1. Introduction
2. Technical Explanation
Nessus uses WMI (Windows Management Instrumentation) to query the installed printer drivers on a remote host. This is normally permitted for administrative tasks but can be abused to gather information about the system’s configuration. An attacker could use this information to identify vulnerable drivers and target them with specific exploits. No CVE is currently associated with this enumeration issue, as it’s considered an information leak rather than a direct exploit path.
- Root cause: The WMI service allows querying of printer driver information without sufficient restriction.
- Exploit mechanism: An attacker uses WMI queries to list installed drivers and their versions. This is typically done remotely using tools like PowerShell or Nessus itself.
- Scope: Windows systems with print services enabled are affected, across multiple versions.
3. Detection and Assessment
You can confirm if a system is vulnerable by checking the WMI service configuration and installed printer drivers. A quick check involves listing the printers via the command line. More thorough assessment uses vulnerability scanners like Nessus.
- Quick checks: Use PowerShell to list installed printers:
Get-WmiObject win32_printer - Scanning: Nessus plugin ID 10419 is used for this check. Other scanners may have similar plugins.
- Logs and evidence: Check the Windows Event Logs for WMI activity related to printer enumeration, specifically events with source “WinRM” or “WMI”.
Get-WmiObject win32_printer4. Solution / Remediation Steps
The best approach is to restrict access to the WMI service and keep systems patched. While disabling print services is an option, it may disrupt business processes.
4.1 Preparation
- Dependencies: Ensure no critical applications rely on WMI for printer management. Roll back by restoring the backup or reverting the WMI configuration.
- Change window: A standard change window is recommended, with approval from IT management.
4.2 Implementation
- Step 1: Restrict access to the WMI service using Group Policy. Configure firewall rules to limit inbound connections to port 135 for WMI.
- Step 2: Review installed printer drivers and remove any unused or outdated ones.
- Step 3: Ensure Windows is up-to-date with the latest security patches.
4.3 Config or Code Example
Before
# No specific WMI access restrictions are in place.After
# Configure Windows Firewall to allow only necessary connections to port 135 (WMI). Use Group Policy to manage this centrally.4.4 Security Practices Relevant to This Vulnerability
Least privilege and regular patching are key practices for mitigating this issue. Keeping software up-to-date reduces the risk of known vulnerabilities in printer drivers being exploited.
- Practice 1: Least privilege limits the impact if WMI is compromised.
- Practice 2: Patch cadence ensures timely updates to address security flaws in printer drivers and Windows itself.
4.5 Automation (Optional)
PowerShell can be used to automate driver removal and firewall rule configuration, but caution is needed when modifying system settings.
# Example PowerShell script for removing unused printers (use with care):
# Get-WmiObject win32_printer | Where-Object {$_.NetworkName -eq "" } | Remove-WmiObject5. Verification / Validation
Confirm the fix by re-running the Nessus scan and verifying that no printer drivers are enumerated. Also, check that print services continue to function as expected.
- Post-fix check: Run
Get-WmiObject win32_printeragain. The output should show fewer or no printers listed if unused ones were removed. - Re-test: Re-run the Nessus scan (plugin ID 10419). It should not report any vulnerable printer drivers.
- Monitoring: Monitor Windows Event Logs for WMI activity and unexpected errors related to print services.
Get-WmiObject win32_printer6. Preventive Measures and Monitoring
Regular security baselines, patch management processes, and CI/CD pipeline checks can help prevent this issue from recurring. For example, ensure that CIS controls related to WMI access are implemented.
- Baselines: Update your security baseline to include restrictions on WMI access.
- Pipelines: Add checks in your deployment pipelines to verify that printer drivers meet security standards.
- Asset and patch process: Implement a regular patch review cycle for Windows and printer drivers.
7. Risks, Side Effects, and Roll Back
Restricting WMI access may impact applications that rely on it. Removing the wrong printer driver could disrupt printing functionality. Roll back by restoring the system backup or reverting the WMI configuration.
- Risk or side effect 2: Removing a required printer driver will stop printing on that device.
- Roll back: Restore the system from backup, or revert the firewall and WMI configuration settings.
8. References and Resources
- Vendor advisory or bulletin: http://www.nessus.org/u?fab99415