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Mitigation Strategies Analysis for dotnet/maui

Mitigation Strategy: Platform-Specific API Least Privilege (MAUI-Centric)

Mitigation Strategy: Enforce the Principle of Least Privilege using MAUI's Permission System.

Description:

  1. Identify MAUI Permission Requests: Examine your MAUI project's platform-specific configuration files:
    • Android: Platforms/Android/AndroidManifest.xml
    • iOS/macOS: Platforms/iOS/Info.plist and Platforms/MacCatalyst/Info.plist
    • Windows: Platforms/Windows/Package.appxmanifest
  2. Minimize Permissions: Remove any <uses-permission> (Android), permission keys (iOS/macOS), or capabilities (Windows) that are not absolutely essential for your application's functionality. Use the most granular permissions available.
  3. MAUI Permissions Class: Utilize the Microsoft.Maui.ApplicationModel.Permissions class for runtime permission requests. This provides a cross-platform abstraction for requesting permissions. Example: 
    var status = await Permissions.CheckStatusAsync<Permissions.Camera>();
if (status != PermissionStatus.Granted)
{
    status = await Permissions.RequestAsync<Permissions.Camera>();
}
if (status == PermissionStatus.Granted)
{
    // Access the camera
}
else
{
    // Handle permission denial
}
  4. Conditional Compilation: Use preprocessor directives (#if ANDROID, #if IOS, etc.) to handle platform-specific permission logic or UI elements related to permissions.
  5. Rationale: Provide clear and concise rationale to the user within the MAUI application explaining why each permission is needed. This is often done through UI elements before calling Permissions.RequestAsync.

Threats Mitigated:

  • Malware Exploitation (High Severity): Limits the damage malware can do if it compromises the app.
  • Data Breaches (High Severity): Reduces the scope of potential data breaches.
  • Privacy Violations (Medium Severity): Protects user privacy.
  • Reputational Damage (Medium Severity): Improves user trust.

Impact:

  • Malware Exploitation: High impact.
  • Data Breaches: High impact.
  • Privacy Violations: High impact.
  • Reputational Damage: Moderate impact.

Currently Implemented:

  • Example: Camera permissions are requested using Permissions.Camera in the CameraService.cs file, and the AndroidManifest.xml and Info.plist files are configured accordingly.

Missing Implementation:

  • Example: Location permissions are requested too broadly. The Info.plist needs to be updated to use NSLocationWhenInUseUsageDescription instead of NSLocationAlwaysUsageDescription. The LocationService.cs file needs to use Permissions.LocationWhenInUse and handle the different permission states.

Mitigation Strategy: Platform-Specific API Input Validation (MAUI Abstraction Layer)

Mitigation Strategy: Validate all data received from platform APIs, leveraging MAUI abstractions where possible.

Description:

  1. Identify MAUI API Usage: Identify all uses of MAUI APIs that interact with the underlying platform and return data. Examples include:
    • Microsoft.Maui.Devices.Sensors (Geolocation, Accelerometer, etc.)
    • Microsoft.Maui.Storage.FileSystem
    • Microsoft.Maui.ApplicationModel.Communication (Email, Phone Dialer, SMS)
    • Microsoft.Maui.Media (MediaPicker)
    • Any custom platform-specific code invoked via DependencyService or handlers.
  2. Implement Validation within MAUI Code: Within your MAUI C# code, immediately after receiving data from these APIs, implement validation checks:
    • Type Checks: Ensure the data is of the expected .NET type.
    • Range/Format Checks: Validate numerical ranges, string formats, etc., based on the expected data.
    • Sanitization: If the data will be used in a WebView or other context where it could be interpreted as code, sanitize it appropriately.
  3. Centralized Validation (MAUI): If you frequently use a particular MAUI API, create a helper class or extension methods within your MAUI project to centralize the validation logic. This promotes consistency and reduces code duplication.
  4. Conditional Validation: If a MAUI API behaves differently or returns different data types on different platforms, use #if ANDROID, #if IOS, etc., to implement platform-specific validation logic.

Threats Mitigated:

  • Code Injection (High Severity): Prevents injection attacks through platform APIs.
  • Buffer Overflows (High Severity): Protects against buffer overflows.
  • Data Corruption (Medium Severity): Ensures data integrity.
  • Logic Errors (Medium Severity): Improves application stability.

Impact:

  • Code Injection: High impact.
  • Buffer Overflows: High impact.
  • Data Corruption: Moderate to high impact.
  • Logic Errors: Moderate impact.

Currently Implemented:

  • Example: Basic type checking is done on data returned by Geolocation.GetLocationAsync() in LocationService.cs.

Missing Implementation:

  • Example: No validation is performed on file paths returned by FileSystem.OpenAppPackageFileAsync in FileAccessService.cs. This needs to be added, including checks for path traversal vulnerabilities. A helper class for file path validation could be created.

Mitigation Strategy: WebView Security (MAUI WebView Control)

Mitigation Strategy: Securely configure and manage MAUI's WebView control.

Description:

  1. Identify WebView Usage: Locate all instances of the Microsoft.Maui.Controls.WebView control in your MAUI XAML or C# code.
  2. Disable JavaScript (If Possible): If the WebView is only used to display static, trusted content, disable JavaScript entirely: 
    <WebView Source="local.html" >
    <WebView.Behaviors>
        <local:DisableJavaScriptBehavior />
    </WebView.Behaviors>
</WebView>
    (You would need to create a custom behavior DisableJavaScriptBehavior that sets the appropriate platform-specific settings to disable JavaScript.)
  3. WebMessageReceived Event: If you must use JavaScript and communicate between the WebView and your MAUI code, use the WebView.WebMessageReceived event and the WebView.PostMessage method (from JavaScript). Never use WebView.EvaluateJavaScriptAsync to execute arbitrary JavaScript from the native side. Treat all messages received in the WebMessageReceived event handler as untrusted. 
    // In your MAUI code:
webView.WebMessageReceived += (sender, args) =>
{
    string message = args.Message; // Validate this message!
    // ... process the message ...
};

// In your JavaScript (within the WebView):
window.chrome.webview.postMessage("Hello from JavaScript!");
  4. Source Property: Carefully control the WebView.Source property.
    • Local Content: If loading local HTML, use a HtmlWebViewSource and ensure the HTML files are stored securely within the app package.
    • Remote Content: If loading remote content, use an UrlWebViewSource and ensure the URL is HTTPS and points to a trusted server. Consider implementing URL filtering to block known malicious domains.
  5. Custom Handlers (Advanced): For very fine-grained control, consider creating custom handlers for the WebView to override platform-specific behavior and security settings.

Threats Mitigated:

  • Cross-Site Scripting (XSS) (High Severity): A major concern with WebView.
  • Data Exfiltration (High Severity): Preventing the WebView from sending data to malicious servers.
  • Platform API Access (High Severity): Preventing compromised WebView content from accessing native platform APIs.

Impact:

  • XSS: High impact.
  • Data Exfiltration: High impact.
  • Platform API Access: High impact.

Currently Implemented:

  • Example: The HelpPage.xaml uses a WebView to display local HTML content. JavaScript is enabled.

Missing Implementation:

  • Example: JavaScript should be disabled for the HelpPage WebView since it's only displaying static content. A custom behavior to disable JavaScript needs to be created and applied. If JavaScript were required, the WebMessageReceived event should be used for communication, and all messages should be validated.

Mitigation Strategy: Secure Storage (MAUI SecureStorage)

Mitigation Strategy: Use MAUI's SecureStorage API for all sensitive data.

Description:

  1. Identify Sensitive Data: List all data within your MAUI application that should be considered sensitive (API keys, tokens, user credentials, etc.).
  2. MAUI SecureStorage API: Use the Microsoft.Maui.Storage.SecureStorage class to store and retrieve this data. This API leverages platform-specific secure storage mechanisms. 
    // Store data:
await SecureStorage.Default.SetAsync("my_secret_key", secretValue);

// Retrieve data:
string secretValue = await SecureStorage.Default.GetAsync("my_secret_key");

// Remove data:
SecureStorage.Default.Remove("my_secret_key");
  3. Error Handling: Implement proper error handling around SecureStorage calls. Handle cases where secure storage might be unavailable or fail.
  4. Avoid Preferences: Do not use MAUI's Preferences API for sensitive data. Preferences is intended for simple application settings, not secrets.

Threats Mitigated:

  • Data Breaches (High Severity): Protects sensitive data stored on the device.
  • Unauthorized Access (Medium Severity): Prevents other apps from accessing the data.

Impact:

  • Data Breaches: High impact.
  • Unauthorized Access: High impact.

Currently Implemented:

  • Example: The user's authentication token is stored using SecureStorage in AuthenticationService.cs.

Missing Implementation:

  • Example: An API key for a third-party service is currently stored in a plain-text configuration file. This needs to be moved to SecureStorage, and the ApiService.cs file needs to be updated to retrieve it from there.