CVE-2025-49683: Windows 10 1507 VHDX RCE Vulnerability

CVE-2025-49683 Overview

CVE-2025-49683 is an integer overflow vulnerability in the Microsoft Windows Virtual Hard Disk (VHDX) component. The flaw allows an unauthorized local attacker to execute arbitrary code when a victim opens a crafted VHDX file. Exploitation requires user interaction, but no prior authentication is needed on the target system.

The vulnerability affects a broad range of Windows desktop and server releases, from Windows 10 1507 through Windows 11 24H2 and Windows Server 2008 through Windows Server 2025. Microsoft addressed the issue through its July 2025 security update cycle. The weakness is classified under CWE-122: Heap-based Buffer Overflow.

Critical Impact

Successful exploitation yields local code execution in the context of the user who mounts the malicious VHDX, with high impact to confidentiality, integrity, and availability.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2) and Windows 11 (22H2, 23H2, 24H2)
• Microsoft Windows Server 2008 SP2, 2008 R2 SP1, 2012, 2012 R2, 2016, 2019, 2022, 2022 23H2
• Microsoft Windows Server 2025

Discovery Timeline

• 2025-07-08 - CVE-2025-49683 published to NVD
• 2025-07-15 - Last updated in NVD database

Technical Details for CVE-2025-49683

Vulnerability Analysis

The vulnerability resides in the Windows VHDX parsing logic, which handles Microsoft's virtual hard disk format used by Hyper-V, disk management utilities, and the Windows shell. When the operating system mounts a VHDX image, it parses metadata regions that describe block allocation, sector size, and region tables.

An integer overflow during size or offset calculations causes the allocator to reserve a buffer smaller than the data that subsequently gets copied into it. The resulting heap-based buffer overflow [CWE-122] corrupts adjacent heap structures and enables an attacker to influence execution flow.

Because VHDX mounting in modern Windows can be triggered by double-clicking a .vhdx or .vhd file in Explorer, the attack does not require administrative tools or virtualization features to be exposed to the attacker.

Root Cause

The root cause is an arithmetic operation on attacker-controlled size fields within VHDX metadata that wraps around the 32-bit integer boundary. The truncated result is used to allocate a heap buffer, while the original untruncated value drives the copy loop. This mismatch produces an out-of-bounds write on the heap.

Attack Vector

An attacker crafts a malicious VHDX file and delivers it through email, removable media, a network share, or a web download. When the victim opens or mounts the file, the vulnerable parser processes the malformed metadata and triggers the overflow. Code executes in the security context of the mounting user, which on default Windows installations includes membership in interactive desktop sessions.

The vulnerability requires user interaction and local attack vector classification, but the social engineering bar is low because VHDX files are commonly used for legitimate software distribution and backups.

No verified public proof-of-concept code has been released. See the Microsoft Security Update Guide for CVE-2025-49683 for vendor technical details.

Detection Methods for CVE-2025-49683

Indicators of Compromise

• Unexpected .vhdx or .vhd files delivered through email attachments, ISO containers, or downloads from untrusted sources
• vhdmp.sys or storvsp.sys crashes or unusual heap corruption events in the Windows kernel event logs
• Child processes spawning from explorer.exe or mmc.exe immediately following a VHDX mount operation
• Mount operations of VHDX files originating from user-writable directories such as %TEMP%, Downloads, or removable drives

Detection Strategies

• Monitor Windows event logs for Microsoft-Windows-VHDMP provider events correlated with crash dumps or Application Error events (Event ID 1000)
• Hunt for process creation events where svchost.exe hosting the vds service or diskmgmt spawns unexpected child processes
• Inspect endpoint telemetry for invocations of Mount-VHD, Mount-DiskImage, or shell-driven VHDX attachment from non-administrative users
• Flag VHDX files arriving via email gateways or web proxies for sandboxed inspection before user delivery

Monitoring Recommendations

• Enable Windows Defender Application Control or AppLocker policies that block execution of binaries launched from mounted VHDX volumes
• Collect Sysmon Event ID 1 (process creation) and Event ID 11 (file create) events filtered for .vhdx and .vhd extensions
• Centralize crash telemetry from WerFault.exe to identify exploitation attempts that fail before achieving code execution
• Audit Group Policy and registry settings that govern automatic mounting of disk image files on user logon

How to Mitigate CVE-2025-49683

Immediate Actions Required

• Apply the July 2025 Microsoft security update referenced in the Microsoft Security Update Guide to all affected Windows clients and servers
• Prioritize patching on systems where users routinely handle disk image files, including developer workstations and IT administrator endpoints
• Block inbound .vhdx, .vhd, and .iso attachments at email gateways unless required for business operations
• Educate users to avoid mounting disk image files received from untrusted sources

Patch Information

Microsoft released cumulative security updates addressing CVE-2025-49683 across all supported Windows 10, Windows 11, and Windows Server branches. Refer to the Microsoft Security Update Guide for CVE-2025-49683 for the specific KB numbers that correspond to each affected operating system build.

Workarounds

• Remove file association handlers for .vhdx and .vhd extensions on systems where users do not need to mount disk images
• Restrict access to the Virtual Disk Service (vds) by limiting non-administrative users from invoking mount operations
• Use Attack Surface Reduction rules to block executable content launched from removable or mounted volumes
• Apply Group Policy to disable automatic mounting of disk images for standard users until patching is complete

# Configuration example: remove default shell handlers for VHDX mounting
reg delete "HKCR\Windows.VhdFile\shell\Mount" /f
reg delete "HKCR\Windows.VhdxFile\shell\Mount" /f

# Verify patch deployment status across endpoints
Get-HotFix | Where-Object { $_.InstalledOn -ge (Get-Date "2025-07-08") }