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attack-surface.md

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Attack Surface Analysis for koajs/koa

Attack Surface: Middleware Error Handling Failures

  • Description: Uncaught exceptions or unhandled promise rejections within Koa middleware can lead to application crashes, information disclosure, or unexpected behavior.
  • How Koa Contributes: Koa's minimalist design relies entirely on middleware for error handling. The framework provides no default error handling beyond a basic console log; it's entirely the developer's responsibility. This is a core design choice of Koa.
  • Example: A middleware that interacts with a database doesn't catch a database connection error, leading to an unhandled promise rejection and application crash.
  • Impact:
    • Denial of Service (DoS) due to application crashes.
    • Information disclosure (stack traces, internal error messages) revealing sensitive details.
  • Risk Severity: High
  • Mitigation Strategies:
    • Implement a global error-handling middleware as the first middleware. try...catch around await next().
    • Log errors securely.
    • Return appropriate HTTP status codes and sanitized error messages. Never expose raw error details.
    • Ensure all promises have await or .catch().
    • Use a dedicated error-handling library if needed.

Attack Surface: Middleware Ordering Vulnerabilities

  • Description: Incorrect ordering of middleware can bypass security checks.
  • How Koa Contributes: Koa's execution flow is completely determined by the order of app.use(). This is a fundamental aspect of Koa's design, providing flexibility but also creating this risk. Koa does not provide any built-in mechanisms to enforce or validate middleware order.
  • Example: Authentication middleware placed after resource access middleware.
  • Impact:
    • Bypass of authentication and authorization.
    • Incomplete logging.
    • Exposure of sensitive data.
  • Risk Severity: High
  • Mitigation Strategies:
    • Carefully plan and document middleware order. Security middleware before business logic.
    • Use a consistent pattern.
    • Thoroughly test to ensure correct order and effective security controls.

Attack Surface: Trust Proxy Misconfiguration

  • Description: Incorrectly configuring Koa's app.proxy can lead to trusting forged X-Forwarded-* headers.
  • How Koa Contributes: Koa provides the app.proxy setting and related header options (app.proxyIpHeader, etc.). The framework itself does the header processing based on this configuration. The vulnerability arises from misusing these Koa-provided features.
  • Example: app.proxy = true without verifying the reverse proxy's trustworthiness.
  • Impact:
    • Bypass of IP-based access control and rate limiting.
    • Spoofing of client IPs in logs.
  • Risk Severity: High
  • Mitigation Strategies:
    • app.proxy = true only if you trust the proxy.
    • Configure app.proxyIpHeader, app.proxyProtocolHeader and app.proxyHostHeader correctly.
    • Ensure the reverse proxy is secure.
    • app.proxy = false (default) if not needed.
    • Validate header values if used for security decisions.

Attack Surface: Asynchronous Operation Issues (Unhandled Promise Rejections)

  • Description: Failure to handle promise rejections in asynchronous Koa middleware.
    • How Koa Contributes: Koa's core is built around asynchronous operations and promises. The framework relies entirely on developers to handle rejections. Koa does not automatically handle them in a safe way.
    • Example: A middleware makes an asynchronous API call but omits a .catch().
    • Impact:
      • Application crashes (DoS).
      • Resource leaks.
    • Risk Severity: High
    • Mitigation Strategies:
      • Ensure all promises have await or .catch().
      • Use a global unhandled rejection handler as a last resort. Prioritize proper handling within middleware.