API Security

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

Authentication

•  Don’t use Basic Auth. Use standard authentication instead (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 header. 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.
•  Avoid storing too much data. JWT is usually shared in headers and they have a size limit.

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 with TLS 1.2+ and secure ciphers to avoid MITM (Man in the Middle Attack).
•  Use HSTS header with SSL to avoid SSL Strip attacks.
•  Turn off directory listings.
•  For private APIs, allow access only from whitelisted IPs/hosts.

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 only server-side encryption.
•  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 data, make sure entity parsing is not enabled to avoid XXE (XML external entity attack).
•  If you are parsing XML, YAML or any other language with anchors and refs, 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.
•  Use non-executable stacks when available.

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 content-type response 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.
•  Continuously run security tests (static/dynamic analysis) on your code.
•  Check your dependencies (both software and OS) for known vulnerabilities.
•  Design a rollback solution for deployments.