CVE-2026-27917: Windows WFP NDIS Driver Use-After-Free

CVE-2026-27917 Overview

CVE-2026-27917 is a Use After Free vulnerability in the Windows Filtering Platform (WFP) NDIS Lightweight Filter Driver (wfplwfs.sys). This kernel-mode driver vulnerability allows an authorized attacker to elevate privileges locally, potentially gaining SYSTEM-level access on affected Windows systems.

Critical Impact

Local privilege escalation through kernel memory corruption in a core Windows networking component could allow attackers with limited access to achieve complete system compromise.

Affected Products

• Windows operating systems with WFP NDIS Lightweight Filter Driver (wfplwfs.sys)
• Windows systems utilizing Windows Filtering Platform networking features
• Enterprise and consumer Windows deployments with affected driver versions

Discovery Timeline

• April 14, 2026 - CVE-2026-27917 published to NVD
• April 14, 2026 - Last updated in NVD database

Technical Details for CVE-2026-27917

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of wfplwfs.sys, this driver operates at the kernel level within the Windows Filtering Platform architecture, which is responsible for network packet filtering and inspection.

The local attack vector requires an authenticated user on the system, but the vulnerability does not require user interaction once the attacker has local access. Successful exploitation leads to high impacts on confidentiality, integrity, and availability, as the attacker can execute arbitrary code with kernel privileges.

Root Cause

The root cause is a Use After Free condition in the wfplwfs.sys driver where memory is freed but subsequently referenced during network filter operations. This occurs when the driver fails to properly invalidate pointers to freed memory structures during certain state transitions or concurrent operations in the NDIS filter path.

When kernel memory is freed but the pointer remains accessible, subsequent operations that dereference this stale pointer can lead to arbitrary memory access. In kernel mode, this typically enables:

• Arbitrary read/write primitives in kernel memory
• Token manipulation for privilege escalation
• Execution of attacker-controlled code with SYSTEM privileges

Attack Vector

The attack requires local access with low privileges (an authenticated user account). The attacker must be able to interact with the Windows Filtering Platform through network operations or driver IOCTLs to trigger the vulnerable code path in wfplwfs.sys.

Exploitation typically involves:

1. Triggering the allocation of a specific kernel object through the WFP driver
2. Causing the object to be freed while maintaining a dangling reference
3. Reallocating the freed memory with attacker-controlled content
4. Triggering the use of the dangling pointer to achieve code execution

The vulnerability requires careful memory grooming and timing to successfully exploit, as indicated by the high attack complexity. However, successful exploitation results in full system compromise through kernel-level privilege escalation.

Detection Methods for CVE-2026-27917

Indicators of Compromise

• Unusual crash dumps or Blue Screen of Death (BSOD) events referencing wfplwfs.sys
• Unexpected processes running with SYSTEM privileges following suspicious network activity
• Anomalous kernel memory access patterns detected by endpoint protection solutions
• Security event logs showing privilege escalation from low-privilege accounts

Detection Strategies

• Monitor for unusual driver loading or unloading events related to WFP components
• Implement kernel-level behavior analysis to detect exploitation attempts targeting wfplwfs.sys
• Deploy endpoint detection and response (EDR) solutions capable of detecting Use After Free exploitation patterns
• Enable Windows Defender Credential Guard and other kernel protection mechanisms

Monitoring Recommendations

• Enable detailed Windows Security event logging for process creation and privilege changes
• Monitor for unusual IOCTL calls to network filter drivers
• Implement anomaly detection for processes spawning with unexpected privilege levels
• Review system crash dumps for evidence of wfplwfs.sys related memory corruption

How to Mitigate CVE-2026-27917

Immediate Actions Required

• Apply the latest Windows security updates from Microsoft addressing CVE-2026-27917
• Restrict local access to systems to only authorized and trusted users
• Implement the principle of least privilege to limit the impact of potential exploitation
• Enable Windows security features such as Secure Boot and Kernel DMA Protection

Patch Information

Microsoft has released security updates to address this vulnerability. Refer to the Microsoft Security Update Guide for specific patch information, affected Windows versions, and detailed remediation guidance. Organizations should prioritize patching systems with local user access that could be targeted for privilege escalation attacks.

Workarounds

• Limit local logon access to trusted administrators only where possible
• Implement application control policies to restrict execution of unauthorized code
• Enable Attack Surface Reduction (ASR) rules in Windows Defender
• Consider network segmentation to limit the impact of compromised systems

# Verify wfplwfs.sys driver version after patching
# Run in elevated PowerShell
Get-WmiObject Win32_PnPSignedDriver | Where-Object {$_.DeviceName -like "*WFP*"} | Select-Object DeviceName, DriverVersion, DriverDate

# Check for pending Windows updates
Get-WindowsUpdate -KBArticleID "KB*" | Where-Object {$_.Title -like "*Security*"}