CVE-2022-24539 is a significant vulnerability found in Microsoft Windows' Hyper-V platform, specifically affecting Shared Virtual Hard Disks (shared VHDX/VHD files). This vulnerability could allow privileged attackers or malicious guests to access sensitive information beyond their assigned permissions. Let's break down what this vulnerability is, its potential impact, how attackers might exploit it, and how you can protect yourself.

What Is CVE-2022-24539?

CVE-2022-24539 is an information disclosure vulnerability in Windows Hyper-V. It allows a user who is running a virtual machine (VM) to access data from other users' VMs or even from the Hyper-V host itself by exploiting the way shared virtual hard disks are handled.

> This vulnerability is unique and different from related CVEs, namely CVE-2022-24490, CVE-2022-26783, and CVE-2022-26785.

What are Shared Virtual Hard Disks?

Shared virtual hard disks are VHDX/VHD disk files that can be mounted simultaneously by multiple VMs, usually to facilitate clustering or high-availability roles.

Windows Server 2022

- Windows 10/11 with Hyper-V enabled

How the Vulnerability Works

When a shared VHDX file is used by multiple VMs, improper isolation of data or disk control elements might allow an attacker with access to one VM to read information that should be only accessible to other VMs or even the host.

Simple Exploit Scenario

*Suppose two virtual machines, VM1 and VM2, are connected to the same shared VHDX disk. Due to the vulnerability, a process in VM1 could scan disk sectors that belong to VM2, revealing files or sensitive data.*

Proof-of-Concept Code (PoC) Snippet

Below is a conceptual PowerShell snippet to show how a malicious guest VM might attempt to access extra information from a shared VHDX:

# Example: Read raw disk sectors from a shared VHDX in a guest VM

$disk = Get-Disk | Where-Object { $_.Bustype -eq 'Msft Virtual Disk' }
$sectorSize = 512
$offset =  # Try to read data at the start of the disk

$bytesToRead = 4096 # Read 4KB
$buffer = New-Object Byte[] $bytesToRead

$fs = [System.IO.File]::Open($disk.Path, 'Open', 'Read', 'ReadWrite')
$fs.Seek($offset, 'Begin') | Out-Null
$fs.Read($buffer, , $bytesToRead) | Out-Null
$fs.Close()

# Save buffer to a file for offline analysis
[System.IO.File]::WriteAllBytes("C:\Temp\leaked-sectors.bin", $buffer)

> *Note: In reality, guest VM access to the VHD file path is limited, but this illustrates what the attack might look like if direct disk access is possible.*

Exploit Details

The real exploitation requires the attacker to have administrative privileges inside a guest VM, which is already a powerful position. The vulnerability doesn't provide direct code execution, but it allows unauthorized reading of disk sectors. Skilled attackers can parse disk structures to extract files, credentials, or virtual machine state information from other VMs.

Threat Model: A rogue admin or user in one VM

- Potential Impact: Data leakage, unauthorized file or credential exposure, intra-VM privacy breach

Mitigation and Fix

Microsoft released a patch addressing this issue in April 2022. Update your Hyper-V hosts as soon as possible. Do not use shared VHD files on untrusted, multi-tenant virtual machines.

- Official Microsoft Security Guide for CVE-2022-24539

Workarounds

External References

- Microsoft Security Response Center (MSRC) entry for CVE-2022-24539
- Hyper-V Shared VHDX overview

Conclusion

CVE-2022-24539 highlights the risks of resource sharing in virtualized environments. If you depend on Hyper-V clustered roles using shared virtual disks, apply updates now! Always isolate your workloads as much as possible and review who has Admin permissions within VMs.

Timeline

Published on: 04/15/2022 19:15:00 UTC
Last modified on: 04/25/2022 15:38:00 UTC