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attack-surface.md

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Attack Surface Analysis for go-chi/chi

Attack Surface: Unexpected Route Matching

  • Description: An attacker crafts a malicious URL that unexpectedly matches a route intended for a different purpose, potentially bypassing security controls. This is a direct consequence of how chi handles routing.
  • How Chi Contributes: chi's routing mechanism, while efficient, can be vulnerable if complex patterns (wildcards, regex) are used without careful consideration. The vulnerability arises from how chi matches routes.
  • Example:
    • Route: /admin/{resource} (intended for admin users only)
    • Attacker URL: /admin/../users (might bypass authentication if /users is a public route and the application logic doesn't handle the .. correctly – chi matches the route, and the application is responsible for handling the ..).
  • Impact: Unauthorized access to sensitive data or functionality.
  • Risk Severity: High
  • Mitigation Strategies:
    • Precise Routes: Use the most specific route patterns possible. Avoid overly broad wildcards.
    • Route Testing: Thoroughly test all routing patterns, including edge cases and boundary conditions.
    • Route Visualization: Use chi's debugging features (e.g., middleware.RouteLog) to verify routing logic.
    • Input Validation: Validate and sanitize all path segments, even if they appear to be handled by the router. Specifically, handle .. (parent directory) sequences appropriately. This is crucial because chi delivers the potentially malicious path to the handler.
    • Regular Audits: Regularly review and audit routing configurations.

Attack Surface: Regular Expression Denial of Service (ReDoS)

  • Description: An attacker provides a crafted input string that triggers excessive CPU consumption in a vulnerable regular expression used in a chi route definition, leading to a denial of service. This is a direct vulnerability because the regex is part of the chi routing configuration.
  • How Chi Contributes: chi allows the use of regular expressions directly in route definitions, making it directly responsible for handling (and potentially mis-handling) the regex.
  • Example:
    • Route: chi.Route("/articles/{slug:[a-zA-Z0-9-]+}", ...) (a seemingly simple regex, but could be vulnerable depending on the input).
    • Attacker Input: A very long string with repeating characters designed to exploit backtracking in the regex engine.
  • Impact: Denial of service; the application becomes unresponsive.
  • Risk Severity: High
  • Mitigation Strategies:
    • Avoid Complex Regex: Prefer simpler, more deterministic routing patterns. Avoid nested quantifiers and alternations.
    • Regex Review: Carefully review any regular expressions used in routes for potential ReDoS vulnerabilities.
    • Regex Testing Tools: Use tools specifically designed to detect ReDoS vulnerabilities.
    • Timeouts: Set timeouts on regular expression matching operations (using the Go standard library's regexp package). This is important because chi uses the standard library's regex engine.
    • Alternative Regex Engine: Consider a safer regular expression engine if performance is critical and ReDoS is a significant concern.

Attack Surface: Middleware Ordering Issues

  • Description: Incorrect ordering of middleware in the chi chain leads to security vulnerabilities, such as bypassing authentication or authorization checks. This is a direct consequence of how chi's middleware system works.
  • How Chi Contributes: chi's middleware system relies on the correct ordering of middleware components, and chi executes them in the order they are defined.
  • Example:
    • Authentication middleware placed after a middleware that accesses sensitive data.
  • Impact: Unauthorized access to protected resources.
  • Risk Severity: High
  • Mitigation Strategies:
    • Careful Planning: Carefully plan and document the middleware chain. Understand the dependencies between middleware.
    • Auth First: Ensure authentication and authorization middleware are applied before any middleware that accesses protected resources.
    • Middleware Testing: Thoroughly test the middleware chain with various request scenarios, including unauthorized requests.
    • Code Review: Review middleware configurations to ensure correct ordering.

Attack Surface: Outdated Chi Version

  • Description: Using an outdated version of chi that contains known vulnerabilities within the chi library itself.
  • How Chi Contributes: This is a direct vulnerability if the issue exists within chi's code.
  • Example: Using a version of chi with a known vulnerability that allows for route hijacking due to a bug in chi's routing logic.
  • Impact: Varies depending on the specific vulnerability; could range from minor information disclosure to complete system compromise.
  • Risk Severity: Variable (depends on the vulnerability), potentially Critical.
  • Mitigation Strategies:
    • Regular Updates: Keep chi updated to the latest stable version.
    • Dependency Management: Use a dependency management tool (like Go modules) to track and update dependencies.
    • Vulnerability Monitoring: Monitor security advisories and vulnerability databases for reported issues related to chi and its dependencies.