CVE-2025-49689: Local Privilege Elevation through VHDX Integer Overflow Vulnerability

Overview

The vulnerability identified as CVE-2025-49689 represents a significant security concern, particularly for systems utilizing Virtual Hard Disk (VHDX) technology. An Integer Overflow or Wraparound in VHDX offers an unauthorized attacker a potential pathway to elevate their privileges locally. This vulnerability, if exploited, could lead to system compromise or data leakage, impacting the confidentiality and integrity of the system. Therefore, it’s imperative for IT administrators and security professionals to understand the potential risk and apply necessary mitigation measures.

Vulnerability Summary

CVE ID: CVE-2025-49689
Severity: High (7.8 CVSS Score)
Attack Vector: Local
Privileges Required: Low
User Interaction: None
Impact: Potential system compromise or data leakage

Affected Products

Product | Affected Versions

Microsoft Windows Server | All versions supporting VHDX
Hyper-V | All versions supporting VHDX

How the Exploit Works

The exploit takes advantage of an integer overflow or wraparound vulnerability in VHDX. An attacker with access to the local system can manipulate the VHDX file, causing an integer to either overflow or wraparound, leading to an incorrect value being set.
This incorrect value can result in unexpected behaviour, potentially allowing the attacker to bypass security measures and elevate their privileges on the local system. The elevated privileges could then be used to compromise the system or leak sensitive data.

Conceptual Example Code

Below is a conceptual example of how an attacker might exploit this vulnerability. Note that this is a simplified representation and the actual exploit would likely be more complex.

# Attacker manipulates the VHDX file causing an integer overflow
$ echo -n "malicious_payload" > /dev/vhdx1
# The manipulated VHDX file is mounted, causing unexpected behaviour
$ mount /dev/vhdx1 /mnt/vulnerable
# Attacker uses the unexpected behaviour to elevate their privileges
$ ./exploit /mnt/vulnerable

In this example, the attacker writes a malicious payload to a VHDX file, causing an integer overflow. When the VHDX file is mounted, the unexpected behaviour caused by the integer overflow is exploited to elevate the attacker’s privileges.