How to remediate – Windows Disabled Command Prompt Enumeration

1. Introduction

The Windows Disabled Command Prompt Enumeration vulnerability checks whether the DisableCMD policy is enabled on a remote host for each local user. This can indicate a potential security issue where command prompt access is restricted, potentially hindering administrative tasks and incident response. Affected systems are typically Windows-based computers managed within an Active Directory domain or with locally applied policies. A successful restriction could impact system availability if legitimate administration requires the command prompt.

2. Technical Explanation

The vulnerability stems from the configuration of the DisableCMD policy via the Windows Registry. Local users may have a registry key at ‘HKLMSoftwarePoliciesMicrosoftWindowsSystemDisableCMD’. An attacker could exploit this by identifying disabled command prompts and attempting to bypass restrictions or escalate privileges if other vulnerabilities exist. The preconditions for exploitation involve having local access to the system and knowledge of user accounts with potentially restricted command prompt access.

• Root cause: Incorrectly configured DisableCMD policy settings in the Windows Registry.
• Exploit mechanism: An attacker could identify disabled command prompts, then attempt to exploit other vulnerabilities to gain elevated privileges or execute commands despite the restriction. For example, if batch processing is allowed (value of 2), an attacker might use a batch script to perform malicious actions.
• Scope: Windows systems with Group Policy or local policy configurations applied.

3. Detection and Assessment

You can confirm whether a system is vulnerable by checking the DisableCMD registry key. A quick check involves examining the current user’s policy settings, while a thorough method requires enumerating all users.

• Quick checks: Use PowerShell to check the current user’s command prompt status: Get-ItemProperty -Path 'HKLM:SoftwarePoliciesMicrosoftWindowsSystem' | Select-Object DisableCMD. An output of ‘1’ indicates a disabled command prompt.
• Scanning: Nessus plugin ID 406988 can detect this vulnerability. This is an example only.
• Logs and evidence: Event logs do not directly record the setting of the DisableCMD policy, but changes to Group Policy objects may be logged in the Security event log.

reg query "HKLMSoftwarePoliciesMicrosoftWindowsSystem" /v DisableCMD

4. Solution / Remediation Steps

The following steps outline how to fix this issue by ensuring command prompts are enabled as needed. These steps should be performed carefully, considering the potential impact on security policies.

4.1 Preparation

• Dependencies: Ensure you have administrative privileges to modify Group Policy settings. Roll back plan: Restore from backup or revert the registry key change.
• Change window needs: This change should be performed during a scheduled maintenance window, and approved by the system owner.

4.2 Implementation

1. Step 1: Open Group Policy Editor (gpedit.msc) on the target machine or domain controller.
2. Step 2: Navigate to User Configuration > Administrative Templates > System.
3. Step 3: Double-click “Prevent access to the command prompt”.
4. Step 4: Set the policy to “Not Configured” or “Disabled”.
5. Step 5: If configured via local security policy, use regedit.exe and navigate to HKLMSoftwarePoliciesMicrosoftWindowsSystem. Delete the DisableCMD key if it exists, or set its value to 0.
6. Step 6: Run gpupdate /force in an elevated command prompt to apply the changes.

4.3 Config or Code Example

Before

reg query "HKLMSoftwarePoliciesMicrosoftWindowsSystem" /v DisableCMD

After

reg delete "HKLMSoftwarePoliciesMicrosoftWindowsSystem" /v DisableCMD /f

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue and related vulnerabilities. Least privilege is key, as restricting command prompt access should be a deliberate decision based on user roles. Input validation isn’t directly applicable here, but secure defaults – enabling the command prompt unless specifically disabled – are preferable.

• Practice 1: Implement least privilege to limit the impact if an account with restricted command prompt access is compromised.
• Practice 2: Regularly review Group Policy settings and local security policies for unnecessary restrictions.

4.5 Automation (Optional)

PowerShell can be used to automate this fix across multiple systems. Use caution when modifying registry keys remotely.

# Example PowerShell script (use with care!)
foreach ($computer in @("computer1", "computer2")) {
  try {
    Remove-ItemProperty -Path "\$computerHKLMSoftwarePoliciesMicrosoftWindowsSystem" -Name DisableCMD -ErrorAction SilentlyContinue
    Write-Host "Removed DisableCMD from $computer"
  } catch {
    Write-Host "Failed to remove DisableCMD from $computer: $($_.Exception.Message)"
  }
}

5. Verification / Validation

Confirm the fix by rechecking the registry key and verifying that command prompts are accessible for affected users. A simple service smoke test can confirm basic functionality.

• Post-fix check: Run reg query "HKLMSoftwarePoliciesMicrosoftWindowsSystem" /v DisableCMD. The key should not exist, or the output should show a value of 0.
• Re-test: Re-run the quick check from section 3 (Get-ItemProperty -Path 'HKLM:SoftwarePoliciesMicrosoftWindowsSystem' | Select-Object DisableCMD) to confirm the policy is no longer enforced.
• Smoke test: Log in as a user who previously had a disabled command prompt and verify that they can open cmd.exe without errors.
• Monitoring: Monitor Group Policy application logs for any failures related to the System settings.

reg query "HKLMSoftwarePoliciesMicrosoftWindowsSystem" /v DisableCMD

6. Preventive Measures and Monitoring

Update security baselines or policies to reflect the desired command prompt configuration. Implement checks in CI/CD pipelines to prevent unintended restrictions during deployment, for example, by scanning Group Policy objects for unwanted settings.

• Baselines: Update a CIS benchmark or GPO template to ensure command prompts are enabled unless specifically disabled based on user roles.
• Asset and patch process: Review Group Policy changes regularly as part of your asset management and patch review cycle.

7. Risks, Side Effects, and Roll Back

Changing the DisableCMD policy could impact security if command prompts are enabled for users who should not have access. The roll back steps involve restoring the original registry key value or Group Policy setting.

• Risk or side effect 1: Enabling command prompts for unintended users may increase the attack surface.
• Risk or side effect 2: Changes to Group Policy can take time to propagate across all systems.
• Roll back: Restore from backup, revert the registry key change (set value to 1), or re-enable the “Prevent access to the command prompt” policy in Group Policy Editor.

8. References and Resources

Link only to sources that match this exact vulnerability. Use official advisories and trusted documentation. Do not include generic