threat-modeling.md

Threat Model Analysis for alibaba/fastjson2

Threat: Unsafe Deserialization / Remote Code Execution (RCE)

• Threat: Unsafe Deserialization / Remote Code Execution (RCE)
  • Description: An attacker crafts a malicious JSON payload designed to exploit fastjson2's deserialization process. This payload, when parsed by fastjson2, can lead to the execution of arbitrary code on the server. This is often achieved by manipulating object instantiation or leveraging known "gadget chains" present in the application's classpath, especially when features like AutoType are enabled or not properly controlled. The attacker sends this malicious JSON to an application endpoint that uses fastjson2 to deserialize it.
  • Impact: Full server compromise, complete control over the application and underlying system, unauthorized data access, data breaches, service disruption, malware installation, and significant reputational damage.
  • Affected fastjson2 Component: JSON.parseObject(), JSON.parseArray(), JSONReader (deserialization functions and components).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Strict Input Validation and Sanitization: Implement rigorous validation and sanitization of all JSON input before deserialization. Define and enforce strict schemas, rejecting any input that deviates.
    • Disable AutoType or Implement Secure Whitelisting: Strongly recommended to disable AutoType globally if your application does not explicitly require it. If AutoType is absolutely necessary, implement a highly restrictive whitelist of explicitly allowed classes for deserialization. Do not rely on blacklists.
    • Keep fastjson2 and Dependencies Up-to-Date: Regularly update fastjson2 and all other dependencies to the latest versions to patch known deserialization vulnerabilities and other security issues. Monitor security advisories specifically for fastjson2.
    • Principle of Least Privilege: Run the application with the minimum necessary privileges to limit the potential damage from a successful RCE exploit.
    • Code Review and Security Audits: Conduct thorough code reviews, specifically focusing on areas where fastjson2 is used for deserialization. Perform regular security audits and penetration testing to identify and address potential deserialization vulnerabilities.
    • Use Safe Deserialization Configurations: Explore and utilize fastjson2's configuration options to restrict deserialization capabilities to only the necessary types and features. Consider using TypeReference to explicitly define expected types during deserialization, avoiding reliance on AutoType.

Threat: Large JSON Payload DoS

• Threat: Large JSON Payload DoS
  • Description: An attacker sends extremely large JSON payloads to the application. When fastjson2 attempts to parse these massive payloads, it consumes excessive server resources (CPU, memory, network bandwidth). This resource exhaustion can lead to a denial of service, making the application unresponsive or unavailable to legitimate users.
  • Impact: Service unavailability for legitimate users, application slowdown, resource exhaustion, potential server crashes, and financial losses due to downtime and service disruption.
  • Affected fastjson2 Component: JSONReader, JSON.parseObject(), JSON.parseArray() (parsing components).
  • Risk Severity: High
  • Mitigation Strategies:
    • Implement Strict Input Size Limits: Enforce limits on the maximum size of incoming JSON requests at both the web server and application levels.
    • Resource Monitoring and Throttling: Implement robust server resource monitoring and request throttling mechanisms to limit the rate of requests and the resources consumed by individual requests.
    • Web Application Firewall (WAF): Deploy a WAF to detect and block malicious requests, including those with excessively large JSON payloads, before they reach the application.
    • Efficient Parsing Configuration (if available): Investigate if fastjson2 offers configuration options for optimized parsing or resource management that can mitigate DoS attacks from large payloads.

Threat: Deeply Nested JSON Payload DoS

• Threat: Deeply Nested JSON Payload DoS
  • Description: An attacker sends JSON payloads with extremely deep nesting levels. Parsing deeply nested JSON structures can cause fastjson2's parsing process to consume excessive CPU resources or lead to stack overflow errors, especially if the parsing algorithm is recursive. This can result in a denial of service, crashing the application or making it unresponsive.
  • Impact: Application crashes, service unavailability, resource exhaustion, potential server instability, and negative user experience.
  • Affected fastjson2 Component: JSONReader, JSON.parseObject(), JSON.parseArray() (parsing components, particularly recursive parsing logic if present).
  • Risk Severity: High
  • Mitigation Strategies:
    • Implement Depth Limits: Enforce limits on the maximum nesting depth of JSON payloads at the application level. Reject requests exceeding the defined depth limit.
    • Consider Iterative Parsing: If possible and supported by fastjson2 or application logic, explore using or configuring fastjson2 for iterative parsing techniques instead of recursive parsing to handle deeply nested structures more efficiently and avoid stack overflow risks.
    • Resource Monitoring and Throttling: Monitor server resources and implement request throttling to mitigate the impact of resource-intensive parsing attempts.
    • WAF with Payload Inspection: A WAF with deep payload inspection capabilities can potentially detect and block requests with excessively deep nesting patterns before they reach the application.

Threat: Parsing Logic Exploits (DoS)

• Threat: Parsing Logic Exploits (DoS)
  • Description: An attacker crafts specifically malformed or edge-case JSON payloads designed to exploit vulnerabilities or inefficiencies within fastjson2's parsing logic itself. These payloads can trigger crashes, infinite loops, or excessive resource consumption within fastjson2's parsing engine, leading to a denial of service. This type of attack targets vulnerabilities in the library's core parsing algorithms.
  • Impact: Application crashes, service unavailability, resource exhaustion, potential server instability, and unpredictable application behavior.
  • Affected fastjson2 Component: JSONReader, JSON.parseObject(), JSON.parseArray() (core parsing logic).
  • Risk Severity: High
  • Mitigation Strategies:
    • Maintain Up-to-Date fastjson2 Version: Regularly update fastjson2 to the latest version to benefit from bug fixes and security patches that address parsing vulnerabilities and improve parsing robustness.
    • Comprehensive Fuzzing and Security Testing: Conduct thorough fuzzing and security testing of the application with a wide range of JSON payloads, including malformed, edge-case, and potentially malicious inputs, to proactively identify parsing vulnerabilities in fastjson2.
    • Robust Error Handling and Recovery: Implement comprehensive error handling in the application to gracefully manage parsing errors and prevent crashes. Ensure the application can recover from parsing failures without causing cascading failures or service disruptions.