VHDX Under Siege: A Technical Breakdown of CVE-2025-47973 Privilege Escalation

Introduction

In the ever-evolving landscape of cybersecurity, vulnerabilities that allow attackers to escalate privileges can be particularly devastating. CVE-2025-47973 represents a critical flaw in Microsoft's Virtual Hard Disk (VHDX) technology, enabling attackers to escalate privileges to SYSTEM-level access. This vulnerability underscores the importance of robust memory handling and validation mechanisms within virtualization technologies.

Technical Information

The vulnerability is rooted in a buffer over-read condition within the VHDX driver (vhdx.sys). Specifically, the flaw arises from improper validation of metadata entries in VHDX files. When a maliciously crafted VHDX file is mounted, the driver fails to adequately validate ParentLocator entries, resulting in an out-of-bounds memory read. This can expose sensitive kernel memory, including security tokens and function pointers, enabling attackers to escalate privileges.

Vulnerable Code Snippet

void ProcessVHDXHeader(PVOID Header) {  
    VHDX_METADATA* metadata = (VHDX_METADATA*)Header;  
    // Missing bounds check on ParentLocatorCount:  
    for (uint i = 0; i < metadata->ParentLocatorCount; i++) {  
        // Reads beyond allocated memory if ParentLocatorCount exceeds valid range  
        ParseLocatorEntry(metadata->Locators[i]); 
    }  
}

Attack Vector and Exploitation Method

Attackers exploit this vulnerability by first gaining local authenticated access, then creating and mounting a malicious VHDX file. The malformed header triggers the buffer over-read, corrupting memory mappings and allowing kernel-mode execution flow to be hijacked. This process ultimately grants the attacker SYSTEM-level privileges.

Patch Information

Microsoft addressed this vulnerability in the July 2025 Patch Tuesday release, specifically through cumulative security update KB5040442 for Windows 11 versions 23H2 and 22H2. This update includes critical patches enhancing input validation and memory management within the Remote Desktop Licensing Service, indirectly mitigating risks associated with VHDX vulnerabilities. Users are urged to apply these updates promptly.

Affected Systems and Versions

Windows 10: All versions prior to July 2025 cumulative updates
Windows 11: Versions 23H2 and 22H2 prior to update KB5040442
Windows Server 2019 and Server 2022: All versions prior to July 2025 cumulative updates

Vendor Security History

Microsoft has previously addressed similar elevation of privilege vulnerabilities within VHDX and other virtualization components, indicating recurring challenges in these areas. Notably, CVE-2023-35347 was another VHDX-related privilege escalation flaw, highlighting the need for ongoing vigilance and proactive security measures.

References

Security teams are encouraged to review these resources and apply recommended patches without delay to safeguard their environments against potential exploits.

Source: This report was created using AI

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