mitigations.md

Mitigation Strategies Analysis for square/retrofit

Mitigation Strategy: Secure Deserialization Practices (Retrofit Converter Configuration)

Strategy: Secure Deserialization Practices (Retrofit Converter Configuration)

• Description:

  1. Choose a Secure Deserializer: When configuring Retrofit, select a well-maintained and actively patched JSON deserialization library (e.g., Moshi, or the latest versions of Gson/Jackson) as your converter.
  2. Configure the Converter (if necessary): If using Gson, avoid using GsonBuilder().enableComplexMapKeySerialization() unless absolutely required, as this can introduce vulnerabilities. For other converters, review their documentation for any security-related configuration options.
  3. Use with Retrofit: Integrate the chosen and configured converter with Retrofit using addConverterFactory().

     // Example using Gson (but be mindful of security considerations)
     Gson gson = new GsonBuilder()
         // ... other Gson configurations ...
         .create();
     
     Retrofit retrofit = new Retrofit.Builder()
         .baseUrl("https://yourdomain.com/")
         .addConverterFactory(GsonConverterFactory.create(gson)) // Use the configured Gson instance
         .build();
     
     // Example using Moshi (generally preferred for security)
     Moshi moshi = new Moshi.Builder()
         // ... other Moshi configurations ...
         .build();
     
     Retrofit retrofit = new Retrofit.Builder()
         .baseUrl("https://yourdomain.com/")
         .addConverterFactory(MoshiConverterFactory.create(moshi)) // Use the configured Moshi instance
         .build();

  4. Define Strict Data Models: Create precise Java/Kotlin classes that match the expected structure of your JSON responses. Avoid generic types. This is crucial for type-safe deserialization. This is used by Retrofit, but not directly configured in Retrofit.
  5. Validate Deserialized Data: Although not directly a Retrofit configuration, after Retrofit deserializes the data using the converter, perform additional validation. This is crucial, but separate from Retrofit's direct configuration.

• Threats Mitigated:

  • Remote Code Execution (RCE) via Deserialization: (Severity: Critical) - Attackers inject malicious objects.
  • Data Tampering: (Severity: High) - Attackers modify JSON data.
  • Denial of Service (DoS): (Severity: Medium) - Malformed JSON causing resource exhaustion.

• Impact:

  • RCE: Risk significantly reduced by choosing a secure converter and configuring it safely.
  • Data Tampering: Risk reduced by using strict data models (although validation is still key).
  • DoS: Risk partially mitigated by using a robust deserializer.

• Currently Implemented:

  • Example: Using MoshiConverterFactory with Moshi 1.15.0.
  • Example: Converter factory configured in NetworkModule.java.

• Missing Implementation:

  • Example: Need to review all Retrofit service interfaces to ensure they use appropriate, specific data models.

Mitigation Strategy: Secure Handling of Sensitive Data (Retrofit Annotations)

Strategy: Secure Handling of Sensitive Data (Retrofit Annotations)

• Description:

  1. Identify Sensitive Data: Determine which data requires special handling (API keys, tokens, PII).
  2. Use @Header for Authentication: Pass API keys and tokens in HTTP headers using the @Header annotation in your Retrofit interface definitions.

     interface ApiService {
         @GET("users")
         Call<List<User>> getUsers(@Header("Authorization") String token); // Use @Header
     
         @POST("login")
         Call<LoginResponse> login(@Body LoginRequest request); // Use @Body for request body
     }

  3. Use @Field, @FieldMap, @Part, and @Body Appropriately:
     • @Field and @FieldMap: For application/x-www-form-urlencoded data (typically POST requests).
     • @Part: For multipart/form-data (e.g., file uploads).
     • @Body: For sending a Java object as the request body (e.g., JSON). Use this for sensitive data that should be in the body, and combine it with POST/PUT/PATCH.
  4. Avoid @Query and @Path for Sensitive Data: Do not use @Query (for query parameters in the URL) or @Path (for path parameters in the URL) to pass sensitive data.
  5. Choose Appropriate HTTP Methods: Use POST, PUT, or PATCH for requests that send sensitive data in the body. Avoid GET for sending sensitive data. This isn't a direct Retrofit annotation, but it's how you use Retrofit.

• Threats Mitigated:

  • Data Exposure via URL Logging: (Severity: High) - Sensitive data in URLs is logged.
  • Data Exposure via Request Body Logging (if misused): (Severity: High) - Improper use of annotations could lead to sensitive data being logged if logging is not carefully managed.

• Impact:

  • Data Exposure via Logging: Risk significantly reduced by using @Header and appropriate HTTP methods, and by avoiding @Query and @Path for sensitive data.

• Currently Implemented:

  • Example: @Header("Authorization") used in ApiService.java.
  • Example: @Body used for POST requests with sensitive data.

• Missing Implementation:

  • Example: Review all Retrofit interface methods to ensure consistent and correct use of annotations.
  • Example: One endpoint incorrectly uses @Query for a user ID; this should be changed to @Path or included in the request body.

Mitigation Strategy: Robust Error Handling (Retrofit Call and Response)

Strategy: Robust Error Handling (Retrofit Call and Response)

• Description:

  1. Use Call.execute() or Call.enqueue(): Use Retrofit's Call object methods to make requests:
     • execute(): For synchronous requests (blocks the current thread).
     • enqueue(): For asynchronous requests (uses a callback).
  2. Handle Response: Check the Response object:
     • response.isSuccessful(): Indicates an HTTP status code in the 200-299 range.
     • response.body(): Gets the deserialized response body (if successful).
     • response.errorBody(): Gets the error body (if not successful). Do not expose this directly to users.
     • response.code(): Gets the HTTP status code.
  3. Catch Exceptions: Wrap Retrofit calls in try-catch blocks to handle:
     • IOException: Network errors.
     • RuntimeException: Other runtime errors (including potential deserialization errors).
  4. Provide User-Friendly Messages: Display generic error messages to users, not raw error messages from response.errorBody().
  5. Consider Custom CallAdapter.Factory (Advanced): For more advanced error handling, you can create a custom CallAdapter.Factory to wrap Retrofit's Call objects and provide a consistent error handling mechanism across your application. This allows you to intercept and transform errors before they reach your application code. This is a more advanced, but directly Retrofit-related, technique.

• Threats Mitigated:

  • Information Disclosure via Error Messages: (Severity: Medium) - Attackers gain insights from error messages.

• Impact:

  • Information Disclosure: Risk significantly reduced by not exposing raw error messages.

• Currently Implemented:

  • Example: try-catch blocks used around Call.execute() in UserRepository.java.

• Missing Implementation:

  • Example: Raw error messages from response.errorBody() are sometimes shown to users.
  • Example: No custom CallAdapter.Factory is used for centralized error handling.