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attack-surface.md

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Attack Surface Analysis for nikic/fastroute

Attack Surface: Regular Expression Denial of Service (ReDoS)

  • Description: Attackers exploit poorly crafted regular expressions in route definitions to cause excessive CPU consumption, leading to a denial of service.
  • FastRoute Contribution: FastRoute's feature of allowing regular expression constraints within route definitions (e.g., {param:\d+}) directly introduces this attack surface if developers use vulnerable regex patterns.
  • Example:
    • Route Definition: /api/v1/users/{username:^([a-zA-Z0-9]+)*$} (Vulnerable regex with nested quantifiers)
    • Malicious URL: /api/v1/users/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa! (Input designed to trigger catastrophic backtracking in the regex engine)
    • Impact: Server CPU spikes to 100%, application becomes unresponsive, effectively denying service to legitimate users.
    • Risk Severity: High to Critical (depending on the severity of service disruption and ease of exploitation)
    • Mitigation Strategies:
      • Secure Regex Design: Carefully design and rigorously test all regular expressions used in route constraints. Avoid using constructs known to be prone to ReDoS, such as nested quantifiers or overlapping alternations. Prefer simpler, more efficient regex patterns.
      • Regex Security Analyzers: Utilize static analysis tools or online regex analyzers to identify potential ReDoS vulnerabilities in route definitions before deployment.
      • Input Sanitization and Validation (Pre-Routing): While regex constraints are a form of validation, consider additional input sanitization or validation before routing to catch potentially malicious inputs early and prevent them from reaching the regex engine.
      • Web Application Firewall (WAF): Deploy a WAF capable of detecting and blocking requests that exhibit ReDoS attack patterns. WAFs can analyze request parameters and identify suspicious regex-triggering inputs.

Attack Surface: Route Definition Complexity and Resource Exhaustion

  • Description: Defining an extremely large number of routes, especially with complex patterns, can increase the computational resources required for route matching, potentially leading to resource exhaustion and denial of service.
  • FastRoute Contribution: FastRoute's design, while optimized, still requires processing route definitions to find a match. An excessive number of routes, particularly with intricate patterns or optional segments, increases the workload for each incoming request.
  • Example:
    • Scenario: An application defines thousands of routes, many with multiple optional segments and parameter constraints, leading to a large and complex routing tree within FastRoute.
    • Attack Vector: An attacker floods the application with requests, even for valid but less frequently used routes. The routing library spends significant CPU time iterating through the massive route collection for each request.
    • Impact: Increased server load, performance degradation for all users, potential application slowdown or even crash due to memory exhaustion or CPU overload under heavy load. This can lead to a denial of service.
    • Risk Severity: High (Can lead to significant performance degradation and potential DoS under load)
    • Mitigation Strategies:
      • Optimize Route Structure: Design routes to be as concise and efficient as possible. Avoid unnecessary complexity in route patterns and minimize the number of optional segments if feasible.
      • Route Grouping and Modularization: Organize routes into logical groups or modules. If possible, load only relevant route groups based on application context or subdomains to reduce the initial route set loaded into FastRoute.
      • Caching (Application Level): Implement caching mechanisms at the application level to store the results of route matching. Cache the resolved route handler for frequently accessed routes to bypass the route matching process for subsequent requests.
      • Rate Limiting and Request Throttling: Implement rate limiting to restrict the number of requests from a single IP or user, mitigating the impact of request flooding aimed at exhausting routing resources.
      • Resource Monitoring and Alerting: Monitor server CPU and memory usage. Set up alerts to detect unusual spikes in resource consumption that might indicate a resource exhaustion attack targeting the routing layer.