CVE-2026-25179: Windows WinSock AFD Privilege Escalation

CVE-2026-25179 Overview

CVE-2026-25179 is a local privilege escalation vulnerability affecting the Windows Ancillary Function Driver for WinSock (AFD.sys). The vulnerability stems from improper validation of specified type of input, which allows an authorized attacker with local access to elevate privileges on the affected system. This kernel-level driver vulnerability presents significant risk as successful exploitation could allow attackers to execute code with SYSTEM privileges.

Critical Impact

An authorized local attacker can exploit improper input validation in the Windows AFD driver to escalate privileges to SYSTEM level, potentially gaining complete control over the affected Windows system.

Affected Products

• Windows Ancillary Function Driver for WinSock (AFD.sys)
• Microsoft Windows (versions specified in security advisory)

Discovery Timeline

• 2026-03-10 - CVE-2026-25179 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2026-25179

Vulnerability Analysis

This vulnerability exists within the Windows Ancillary Function Driver for WinSock (AFD.sys), which is a critical kernel-mode driver that provides the core networking stack functionality for Windows Sockets API. The AFD driver operates at the kernel level and handles communication between user-mode applications and the underlying transport protocols.

The flaw is classified under CWE-1287 (Improper Validation of Specified Type of Input), indicating that the driver fails to properly validate the type of input it receives before processing. In kernel drivers like AFD.sys, improper type validation can lead to type confusion scenarios where the driver processes data as an incorrect type, potentially leading to memory corruption and privilege escalation.

Given the local attack vector with high complexity, exploitation requires the attacker to already have authenticated access to the target system. However, once exploited, the impact is severe—affecting confidentiality, integrity, and availability of the system. The kernel-level nature of this vulnerability means successful exploitation could bypass user-mode security controls entirely.

Root Cause

The root cause of CVE-2026-25179 lies in the improper validation of input types within the AFD driver. When processing requests through the WinSock interface, the driver fails to adequately verify that the specified input matches expected types before performing operations. This type confusion vulnerability allows attackers to provide malformed or unexpected input that the driver incorrectly interprets, leading to unintended behavior in the kernel context.

Kernel drivers must rigorously validate all input from user-mode applications since they operate with highest system privileges. The failure to properly validate input types in AFD.sys creates an exploitable condition that can be leveraged for privilege escalation.

Attack Vector

The attack requires local access to the target Windows system with at least low-privilege authenticated access. The attacker must craft a specific sequence of WinSock API calls that trigger the vulnerable code path in the AFD driver. The high attack complexity rating indicates that exploitation may require specific conditions or timing to be successful.

The exploitation flow typically involves:

1. An authenticated low-privilege user creating a malicious application or script
2. The application making specially crafted calls to the WinSock API
3. These calls propagating to the AFD driver with improper type specifications
4. The driver incorrectly processing the input due to validation failures
5. The attacker leveraging the resulting memory corruption or type confusion to escalate privileges

No verified proof-of-concept code is currently available. The vulnerability mechanism involves improper type validation in the AFD driver's input handling routines. For detailed technical information, refer to the Microsoft Security Update for CVE-2026-25179.

Detection Methods for CVE-2026-25179

Indicators of Compromise

• Unusual process behavior with SYSTEM privileges originating from non-standard parent processes
• Unexpected access patterns or IOCTL calls to AFD.sys driver
• Suspicious user-mode applications making anomalous WinSock API calls
• Signs of privilege escalation from low-privilege user accounts

Detection Strategies

• Monitor for unusual kernel driver access patterns, particularly to AFD.sys
• Implement behavioral detection for privilege escalation attempts from low-privilege processes
• Deploy endpoint detection and response (EDR) solutions capable of monitoring kernel-level activities
• Utilize SentinelOne's Singularity platform for real-time detection of exploitation attempts targeting kernel drivers

Monitoring Recommendations

• Enable detailed Windows Security Event logging, particularly Event ID 4688 (Process Creation) with command-line auditing
• Configure kernel object access auditing to detect anomalous driver interactions
• Implement network behavior analytics to identify unusual WinSock activity patterns
• Leverage SentinelOne's Storyline technology to correlate suspicious activities across the attack chain

How to Mitigate CVE-2026-25179

Immediate Actions Required

• Apply the latest Microsoft security updates addressing CVE-2026-25179 immediately
• Review and restrict local user access to minimize potential attack surface
• Implement least privilege principles to limit the impact of potential exploitation
• Enable SentinelOne's Singularity XDR for comprehensive endpoint protection and threat detection

Patch Information

Microsoft has released a security update to address this vulnerability. System administrators should apply the patch available through Windows Update or the Microsoft Update Catalog. For detailed patch information and affected product versions, refer to the Microsoft Security Update Guide for CVE-2026-25179.

Workarounds

• Limit local access to systems to only essential personnel until patches can be applied
• Implement application whitelisting to prevent unauthorized executables from running
• Enable Windows Defender Credential Guard where supported to add additional protection layers
• Monitor systems closely for signs of exploitation attempts using endpoint security solutions

# Verify AFD driver version and patch status
driverquery /v | findstr /i "afd"

# Check Windows Update history for relevant security updates
wmic qfe list brief | findstr /i "KB"