API security testing and the OWASP API Security Top 10

Your mobile app, your single-page front end, and your partner integrations all talk to APIs, and those APIs are where the data lives. Attackers know this. API attacks have become a primary breach vector precisely because teams secure the web page and forget the endpoints behind it. API security testing targets the failures that are specific to this layer.

Why APIs fail differently

A web page hides structure behind a user interface. An API exposes it directly: objects, identifiers, and actions, available to anyone who can send a request. The most damaging API flaws are about authorization, not injection. If the endpoint trusts the client to ask only for its own data, an attacker simply asks for everyone's.

The OWASP API Security Top 10

OWASP maintains a list of the most critical API risks. The headline items shape most testing:

• Broken object level authorization (BOLA). The number one API risk. Changing an ID in a request returns data that belongs to another user.
• Broken authentication. Weak tokens, missing expiry, and flawed login flows that let attackers impersonate users.
• Broken object property level authorization. Reading or writing fields a user should not be able to touch.
• Unrestricted resource consumption. No rate limits, so an attacker can scrape, brute force, or run up your bill.
• Broken function level authorization. Regular users reaching admin-only functions.
• Server-side request forgery, security misconfiguration, and improper inventory of which APIs even exist.

What API testing covers

• Authorization at the object and function level, tested as multiple users and roles.
• Authentication and token handling, including expiry and replay.
• Input validation and injection across every parameter.
• Rate limiting and resource abuse.
• The full API inventory, including the old version everyone forgot to turn off.

Tools find some of it, people find the rest

Tooling is good at fuzzing inputs and flagging misconfigurations, and it should run continuously. But BOLA and broken authorization need a tester acting as different users to see that the wrong one gets the data. That is judgment, not signature matching, and it is where the serious findings live.

APIs and compliance

If APIs move regulated or personal data, frameworks expect them tested. NIS2, DORA, and SOC 2 all push toward demonstrable security testing of the systems that handle sensitive data, and APIs are usually at the center of that flow.

Most API breaches are not clever. They are an endpoint that trusted the client to ask only for its own data.

We test APIs as part of application and cloud security. Book a scoping call to map your endpoints.