How to remediate – VMware vCenter Active Virtual Machines

1. Introduction

The VMware vCenter Active Virtual Machines vulnerability allows enumeration of active virtual machines running on a server. This means someone with valid credentials for vCenter can discover details about your VMs, including their IP addresses. This information could be used to map your infrastructure and potentially identify targets for further attacks. Confidentiality may be impacted by revealing VM details.

2. Technical Explanation

This vulnerability occurs because VMware vCenter allows listing active virtual machines using standard authentication. An attacker with legitimate credentials can query the server to obtain information about running VMs. There is no known CVE associated with this specific enumeration issue, but it represents a potential reconnaissance step in an attack chain. For example, an attacker could use these details to identify unpatched systems or those with sensitive data.

• Root cause: Insufficient restrictions on querying active virtual machine information via the vCenter API.
• Exploit mechanism: An attacker authenticates to vCenter and uses the API to request a list of running VMs and their associated IP addresses.
• Scope: VMware vCenter servers, all versions where VM enumeration is permitted through standard authentication.

3. Detection and Assessment

You can confirm if your system is vulnerable by checking access permissions or attempting to enumerate VMs directly. A quick check involves verifying the API endpoint accessibility.

• Quick checks: Check vCenter user roles and permissions to see who has rights to view VM details.
• Scanning: Nessus plugin ID 16894 can identify accessible vCenter instances, but does not directly confirm enumeration. This is an example only.
• Logs and evidence: Review vCenter logs for API calls related to virtual machine listing. Look for events indicating successful VM enumeration requests.

curl -k -u username:password https://your_vcenter_server/api/vm 

4. Solution / Remediation Steps

The following steps reduce the risk of this vulnerability by limiting access to VM information.

4.1 Preparation

• No services need to be stopped for these changes, but plan a maintenance window if you anticipate performance impacts from permission adjustments. A roll back plan is to restore the previous snapshot.
• Changes should be approved by the system administrator and security team.

4.2 Implementation

1. Step 1: Review vCenter user roles and permissions. Identify any users or groups with unnecessary access to VM details.
2. Step 2: Modify those roles to restrict access to only necessary information. Use the principle of least privilege.
3. Step 3: Test changes by logging in as a test user with limited permissions and verifying they cannot enumerate VMs.

4.3 Config or Code Example

Before

Role: Administrator - Full access to all vCenter features, including VM details.

After

Role: Custom Role - Limited access to specific vCenter features, excluding direct VM enumeration.

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue.

• Practice 1: Least privilege – granting users only the minimum permissions needed reduces impact if credentials are compromised.
• Practice 2: Regular access reviews – periodically check user roles and permissions to ensure they remain appropriate.

4.5 Automation (Optional)

PowerCLI can be used to automate permission adjustments, but caution is advised due to the complexity of vCenter roles.

# Example PowerCLI script - use with care!
# Get-VCRole -Name "Administrator" | Remove-VCPrivilege -Privilege "VirtualMachine.InventoryRead"
# This removes a privilege; test thoroughly before deploying to production.

5. Verification / Validation

Confirm the fix by verifying that users with limited permissions cannot enumerate VMs.

• Post-fix check: Log in as a user with restricted permissions and attempt to list VMs using the API. Expected output should be an error message indicating insufficient privileges.
• Re-test: Re-run the curl command from section 3, using credentials that *should* no longer have access. The request should fail.
• Smoke test: Verify core vCenter functionality (e.g., VM power on/off) still works for users with appropriate permissions.
• Monitoring: Review vCenter logs for failed API calls related to VM enumeration attempts from restricted users. This is an example only.

curl -k -u limited_user:password https://your_vcenter_server/api/vm - should return 403 Forbidden

6. Preventive Measures and Monitoring

Update security baselines to reflect least privilege principles.

• Baselines: Update your vCenter security baseline or policy to enforce the principle of least privilege for user roles. For example, a CIS control related to access management.
• Pipelines: Integrate permission checks into your CI/CD pipeline to prevent overly permissive role configurations from being deployed.
• Asset and patch process: Review vCenter configuration changes regularly as part of your asset and patch management cycle.

7. Risks, Side Effects, and Roll Back

Incorrect permission adjustments could disrupt vCenter functionality.

• Risk or side effect 2: Changes to default roles can have unintended consequences. Test thoroughly in a non-production environment first.
• Roll back: Restore the previous vCenter snapshot, or manually re-add the necessary privileges to affected roles.

8. References and Resources

Links related to this exact vulnerability.

• Vendor advisory or bulletin: VMware vCenter Guide
• NVD or CVE entry: No specific CVE is associated with this enumeration issue, but search for related vulnerabilities in VMware products.
• Product or platform documentation relevant to the fix: VMware vSphere Security Hardening Guide