function Driver for WinSock (AFD.sys) that allows an authorized attacker to elevate privileges locally. This kernel-level driver vulnerability enables attackers with low-privilege access to execute code with elevated system privileges, potentially gaining complete control over affected Windows systems.

Critical Impact

Local privilege escalation through kernel driver exploitation could allow attackers to bypass security controls, install persistent malware, and compromise entire Windows systems.

Affected Products

• Windows Ancillary Function Driver for WinSock (AFD.sys)
• Microsoft Windows Operating Systems

Discovery Timeline

• April 14, 2026 - CVE-2026-27922 published to NVD
• April 14, 2026 - Last updated in NVD database

Technical Details for CVE-2026-27922

Vulnerability Analysis

This Use After Free (CWE-416) vulnerability exists within the Windows Ancillary Function Driver for WinSock, commonly known as AFD.sys. This kernel-mode driver handles the WinSock network socket operations for Windows and serves as a critical interface between user-mode network applications and the underlying TCP/IP stack.

The vulnerability occurs when the driver improperly manages memory objects during socket operations. Specifically, after a memory object is freed, the driver may continue to reference or use that memory location. This creates a condition where an attacker can manipulate the freed memory to achieve arbitrary code execution within the kernel context.

Due to the local attack vector and requirement for low-level privileges, an attacker must first obtain initial access to the target system. However, the high complexity involved does not diminish the severity, as successful exploitation grants complete system compromise.

Root Cause

The root cause stems from improper memory lifecycle management within AFD.sys. When handling specific WinSock operations, the driver fails to properly invalidate pointers after freeing associated memory objects. This dangling pointer condition allows attackers to craft malicious input that triggers use of the freed memory, enabling controlled memory corruption in kernel space.

Attack Vector

The attack vector is local, requiring an attacker to have authenticated access to the target system with low-level user privileges. The exploitation involves:

1. An attacker with local access creates specially crafted socket operations targeting the AFD driver
2. The attacker triggers a sequence of operations that causes premature memory deallocation
3. The freed memory is reallocated with attacker-controlled content
4. When the driver references the dangling pointer, it processes attacker-controlled data in kernel context
5. This allows arbitrary code execution with SYSTEM privileges

The vulnerability is exploited through interactions with the AFD driver's I/O control (IOCTL) interface. An attacker would send specific socket requests to trigger the use-after-free condition. For detailed technical information, refer to the Microsoft Security Update.

Detection Methods for CVE-2026-27922

Indicators of Compromise

• Unusual IOCTL requests to the AFD.sys driver from non-standard processes
• Unexpected memory allocation patterns in kernel space associated with network socket operations
• Privilege escalation events from low-privilege user accounts
• Anomalous process creation with SYSTEM privileges originating from network-related operations

Detection Strategies

• Monitor for suspicious interactions with AFD.sys through kernel-level telemetry
• Deploy behavioral analysis rules to detect privilege escalation patterns targeting WinSock operations
• Implement SentinelOne's kernel protection capabilities to detect exploitation attempts against kernel drivers
• Enable detailed Windows Security event logging for privilege changes and process creation

Monitoring Recommendations

• Enable Windows Defender Exploit Guard and Attack Surface Reduction rules
• Configure endpoint detection solutions to monitor AFD.sys driver activity
• Implement SentinelOne's Storyline technology to correlate network socket activity with subsequent privilege changes
• Review Windows Event logs for Event ID 4688 (Process Creation) with elevated token privileges

How to Mitigate CVE-2026-27922

Immediate Actions Required

• Apply the latest Windows security updates from Microsoft as soon as available
• Restrict local access to critical systems to authorized personnel only
• Enable SentinelOne's behavioral AI to detect and prevent exploitation attempts
• Implement application control policies to limit execution of untrusted code

Patch Information

Microsoft has released a security update addressing this vulnerability. Organizations should apply the patch available through the Microsoft Security Update Guide. The update resolves the improper memory handling in AFD.sys by ensuring proper pointer invalidation after memory deallocation.

Workarounds

• Limit local user access and enforce least-privilege principles across all Windows endpoints
• Deploy additional monitoring on systems where patching cannot be immediately applied
• Use network segmentation to limit lateral movement potential if exploitation occurs
• Consider disabling non-essential network services on critical systems until patches are applied

# Verify current Windows patch level
wmic qfe list brief | findstr /i "KB"

# Check AFD.sys driver version
driverquery /v | findstr /i "afd"