Threat Model Analysis for square/retrofit

Threat: Base URL Manipulation

Threat: Base URL Manipulation
- Description: An attacker modifies the application's configuration to change the Retrofit base URL, redirecting all API calls to a malicious server. The attacker can then intercept, modify, or fabricate API requests and responses.
- Impact: Complete compromise of API communication; data theft, data manipulation, impersonation of the legitimate server, leading to data breaches, account takeovers, and application malfunction.
- Retrofit Component Affected: Retrofit.Builder().baseUrl() - The base URL setting is the direct target.
- Risk Severity: Critical
- Mitigation Strategies:
  - Securely store configuration data (e.g., Android Keystore, encrypted preferences).
  - Implement code signing and integrity checks.
  - Consider hardcoding and obfuscating the base URL (trade-off: reduced flexibility).
  - Use certificate pinning (see below) as a crucial additional defense.

Threat: Malicious Interceptor Injection
- Description: An attacker injects a malicious OkHttp Interceptor into the Retrofit client. The interceptor can modify requests or responses, stealing sensitive data, injecting malicious content, or altering API behavior.
- Impact: Data tampering, data leakage, potential for code execution (depending on how the application handles responses), leading to severe security breaches.
- Retrofit Component Affected: OkHttpClient.Builder().addInterceptor() and OkHttpClient.Builder().addNetworkInterceptor() - The interceptor mechanism is the attack vector.
- Risk Severity: High to Critical (depending on the interceptor's capabilities)
- Mitigation Strategies:
  - Carefully vet all dependencies, ensuring libraries providing interceptors are trusted and updated.
  - Minimize interceptor usage; use only when absolutely necessary.
  - Thoroughly review and audit all interceptor code.
  - Implement robust client-side input validation and output encoding.

Threat: Compromised Converter Factory
- Description: An attacker replaces the legitimate converter factory (e.g., GsonConverterFactory) with a malicious one, manipulating the serialization/deserialization process. This can lead to data corruption, injection of malicious data, or potentially code execution.
- Impact: Data corruption, potential for code execution (if the attacker can inject and trigger malicious code), leading to significant security vulnerabilities.
- Retrofit Component Affected: Retrofit.Builder().addConverterFactory() - The converter factory mechanism is the target.
- Risk Severity: High to Critical (depending on the converter's capabilities and how the application handles deserialized data)
- Mitigation Strategies:
  - Use well-vetted and maintained converter factories from trusted sources (e.g., official libraries).
  - Regularly update dependencies to address known vulnerabilities.
  - Avoid custom converter factories unless absolutely necessary; if used, rigorously review and test them.

Threat: Missing or Incorrect Certificate Pinning
- Description: The application fails to implement certificate pinning or implements it incorrectly, allowing a Man-in-the-Middle (MitM) attack with a fake certificate. The attacker intercepts and decrypts communication.
- Impact: Complete compromise of API communication confidentiality and integrity; data theft and potential modification.
- Retrofit Component Affected: OkHttpClient.Builder().certificatePinner() (Retrofit relies on OkHttp for TLS/SSL).
- Risk Severity: Critical
- Mitigation Strategies:
  - Implement certificate pinning using OkHttp's CertificatePinner.
  - Regularly update pinned certificates and have a robust update process.
  - Thoroughly test certificate pinning.