1. Introduction
VMware Inactive Virtual Machines refers to the possibility of listing virtual machines that are powered off within a VMware vSphere environment. This could allow an attacker with valid credentials to gain information about your infrastructure, potentially aiding in further attacks. Systems affected are typically those running VMware vSphere. A successful enumeration does not directly impact confidentiality, integrity or availability but provides reconnaissance data for attackers.
2. Technical Explanation
- Root cause: The vSphere API does not filter inactive virtual machines when listing resources.
- Exploit mechanism: An attacker uses valid vSphere credentials to query the API and retrieve a list of all virtual machines, including those that are powered off.
- Scope: VMware vSphere versions are affected. Specific versions have not been identified in this report.
3. Detection and Assessment
You can confirm vulnerability by checking for inactive VMs via the vSphere client or command line interface. A thorough assessment involves attempting to enumerate all virtual machines using API calls.
- Quick checks: Log into the vSphere Client and check the list of virtual machines. Note any powered-off VMs.
- Scanning: Nessus plugin ID 16879 can be used as an example for detecting this issue, but results should be verified manually.
- Logs and evidence: Review vSphere logs for API calls related to listing virtual machines (vmware_vsphere.log). Look for patterns indicating enumeration of all VMs regardless of power state.
# Example command placeholder:
# vmcli -s -u -p vm list
4. Solution / Remediation Steps
The primary solution is to limit access to vSphere and regularly review user permissions. While complete removal of enumeration isn’t possible without disabling API access, reducing the attack surface is key.
4.1 Preparation
- Ensure you have valid credentials to revert changes if needed. A roll back plan involves restoring from the pre-change snapshot.
- Changes should be performed during a scheduled maintenance window with appropriate approval.
4.2 Implementation
- Step 1: Review vSphere user roles and permissions. Ensure users only have access to the resources they require.
- Step 2: Implement multi-factor authentication for all vSphere accounts.
- Step 3: Regularly audit vSphere logs for suspicious activity, including unexpected VM enumeration attempts.
4.3 Config or Code Example
Before
# User has broad permissions, allowing full VM access
permissions = "full"
After
# User has limited permissions, restricting access to specific VMs or folders.
permissions = "limited"
4.4 Security Practices Relevant to This Vulnerability
List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.
- Practice 1: Least privilege access to reduce the impact if credentials are compromised.
- Practice 2: Regular security audits of user permissions and activity logs.
4.5 Automation (Optional)
# Example PowerShell script to review vSphere permissions:
# Get-VSPermission -Server | Where-Object {$_.Role -eq "full"} | Format-Table User, Role
5. Verification / Validation
Confirm the fix by verifying that user accounts with limited permissions cannot enumerate all virtual machines. Check API access and log files for evidence of restricted enumeration.
- Post-fix check: Log in as a user with limited permissions and attempt to list VMs via the vSphere Client or API. Verify only permitted VMs are visible.
- Re-test: Re-run the earlier detection method (API query) using the limited permission account to confirm reduced enumeration results.
- Smoke test: Ensure core VM operations (power on/off of allowed VMs) still function as expected for authorized users.
- Monitoring: Monitor vSphere logs for failed API calls related to unauthorized VM enumeration attempts.
# Post-fix command and expected output:
# vmcli -s -u -p vm list
# Expected Output: Only permitted VMs are listed.
6. Preventive Measures and Monitoring
Suggest only measures that are relevant to the vulnerability type. Use “for example” to keep advice conditional, not prescriptive.
- Baselines: Update your vSphere security baseline to include least privilege access controls for user accounts.
- Pipelines: Integrate permission reviews into your change management process.
- Asset and patch process: Implement a regular review cycle (e.g., quarterly) for vSphere user permissions and API access logs.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 2: Increased administrative overhead for managing user permissions. Mitigation: Use role-based access control where possible.
- Roll back: Restore the pre-change vCenter snapshot if issues occur. Revert permission settings to their original values.
8. References and Resources
- Vendor advisory or bulletin: VMware vSphere Documentation
- NVD or CVE entry: No specific CVE is associated with this enumeration issue.
- Product or platform documentation relevant to the fix: VMware vSphere Security Configuration