The security of your API should be one of the top priorities of companies. Without proper security testing, your APIs could be open to attack and exploitation. In this article, we will explore what API security testing is, why you need it, and best practices to follow. We will also take a look at some best API security testing open source tools that you can use in your own projects. Let’s get started!

Understanding API Security Testing

API security testing is a process of testing APIs to ensure that they are secure and free from vulnerabilities. You can either test things by hand or through automation. Automated API security testing tools help you speed up the process while also making it more accurate.

API security is the process of making your API endpoints secure from potential attackers and building your APIs in a way that makes them more resistant to security risks.

API Security Testing: Why Do You Need It?

API security testing is important because it helps to identify potential vulnerabilities in your APIs before they are exploited by attackers. By performing regular security tests, you can fix any vulnerabilities that are found before they are exploited. This will help to keep your API users safe and secure.

Some other nasty outcomes of an API security breach could be:

  • Customer data is leaked. It’s then marketed on the dark web
  • Your website and company may be severely damaged if you suffer a security breach. Your brand’s reputation in the market can be greatly affected by this
  • If we don’t take action, the number of users and revenue will decrease

Best API Security Testing Open Source Tools

There are many different API security testing open source tools available. Here are some of the best API security testing open source tools:

  • JWT
  • OAuth
  • HAWK Authentication
  • crAPI
  • Curity Identity Server Community Edition

What is REST API?

REST is an API design style that stands for “Representational State Transfer.” This simply means that it is a set of rules followed by designers to create consistent and easily navigated APIs.

REST API is used by almost every major corporation, including Facebook, YouTube, and others. REST API is widely utilized in open-source CMSes such As WordPress, Magento, and others.

Remember that the REST API is a design approach for APIs and is therefore platform-independent. Any programming language may be used to create a Rest API (PHP, Python, etc.). The data is most commonly exchanged in XML or JSON. It’s not clear yet.

While the REST API is designed to be secure, there are still some common vulnerabilities that you should be aware of to avoid any potential issues.

Steps Required for API Security Testing

Step 1: Test for API Input Fuzzing

Fuzzing means feeding the API random data and observing the output for anything that would suggest the API processed that data. This could be information, an error message, or anything else.

If you’re looking to automate your input process, Fuzzapi is an open-source fuzzing tool that may be of use to you. For numerical inputs, try 0 or negative numbers; for string inputs try SQL queries or system commands; and for random characters, get creative with “, ‘, // etc.

Step 2: Test for API Injection Attacks

  • SQL Injection

One of the most prevalent injection attacks is SQL injection. This attack injects malicious code into an API that uses SQL databases. The goal of this type of attack is to gain access to sensitive data or to execute unauthorized commands on the database.

To test for SQL injection vulnerabilities, try inputting characters such as “, ‘; // etc. into numerical and string fields. If the API processes this data, it’s susceptible to SQL injection attacks.

  • XML Injection

Another common type of injection attack is XML injection. This attack targets APIs that use XML for data storage and processing. The goal of this type of attack is to gain access to sensitive data or to modify XML documents in an unauthorized way.

  • Command Injection

API input can also be transferred by various operating system commands. Please note that the aforementioned commands will only work if you’re using a compatible Operating System. For instance, Linux users can type in “rm /” to remove an entire root directory while Windows users have to execute different sets of commands. If you were to URL encode the command mentioned earlier, it would look something like rm%20/.

Step 3: Test for Parameter Tampering

Parameters transmitted via an API request are frequently vulnerable to manipulation. An attacker may tamper with the values of a product and essentially buy it for free by altering them.

Step 4: Test for Unhandled HTTP Methods

API-enabled web applications frequently utilize a variety of HTTP methods. These HTTP procedures are utilized for saving, removing, or obtaining data. As a result, if a server does not support an API method, it should generally produce an error.

To test your API endpoint for authentication vulnerabilities, make a HEAD request. You may send HEAD requests in a variety of ways.

Exploring the Best API Security Testing Open Source Tools Even Further


The most popular approach to generate access tokens for apps is through JWTs or JSON Web Tokens. The open standard of JSON Web Token adheres to RFC-7519, allowing for secure data transmission between clients and servers.

JWT works by the server generating a certificate to approve the user’s identity, which it sends to the client. Then, whenever the client makes subsequent requests to the server, they include that token/certificate as proof of their identity.

The tokens are signed cryptographically but not encrypted. For this reason, the token must be HTTPS so that it can be trusted; this also guarantees that there is no man-in-the-middle who can modify or interpret the token.


OAuth Tools enables you to decode OAuth tokens, such as JWT and Access Token. You can test your product in different areas to ensure that it is effective. If needed, the custom environment feature allows for use of things like a custom URL or key.

You can also export and import your settings into a JSON file, so you won’t have to fill out the forms again to test the tokens. You may use OAuth Tools to test various OAuth flows and capabilities, such as explicit flow, hybrid flow, token revocation, logout flow, and more.

HAWK Authentication

Hawk is a widely used technology for authenticating users, but it wasn’t developed by the original creators of OAuth. HAWK aims to replace 2-legged authentication and employ a far simpler type of authentication. It’s primarily used for HTTP authentication and performs HMAC digests.

HAWK uses client credentials, such as a cryptographic verifier and a key, in the same way as HTTP Basic authentication. The key is used to calculate the MAC value of the request, rather than for authentication purposes.


The Completely Ridiculous API (crAPI) may help your team simulate the ten most essential security elements of an API in a mock environment. crAPI has fully closed every loophole that an API should avoid. This makes it a wonderful example of how not to build API security.

Curity Identity Server

The Curity Identity Server Community Edition is a free method to test the Curity Identity Server. By using it, you can protect access to your APIs. The Identity Server authenticates your API endpoints using OpenID Connect and OAuth 2.0 standards. It allows you to sign in once for all of your web applications, mobile apps, and API endpoints, making it more convenient for you.

Apart from these open sources API security testing tools, there are also commercial tools that can serve you just as well if not better. Some of the finest commercial API security tools are:

  • Astra Security
  • Postman
  • Katalon Studio
  • Apache JMeter
  • Taurus

API Security Best Practices

In order to best secure your API, consider following these best practices:

  • Between the customer and server, always use SSL/TLS encryption
  • Implement proper access control measures like role-based access control, least privilege, etc.
  • Do not put critical information in the API, such as credit card numbers, social security numbers, and other sensitive information
  • Perform input validation on all user input to prevent malicious payloads
  • Keep your API up to date with the most recent security updates


API security is a critical concern for any organization that exposes its APIs to external consumers. By following the best practices listed above and using some of the best open source or commercial tools available, you can ensure that your API is well-protected against potential threats.

About the Author
Ankit Pahuja is marketing leader & evangelist at Astra Security. You can contact him from here.

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