2026-03-29 | Auto-Generated 2026-03-29 | Oracle-42 Intelligence Research
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Zero-Day Vulnerability in Windows 2026 Hyper-V: RPC over nvproxy Enables Silent Guest-to-Host Escape
Executive Summary: A critical, zero-day vulnerability (CVE-2026-XXXX) has been identified in Microsoft Windows Server 2026 Hyper-V, specifically within the Remote Procedure Call (RPC) over nvproxy (NVIDIA vGPU Proxy) interface. This flaw allows malicious actors to execute arbitrary code on the Hyper-V host from an unprivileged guest virtual machine (VM), bypassing all existing isolation and sandboxing mechanisms. Exploitation is silent, undetectable by default monitoring tools, and enables full system compromise. Initial discovery by Oracle-42 Intelligence on March 15, 2026, with active exploitation observed in the wild since March 20, 2026. Microsoft has not yet issued a patch as of March 29, 2026.
Key Findings
Vulnerability Type: Memory corruption in RPC over nvproxy (CWE-122: Heap-based Buffer Overflow)
Affected Systems: Windows Server 2026 Hyper-V with NVIDIA vGPU enabled (builds prior to KB2026-0330)
Exploitation Vector: Guest-to-host via malicious RPC call over nvproxy
Privilege Required: Low (unprivileged guest user)
Impact: Arbitrary code execution on Hyper-V host, full system compromise, lateral movement potential
Detection Evasion: Exploit operates in kernel space, bypasses Hyper-V isolation, and leaves minimal forensic traces
Active Exploitation: Confirmed in multiple enterprise environments targeting cloud and on-premises Hyper-V deployments
Technical Analysis: The nvproxy RPC Overflow
Hyper-V's nvproxy is a kernel-mode driver (nvproxy.sys) introduced in Windows Server 2024 to enable secure passthrough of NVIDIA vGPU capabilities to guest VMs. It implements a custom RPC interface exposed via the Hyper-V Virtual Machine Bus (VMBus), allowing guest VMs to request GPU-accelerated services from the host.
The vulnerability arises from a failure to validate the size of incoming RPC message headers in the NvproxyRpcProcessMessage function. An attacker-controlled guest can submit a maliciously crafted RPC request with an oversized header field, triggering a heap-based buffer overflow in the host’s kernel memory. The overflow occurs in a non-paged pool used to store vGPU context data, enabling the attacker to overwrite adjacent kernel structures, including function pointers and privilege tokens.
Crucially, the exploit leverages the DEVICE_OBJECT and DRIVER_OBJECT manipulation techniques previously seen in OSU 2024-001 research, allowing the attacker to:
Bypass Hyper-V’s virtualization-based security (VBS) and Credential Guard
Escalate privileges from guest user to SYSTEM on the host
Execute arbitrary kernel code with full SID integrity
Due to nvproxy’s deep integration with the Windows graphics stack and Hyper-V’s IOMMU bypass, the attack is invisible to most endpoint detection and response (EDR) systems. Memory forensics reveals only transient artifacts, as the exploit overwrites freed or reused kernel memory before forensic tools can capture it.
Chain of Exploitation: From Guest to Host Dominance
The attack follows a multi-stage kill chain:
Reconnaissance: Attacker identifies Hyper-V hosts with NVIDIA vGPU enabled via WMI or RDP reconnaissance.
Delivery: Malicious payload is delivered to a guest VM via phishing, supply chain compromise, or lateral movement.
RPC Crafting: Guest sends a specially crafted RPC message over VMBus with a header size field set to 0xFFFFFFFF, triggering the overflow.
Memory Corruption: Buffer overflow corrupts kernel heap, overwriting a function pointer in a vGPU context object.
Code Execution: The overwritten pointer is invoked during GPU context switching, executing attacker-controlled shellcode in kernel mode.
Privilege Escalation: Shellcode patches the host’s SeTokenObject to grant SYSTEM privileges to the guest process.
Persistence: A new kernel thread is spawned, opening a reverse shell via a hidden TCP port (4444/tcp).
Lateral Movement: Attacker pivots to other VMs or the host’s management network.
Notably, the exploit does not require any user interaction within the guest VM and operates entirely within the confines of the Hyper-V virtualization stack, making it undetectable by guest-level monitoring.
Impact Assessment: Why This Vulnerability Is Catastrophic
The implications of this zero-day are severe:
Cloud Environments: Compromise of Hyper-V hosts in Azure Stack HCI or on-premises data centers enables theft of intellectual property, customer data, and cryptographic keys.
Isolation Breakdown: Hyper-V’s vaunted security model—long considered more robust than VMware’s—is fundamentally undermined.
Undetectability: Current EDR solutions (CrowdStrike, SentinelOne) fail to detect the exploit due to its kernel-level operation and transient memory artifacts.
Patch Gap: Microsoft has not released a fix as of March 29, 2026, leaving tens of thousands of enterprises exposed.
Exploit Kit Availability: Early indicators suggest this vulnerability has been weaponized and is being sold in underground forums for $500,000.
Recommendations for Immediate Mitigation
Organizations must act immediately to reduce risk:
1. Disable nvproxy via Group Policy (Emergency Mitigation)
Apply the following registry change to disable nvproxy on all Hyper-V hosts: