Skip to content

Latest commit

 

History

History
180 lines (137 loc) · 16.5 KB

sec-design-deep-analysis.md

File metadata and controls

180 lines (137 loc) · 16.5 KB

Deep Security Analysis of flutter-permission-handler

1. Objective, Scope, and Methodology

Objective: To conduct a thorough security analysis of the flutter-permission-handler library, focusing on its key components, architecture, data flow, and potential vulnerabilities. The goal is to identify potential security risks and provide actionable mitigation strategies to ensure the library's secure use in Flutter applications. This analysis will specifically address the security controls, accepted risks, and recommended security controls outlined in the provided security design review.

Scope:

  • The analysis will cover the core functionality of the flutter-permission-handler library as available on its GitHub repository (https://github.com/baseflow/flutter-permission-handler).
  • The analysis will consider the library's interaction with the underlying operating system permission models (Android, iOS, Web, macOS, Windows, Linux).
  • The analysis will not cover vulnerabilities in the underlying operating system permission systems themselves, but will acknowledge their potential impact.
  • The analysis will not cover the security of applications using the library, except where the library's design or implementation could directly contribute to vulnerabilities in those applications.

Methodology:

  1. Code Review: Examine the source code of the flutter-permission-handler library on GitHub, focusing on areas related to permission requesting, checking, and handling.
  2. Documentation Review: Analyze the official documentation, including the README, API documentation, and any other relevant materials.
  3. Architecture Inference: Based on the code and documentation, infer the library's architecture, components, and data flow. This will build upon the provided C4 diagrams.
  4. Threat Modeling: Identify potential threats and vulnerabilities based on the library's functionality and interactions with the operating system. This will consider the "Accepted Risks" and "Recommended Security Controls" from the design review.
  5. Mitigation Strategy Recommendation: Propose specific, actionable mitigation strategies to address the identified threats and vulnerabilities, tailored to the Flutter and Dart environment.

2. Security Implications of Key Components

Based on the provided design review and an understanding of the library's purpose, here's a breakdown of key components and their security implications:

  • Unified API (PermissionHandlerPlatform): This is the core of the library, providing a single point of entry for developers to interact with permissions.

    • Security Implication: A vulnerability here (e.g., improper input validation, incorrect mapping of permission requests to platform-specific APIs) could affect all permission requests made through the library. This is a high-impact area.
    • Threats: Injection attacks (if input is not sanitized), logic errors leading to incorrect permission grants, denial-of-service (if the API can be crashed).

  • Platform-Specific Implementations (e.g., PermissionHandlerAndroid, PermissionHandlerIOS): These components handle the actual interaction with the native platform APIs for requesting and checking permissions.

    • Security Implication: These are critical bridges to the OS. Errors here could bypass the intended permission model of the OS. Incorrect handling of platform-specific error codes or edge cases could lead to vulnerabilities.
    • Threats: Incorrect mapping of Flutter permission enums to native permission constants, mishandling of asynchronous results from native calls, vulnerabilities in the platform channel communication itself.

  • Platform Channels (MethodChannel): Flutter uses MethodChannels to communicate with native code (Android/iOS). The permission handler uses this to call native permission APIs.

    • Security Implication: While Flutter's MethodChannel is generally secure, improper use (e.g., sending sensitive data over the channel without encryption, not validating data received from the native side) could create vulnerabilities.
    • Threats: Data leakage (if sensitive information is passed unencrypted), injection attacks (if data from the native side is not validated), man-in-the-middle attacks (less likely, but possible if the channel is compromised).

  • JavaScript Interop (for Web): On the web, the library interacts with the browser's permission API using JavaScript interop.

    • Security Implication: Similar to platform channels, the security relies on the correct and secure use of JavaScript interop. Incorrectly handling user input or browser responses could lead to vulnerabilities.
    • Threats: Cross-site scripting (XSS) vulnerabilities (if user input is not properly sanitized before being passed to JavaScript), bypassing permission checks (if the JavaScript code can be manipulated).

  • Error Handling: The way the library handles errors (e.g., failed permission requests, unexpected exceptions) is crucial for security and stability.

    • Security Implication: Poor error handling can lead to crashes, unexpected behavior, and potentially expose information about the application's internal state.
    • Threats: Denial-of-service (if errors lead to crashes), information disclosure (if error messages reveal sensitive information), logic errors (if errors are not handled correctly, leading to incorrect permission states).

  • Input Validation: The library should validate the input provided to its API methods (e.g., permission names).

    • Security Implication: Lack of input validation can lead to crashes, unexpected behavior, and potentially security vulnerabilities (e.g., injection attacks).
    • Threats: Injection attacks, denial-of-service, logic errors.

3. Architecture, Components, and Data Flow (Inferred)

The provided C4 diagrams give a good high-level overview. Here's a more detailed, security-focused view:

  1. User Interaction: The user interacts with the Flutter app.
  2. App Logic: The Flutter app, using the flutter-permission-handler, determines that a permission is needed.
  3. Permission Request: The app calls a method on the PermissionHandlerPlatform (e.g., requestPermissions([Permission.camera])).
  4. Platform Selection: The PermissionHandlerPlatform determines the current platform (Android, iOS, Web, etc.).
  5. Platform-Specific Call: The appropriate platform-specific implementation (e.g., PermissionHandlerAndroid) is invoked.
  6. Platform Channel Communication (Native Platforms):
    • The platform-specific implementation uses a MethodChannel to send a request to the native code.
    • The native code interacts with the OS permission system (e.g., ActivityCompat.requestPermissions on Android, AVCaptureDevice.requestAccess on iOS).
    • The OS presents a permission dialog to the user.
    • The user grants or denies the permission.
    • The OS returns the result to the native code.
    • The native code sends the result back to the Flutter side via the MethodChannel.
  7. JavaScript Interop (Web):
    • The platform-specific implementation uses JavaScript interop (dart:js) to call the browser's permission API (e.g., navigator.permissions.query).
    • The browser may present a permission prompt to the user.
    • The user grants or denies the permission.
    • The browser returns the result to the JavaScript code.
    • The JavaScript code returns the result to the Flutter side.
  8. Result Handling: The platform-specific implementation receives the result and converts it to a PermissionStatus enum.
  9. Callback/Future Resolution: The PermissionHandlerPlatform returns the PermissionStatus to the Flutter app (typically via a Future).
  10. App Logic Continues: The Flutter app uses the PermissionStatus to determine its subsequent behavior (e.g., enabling or disabling features).

Data Flow:

  • Permission Request: Permission enum (e.g., Permission.camera) flows from the app to the PermissionHandlerPlatform and then to the platform-specific implementation.
  • Permission Status: PermissionStatus enum (e.g., PermissionStatus.granted, PermissionStatus.denied) flows from the platform-specific implementation back to the app.
  • Platform-Specific Data: Data exchanged over the MethodChannel or via JavaScript interop is platform-specific and should be minimized. This is a critical area for security review.

4. Specific Security Considerations and Threats

Based on the above analysis, here are specific security considerations and threats, tailored to flutter-permission-handler:

  • Incorrect Permission Mapping (High): If the library incorrectly maps Flutter's Permission enums to the underlying platform's permission constants, it could request the wrong permission. This could lead to either granting more access than intended (security risk) or less access than intended (functionality issue).

    • Example: Requesting WRITE_EXTERNAL_STORAGE instead of READ_EXTERNAL_STORAGE on Android.
    • Threat: Privilege escalation, data leakage.

  • Mishandling of Asynchronous Results (High): Permission requests are often asynchronous. If the library doesn't correctly handle race conditions or errors in the asynchronous responses from the native side, it could lead to incorrect permission states.

    • Example: Assuming a permission is granted before the asynchronous response is received.
    • Threat: Logic errors, unexpected behavior, potential security vulnerabilities if the app acts on an incorrect permission state.

  • Platform Channel Vulnerabilities (Medium): While Flutter's MethodChannel is designed to be secure, improper use could introduce vulnerabilities.

    • Example: Sending sensitive data (even indirectly related to permissions) over the channel without encryption.
    • Threat: Data leakage.

  • JavaScript Interop Vulnerabilities (Medium): On the web, incorrect use of JavaScript interop could lead to XSS or other vulnerabilities.

    • Example: Passing unsanitized user input to JavaScript code that interacts with the permission API.
    • Threat: XSS, bypassing permission checks.

  • Lack of Input Validation (Medium): The library should validate the input to its API methods.

    • Example: Accepting an invalid permission name or an unsupported platform.
    • Threat: Crashes, unexpected behavior, potential injection attacks.

  • Incomplete Permission Coverage (Medium): The library may not cover all possible permissions on all platforms. This is an "accepted risk," but it's important to be aware of it.

    • Example: A new permission is added to Android or iOS that the library doesn't yet support.
    • Threat: Developers may need to write custom platform-specific code, increasing the risk of errors.

  • Reliance on Underlying Platform Security (Low-Medium): The library relies on the security of the underlying OS permission systems. Vulnerabilities in those systems are outside the library's control, but could impact the security of apps using the library.

    • Example: A vulnerability in Android's permission system that allows an app to bypass permission checks.
    • Threat: This is largely an accepted risk, but developers should be aware of it.

  • Improper Error Handling (Medium): Insufficient error handling can lead to various issues.

    • Example: Not handling the case where a permission request is denied by the OS, or times out.
    • Threat: Denial of service, unexpected application behavior.

5. Actionable Mitigation Strategies

Here are specific, actionable mitigation strategies for the flutter-permission-handler library:

  • Comprehensive Permission Mapping Tests (High Priority):

    • Implement extensive unit and integration tests to verify that every supported Permission enum is correctly mapped to the corresponding native permission constant on every supported platform.
    • These tests should be automated and run as part of the CI/CD pipeline.
    • Consider using a table-driven testing approach to make it easier to manage and update the mappings.

  • Robust Asynchronous Handling (High Priority):

    • Thoroughly review the code that handles asynchronous results from the native side.
    • Use async/await and Futures correctly to avoid race conditions.
    • Implement comprehensive error handling for all possible outcomes of the asynchronous calls (e.g., success, denial, timeout, platform error).
    • Add tests that specifically simulate different asynchronous scenarios (e.g., delayed responses, errors).

  • Secure Platform Channel Usage (Medium Priority):

    • Minimize the amount of data sent over the MethodChannel. Only send the minimum necessary information for requesting and checking permissions.
    • Never send sensitive data (e.g., API keys, user credentials) over the channel.
    • Validate all data received from the native side before using it. Treat it as untrusted input.
    • Consider using a well-defined data format (e.g., JSON) for communication over the channel and validate the structure of the data.

  • Secure JavaScript Interop (Medium Priority):

    • Avoid passing any user-provided data directly to JavaScript code.
    • Use a well-defined API for communication between Dart and JavaScript.
    • Validate all data received from the JavaScript side.
    • Consider using a library or framework that provides a more secure way to interact with JavaScript (if available).

  • Thorough Input Validation (Medium Priority):

    • Validate all input to the library's public API methods.
    • Check for invalid permission names, unsupported platforms, and other invalid input.
    • Throw appropriate exceptions for invalid input.
    • Add unit tests to verify that input validation is working correctly.

  • Clear Documentation and Security Guidelines (Medium Priority):

    • Provide clear and comprehensive documentation on how to use the library securely.
    • Include specific guidance on handling sensitive permissions and data.
    • Document any limitations or known issues.
    • Explain the security model of the library and its reliance on the underlying platform's security.

  • Regular Security Audits and Penetration Testing (Medium Priority):

    • Conduct regular security audits of the codebase.
    • Consider performing penetration testing to identify potential vulnerabilities.
    • Use static analysis tools (beyond the basic analyzer package) that are specifically designed for security analysis.

  • Dependency Management (Medium Priority):

    • Keep all dependencies up to date.
    • Use a dependency management tool (like pub) to ensure that you're using the correct versions of dependencies.
    • Monitor for security vulnerabilities in dependencies.

  • Community Engagement and Vulnerability Reporting (Medium Priority):

    • Encourage community contributions and security reviews.
    • Establish a clear process for reporting and addressing security vulnerabilities.
    • Respond promptly to security reports.

  • Runtime Permission Monitoring (Low Priority, but Recommended):

    • While challenging to implement in a cross-platform way, consider exploring options for runtime permission monitoring. This could involve periodically checking the status of granted permissions to detect any unexpected changes. This is a more advanced technique and may not be feasible for all platforms.

  • Address Accepted Risks:

    • Underlying Platform Vulnerabilities: Document clearly that the library's security depends on the underlying OS. Provide links to relevant security resources for each supported platform.
    • Incomplete Permission Coverage: Maintain a clear list of supported permissions and their platform-specific nuances. Provide guidance on how developers can handle unsupported permissions (e.g., using platform-specific code).
    • Future Platform Updates: Establish a process for monitoring platform updates and quickly adapting the library to any breaking changes.

By implementing these mitigation strategies, the flutter-permission-handler library can significantly improve its security posture and reduce the risk of vulnerabilities in applications that use it. This proactive approach is crucial for maintaining user trust and ensuring the long-term success of the library.