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How to remediate – WMI Firewall Rule Enumeration

Contents

1. Introduction

The WMI Firewall Rule Enumeration vulnerability allows an attacker with valid credentials to obtain a list of firewall rules on a Windows host. This information can help them identify open ports and services, potentially leading to further exploitation. Affected systems are typically those running the Windows operating system. A successful exploit could reduce confidentiality by revealing network configuration details.

2. Technical Explanation

This vulnerability occurs because the Windows Management Instrumentation (WMI) interface allows enumeration of firewall rules with supplied credentials. An attacker can connect to a remote host and query WMI for this information. There is no known CVE associated with this specific enumeration, but it represents an information disclosure risk. An example attack involves using PowerShell or other scripting languages to access the WMI object representing firewall rules.

  • Root cause: The WMI interface does not sufficiently restrict access to firewall rule data based on user privileges.
  • Exploit mechanism: An attacker uses a script to connect to the target host via WMI and query for firewall rule information. For example, using PowerShell’s Get-WmiObject cmdlet.
  • Scope: Windows operating systems are affected. Specific versions may have differing levels of access control but are generally vulnerable if credentials allow WMI access.

3. Detection and Assessment

You can confirm vulnerability by checking for the ability to enumerate firewall rules via WMI with valid user credentials. A quick check involves attempting a simple query using PowerShell. A thorough method is to review event logs for suspicious WMI activity.

  • Quick checks: Run the following PowerShell command as a user with access to the target host: Get-WmiObject -Class Win32_FirewallRule. If rules are returned, the system is vulnerable.
  • Scanning: Nessus plugin ID 10498 can detect this vulnerability. This is an example only and may require updates.
  • Logs and evidence: Check Windows Event Logs for event IDs related to WMI activity (e.g., 672, 673) that indicate firewall rule queries. Look in the Microsoft-Windows/WindowsFilteringPlatform/FirewallRule log.
Get-WmiObject -Class Win32_FirewallRule

4. Solution / Remediation Steps

The primary solution is to restrict access to WMI based on the principle of least privilege. This limits the potential impact if credentials are compromised.

4.1 Preparation

  • Dependencies: Ensure you have administrative privileges to modify local security policies. Roll back plan: Restore the system snapshot if issues occur.
  • Change window needs: A standard change window may be appropriate depending on your organisation’s policy. Approval from a senior IT administrator may be needed.

4.2 Implementation

  1. Step 1: Open Local Security Policy (secpol.msc).
  2. Step 2: Navigate to Local Policies > User Rights Assignment.
  3. Step 3: Locate the policy “Access this computer from the network”.
  4. Step 4: Remove any unnecessary user accounts or groups from this policy. Limit access only to those who require it.
  5. Step 5: Restart the system for changes to take effect.

4.3 Config or Code Example

Before

Users group is included in "Access this computer from the network" policy.

After

Only specific administrative accounts are included in "Access this computer from the network" policy. The Users group has been removed.

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate this vulnerability type.

  • Practice 1: Least privilege access reduces the impact if an attacker gains credentials. Grant users only the permissions they need to perform their tasks.
  • Practice 2: Regularly review user accounts and group memberships to ensure appropriate access levels are maintained.

4.5 Automation (Optional)

PowerShell can be used to manage local security policy settings, but caution is advised as incorrect changes can lock you out of the system.

# Example PowerShell script - use with care!
# Get-LocalUser | Where-Object {$_.Enabled -eq $true} | ForEach-Object {
#   Remove-LocalUserMember -Group "Access this computer from the network" -Member $_.Name
# }

5. Verification / Validation

Confirm the fix by attempting to enumerate firewall rules via WMI with a user account that should no longer have access. A negative test involves trying to connect using a standard user account.

  • Post-fix check: Run Get-WmiObject -Class Win32_FirewallRule as a non-administrative user. You should receive an “Access Denied” error.
  • Re-test: Repeat the initial detection method (PowerShell query) with the restricted user account to confirm access is blocked.
  • Smoke test: Verify that users can still perform their normal tasks, such as accessing network shares or applications they previously used.
  • Monitoring: Monitor Windows Event Logs for failed WMI queries from unauthorized accounts. Look for event ID 673 with a failure code.
Get-WmiObject -Class Win32_FirewallRule # Expected output: Access Denied

6. Preventive Measures and Monitoring

Update security baselines to reflect least privilege principles for WMI access. Implement regular patch cycles.

  • Baselines: Update your Windows security baseline or Group Policy Object (GPO) to enforce strict control over the “Access this computer from the network” user right assignment.
  • Pipelines: Incorporate checks in your CI/CD pipeline to validate WMI access settings during system builds and deployments.
  • Asset and patch process: Implement a regular patch cycle for Windows operating systems, including security updates that address WMI vulnerabilities. A monthly review is sensible.

7. Risks, Side Effects, and Roll Back

  • Risk or side effect 1: Blocking legitimate user access. Mitigation: Carefully review affected accounts and restore access if needed.
  • Roll back: Step 1: Open Local Security Policy (secpol.msc). Step 2: Navigate to Local Policies > User Rights Assignment. Step 3: Add any previously removed user accounts or groups back to the “Access this computer from the network” policy. Step 4: Restart the system.

8. References and Resources

Links only to sources that match this exact vulnerability.

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