Quick answer: API penetration testing is a security service that uncovers the authorization, authentication and business logic flaws of the application programming interfaces (APIs) behind an organization's web and mobile applications through controlled attacks. In modern applications data often leaks not at the interface but at the API layer; the most common flaws are broken object level authorization (BOLA), broken authentication and excessive data exposure. DSET runs this test with its local AI engine KAOS; KAOS scans every endpoint, verifies every flaw it finds with a working proof and reports without false positive noise.

No matter how secure an application's interface looks, the real data traffic flows at the API layer. Attackers look here too. API penetration testing is a service that examines this layer through an attacker's eyes and proves authorization and business logic flaws. This article explains what API penetration testing is, which flaws it targets and the difference of the DSET and KAOS approach.

What is API penetration testing

API penetration testing examines an application's REST, GraphQL or SOAP interfaces in a defined scope through controlled attacks. The goal is to prove whether one endpoint can reach another user's data, whether authentication can be bypassed and whether business logic can be abused. Its difference from classic web penetration testing is that it looks not at the interface but directly at the service layer. For this reason API testing gives the most complete coverage together with web application penetration testing methodology.

Which flaws it targets

The frame of API testing is the OWASP API Security Top 10 list. At the top of this list is broken object level authorization, where one user's identity can be used to reach another user's resource.

Flaw class What it means Typical result
Broken object authorization (BOLA) Identity is checked but resource ownership is not Access to another user's data
Broken authentication Token and session management is weak Account takeover
Excessive data exposure API returns more fields than needed Sensitive data leak
Business logic abuse The flow is not forced in the expected order Free transaction, limit bypass
Insufficient rate limiting Request count is unlimited Brute force and denial of service

For the detailed frame of each flaw class the OWASP API Security Top 10 guide is the reference point. For general web flaws the OWASP Top 10 web application security guide is complementary.

When is API penetration testing done

The right practice is to do it before a new API goes live, after a major version change and at regular intervals. Every organization with a mobile application should plan a separate test for the API the application talks to; because the mobile client can be controlled, but the authorization behind it must be proven on the server side. Before the test the scope must be clearly drawn, for which the penetration testing preparation and scoping guide should be followed.

The KAOS and DSET approach

DSET runs API penetration testing with its local AI engine KAOS. KAOS maps the API schema and the endpoints, tests authorization flaws with two different user contexts and verifies every finding with a working proof. The difference is this: every line a scanner calls a possible flaw does not enter the report until it is proven with a real exploit under expert oversight. For this reason the DSET report, with the principle of proof based verification, filters out false positive noise. The same approach holds in our cloud penetration testing service and for AI applications in our LLM application penetration testing service.

Frequently asked questions

Are API penetration testing and web penetration testing the same thing? No, the two look at different layers but complement each other. Web penetration testing examines the application visible through the browser, while API penetration testing directly tests the service layer behind the interface. In an organization with a mobile application the real risk is often at the API layer, because the client cannot be controlled but authorization must be proven on the server.

Is a separate test needed for a GraphQL API? GraphQL carries many of the same flaw classes as REST but also adds its own risks, for example pulling excessive data with nested queries and schema exposure through introspection. For this reason GraphQL endpoints must be tested additionally for query depth and field level authorization. The DSET test covers REST and GraphQL interfaces together.

Is production data at risk during the test? In a well planned test no. The scope of the test, which endpoints and which data sets will be tested and whether destructive operations will be done, is set in advance with a contract. Operations that change and delete data are not run without a separate and explicit approval. When possible the test is run on a production copy environment.

Sources

To uncover the authorization and business logic flaws of your API layer with a proof based test, contact DSET. We provide API penetration testing and consulting from our Ankara Hacettepe Teknokent laboratory.