API Penetration Test

A web service, or API, is a mechanism for communication using a machine-readable format. Many modern applications rely on some form of API in the background. In such cases, the API is usually tested as part of a web, mobile or desktop application.

This page focuses on testing standalone APIs that are exposed, for example, to customers or business partners, who then integrate the API into their own software solutions.

Benefits

From a security perspective, web services face very similar challenges to web applications. APIs are often developed as custom solutions and may therefore contain unique vulnerabilities. As they are frequently exposed to the internet, they are also a target of continuous and widespread attacks.

Some issues can be identified using automated security tools. However, certain types of vulnerabilities, such as application logic flaws, cannot be detected reliably in this way. For this reason, our approach always combines advanced automated tools (including commercial ones) with careful manual testing.

The most commonly encountered interfaces are SOAP and REST APIs. However, we also have experience with GraphQL, gRPC, and other technologies.

Testing Process

For web services, or APIs, a pure black box approach (without any prior knowledge of the tested subject) is generally less suitable than for other types of testing. In such cases, the tester may spend more time understanding “how it works” rather than analysing “where the weakness lies”.

For effective testing, it is highly beneficial to have access to a reference client implementation, a SoapUI project, an OpenAPI specification, or another form of detailed documentation describing the available methods and parameters. Sample API calls can also be very helpful.

The overall effort required for testing depends on the number of methods, parameters, test scenarios, the authentication mechanism, and the number of user roles included in scope. In some cases, it is reasonable not to test the entire API, but only a carefully selected representative subset of calls.

Our testing is based on relevant parts of the OWASP WSTG (OWASP Web Security Testing Guide) and the OWASP API Security project. Within the testing team, we continuously share practical experience from many previous projects.

Other Types of Tests

As already mentioned, many modern applications rely on APIs in the background. If a client application is available, we recommend not testing the API in isolation, but rather as part of a web, mobile or desktop application.

A more detailed analysis of the web service source code can be performed as part of a security code review.

We also offer a wide range of other penetration testing services, see Penetration Testing – Overview.

Final Report

The results of the penetration test are documented in a final report, which contains details of the testing process, a description and classification of all the vulnerabilities found, and recommendations for mitigating the risks. We deliver the report securely in MS Word and PDF formats. The results can also be presented in a management presentation or a technical workshop.