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api-security.md

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API Security Checklist

Authentication

  • Consider not using Basic Auth. Use standard authentication (e.g. JWT, OAuth).
  • Don't reinvent the wheel in Authentication, token generation, password storage. Use the standards.
  • Use Max Retry and jail features in Login.
  • Use encryption on all sensitive data.

JWT (JSON Web Token)

  • Use a random complicated key (JWT Secret) to make brute forcing the token very hard.
  • Don't extract the algorithm from the payload. Force the algorithm in the backend (HS256 or RS256).
  • Make token expiration (TTL, RTTL) as short as possible.
  • Don't store sensitive data in the JWT payload, it can be decoded easily.

OAuth

  • Always validate redirect_uri server-side to allow only whitelisted URLs.
  • Always try to exchange for code and not tokens (don't allow response_type=token).
  • Use state parameter with a random hash to prevent CSRF on the OAuth authentication process.
  • Define the default scope, and validate scope parameters for each application.

Access

  • Limit requests (Throttling) to avoid DDoS / brute-force attacks.
  • Use HTTPS on server side to avoid MITM (Man in the Middle Attack).
  • Use HSTS header with SSL to avoid SSL Strip attack.

Input

  • Use the proper HTTP method according to the operation: GET (read), POST (create), PUT/PATCH (replace/update), and DELETE (to delete a record), and respond with 405 Method Not Allowed if the requested method isn't appropriate for the requested resource.
  • Validate content-type on request Accept header (Content Negotiation) to allow only your supported format (e.g. application/xml, application/json, etc.) and respond with 406 Not Acceptable response if not matched.
  • Validate content-type of posted data as you accept (e.g. application/x-www-form-urlencoded, multipart/form-data, application/json, etc.).
  • Validate user input to avoid common vulnerabilities (e.g. XSS, SQL-Injection, Remote Code Execution, etc.).
  • Don't use any sensitive data (credentials, Passwords, security tokens, or API keys) in the URL, but use standard Authorization header.
  • Use an API Gateway service to enable caching, Rate Limit policies (e.g. Quota, Spike Arrest, or Concurrent Rate Limit) and deploy APIs resources dynamically.

Processing

  • Check if all the endpoints are protected behind authentication to avoid broken authentication process.
  • User own resource ID should be avoided. Use /me/orders instead of /user/654321/orders.
  • Don't auto-increment IDs. Use UUID instead.
  • If you are parsing XML files, make sure entity parsing is not enabled to avoid XXE (XML external entity attack).
  • If you are parsing XML files, make sure entity expansion is not enabled to avoid Billion Laughs/XML bomb via exponential entity expansion attack.
  • Use a CDN for file uploads.
  • If you are dealing with huge amount of data, use Workers and Queues to process as much as possible in background and return response fast to avoid HTTP Blocking.
  • Do not forget to turn the DEBUG mode OFF.

Output

  • Send X-Content-Type-Options: nosniff header.
  • Send X-Frame-Options: deny header.
  • Send Content-Security-Policy: default-src 'none' header.
  • Remove fingerprinting headers - X-Powered-By, Server, X-AspNet-Version, etc.
  • Force content-type for your response, if you return application/json then your response content-type is application/json.
  • Don't return sensitive data like credentials, Passwords, or security tokens.
  • Return the proper status code according to the operation completed. (e.g. 200 OK, 400 Bad Request, 401 Unauthorized, 405 Method Not Allowed, etc.).

Source: API Security Checklist