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Attack Tree Analysis for square/retrofit

Objective: To exfiltrate sensitive data from the application or execute arbitrary code on the application's backend server by exploiting Retrofit-specific vulnerabilities or misconfigurations.

Attack Tree Visualization

[Attacker's Goal: Exfiltrate Data or Execute Arbitrary Code] | |--- [Exploit Retrofit Configuration/Usage] | | | |--- [1a. MITM w/o Proper Retrofit Config] | |--- [Exploit Dependencies of Retrofit] | |--- [4. Exploit Converter Vulnerabilities] | |--- [4a. Exploit Known Converter Vuln. (e.g., Jackson RCE)] |--- [4b. Exploit Known Converter Vuln. (e.g., Gson DoS)] |--- [4c. Supply Malicious Config to Existing Converter (e.g., Gson, Jackson)]

Attack Tree Path: 1a. MITM w/o Proper Retrofit Config

  • Description: An attacker intercepts network traffic between the application and the server because the application does not properly implement TLS/SSL and, crucially, certificate pinning. Retrofit relies on the underlying OkHttpClient for secure communication, and if this is not configured correctly, the application is vulnerable to Man-in-the-Middle attacks. The attacker can then view and modify requests and responses, potentially stealing sensitive data (credentials, API keys, user data) or injecting malicious data.
  • Likelihood: Medium (High if on a public/compromised network or if no HTTPS is used)
  • Impact: Very High (Complete compromise of communication, leading to data theft or potentially code execution if the attacker can modify responses to include malicious payloads.)
  • Effort: Low (Readily available tools like mitmproxy, Burp Suite, etc., make this easy.)
  • Skill Level: Low (Basic understanding of networking and MITM tools is sufficient.)
  • Detection Difficulty: Medium (Requires network traffic analysis. Easier to detect if no HTTPS is used; harder with HTTPS but no pinning. Application-level monitoring can help detect anomalous behavior.)
  • Mitigation:
    • Implement certificate pinning using CertificatePinner in OkHttpClient.Builder.
    • Use a strong TLS configuration.
    • Regularly update pinned certificates.
    • Consider using a network security configuration (Android) or similar mechanisms.
    • Never trust all certificates.

Attack Tree Path: 4a. Exploit Known Converter Vulnerability (e.g., Jackson RCE)

  • Description: The application uses a vulnerable version of a data converter library (e.g., Jackson, Gson) that has a known Remote Code Execution (RCE) vulnerability. Attackers can craft malicious input (e.g., a specially crafted JSON payload) that, when deserialized by the vulnerable converter, triggers the execution of arbitrary code on the application's backend. This is a classic deserialization vulnerability.
  • Likelihood: Low to Medium (Depends on the specific vulnerability and whether a patch is applied. Higher if the application uses an outdated version of a popular library.)
  • Impact: Very High (Complete system compromise; the attacker can execute arbitrary code.)
  • Effort: Low to Medium (Public exploits for known vulnerabilities are often available.)
  • Skill Level: Low to Medium (Depends on the complexity of the exploit; script kiddies can often use publicly available exploits.)
  • Detection Difficulty: Medium (Requires vulnerability scanning and potentially dynamic analysis. Intrusion detection systems might detect known exploit patterns.)
  • Mitigation:
    • Keep converter libraries (Jackson, Gson, etc.) updated to the latest versions.
    • Monitor for CVEs related to your chosen converters.
    • Implement input validation and sanitization before deserialization.
    • Use a Web Application Firewall (WAF) to filter malicious payloads.

Attack Tree Path: 4b. Exploit Known Converter Vulnerability (e.g., Gson DoS)

  • Description: Similar to 4a, but the vulnerability leads to a Denial-of-Service (DoS) rather than RCE. The attacker sends a crafted input that causes the converter to consume excessive resources (CPU, memory), making the application unresponsive.
  • Likelihood: Low to Medium
  • Impact: Medium (Service disruption)
  • Effort: Low to Medium
  • Skill Level: Low to Medium
  • Detection Difficulty: Medium (Performance monitoring and anomaly detection)
  • Mitigation:
    • Keep converter libraries updated.
    • Implement input validation and size limits.
    • Use rate limiting and other DoS prevention mechanisms.

Attack Tree Path: 4c. Supply Malicious Config to Existing Converter (e.g., Gson, Jackson)

  • Description: Even with up-to-date converter libraries, insecure configuration can lead to vulnerabilities. The most common example is enabling polymorphic type handling in Jackson (enableDefaultTyping()) without proper safeguards. This allows an attacker to specify arbitrary classes to be instantiated during deserialization, potentially leading to RCE. Similar vulnerabilities can exist in other converters if they are configured to handle untrusted input in an unsafe way.
  • Likelihood: Medium (This is a common misconfiguration, especially with Jackson.)
  • Impact: High to Very High (Potential for code execution, data exfiltration.)
  • Effort: Low to Medium (Exploits for common misconfigurations are often publicly available.)
  • Skill Level: Low to Medium (Requires understanding of deserialization vulnerabilities.)
  • Detection Difficulty: Medium to High (Requires careful configuration review and potentially dynamic analysis. Static analysis tools can help identify insecure configurations.)
  • Mitigation:
    • Configure converters securely. Avoid enabling features that are not needed.
    • For Jackson, do not enable default typing (enableDefaultTyping()) unless you fully understand the security implications and have implemented appropriate whitelisting of allowed classes. Use @JsonTypeInfo with a safe TypeIdResolver or a custom TypeResolverBuilder.
    • For Gson, be aware of potential issues with complex object graphs and custom type adapters. Avoid deserializing untrusted data into generic types.
    • Implement strict input validation and sanitization.
    • Use a "deny-list" approach for deserialization, only allowing known safe types.