In the age of microservices and mobile apps, the API (Application Programming Interface) is the backbone of modern software. Unfortunately, because of its public nature, it is one of attackers’ favorite targets. In this article we walk through the most important practices for securing an API to minimize the risk of a data breach.
TL;DR - Key takeaways
- Authentication and Authorization
- Rate Limiting and Throttling
- Input Validation
1. Authentication and Authorization
Never trust requests from unknown sources. Even an internal API should be protected. The most common flaw (OWASP API1:2023 – Broken Object Level Authorization) is a case where an authenticated user can reach another user’s data simply by changing an ID in the URL parameters.
Always verify that the token in the Authorization header actually permits modifying the specific object in the database. Do not rely on hiding endpoints alone.
2. Rate Limiting and Throttling
Without limits on the number of requests, your API is exposed not only to DDoS attacks but also to password guessing (brute-force) and scraping.
- Set a per-IP limit (e.g., 100 requests / minute).
- Set a separate, stricter limit for login and password-reset endpoints (e.g., 5 attempts / 15 minutes).
- Return a 429 Too Many Requests status code.
Red Team Tip
Attackers often bypass simple IP-based limits using rotating proxy servers. On top of per-IP limits, enforce limits tied directly to the user account (or the issued API key).
3. Input Validation
The golden rule of security is: "Never trust user input." Whether you work with Node.js, Python, or Java, unvalidated input is an open invitation to SQL Injection, NoSQL Injection, or XSS.
Use schemas (e.g., Joi, Zod) to strictly define the expected structure of the request body.
Summary
API security is an ongoing process. Technologies change, and attack techniques evolve with them. The points above are the absolute minimum. Run code reviews and penetration tests regularly to make sure your defenses actually hold.