Hayden

In July 2025, a critical security alert was issued for VMware virtualization environments. CVE-2025-41238, with a CVSS score of 9.3, is a critical heap overflow vulnerability that allows virtual machine escape to host system execution—a severe security flaw.

This vulnerability was exploited as a zero-day during the Pwn2Own Berlin hacking competition in May 2025, and patches are now available. Today, we’ll provide a step-by-step guide to understand the exact cause of this dangerous vulnerability and implement complete remediation.

 

 

1. Understanding CVE-2025-41238 Vulnerability

CVE-2025-41238 is a heap overflow vulnerability in VMware’s PVSCSI (Paravirtualized SCSI) controller. This vulnerability is particularly dangerous because attackers with administrative privileges inside a virtual machine can execute arbitrary code on the host system.

Key Risk Factors

  • CVSS Score: 9.3 (Critical rating)
  • Affected Products: VMware ESXi, Workstation, Fusion
  • Attack Vector: Local administrator privileges required
  • Impact Scope: Virtual machine escape leading to host code execution

Platform-Specific Risk Levels

  • ESXi Environment: Limited to VMX sandbox but exploitable only with unsupported configurations
  • Workstation/Fusion: Direct code execution on host machine (higher risk)

 

 

2. Detailed Analysis of Affected VMware Products and Versions

Identifying VMware products and versions affected by this vulnerability is the first step.

ESXi Version Impact Analysis

Product Affected Versions Patched Version Download Link
VMware ESXi 8.0 8.0 U3 and below ESXi80U3f-24784735 Download Patch
VMware ESXi 8.0 8.0 U2 and below ESXi80U2e-24789317 Download Patch
VMware ESXi 7.0 7.0 U3 and below ESXi70U3w-24784741 Download Patch

Desktop Virtualization Products

Product Affected Versions Patched Version
VMware Workstation Pro 17.6.3 and below 17.6.4
VMware Fusion 13.6.3 and below 13.6.4
VMware Tools 13.0.0 and below 13.0.1.0

 

 

3. Immediate Risk Assessment Methods

Before applying patches, let’s first assess the current environment’s risk level.

Version Check Methods for ESXi Environment

# SSH to ESXi host and execute
vmware -vl

# Or check via web management interface
# https://[ESXi_IP]/ui → Host → Summary

Multi-host Verification in vCenter

  1. Access vSphere Client (HTML5 Client)
  2. Navigate to Hosts and Clusters → Select each host
  3. Check VMware ESXi version in Summary tab
  4. Verify Build Number is 24784735 or higher

Workstation/Fusion Version Check

VMware Workstation: Help → About VMware Workstation Pro
VMware Fusion: VMware Fusion → About VMware Fusion

 

 

4. Step-by-Step Complete Patch Application

4-1. ESXi Environment Patch Application (Production Environment)

Prerequisites

  • Complete Backup: vCenter and all virtual machine backups
  • Maintenance Window: Plan for minimum 2-4 hours downtime
  • Rollback Plan: Backup existing configurations and recovery procedures

ESXi 8.0 Patch Application Process

  1. Download and Upload Patch 
    # SSH to ESXi host
cd /tmp

# Upload patch file (via SCP or datastore upload)
# For ESXi80U3f-24784735 patch

# Pre-installation check
esxcli software profile get
  2. Enter Maintenance Mode 
    # Enter maintenance mode via command
vim-cmd hostsvc/maintenance_mode_enter

# Or via vSphere Client:
# Host → Actions → Enter Maintenance Mode
  3. Execute Patch Installation 
    # Install patch from ZIP file
esxcli software profile update -d /tmp/[patch_filename].zip -p [profile_name]

# Example:
esxcli software profile update -d /tmp/ESXi80U3f-24784735.zip -p ESXi-8.0.3-24784735-standard
  4. Reboot and Verification 
    # System reboot
reboot

# Verify version after reboot
vmware -vl

ESXi 7.0 Patch Application Method

ESXi 7.0 users should apply the ESXi70U3w-24784741 patch as follows:

# ESXi 7.0 specific patch command
esxcli software profile update -d /tmp/ESXi70U3w-24784741.zip -p ESXi-7.0.3-24784741-standard

4-2. VMware Workstation Pro 17.6.4 Upgrade

  1. Backup Current Version
    • Backup all virtual machine files
    • Backup configuration files (preferences.ini, vmx files, etc.)
  2. Download Latest Version
  3. Execute Upgrade 
    # Run as administrator on Windows
VMware-workstation-17.6.4.exe
  4. Post-Upgrade Verification
    • Verify 17.6.4 version in Help → About VMware Workstation Pro
    • Confirm existing virtual machines operate normally

4-3. VMware Fusion 13.6.4 Upgrade (macOS)

  1. Download and Install 
    # Verify in terminal
/Applications/VMware\ Fusion.app/Contents/MacOS/vmware-vmx --version
  2. Enable Automatic Updates
    • VMware Fusion → Preferences → Software Update
    • Check Check for updates automatically

 

 

5. Essential VMware Tools Security Update

In conjunction with CVE-2025-41239, VMware Tools must also be updated.

Windows Virtual Machine VMware Tools Update

  1. Update via vSphere Client
    • Select virtual machine → Actions → Guest OS → Install/Upgrade VMware Tools
  2. Manual Download and Install

Linux Virtual Machine VMware Tools Update

# Ubuntu/Debian environment
sudo apt update && sudo apt install open-vm-tools

# RHEL/CentOS environment  
sudo yum update open-vm-tools

 

 

6. Post-Patch Security Verification Methods

Vulnerability Scanning Tool Usage

Qualys VMDR users can scan with the following QIDs:

  • QID 216348: CVE-2025-41236 (VMXNET3)
  • QID 216349: CVE-2025-41237 (VMCI)
  • QID 383581: CVE-2025-41238 (PVSCSI)
  • QID 383582: CVE-2025-41239 (vSockets)

Manual Verification Method

# Verify patch application in ESXi environment
esxcli software profile get | grep "Build Profile"

# Verify Build Number is at or above:
# ESXi 8.0: 24784735 or higher
# ESXi 7.0: 24784741 or higher

 

 

7. Additional Security Hardening Measures

Network Segmentation and Access Control

  1. Management Network Isolation
    • Configure dedicated VLANs for vMotion, vSAN, and management traffic
    • Restrict management port access through firewalls
  2. vCenter Access Restriction 
    # vCenter Server firewall settings
Port 443 (HTTPS): Allow only administrator IP ranges
Port 22 (SSH): Enable only when necessary

Virtual Machine Security Configuration Hardening

# Security settings to add to VMX file
isolation.tools.copy.disable = "TRUE"
isolation.tools.paste.disable = "TRUE"
isolation.tools.setGUIOptions.enable = "FALSE"
RemoteDisplay.maxConnections = "1"

 

 

8. Temporary Defense Measures When Immediate Response Is Not Possible

Discontinue PVSCSI Usage (Temporary Measure)

If immediate patch application is not possible, temporarily discontinue PVSCSI controller usage:

  1. Shut down virtual machine
  2. Edit virtual machine settings → Hardware → Hard Disk
  3. Change SCSI Controller type to LSI Logic SAS or LSI Logic Parallel
  4. Restart virtual machine

Warning: This is a temporary measure that may cause performance degradation.

Enhanced Network Access Restrictions

# ESXi firewall hardening
esxcli network firewall ruleset set --ruleset-id sshServer --enabled false
esxcli network firewall ruleset set --ruleset-id ntpClient --enabled false

 

 

9. Cloud Environment-Specific Response Plans

AWS VMware Cloud on AWS

In AWS VMC environments, VMware manages patches directly:

  • Check patch schedule in VMC Console
  • Enable automatic patch update settings

Azure VMware Solution

Microsoft has already announced the patch schedule:

  • Complete patching within 30 days commitment
  • New deployment environments provided with patches applied

Google Cloud VMware Engine

 

 

10. Long-term Security Management Strategy

Automated Patch Management System Implementation

  1. Utilize vSphere Lifecycle Manager
    • Apply consistent patches with cluster image management functionality
    • Implement zero-downtime patching with Rolling Update method
  2. Configure VMware vSphere Update Manager 
    # Update Manager automatic download settings
Admin → System Configuration → Patch Download → Enable Automatic Download

Enhanced Security Monitoring

  • Deploy VMware Aria Operations for Logs
  • Integrate with SIEM solutions for real-time threat detection
  • Establish regular vulnerability scanning schedules

 

 

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