Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability (CVE-2025-21335) Analysis and Mitigation Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2025-21335) is a Use-After-Free (UAF) flaw residing in the Windows Hyper-V NT Kernel Integration Virtual Service Provider (VSP). It occurs when the Hyper-V VSP processes communication sessions with guest operating systems or local virtualization components. The system fails to properly nullify or invalidate pointers to memory objects that have already been freed. Consequently, the kernel attempts to reuse these dangling pointers, leading to kernel memory corruption that can be leveraged to hijack the execution flow.

2. Exploitation Mechanics & Attack Scenario

To exploit this vulnerability, an attacker must first gain local execution capabilities on the target Windows system with low-privileged user access. The attacker then crafts and sends malicious VMBus messages or specific I/O requests to the VSP channel. By manipulating the kernel pool memory layout (Pool Feng Shui), the attacker forces the deallocation of a target kernel object and replaces its memory space with attacker-controlled data. When the kernel subsequently dereferences the freed pointer, it executes the attacker's payload within the kernel context (Ring 0), resulting in an elevation of privilege to SYSTEM.

3. Infrastructure & Business Impact

As this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, it poses an immediate and severe threat to enterprise environments. If a virtualization host is compromised, the confidentiality, integrity, and availability of all virtual machines (VMs) running on that host are entirely compromised. In multi-tenant cloud or enterprise virtualization infrastructures, gaining host kernel-level access allows attackers to perform lateral movement across the internal network and deploy ransomware, causing catastrophic business disruption.