mitigations.md

Mitigation Strategies Analysis for dart-lang/shelf

Mitigation Strategy: Explicit Middleware Ordering and Testing (using shelf's Pipeline)

• Description:

  1. Centralize Middleware: Create a dedicated file (e.g., middleware.dart) to define and manage all shelf middleware.
  2. Define Order (Pipeline): Within this file, explicitly define the order in which middleware should be applied using shelf's Pipeline. Prioritize security-related middleware (authentication, authorization, CORS using shelf_cors_headers) before any middleware that handles business logic or data access. Example:

     final handler = Pipeline()
         .addMiddleware(corsMiddleware()) // From shelf_cors_headers
         .addMiddleware(authenticationMiddleware()) // Custom or from a package
         .addMiddleware(authorizationMiddleware())  // Custom or from a package
         .addHandler(myBusinessLogicHandler);

  3. Unit Tests (shelf.Request/Response): Write unit tests for each individual middleware component, using shelf.Request and shelf.Response objects to simulate requests and verify responses.
  4. Integration Tests (shelf.Handler): Write integration tests for the entire middleware chain, using a shelf.Handler that represents the complete pipeline. Simulate various request scenarios, including bypass attempts.
  5. Fail-Closed (shelf.Response): In each middleware, if a security check fails, immediately return a shelf.Response indicating failure (e.g., 401, 403) and do not call innerHandler.

• Threats Mitigated:

  • Middleware Bypass (Severity: High): Attackers could access protected resources by circumventing shelf middleware.
  • Incorrect Authorization (Severity: High): Misconfigured authorization middleware could grant incorrect access.
  • CORS Misconfiguration (Severity: Medium): Improper shelf_cors_headers configuration could allow unauthorized cross-origin requests.

• Impact:

  • Middleware Bypass: Significantly reduces unauthorized access risk.
  • Incorrect Authorization: Enforces correct authorization rules.
  • CORS Misconfiguration: Prevents unauthorized cross-origin requests.

• Currently Implemented: (Example: Partially implemented. Middleware order is defined, but integration tests are missing.)

• Missing Implementation: (Example: Comprehensive integration tests for the shelf middleware chain are missing.)

Mitigation Strategy: Host Header Validation (using shelf.Request)

• Description:

  1. Whitelist: Create a list of allowed hostnames.
  2. Validation Middleware (shelf.Request): Create a shelf middleware component that extracts the Host header using request.requestedUri.host from the shelf.Request object.
  3. Comparison: Compare the extracted host against the whitelist (case-insensitive).
  4. Rejection (shelf.Response): If the host is invalid, return a 400 Bad Request shelf.Response and do not proceed.

• Threats Mitigated:

  • Host Header Attack (Severity: High): Prevents manipulating the Host header.
  • Cache Poisoning (Severity: Medium): Helps prevent some cache poisoning attacks.

• Impact:

  • Host Header Attack: Eliminates this attack vector.
  • Cache Poisoning: Reduces related cache poisoning risks.

• Currently Implemented: (Example: Not implemented.)

• Missing Implementation: (Example: Host header validation middleware is missing.)

Mitigation Strategy: Request Header Sanitization (using shelf.Request)

• Description:

  1. Identify Critical Headers: Determine which headers require validation/sanitization.
  2. Sanitization Functions: Create functions to sanitize/validate specific header values.
  3. Middleware Application (shelf.Request): Apply these functions within shelf middleware, using request.headers to access header values, before using them in application logic.

• Threats Mitigated:

  • Injection Attacks (Severity: High): Prevents injecting malicious data via headers.
  • Request Smuggling (Severity: High): Reduces request smuggling risks.

• Impact:

  • Injection Attacks: Significantly reduces injection vulnerability risks.
  • Request Smuggling: Mitigates a complex attack vector.

• Currently Implemented: (Example: Basic sanitization for some headers.)

• Missing Implementation: (Example: Comprehensive sanitization is missing for several headers.)

Mitigation Strategy: Explicit and Audited Route Definitions (using shelf_router)

• Description:

  1. Centralized Routing (shelf_router): Define all routes in one place using shelf_router.
  2. Explicit Patterns (shelf_router): Use clear, specific route patterns with shelf_router. Avoid broad wildcards.
  3. Route Documentation: Document each route's purpose and security.
  4. Regular Audits: Periodically review defined routes.
  5. Separate Routers (shelf_router): Use separate shelf_router instances for internal and external APIs.
  6. mount with Caution (shelf_router): Carefully review the route structure when using shelf_router's mount.

• Threats Mitigated:

  • Unintended Route Exposure (Severity: High): Prevents access to unintended endpoints.
  • Information Disclosure (Severity: Medium): Reduces information leakage.

• Impact:

  • Unintended Route Exposure: Reduces the attack surface.
  • Information Disclosure: Minimizes information leakage.

• Currently Implemented: (Example: Routes defined in routes.dart, but audits are infrequent.)

• Missing Implementation: (Example: Regular route audits are not performed.)

Mitigation Strategy: Constant-Time Comparisons for Authentication (within shelf Middleware)

• Description:

  1. Identify Secret Comparisons: Locate comparisons of passwords, tokens, etc., within your shelf middleware.
  2. Use crypto Package: Use Dart's crypto package (or a similar library) for constant-time comparisons.
  3. Replace Direct Comparisons: Replace direct comparisons (e.g., ==) with constant-time functions.
  4. Avoid Early Returns: Structure the logic to avoid early returns based on the comparison, maintaining consistent timing.

• Threats Mitigated:

  • Timing Attacks (Severity: Medium): Prevents timing-based information leakage.

• Impact:

  • Timing Attacks: Eliminates timing attack risks related to secret comparisons.

• Currently Implemented: (Example: Not implemented.)

• Missing Implementation: (Example: Direct string comparisons are used in authentication middleware.)

Mitigation Strategy: File Size Limits (using shelf_static)

• Description:

  1. Use shelf_static: If serving static files, use the shelf_static package.
  2. Configure maxSize: Set the maxSize parameter in createStaticHandler to limit the maximum file size that can be served. Example:

     import 'package:shelf_static/shelf_static.dart';
     
     final handler = createStaticHandler('public', defaultDocument: 'index.html', maxSize: 10 * 1024 * 1024); // 10 MB limit

• Threats Mitigated:

  • Denial of Service (DoS) (Severity: Medium): Prevents attackers from requesting excessively large files to exhaust server resources.

• Impact:

  • Denial of Service: Improves resilience to DoS attacks targeting file serving.

• Currently Implemented: (Example: shelf_static is used, but maxSize is not configured.)

• Missing Implementation: (Example: The maxSize parameter is not set, allowing arbitrarily large files to be served.)

Mitigation Strategy: Custom Rate Limiting Middleware (using shelf)

• Description:

  1. Implement Middleware: Create a custom shelf middleware to track request counts.
  2. Track Requests: Store request counts per IP address or user (using a shelf.Request extension or a persistent store like Redis if needed for distributed systems).
  3. Enforce Limits: Check if the request count exceeds a predefined limit within a time window.
  4. Reject Requests (shelf.Response): If the limit is exceeded, return a 429 Too Many Requests shelf.Response.

• Threats Mitigated:

  • Denial of Service (DoS) (Severity: Medium to High): Prevents attackers from overwhelming the server with requests.
  • Brute-Force Attacks (Severity: Medium): Can help mitigate brute-force attacks against authentication endpoints.

• Impact:

  • Denial of Service: Improves resilience to DoS attacks.
  • Brute-Force Attacks: Makes brute-force attacks more difficult.

• Currently Implemented: (Example: Not implemented.)

• Missing Implementation: (Example: No rate limiting is implemented, leaving the application vulnerable to request flooding.)