attack-surface.md

Attack Surface Analysis for dart-lang/shelf

Attack Surface: Path Traversal (via shelf_static or custom handlers)

• Description: Attackers use ../ sequences in URLs to attempt to access files outside the intended directory.
  • How Shelf Contributes: shelf_static and custom file-serving logic within shelf handlers require careful path sanitization, which is the developer's responsibility. shelf does not automatically prevent this, making it a direct concern.
  • Example: GET /static/../../etc/passwd
  • Impact: Unauthorized access to sensitive files on the server, potentially leading to complete system compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Developers: Never directly use user-provided input to construct file paths.
    • Developers: Sanitize and validate all URL path components influencing file access.
    • Developers: Use path.normalize from the path package to resolve relative paths safely.
    • Developers: After normalization, verify that the resulting path is within the intended directory (using string comparison or a dedicated library).
    • Developers/Users: Consider using a dedicated, well-vetted static file server (like nginx) in production instead of relying solely on shelf_static.

Attack Surface: Routing Ambiguities and Overlapping Routes

• Description: Poorly defined routes with overlaps can lead to unexpected handler invocation.
  • How Shelf Contributes: shelf's routing logic depends on the order and specificity of route definitions. Ambiguities are possible if not carefully managed, and this is a direct function of how shelf handles routing.
  • Example: /users/<id> and /users/admin could be ambiguous if not handled correctly.
  • Impact: Attackers might reach unintended handlers, potentially bypassing security checks or accessing unauthorized resources.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers: Design routes to be clear and unambiguous, avoiding overlaps.
    • Developers: Use shelf_router for explicit and well-defined route definitions.
    • Developers: Thoroughly test routing logic with various inputs, including edge cases.
    • Developers: Log routing decisions to aid in debugging and auditing.

Attack Surface: Regular Expression Denial of Service (ReDoS) in Routing

• Description: Attackers exploit poorly crafted regular expressions in route definitions to cause excessive CPU consumption.
  • How Shelf Contributes: If shelf_router is used with regular expressions in route patterns, those expressions are directly used for matching by shelf. This is a direct vulnerability introduced by shelf's routing mechanism.
  • Example: A route defined with the regex ^/(a+)+$ could be vulnerable.
  • Impact: Denial of service due to server resource exhaustion.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers: Avoid complex or nested regular expressions in routing.
    • Developers: If regular expressions are necessary, use a library that provides protection against ReDoS (e.g., by limiting backtracking).
    • Developers: Thoroughly test regular expressions with various inputs, including potentially malicious ones.
    • Developers: Prefer simpler string matching or parameter extraction where possible.

Attack Surface: Middleware Ordering Issues

• Description: Incorrect order of middleware execution can bypass security checks.
  • How Shelf Contributes: shelf allows chaining middleware, and the order is critical for security. The framework itself provides the mechanism for middleware chaining, making ordering a direct shelf concern.
  • Example: Authentication middleware placed after authorization middleware.
  • Impact: Security checks might be bypassed, leading to unauthorized access.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers: Carefully consider the order of middleware components.
    • Developers: Place security-related middleware (authentication, authorization, input validation) before middleware that handles business logic or accesses sensitive data.
    • Developers: Document the intended order and purpose of each middleware component.

Attack Surface: Exception Handling Failures in Middleware/Handlers

• Description: Unhandled exceptions can leak sensitive information or cause denial of service.
  • How Shelf Contributes: While application logic is responsible for handling exceptions, shelf's request/response pipeline and the way it handles uncaught exceptions within middleware and handlers are directly relevant. shelf provides a default error handler, but it might reveal too much information in production.
  • Example: An unhandled database exception revealing database connection details.
  • Impact: Information disclosure (stack traces, internal implementation details), potential denial of service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers: Implement robust error handling in all middleware and handlers.
    • Developers: Catch all expected exceptions and return appropriate HTTP error responses (e.g., 500 Internal Server Error) without revealing sensitive information.
    • Developers: Use a centralized error handling mechanism for consistency.
    • Developers: Log all unhandled exceptions for debugging and auditing.

Attack Surface: Improper Handling of Futures

• Description: Incorrect use of Futures can lead to race conditions, data inconsistencies, or unhandled exceptions.
  • How Shelf Contributes: shelf heavily relies on asynchronous programming with Futures for its core request handling. The framework's design necessitates the correct use of Futures.
  • Example: Accessing request.read() without awaiting it.
  • Impact: Race conditions, data corruption, unhandled exceptions, denial of service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers: Always await Futures when their results are needed.
    • Developers: Use try-catch blocks within async functions to handle potential errors.
    • Developers: Use .catchError or .whenComplete to handle errors and cleanup resources associated with Futures.