Hayden

Virtualization security is once again in the spotlight. On July 15, 2025, VMware released VMSA-2025-0013, a critical security advisory alerting IT administrators to vulnerabilities requiring immediate attention. Among these, CVE-2025-41239 stands out as a memory leak vulnerability in vSockets communication that poses risks of sensitive information disclosure.

This guide examines what this vulnerability is, the risks it presents, and how to safely apply the necessary patches.

 

 

1. CVE-2025-41239 Vulnerability Overview and Discovery

CVE-2025-41239 is an information disclosure vulnerability caused by uninitialized memory usage in vSockets. The vulnerability was discovered during Pwn2Own 2025 in Berlin, Germany, by security researcher Nguyen Hoang Thach (@hi_im_d4rkn3ss) from STARLabs SG.

What are vSockets?

vSockets (Virtual Sockets) is a protocol used in VMware environments for communication between virtual machines and hosts, or between virtual machines themselves. Unlike traditional network sockets, vSockets operate directly at the virtualization layer, providing more efficient communication.

Root Cause of the Vulnerability

The fundamental cause of this vulnerability is the use of uninitialized memory in vSockets. When a program allocates memory, it may contain data from previous usage. If this memory isn’t properly initialized, previous data can be exposed.

 

 

2. Identifying Affected Systems

The following products and versions are affected by CVE-2025-41239:

Affected Products:

  • VMware ESXi (All 7.0.x, 8.0.x versions)
  • VMware Workstation Pro (All 17.x versions)
  • VMware Fusion (All 13.x versions)
  • VMware Tools for Windows (11.x, 12.x, 13.x versions)

Important note: For VMware Tools, only the Windows version is affected. Linux and macOS versions of VMware Tools are not impacted by this vulnerability.

CVSS Scores:

  • ESXi, Workstation, Fusion: 7.1 (Important)
  • VMware Tools: 6.2 (Moderate)

 

 

3. Attack Scenarios and Exploitation Requirements

To exploit CVE-2025-41239, the following conditions are required:

Prerequisites:

  • Local administrative privileges within the virtual machine (Administrator or root)
  • Active processes using vSockets

Information attackers can obtain:

  • Cryptographic keys
  • Kernel pointers
  • Sensitive memory data
  • Communication content from other processes

This information can serve as a foundation for additional attacks, making it particularly dangerous in multi-tenant environments or cloud service provider infrastructures.

 

 

4. Step-by-Step Patch Application Guide

4-1. Version Verification

Before applying patches, verify your current installed versions.

VMware Tools Version Check:

On Windows:

  1. Start Menu → Programs and Features
  2. Locate VMware Tools and check version
  3. Or via Command Prompt: "C:\Program Files\VMware\VMware Tools\vmtoolsd.exe" -v

ESXi Version Check:

vmware -v
# Or check host information in vSphere Client

4-2. Patch Download and Installation

VMware Tools Patches:

Fixed versions for affected Windows VMware Tools:

Current Version Fixed Version Download Link
13.x series VMware Tools 13.0.1.0 VMware Tools Download
12.x, 11.x series VMware Tools 12.5.3 VMware Tools 12.5.3

Installation Steps:

  1. Run the downloaded installer with administrator privileges
  2. Select Custom Installation to install only required components
  3. Virtual machine reboot required after installation

ESXi Patches:

ESXi Version Fixed Version Build Number
ESXi 8.0.x ESXi80U3f-24784735 Build 24784735
ESXi 7.0.x ESXi70U3w-24784741 Build 24784741

ESXi Patch Application:

  1. Access vSphere Client
  2. Navigate to Host → Updates → Baselines
  3. Create new patch baseline and apply
  4. Enter Maintenance Mode and reboot

4-3. Post-Patch Verification

VMware Tools Verification:

"C:\Program Files\VMware\VMware Tools\vmtoolsd.exe" -v

Confirm the output shows version 13.0.1.0 or higher, or 12.5.3.

ESXi Verification:

vmware -v
esxcli system version get

 

 

5. Patch Application Best Practices and Considerations

5-1. Pre-Patch Preparation

Backup Procedures:

  • Create virtual machine snapshots
  • Backup ESXi configuration (vicfg-cfgbackup)
  • Separate backup of critical data

Checklist Items:

  • List of currently running critical services
  • Applications with dependencies
  • Network connectivity test plan

5-2. Staged Patch Deployment Strategy

Approach for Large Environments:

  1. Apply and verify patches in test environment first
  2. Sequential application starting with non-critical systems
  3. Production environment updates during maintenance windows
  4. Monitoring and rollback plans at each stage

 

 

6. Additional Security Hardening Measures

Additional security measures to implement alongside CVE-2025-41239 patches:

Virtual Machine Security Settings:

  • Remove unnecessary virtual hardware (remove VMXNET3 adapters if not needed)
  • Enable Guest OS firewall
  • Apply principle of least privilege

ESXi Host Security Hardening:

 

 

7. Understanding Related Vulnerabilities

VMSA-2025-0013 includes three additional vulnerabilities besides CVE-2025-41239:

CVE Number Component CVSS Score Severity
CVE-2025-41236 VMXNET3 Adapter 9.3 Critical
CVE-2025-41237 VMCI 9.3 Critical
CVE-2025-41238 PVSCSI Controller 9.3 Critical
CVE-2025-41239 vSockets 7.1 Important

Unlike the other three vulnerabilities, CVE-2025-41239 is limited to information disclosure and does not lead to code execution. However, the leaked information can serve as a foundation for other attacks, making it still significant.

 

 

8. Interim Mitigation for Delayed Patching

When immediate patching is not feasible:

  1. Enhanced Virtual Machine Isolation
    • Network segmentation
    • Strengthened access controls
  2. Enhanced Monitoring
    • vSockets-related log monitoring
    • Detection of abnormal memory access patterns
  3. Least Privilege Policy
    • Minimize administrator account usage within virtual machines
    • Monitor privilege escalation

Important: These measures are temporary solutions. Official patches should be applied as soon as possible.

 

In conclusion, while CVE-2025-41239 doesn’t lead to immediate system compromise, it represents a significant vulnerability that can provide the foundation for additional attacks through sensitive information disclosure. Organizations using VMware Tools in Windows environments should prioritize updating to the latest versions.

 

 

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