API security checklist

API Security Checklist

Checklist of the most important security countermeasures when designing, testing, and releasing your API.

  • Authentication
    • Don’t use 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.).
  • CI & CD
    • Audit your design and implementation with unit/integration tests coverage.
    • Use a code review process and disregard self-approval.
    • Ensure that all components of your services are statically scanned by AV software before pushing to production, including vendor libraries and other dependencies.
    • Design a rollback solution for deployments.

See also:

  • yosriady/api-development-tools - A collection of useful resources for building RESTful HTTP+JSON APIs.
  • https://r.bluethl.net/how-to-design-better-apis
  • https://datatracker.ietf.org/doc/html/rfc7807
  • https://fusionauth.io/learn/expert-advice/oauth/complete-list-oauth-grants