mitigations.md

Mitigation Strategies Analysis for koajs/koa

Mitigation Strategy: Middleware Ordering and Centralized Error Handling (Koa-Specific)

• Description:

  1. Koa Middleware Chain Planning: Before implementing any Koa middleware, meticulously plan the execution order. Document this order, clearly stating the purpose of each middleware and its dependencies. This is crucial in Koa due to its reliance on the middleware chain for all request processing.
  2. Early Security Middleware: Within the Koa application setup (app.use(...)), position security-related middleware (authentication, authorization, rate limiting, request validation before it reaches the route handler) as early as possible. This leverages Koa's sequential execution to prevent unauthorized or malformed requests from reaching sensitive parts of the application.
  3. Koa-Specific Error Handling: Implement a custom error-handling middleware as the very first middleware in the Koa stack (app.use(...)). This middleware should:
     • Use a try...catch block around await next(). This is essential to catch errors thrown by any subsequent Koa middleware.
     • Within the catch block:
       • Log error details (including stack traces from err.stack) to a secure location (file, dedicated service). Never expose these details in the response sent to the client.
       • Determine an appropriate HTTP status code based on the error. Utilize Koa's ctx.status for this.
       • Set a generic, user-friendly error message in the response body (ctx.body). Avoid revealing internal implementation details.
  4. Koa-Specific Testing: Write tests (using tools like supertest with Koa) that specifically verify:
     • The correct execution order of middleware.
     • That the error-handling middleware catches errors thrown by other middleware (using ctx.throw or other error-throwing mechanisms).
     • That the responses to clients are sanitized and do not leak sensitive information.
  5. Code Reviews (Koa Focus): During code reviews, specifically check:
     • The order of app.use(...) calls.
     • The error handling logic within the custom error middleware, ensuring it adheres to Koa's context (ctx) and error handling patterns.

• Threats Mitigated:

  • Authentication Bypass (Severity: Critical): Incorrect Koa middleware order can allow unauthenticated requests to bypass authentication checks implemented in later middleware.
  • Authorization Bypass (Severity: Critical): Similar to authentication, incorrect order can allow unauthorized access to resources.
  • Information Leakage (Severity: High): Koa's default error handling can expose stack traces. The custom error handler prevents this specifically within the Koa context.
  • Denial of Service (DoS) (Severity: Medium): Unhandled errors within the Koa middleware chain can lead to application crashes.
  • Request Smuggling (Severity: High): If request parsing middleware is placed after security middleware.

• Impact:

  • Authentication/Authorization Bypass: Risk reduced to near zero with correct Koa middleware ordering.
  • Information Leakage: Risk significantly reduced by preventing Koa's default error handler from exposing details and by using a custom handler.
  • Denial of Service: Risk reduced by gracefully handling errors within the Koa middleware chain.
  • Request Smuggling: Risk reduced by correct ordering.

• Currently Implemented:

  • Authentication middleware (authMiddleware.js) is present but its position in the Koa stack is not guaranteed to be optimal.
  • Basic error handling middleware (errorMiddleware.js) exists but logs only to the console and is not the first middleware.

• Missing Implementation:

  • errorMiddleware.js must be moved to be the first middleware registered with app.use().
  • errorMiddleware.js needs to be updated to send logs to a secure logging system, not just the console.
  • Specific tests to verify Koa middleware order and error handling are missing.
  • Rate limiting middleware is missing.
  • Authorization middleware is missing.

Mitigation Strategy: Secure Context (ctx) Usage (Koa-Specific)

• Description:

  1. Avoid Sensitive Data on ctx: Never directly store sensitive data (passwords, API keys, etc.) on Koa's ctx object without proper encryption or secure storage mechanisms. The ctx object is passed through the entire middleware chain, increasing the risk of exposure.
  2. Namespacing on ctx: When adding custom properties to Koa's ctx object, always use a namespace. This prevents naming collisions with other middleware or Koa's internal properties. Example: ctx.myApp.userData instead of ctx.userData.
  3. ctx Immutability (Best Practice): Treat Koa's ctx object as immutable whenever possible. Avoid modifying it directly within middleware unless absolutely necessary. This helps prevent unintended side effects and makes the flow of data through the Koa middleware chain easier to understand.
  4. ctx.state Usage: Use ctx.state judiciously for passing data between Koa middleware. Avoid storing sensitive data in ctx.state unless you are certain about the security implications and the lifecycle of the data within the middleware chain.
  5. Sanitize ctx Before Logging: If you need to log the Koa ctx object for debugging, ensure you sanitize it first, removing any sensitive information that might be present. This is crucial because ctx can accumulate data throughout the middleware chain.

• Threats Mitigated:

  • Information Leakage (Severity: High): Prevents sensitive data stored on Koa's ctx from being accidentally exposed to other middleware, in logs, or in error responses.
  • Middleware Conflicts (Severity: Medium): Namespaces prevent different Koa middleware from accidentally overwriting each other's data on the ctx object.
  • Logic Errors (Severity: Low): Promoting immutability of ctx helps prevent unexpected behavior caused by unintended modifications within the Koa middleware chain.

• Impact:

  • Information Leakage: Risk significantly reduced by avoiding direct storage of sensitive data on Koa's ctx and sanitizing before logging.
  • Middleware Conflicts: Risk minimized by using namespaces for custom properties on ctx.
  • Logic Errors: Risk reduced by encouraging immutability of the ctx object.

• Currently Implemented:

  • No sensitive data is currently stored directly on ctx.

• Missing Implementation:

  • No consistent use of namespaces for custom data added to Koa's ctx object.
  • No explicit guidelines or code review checks to enforce the recommended immutability of ctx.
  • No sanitization of ctx before logging.

Mitigation Strategy: Enforce Security Headers with koa-helmet (Koa-Specific Integration)

• Description:

  1. Installation: Install the koa-helmet middleware, which is specifically designed for Koa.js: npm install koa-helmet.
  2. Koa Integration: Add koa-helmet as middleware within your Koa application using app.use(helmet()). Place it early in the middleware stack, ideally right after the error handling middleware. This ensures that the security headers are set for all responses, even for errors.
  3. Configuration (Koa-Specific): Customize koa-helmet's settings, if needed, using the options object passed to the helmet() function. This is done within the Koa application setup. For example, to configure a Content Security Policy (CSP):

     app.use(helmet({
       contentSecurityPolicy: {
         directives: {
           defaultSrc: ["'self'"],
           scriptSrc: ["'self'", 'example.com'],
           // ... other directives ...
         },
       },
     }));

  4. Testing (Koa Context): Use tools like supertest to make requests to your Koa application and assert that the expected security headers are present in the responses. This verifies the correct integration of koa-helmet within the Koa context.

• Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: High): Mitigated by koa-helmet setting Content-Security-Policy, X-XSS-Protection.
  • Clickjacking (Severity: High): Mitigated by koa-helmet setting X-Frame-Options.
  • MIME Sniffing (Severity: Medium): Mitigated by koa-helmet setting X-Content-Type-Options.
  • Man-in-the-Middle (MITM) Attacks (Severity: Critical): Mitigated by koa-helmet setting Strict-Transport-Security (HSTS).
  • Data Exfiltration (Severity: High): Content-Security-Policy set by koa-helmet can help prevent data exfiltration.

• Impact:

  • XSS, Clickjacking, MIME Sniffing, MITM, Data Exfiltration: Risk significantly reduced by koa-helmet setting appropriate security headers in all responses from the Koa application.

• Currently Implemented:

  • Not implemented.

• Missing Implementation:

  • koa-helmet needs to be installed and integrated into the Koa application using app.use().
  • Appropriate CSP rules and other koa-helmet configurations need to be defined based on the application's specific requirements.