API Security Testing: Common Vulnerabilities and How to Prevent Them

The most frequently exploited API weakness allows one authenticated user to access or modify another user's data simply by changing an identifier in the request. This class of flaw is rarely caught by automated tools and requires manual, authenticated testing to uncover.

Weak token validation, missing expiration, and the absence of rate limiting on sensitive endpoints allow attackers to brute force credentials or abuse business logic at scale. Assessments verify token handling end to end, not just at the login endpoint.

APIs frequently return more fields than the client interface displays, leaking internal identifiers or sensitive attributes to anyone inspecting network traffic. Reviewing raw API responses, not just the rendered UI, is essential to catching this.