CVE-2025-49689: Windows 10 1507 Privilege Escalation Flaw

CVE-2025-49689 Overview

CVE-2025-49689 is an integer overflow vulnerability in the Microsoft Windows Virtual Hard Disk (VHDX) component. The flaw allows a local attacker to elevate privileges on affected systems by supplying a crafted VHDX file that triggers arithmetic wraparound during disk image parsing. Successful exploitation requires user interaction, such as mounting or opening the malicious virtual disk. The vulnerability affects a wide range of Windows client and server releases, from Windows 10 1507 through Windows 11 24H2 and Windows Server 2008 through Windows Server 2025. Microsoft published the advisory on July 8, 2025, and tracks the issue under [CWE-125].

Critical Impact

A local attacker who convinces a user to mount a crafted VHDX file can gain high impact to confidentiality, integrity, and availability through privilege escalation.

Affected Products

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

Discovery Timeline

• 2025-07-08 - CVE-2025-49689 published to NVD
• 2025-07-15 - Last updated in NVD database

Technical Details for CVE-2025-49689

Vulnerability Analysis

The vulnerability resides in the Windows VHDX parsing logic, which handles Virtual Hard Disk v2 image files used by Hyper-V and the built-in disk mounting subsystem. An integer overflow occurs when size or offset fields inside a malformed VHDX structure are multiplied or added without bounds validation. The wraparound produces an undersized allocation, which subsequent read operations then exceed.

Microsoft classifies the underlying weakness as an out-of-bounds read ([CWE-125]) resulting from the overflow. The read occurs within a privileged kernel-mode context that processes mounted virtual disks. Attackers can leverage the corrupted state to achieve local privilege escalation to SYSTEM.

The Exploit Prediction Scoring System rates this issue in the upper quartile of likely-exploited vulnerabilities. Microsoft has not reported in-the-wild exploitation, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog.

Root Cause

The defect stems from missing validation of attacker-controlled integer fields parsed from the VHDX header and metadata tables. When these values are used in size calculations, the result wraps around the maximum unsigned integer boundary. The kernel allocates a buffer based on the wrapped value, then reads more data than the buffer can hold, producing an out-of-bounds read.

Attack Vector

Exploitation requires local access and user interaction. An attacker delivers a crafted VHDX file through phishing, removable media, or a network share. When a user double-clicks or otherwise mounts the file, the Windows storage stack parses the malformed structures and triggers the overflow. No prior authentication on the target is required to stage the file, but a logged-on user must perform the mount action.

The vulnerability is described in prose only. See the Microsoft CVE-2025-49689 Advisory for vendor-supplied technical details.

Detection Methods for CVE-2025-49689

Indicators of Compromise

• Unexpected .vhdx or .vhd files appearing in user download directories, temporary folders, or email attachment caches.
• Mount or attach events for VHDX files originating from untrusted sources, recorded under Microsoft-Windows-VHDMP operational logs.
• Crashes or kernel bug checks referencing vhdmp.sys shortly after a virtual disk mount.
• Process creation chains where Explorer or a mail client launches vds.exe or diskmgmt.msc against attacker-supplied disk images.

Detection Strategies

• Monitor Windows Event Log channel Microsoft-Windows-VHDMP-Operational for mount events tied to files in user-writable paths.
• Correlate file write events for VHDX extensions with subsequent mount operations performed by non-administrative users.
• Alert on kernel crashes or driver faults in vhdmp.sys and storvsp.sys, which can indicate exploitation attempts.

Monitoring Recommendations

• Track endpoints that lack the July 2025 cumulative update and flag any VHDX mount activity on those hosts.
• Inspect email gateways and web proxies for inbound VHDX file transfers and quarantine unsigned images.
• Audit Hyper-V administrator group membership and review automation that mounts disk images on behalf of users.

How to Mitigate CVE-2025-49689

Immediate Actions Required

• Apply the July 2025 Patch Tuesday cumulative update for all affected Windows client and server versions.
• Block delivery of .vhd and .vhdx attachments at the email gateway unless explicitly required for business workflows.
• Restrict mounting of virtual disk files to administrative users via Group Policy and AppLocker file rules.
• Educate users on the risk of opening disk image files received from untrusted sources.

Patch Information

Microsoft has released security updates addressing CVE-2025-49689 for all affected platforms. Refer to the Microsoft CVE-2025-49689 Advisory for the specific KB numbers that apply to each Windows build. Install the updates through Windows Update, WSUS, or your patch management platform.

Workarounds

• Disable automatic mounting of virtual disks by removing file association handlers for .vhd and .vhdx on user workstations.
• Use Attack Surface Reduction rules and SmartScreen to block execution of disk image files downloaded from the internet.
• On systems where Hyper-V is not required, remove the Microsoft-Hyper-V and HypervisorPlatform optional features.

# Remove file association so VHDX files do not auto-mount on double-click
cmd /c assoc .vhdx=
cmd /c assoc .vhd=

# Disable Hyper-V management tools on systems that do not need them
Dism /Online /Disable-Feature /FeatureName:Microsoft-Hyper-V-All /NoRestart