Hayden

On July 15, 2025, Broadcom released VMSA-2025-0013, a critical security advisory that sent shockwaves through the VMware virtualization community. CVE-2025-41236, with a CVSS score of 9.3, represents a critical vulnerability enabling VM escape scenarios that could compromise entire virtualization infrastructures. This comprehensive guide covers everything from understanding the vulnerability’s impact to implementing complete remediation strategies for production environments.

 

 

1. Why CVE-2025-41236 Poses Such a Critical Threat

CVE-2025-41236 is an integer overflow vulnerability in VMware’s VMXNET3 virtual network adapter. This vulnerability presents extraordinary risks for several reasons:

VM Escape Potential

  • Attackers with administrative privileges inside a guest VM can execute arbitrary code on the host system
  • In cloud environments, this could potentially impact other tenants’ virtual machines
  • Complete virtualization infrastructure security can be compromised

Widespread Impact Scope

VMXNET3 is VMware’s most widely deployed virtual network adapter. This makes the vulnerability particularly dangerous because:

  • It’s enabled by default in most VMware environments
  • Multi-tenant environments face tenant isolation breakdown
  • Service providers risk customer data exposure

 

 

2. Affected VMware Products and Versions

The following products are impacted by CVE-2025-41236:

Product Affected Versions Fixed Version
VMware ESXi 8.0 8.0 ~ 8.0 U3e ESXi80U3f-24784735
VMware ESXi 7.0 7.0 ~ 7.0 U3v ESXi70U3w-24784741
VMware Workstation Pro 17.x 17.6.4
VMware Fusion 13.x 13.6.4
VMware Cloud Foundation 5.x, 4.5.x See KB88287
VMware vSphere Foundation Affected Apply latest patches

Important Note: Non-VMXNET3 virtual adapters are not affected by this vulnerability. However, most environments use VMXNET3 as the default adapter type.

 

 

3. Quick Environment Assessment

Checking VMXNET3 Adapter Usage

In vSphere Client, follow these steps:

  1. Right-click virtual machine → Edit Settings
  2. Check Network Adapter section
  3. Verify Adapter Type shows VMXNET3

Bulk Assessment with PowerCLI

For large-scale environments, use PowerCLI for efficient assessment:

# Check all VMs using VMXNET3 adapters
Get-VM | Get-NetworkAdapter | Where-Object {$_.Type -eq "Vmxnet3"} | 
Select-Object Parent, Name, Type | Format-Table -AutoSize

 

 

4. ESXi Host Patching – vCenter Update Manager Method

4.1 vSphere Lifecycle Manager Approach (Recommended)

Step 1: Create Baseline

  1. Access vSphere Client → Lifecycle Manager
  2. Baselines → New Baseline
  3. Select Patch Baseline
  4. Name: “VMSA-2025-0013 Critical Patches”
  5. Choose Dynamic baseline type
  6. Severity: Select Critical

Step 2: Host Compliance Check

  1. Navigate to Hosts and Clusters view
  2. Select target host → Updates tab
  3. Click Check Compliance
  4. Verify missing patches show ESXi80U3f-24784735 or ESXi70U3w-24784741

Step 3: Apply Patches

  1. Click Remediate button
  2. Configure Maintenance Mode options
  3. Set VM Migration preferences (for clustered environments)
  4. Click Start Remediation

4.2 Command Line Direct Patching

For direct SSH access to ESXi hosts:

Step 1: Enter Maintenance Mode

# Switch ESXi host to maintenance mode
esxcli system maintenanceMode set --enable true

Step 2: Upload Patch File

  1. Download appropriate patch ZIP from Broadcom Support Portal
  2. Upload to datastore (e.g., datastore1)

Step 3: Install Patch

For ESXi 8.0:

# Update patch profile
esxcli software profile update -d /vmfs/volumes/datastore1/VMware-ESXi-8.0U3f-24784735-depot.zip -p ESXi-8.0U3f-24784735-standard

# Reboot system
reboot

For ESXi 7.0:

# Update patch profile
esxcli software profile update -d /vmfs/volumes/datastore1/VMware-ESXi-7.0U3w-24784741-depot.zip -p ESXi-7.0U3w-24784741-standard

# Reboot system
reboot

Step 4: Exit Maintenance Mode

# Exit maintenance mode after reboot
esxcli system maintenanceMode set --enable false

 

 

5. VMware Workstation and Fusion Updates

Workstation Pro 17.6.4 Update

  1. Help → Check for Updates
  2. If automatic update isn’t detected:

Fusion 13.6.4 Update

  1. VMware Fusion → Check for Updates
  2. For manual update:

 

 

6. VMware Tools Update for Additional Security

CVE-2025-41239 affects VMware Tools’ vSockets component. Windows guest operating systems running VMware Tools are particularly impacted.

Automatic VMware Tools Update Configuration

  1. Right-click VM → Guest OS → Install/Upgrade VMware Tools
  2. Options tab → VMware Tools → Upgrade Policy
  3. Select Upgrade automatically

Bulk Update with PowerCLI

# Update VMware Tools on all powered-on VMs
Get-VM | Where-Object {$_.PowerState -eq "PoweredOn"} | 
Update-Tools -NoReboot

 

 

7. Post-Patch Security Verification

Verify Successful Patch Application

# Check ESXi build number
vmware -v

# Expected results:
# ESXi 8.0: VMware ESXi 8.0.3 build-24784735
# ESXi 7.0: VMware ESXi 7.0.3 build-24784741

Verify VMXNET3 Driver Version

# Check VMXNET3 driver information
esxcli software vib list | grep vmxnet3

Test VM Network Connectivity

After patching, verify all VMs maintain proper network connectivity:

  1. Execute ping tests from each VM
  2. Verify network throughput
  3. Validate application service functionality

 

 

8. Automated Security Update Framework

vSphere Lifecycle Manager Policy Configuration

  1. Policies → New Policy
  2. Enable Auto-remediation options
  3. Configure Maintenance Windows
  4. Set up Notifications

PowerCLI Automation Script Example

# Weekly security patch verification and notification script
$clusters = Get-Cluster
foreach ($cluster in $clusters) {
    $compliance = Get-Compliance -Entity $cluster
    if ($compliance.Status -ne "Compliant") {
        Send-MailMessage -To "admin@company.com" -Subject "Security Patch Required" -Body "Cluster $cluster requires security updates"
    }
}

 

 

CVE-2025-41236 represents a critical threat to VMware virtualization environments. However, by following the systematic patching procedures and security hardening measures outlined in this guide, organizations can effectively eliminate these risks. Speed of response is crucial. This vulnerability was demonstrated at Pwn2Own Berlin 2025, proving its exploitability. Begin patch deployment immediately. 🙂

 

Key Reference Materials

 

 

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