mitigations.md

Mitigation Strategies Analysis for expressjs/express

Mitigation Strategy: Middleware Management: Principle of Least Privilege & Audits (Express-Specific Aspects)

• Mitigation Strategy: Employ the principle of least privilege for Express middleware and conduct regular audits of that middleware.

• Description:

  1. Inventory (Express Focus): Create a list of all middleware currently used in the Express application. This is found directly in your app.use() calls. Focus on how each middleware interacts with the Express request/response cycle.
  2. Justification (Express Focus): For each middleware, document why it's needed within the context of Express. Is it handling routing, request parsing, response modification, or interacting with Express's error handling? If a middleware's role is purely external (e.g., database interaction), it's less of an Express-specific concern.
  3. Configuration Review (Express Focus): Examine the configuration of each middleware, paying attention to options that affect how Express handles requests and responses. Are there any Express-specific settings (e.g., route-specific middleware, error handling options) that could be tightened?
  4. Vulnerability Scanning: Run npm audit (or yarn audit). This is crucial for all dependencies, but especially important for middleware that directly interacts with the request/response cycle.
  5. Update/Replace: Address vulnerabilities by updating or replacing middleware.
  6. Documentation: Keep the middleware inventory and audit results documented, focusing on the Express-specific aspects.

• Threats Mitigated:

  • Vulnerable Middleware (Severity: High to Critical): Exploitation of vulnerabilities in Express middleware that handles requests/responses can lead to complete application compromise.
  • Unnecessary Exposure (Severity: Low to Medium): Using unnecessary Express middleware increases the attack surface related to request handling.

• Impact:

  • Vulnerable Middleware: Significantly reduces the risk of exploitation by ensuring Express-specific middleware is secure.
  • Unnecessary Exposure: Reduces the Express-specific attack surface.

• Currently Implemented:

  • Example: npm audit is run. Basic inventory of middleware is present.

• Missing Implementation:

  • Example: Formal middleware inventory with Express-specific justification is missing. No regular manual audits focused on Express interaction.

Mitigation Strategy: Secure Middleware Configuration: helmet (Express-Specific Aspects)

• Mitigation Strategy: Implement and thoroughly configure the helmet middleware, focusing on its interaction with Express's response headers.

• Description:

  1. Installation: npm install helmet
  2. Basic Usage: app.use(helmet()); This adds several security-related HTTP headers through Express's response object.
  3. Customization (Express Focus): Configure each helmet middleware, paying attention to how it modifies the Express response:
     • contentSecurityPolicy: Define a strict CSP. This is crucial for controlling which resources Express is allowed to load.
     • hsts: Enforce HTTPS connections through Express.
     • frameguard: Control how Express allows the application to be framed.
     • hidePoweredBy: Remove the X-Powered-By header, which is set by Express by default.
     • xssFilter: Enable, but rely primarily on CSP.
  4. Testing: Verify that the headers are being set correctly by Express.

• Threats Mitigated:

  • XSS (Severity: High): CSP, managed through Express's response, is a primary defense.
  • Clickjacking (Severity: Medium): frameguard, applied via Express, prevents framing.
  • MITM (Severity: High): HSTS, enforced by Express, mandates HTTPS.
  • Information Disclosure (Severity: Low): hidePoweredBy removes an Express-specific header.

• Impact: Directly impacts how Express sets response headers, mitigating several key threats.

• Currently Implemented:

  • Example: helmet is included with default settings.

• Missing Implementation:

  • Example: CSP is not configured. HSTS is not fully configured.

Mitigation Strategy: Secure Middleware Configuration: csurf (Express-Specific Aspects)

• Mitigation Strategy: Implement CSRF protection using csurf, leveraging Express's session management and request handling.

• Description:

  1. Installation: npm install csurf
  2. Session Middleware: csurf relies on Express session middleware (e.g., express-session).
  3. Basic Usage:

     const csrfProtection = csrf({ cookie: true });
     app.use(csrfProtection); // Integrates with the Express request lifecycle.

  4. Token Integration (Express Focus): Use req.csrfToken() (an Express request object method) to get the token and include it in forms. This is directly tied to Express's request handling.
  5. AJAX Requests: Include the token in a request header (handled by Express).
  6. Error Handling: Handle EBADCSRFTOKEN errors within Express's error handling.

• Threats Mitigated:

  • Cross-Site Request Forgery (CSRF) (Severity: High): csurf integrates with Express to prevent CSRF.

• Impact: Directly uses Express's request and session mechanisms to prevent CSRF.

• Currently Implemented:

  • Example: No CSRF protection.

• Missing Implementation:

  • Example: Entire csurf implementation is missing.

Mitigation Strategy: Secure Middleware Configuration: Rate Limiting (express-rate-limit) (Express-Specific Aspects)

• Mitigation Strategy: Implement rate limiting using express-rate-limit, controlling request flow within Express.

• Description:

  1. Installation: npm install express-rate-limit
  2. Basic Usage:

     const limiter = rateLimit({ /* options */ });
     app.use(limiter); // Applied directly to the Express application.

  3. Route-Specific Limits (Express Focus): Apply different rate limits to different Express routes.
  4. Keying (Express Focus): Use different keys (e.g., IP, user ID from req.user) within the context of Express requests.
  5. Error Handling (Express Focus): Customize the error response within Express's error handling.

• Threats Mitigated:

  • Brute-Force Attacks (Severity: High): Limits requests processed by Express.
  • DoS Attacks (Severity: High): Prevents overwhelming the Express server.

• Impact: Directly controls the rate of requests handled by Express.

• Currently Implemented:

  • Example: Basic global rate limiter.

• Missing Implementation:

  • Example: No route-specific limits. No custom Express error handling.

Mitigation Strategy: Secure Middleware Configuration: Body Parsing Limits (Express-Specific Aspects)

• Mitigation Strategy: Configure Express's body parsing middleware (express.json(), express.urlencoded()) with size limits.

• Description:

  1. Identify Body Parsers: These are specifically Express middleware: express.json() and express.urlencoded().
  2. Set limit Option:

     app.use(express.json({ limit: '100kb' })); // Directly configures Express's JSON parser.
     app.use(express.urlencoded({ extended: true, limit: '50kb' })); // Configures Express's URL-encoded parser.

  3. Content Type (Express Focus): Only enable the parsers you need for your Express routes.
  4. Error Handling (Express Focus): Handle errors within Express's error handling related to exceeding the body size.

• Threats Mitigated:

  • DoS Attacks (Severity: High): Prevents large requests from overwhelming Express's parsing capabilities.

• Impact: Directly controls how Express parses request bodies.

• Currently Implemented:

  • Example: express.json() is used without limits.

• Missing Implementation:

  • Example: limit option is not set.

Mitigation Strategy: Secure Routing: Explicit Definitions & Input Validation (Express-Specific Aspects)

• Mitigation Strategy: Define Express routes explicitly, avoid overly broad patterns, and validate route parameters within Express's routing system.

• Description:

  1. Specific Routes: Use specific route paths in your app.get(), app.post(), etc., calls. This is fundamental to Express routing.
  2. Route Parameter Validation (Express Focus): Validate route parameters (accessed via req.params) before using them. Use a validation library within your Express route handlers.
  3. Regular Expression Caution (Express Focus): If using regular expressions within Express routes (using path-to-regexp), be extremely careful.
  4. Route Ordering (Express Focus): The order of route definitions in Express matters.
  5. Method-Specific Handlers (Express Focus): Use specific HTTP methods (GET, POST, etc.) within Express.

• Threats Mitigated:

  • Unintended Functionality Exposure (Severity: Medium to High): Prevents access to unintended Express routes.
  • Injection Attacks (Severity: High): Validation within Express route handlers mitigates injections.
  • ReDoS (Severity: Medium to High): Careful use of regular expressions within Express routing is crucial.

• Impact: Directly affects how Express matches and handles routes.

• Currently Implemented:

  • Example: Routes are generally specific, but validation is inconsistent.

• Missing Implementation:

  • Example: Consistent validation library not used in all Express route handlers.

Mitigation Strategy: Secure Error Handling & 404s (Express-Specific Aspects)

• Mitigation Strategy: Implement custom 404 and global error handlers within Express.

• Description:

  1. Custom 404 Handler (Express Focus): Create an Express middleware function specifically for 404s:

     app.use((req, res, next) => { // This is an Express middleware.
       res.status(404).send('Not Found');
     });

  2. Global Error Handler (Express Focus): Create an Express middleware function for all unhandled errors:

     app.use((err, req, res, next) => { // This is an Express error-handling middleware.
       console.error(err.stack);
       res.status(500).send('Something broke!');
     });

  3. Avoid res.send(err) (Express Focus): Never send the raw error object through Express's res.send().
  4. Environment-Specific Handling (Express Focus): Use environment variables to control error detail within Express.

• Threats Mitigated:

  • Information Disclosure (Severity: Low to Medium): Prevents leaking information through Express's error responses.

• Impact: Directly controls how Express handles errors and 404s.

• Currently Implemented:

  • Example: Basic global error handler logs to console, sends error to client.

• Missing Implementation:

  • Example: No custom 404 handler. Error handler leaks info.

Mitigation Strategy: Regular Expression Denial of Service (ReDoS) Prevention (Express-Specific Aspects)

• Mitigation Strategy: Minimize and vet regular expressions used within Express routes (which use path-to-regexp).

• Description:

  1. Prefer String Routes: Use simple string-based routes in app.get(), app.post(), etc., whenever possible. This avoids path-to-regexp entirely.
  2. ReDoS Testing (Express Focus): If you must use regular expressions in Express routes, use a ReDoS checker.
  3. Input Validation (Express Focus): Validate input before it reaches the Express routing layer (and path-to-regexp).
  4. Simple Expressions (Express Focus): Keep regular expressions within Express routes as simple as possible.
  5. Timeouts/Alternative Libraries (Advanced): Consider, but these are less directly tied to Express itself.

• Threats Mitigated:

  • ReDoS (Severity: Medium to High): Specifically targets ReDoS vulnerabilities within Express's routing mechanism.

• Impact: Directly addresses ReDoS risks arising from Express's use of path-to-regexp.

• Currently Implemented:

  • Example: No specific ReDoS prevention.

• Missing Implementation:

  • Example: Regular expressions in routes are not tested. Input validation doesn't limit input to routing.