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attack-surface.md

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Attack Surface Analysis for dotnet/maui

Attack Surface: Platform API Abuse via Bridge

  • Description: Exploitation of vulnerabilities in the way .NET MAUI interacts with native platform APIs (e.g., camera, contacts, file system, sensors). This includes both vulnerabilities in the bridge itself and improper use of the APIs by the application. The bridge is the MAUI-specific component.
  • How MAUI Contributes: MAUI provides the abstraction layer and bridging mechanisms that allow C# code to call native APIs. This bridge is a potential point of failure, unique to MAUI (and similar cross-platform frameworks), and the ease of access to powerful APIs increases the risk of misuse.
  • Example: An attacker crafts a malicious contact entry (e.g., with a specially formatted name or phone number) that, when accessed by a MAUI app through the Contacts API, triggers a buffer overflow or code injection vulnerability in the MAUI renderer or handler responsible for displaying contact information. This exploits a MAUI-specific component. Another example: a MAUI app misuses a platform API due to an incorrect assumption about how the MAUI bridge handles data types, leading to a vulnerability.
  • Impact: Data breaches (contacts, files, location data), privilege escalation, device compromise, denial of service.
  • Risk Severity: Critical to High (depending on the specific API and vulnerability).
  • Mitigation Strategies:
    • Principle of Least Privilege: Request only the absolute minimum necessary permissions. Clearly justify each permission request.
    • Input Validation: Treat all data received from platform APIs as untrusted. Thoroughly validate data types, lengths, formats, and expected values before using the data. This is crucial because the MAUI bridge may perform implicit conversions.
    • Secure Storage: Use platform-provided secure storage mechanisms (Keychain on iOS, Keystore on Android) for sensitive data obtained from platform APIs.
    • API Usage Review: Carefully review the security documentation for each platform API used, and the MAUI documentation on how to interact with that API.
    • Regular Updates: Keep the .NET MAUI framework, platform SDKs, and all NuGet packages up-to-date. This is critical for patching vulnerabilities in the bridge itself.

Attack Surface: Cross-Context Scripting (XCS) in WebViews

  • Description: A specialized form of Cross-Site Scripting (XSS) that targets the communication bridge between the .NET MAUI application code and JavaScript running within a WebView control. The bridge is the MAUI-specific attack vector.
  • How MAUI Contributes: MAUI's WebView allows embedding web content. The WebView.InvokeAsync method (and any custom JavaScript bridge) provides a communication channel unique to MAUI (and similar frameworks) that can be exploited. This is not a standard web XSS; it's about crossing the native/web boundary.
  • Example: An attacker injects malicious JavaScript into a WebView. This JavaScript then calls a .NET method exposed by the MAUI app (via InvokeAsync or a custom bridge) using malicious parameters, causing the .NET code to perform unauthorized actions because of how MAUI handles the interop.
  • Impact: Data exfiltration, access to native device capabilities (bridged through MAUI), privilege escalation, potentially full application compromise.
  • Risk Severity: Critical to High (depending on the exposed .NET methods).
  • Mitigation Strategies:
    • Content Source Control: Load WebView content only from trusted sources.
    • Input/Output Sanitization: Strictly sanitize and validate all data passed between the .NET code and the WebView (both directions). This is critical because of the MAUI interop layer.
    • Content Security Policy (CSP): Implement a strict CSP within the WebView.
    • Minimize Exposed .NET Methods: Expose only the absolute minimum necessary .NET methods to the WebView. Carefully review the security implications of each exposed method in the context of MAUI's bridging.
    • WebView Isolation (if possible): Explore platform-specific options for running the WebView in a separate process.

Attack Surface: Vulnerable Renderers/Handlers

  • Description: Exploitation of vulnerabilities in the platform-specific MAUI renderers (or handlers) that translate the abstract UI into native UI elements. These are MAUI-specific components.
  • How MAUI Contributes: MAUI relies entirely on these renderers/handlers for UI presentation. Bugs in these MAUI-provided components are directly attributable to the framework.
  • Example: A specially crafted string or image, when processed by a vulnerable MAUI renderer for a Label or Image control, triggers a buffer overflow or memory corruption vulnerability. This is a vulnerability within MAUI itself.
  • Impact: Denial of service, potentially arbitrary code execution (depending on the vulnerability).
  • Risk Severity: High (potential for code execution, but often difficult to exploit).
  • Mitigation Strategies:
    • Framework Updates: Keep the .NET MAUI framework and all related NuGet packages updated. This is the primary mitigation, as renderer vulnerabilities are patched in framework updates.
    • Minimize Custom Renderers: Avoid using custom renderers unless absolutely necessary. If custom renderers are required, perform thorough security testing, including fuzzing.
    • Input Validation (Indirectly): Validating data before it reaches the MAUI renderer can mitigate some risks, although it won't address all renderer vulnerabilities.