Attack Surface: TLS/SSL Misconfiguration
Description: Incorrect TLS/SSL settings within OkHttp can expose communications to interception and manipulation. This is the most critical area.
OkHttp Contribution: OkHttp provides extensive TLS/SSL configuration options (e.g., ConnectionSpec, CertificatePinner, custom TrustManager, custom HostnameVerifier). Incorrect use of any of these creates the vulnerability.
Example: Using a custom TrustManager that doesn't properly validate certificates (e.g., accepts all certificates), or allowing weak cipher suites via an improperly configured ConnectionSpec, or a flawed HostnameVerifier.
Impact: Man-in-the-middle (MitM) attacks, data interception, data modification. Complete compromise of communication security.
Risk Severity: Critical
Mitigation Strategies:
* Strongly prefer using the system's default TrustManager and HostnameVerifier. Avoid custom implementations unless absolutely necessary and you have deep expertise in TLS.
* Explicitly configure ConnectionSpec to use only strong cipher suites and TLS 1.2 or 1.3. Never allow known weak ciphers or outdated TLS versions. Use ConnectionSpec.RESTRICTED_TLS as a starting point.
* If using certificate pinning (via CertificatePinner), implement it correctly and thoroughly test it. Have a robust plan for pin updates and handling pin failures. Incorrect pinning is worse than no pinning.
* Regularly review and update TLS configurations based on current best practices and security advisories.
* Ensure the underlying platform (Android, Java) is up-to-date and configured securely, as OkHttp relies on platform-provided TLS capabilities.
Attack Surface: Protocol Downgrade Attacks (Controlled by OkHttp Configuration)
Description: While the environment plays a role, OkHttp's configuration can prevent downgrades, making this a direct OkHttp concern.
OkHttp Contribution: OkHttp's protocols() method allows developers to explicitly control which HTTP versions are allowed.
Example: The application doesn't explicitly set allowed protocols, allowing a MitM to force a downgrade to HTTP/1.1.
Impact: Increased susceptibility to request smuggling and other HTTP/1.1-specific attacks.
Risk Severity: High
Mitigation Strategies:
* Use OkHttpClient.Builder.protocols() to explicitly restrict the allowed protocols to Protocol.HTTP_2 and/or Protocol.H2_PRIOR_KNOWLEDGE (if appropriate) and Protocol.HTTP_3. Do not include Protocol.HTTP_1_1 in the list unless absolutely necessary for compatibility with a specific, trusted server. If you must support HTTP/1.1, ensure the server is well-configured to mitigate HTTP/1.1 vulnerabilities.
Attack Surface: Proxy Misconfiguration (Directly via OkHttp)
Description: Incorrect proxy settings within OkHttp can lead to traffic interception.
OkHttp Contribution: OkHttp allows configuring proxies via OkHttpClient.Builder.proxy() and proxySelector(). The vulnerability lies in how these are used.
Example: The application is configured to use a user-supplied proxy without validation, and the user provides a malicious proxy address. Or, a hardcoded proxy is used without proper authentication.
Impact: Traffic interception, data modification, redirection to malicious sites.
Risk Severity: High
Mitigation Strategies:
* Never allow users to directly configure the proxy used by OkHttp without strict validation and sanitization. Ideally, avoid user-configurable proxies entirely.
* If a proxy is required, use a known, trusted, and authenticated proxy server. Hardcode the proxy configuration if possible, and ensure the proxy server itself is secure.
* If using proxySelector(), ensure it handles proxy failures gracefully and never falls back to an insecure configuration (e.g., direct connection when a proxy is expected).
Attack Surface: Redirect Handling Vulnerabilities (Controlled by OkHttp)
Description: OkHttp's redirect handling can be misused to follow malicious redirects.
OkHttp Contribution: OkHttp follows redirects by default, controlled by followRedirects() and followSslRedirects().
Example: A server returns a 302 redirect to a malicious URL, and OkHttp automatically follows it because redirects are enabled.
Impact: Phishing attacks, malware distribution, exploitation of open redirects on trusted servers.
Risk Severity: High
Mitigation Strategies:
* If redirects are not needed, disable them with followRedirects(false) and followSslRedirects(false). This is the safest option.
* If redirects are necessary, validate the Location header in the response before OkHttp follows the redirect. Implement whitelisting of allowed redirect domains if possible. Do not blindly follow redirects.
* Limit the number of redirects followed to prevent infinite loops (OkHttp has a default limit, but consider lowering it if appropriate).
Attack Surface: Header Injection (via OkHttp's Header Handling)
Description: Injecting malicious HTTP headers through OkHttp's request building.
OkHttp Contribution: OkHttp provides methods for setting request headers (e.g., Headers.Builder). The vulnerability is in how user input is used with these methods.
Example: An attacker provides a username containing newline characters and malicious header values, which are then included in a request header using Headers.Builder.add().
Impact: Request smuggling, response splitting, cache poisoning, session fixation.
Risk Severity: High
Mitigation Strategies:
* Strictly validate and sanitize all user-provided data before using it in HTTP headers. Use OkHttp's Headers.Builder correctly, and ensure header names and values conform to RFC specifications. Never construct headers from raw, unsanitized strings.
* Consider using a dedicated library for header sanitization to ensure thoroughness. Assume all user input is potentially malicious.