4 testing techniques and tools for API security

February 23, 2022
api security

Understanding the importance of API security is just the first step in an extensive process of securing your APIs from different kinds of attacks. API usage is extremely common throughout many industries and companies, making them an easy target for both amateur and seasoned hackers alike.

APIs often connect to vital information such as business information, customer data, and software functions, making API security strategies paramount. API security will also overlap in various systems and functions within an organization, and an appropriate amount of time and resources must be put towards making this a part of daily operations.

4 Testing Techniques for API security

Different testing techniques are required to detect all possible security vulnerabilities related to different aspects of API security.

Testing for unhandled HTTP methods

A great deal of web application security testing uses different HTTP methods to communicate through APIs and carry out various activities such as storage, deletion, or retrieval of data. If the HTTP method isn’t supported by the server, it might display an error, but if it isn’t supported from the server-side, this can present a security vulnerability. To see if this is the case, you can make a HEAD request to the API endpoint and verify the authentication possibility. For complete safety, test all the common HTTP methods including POST, GET, PATCH, DELETE, etc.

Testing for parameter tampering

Parameter tampering is usually done by using form fields that are hidden from view. The presence of these fields can be detected with the help of a browser element inspector. Once you’ve incorporated one, test it with different kinds of values to understand the extent of the exploitation possibilities and the reaction of the API. In most cases it’s easy to tamper with the parameters sent through API requests, leading to unauthorized data leaks from the user’s account, revenue losses, etc.

Testing for command injection attacks

Command injection attacks in REST API occur when operating commands are inserted into API inputs, opening up backdoors for exploitation. Testers need to run operating system commands that function appropriately with the particular version of the API server. If the API content is shown in the form of a URL, the command can be appended onto the URL to check for execution on the server.

Testing for API input fuzzing

Fuzzing basically involves trying out different kinds of inputs until one of them uncovers a security vulnerability that can be exploited further. If an error is returned or if the API crashes instead of processing the request, you know you have an avenue for a successful attack. For API inputs that accept numerical terms, testers could try large numbers, zero, or negative values. For strings, try inputting system commands, SQL queries, or non-text characters.

4 Open Source API Security Testing Tools

It’s always a good idea to include automated testing tools for the security of production APIs with a regular schedule of development and releases. The tools should be used to test security-related simulations, evaluate the security at the API endpoints, look into business logic vulnerabilities, and resolve security issues which have been discovered.


This is an open source toolkit that allows you to build RESTful APIs using two development styles – bottom-up and top-down. The former involves using Swagger to build the API and generate the code using other specifications. The latter option lets Swagger use the existing code to build up the necessary documentation on API parameters, outputs, and associated operations.


An API functional testing tool, SoapUI has many useful features, such as a simple drag-and-drop interface for testing, options for customization, and a library with functional testing elements for conducting automated API tests. The tool also provides source code to build the necessary features, and you can reuse the available load test or security scans for doing tests. There are also options for data-driven testing simulations to understand users’ approaches to the API.


Fiddler looks into the security of specific HTTP requests and provides API testing extensions for Java, Ruby, and other commonly used frameworks. Other characteristics include a simple UI for grouping and organizing API requests and debugging different client requests for various OS options such as Windows, Mac, mobiles, etc. It tests the security of cookies, caches, and headers in the communication from clients to the server, and uses mock requests with no code changes.


This is a load testing tool that also evaluates security by using CSV files and inputting different values to understand the potential for a cyberattack. It also includes embedded API tests in the building process, and works on understanding the capacity for advanced performance by running tests and their replays for better analysis.

This article was meant to provide insight into the different testing techniques that should be included in an API security testing process, along with the different tools used for more efficient testing. Once a company has decided on following the API security approach, it’s important to understand the different options available in the market so they can take a more informed approach.


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