How to remediate – Windows Store Application Enumeration

1. Introduction

The Windows Store Application Enumeration vulnerability allows an attacker to obtain a list of applications installed on a system via the Windows Store. This information can help attackers identify potential targets and plan further attacks. Affected systems are typically Windows computers with access to the Microsoft Store. A successful exploit could lead to information disclosure, potentially impacting confidentiality.

2. Technical Explanation

This vulnerability occurs because of how Windows manages application lists from the Store. An attacker can use WMI and PowerShell commands, executed locally on a system with appropriate credentials, to query for installed applications. There is no known CVE associated with this specific enumeration issue. An example attack would involve an attacker gaining access to a user account and then running a script to list all Windows Store apps.

• Root cause: The WMI interface exposes application lists without sufficient restriction.
• Exploit mechanism: An attacker uses PowerShell or WMI queries to retrieve the installed application list. For example, using `Get-AppxPackage` in PowerShell.
• Scope: Windows 10 and later versions are affected.

3. Detection and Assessment

You can confirm vulnerability by checking for the presence of the necessary commands and their ability to list Store apps. A thorough method involves running a script that attempts to enumerate applications.

• Quick checks: Verify PowerShell is present and functional on the target system.
• Scanning: Nessus plugin ID 16829 can identify this issue as an example only.
• Logs and evidence: Application event logs may show usage of `Get-AppxPackage` or similar commands, but this is not a reliable indicator.

powershell Get-AppxPackage | select Name, PackageFullName

4. Solution / Remediation Steps

The primary solution is to restrict access to the PowerShell command used for enumeration or monitor its use closely.

4.1 Preparation

• There are no dependencies, but ensure you have administrative privileges. Roll back by restoring the backup if needed.
• A standard change window may be appropriate depending on your organisation’s policies.

4.2 Implementation

1. Step 1: Use Group Policy or Intune to restrict PowerShell execution policy to prevent running scripts.
2. Step 2: If restricting PowerShell is not possible, monitor the use of `Get-AppxPackage` in event logs.

4.3 Config or Code Example

Before

powershell Get-AppxPackage | select Name, PackageFullName

After

Set-ExecutionPolicy RemoteSigned -Scope LocalMachine -Force 

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate this vulnerability type.

• Practice 1: Least privilege reduces the impact if an attacker gains access to a user account.
• Practice 2: Monitoring PowerShell usage helps detect and respond to malicious activity.

4.5 Automation (Optional)

# Example PowerShell script to set execution policy across multiple machines
# Requires appropriate permissions and remote management configuration
# Invoke-Command -ComputerName $computerList { Set-ExecutionPolicy RemoteSigned -Scope LocalMachine -Force }

5. Verification / Validation

• Post-fix check: Run `Get-AppxPackage` in PowerShell. It should return an error if execution policy is restricted.
• Re-test: Re-run the detection script from Section 3. The script should no longer be able to list applications.
• Smoke test: Verify that other legitimate PowerShell scripts continue to function as expected.
• Monitoring: Monitor event logs for attempts to execute `Get-AppxPackage` and alert on unexpected usage.

powershell Get-AppxPackage | select Name, PackageFullName # Should return an error

6. Preventive Measures and Monitoring

Update security baselines and add checks in deployment pipelines to prevent similar issues.

• Baselines: Update your PowerShell execution policy baseline to a more restrictive setting.
• Asset and patch process: Review system configurations regularly to ensure compliance with security policies.

7. Risks, Side Effects, and Roll Back

Restricting PowerShell execution policy may break legitimate scripts that rely on running unsigned code.

• Risk or side effect 1: Restricting PowerShell can impact system functionality if not carefully planned.
• Risk or side effect 2: Users may require exceptions for specific scripts, increasing administrative overhead.
• Roll back: Restore the original execution policy setting using `Set-ExecutionPolicy Unrestricted -Scope LocalMachine -Force`.

8. References and Resources

• Vendor advisory or bulletin: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.security/set-executionpolicy?view=powershell-7.3
• NVD or CVE entry: Not applicable for this specific enumeration issue.
• Product or platform documentation relevant to the fix: https://learn.microsoft.com/en-us/windows/security/threats/enumeration