API Pentesting – Everything You Need to Know In 2024

The role of Application Programming Interfaces or API is significant in the present time where software and applications are replacing every conventional way of procedures by which we do things.  In this context, knowing what is API pen testing is extremely important. In this blog, we help get a complete understanding of it. 

What Is API Pen Testing?

API stands for Application Programming Interface. In the software or application development process, you may be required to make multiple software applications to interact with each other. The API serves as a platform where you can make it happen smoothly. However, APIs have become the target of attackers today. API pentesting aims to identify vulnerabilities within the API environment.  Now, let’s understand why it is important.  

  • A detailed API pentest helps developers ensure that appropriate business rules and logic recommended for software development are applied at the implementation stage. 
  • API testing allows you to figure out how likely the interface is to face trouble in the case of a high volume of API calls. By foreseeing such interruptions, developers can take measures to address them. 
  • During simulated API pen testing, the testers send a high volume of load to the API to see how much it can handle. The failure rate is measured and recorded for future reference. 
  • Organizations are increasingly choosing API pentesting as a practical measure to ensure their compliance with privacy regulations and legal mandates. 
  • Periodical penetration testing is the most recommended way for organizations to foresee the chances of security breaches and take proactive measures. 
  • Developers can only know whether they can expand an application buildup by knowing if the API can handle that. Pentesting helps figure that out. 

How To Conduct API Pentesting?

By performing API pentesting, you gain clarity on the security posture of your API. It helps you verify whether you need to take any proactive measures to improve its defense capabilities. Here is a step-by-step procedure for conducting API testing.

Api pentesting

Evaluating the API:

After the green signal for the pen testing API is obtained, evaluate the environment to know the nature of the architecture, endpoints, databases, use of third-party APIs etc. 

Preparing the test environment:

Next, set up the environment ready for the planned testing. Install the necessary API penetration testing tools. If you are intending to test the traffic on  HTTP and HTTPS, make sure to get ready with the appropriate proxy configuration for the same. 

Checking authorization/authentication requirements:

Verify the endpoints for which you require authorization/authentication and the ones that do not require it. Check how the authentication mechanism responds to brute-force attacks. 

Scanning for vulnerabilities:

In this stage, the API pen tester will scan the environment for all potential vulnerabilities. Some of the common vulnerabilities that are found in the scanning are Insecure Direct Object References (IDOR), Cross-Site Scripting (XSS), XML External Entity (XXE) and SQL Injection. 

Analysing the responses:

While analysing the responses, sensitive data must be avoided. Likewise, ensure that there are no vulnerabilities associated with the HTTP headers by carefully analysing them. 

Performing automation tests:

Make use of every available automation tool to cover the maximum areas in the API infrastructure where vulnerabilities could be present. In addition to the specialized tools, you can utilize scripts. Do not forget to assess the automation test results. 

Drafting a detailed report:

Once you have identified the API vulnerabilities through various testing procedures, prepare a detailed list of them. Alongside each vulnerability, include the procedure through which you got to know them. This will help you in future testing and remediation steps. 

Common API vulnerabilities

API vulnerabilities are evolving every day, just like any other cyber security risk. Some of the common vulnerabilities we can list include broken authentication, injection attacks, insufficient authorization controls, inadequate input validation and insecure direct object references.

API Security Testing Tools

There are a variety of tools used in API security testing. These specially designed tools enable the testers to test the APIs by automating various minute tasks in the testing procedure. It also facilitates the validation of responses received to the sent requests. Here are the most used API penetration testing tools.

security tools


Like JMeter, Taurus is widely used for performance testing. It facilitates ongoing testing of the web applications and comes with automation-friendly capabilities. 

Apache JMeter:

As a highly efficient tool for measuring the performance of web applications. It comes with compatibility with a variety of protocols, such as FTP, HTTP, and HTTPS. Apache JMeter is an open-source tool which makes it highly popular among emerging API pentesters. 


Postman is a reputed collaboration tool used in API development. Its automated testing capabilities and user-friendly interface allow quick and detailed management of requests and subsequent responses.

Katalon Studio:

Katalon Studio is popular among several API penetration testing experts for its built-in features supporting a various of API environments such as desktop, web, and mobile. Additionally, it has advanced automation features. 


AppKnox is basically a mobile app security testing tool. You can use it for identifying and addressing API security risks in both iOS and Android applications. 


Insomnia is another open-source API testing tool too. It has an intuitive interface and  sophisticated features. Insomnia works perfectly to test diverse API environments and protocols.

Common API Security Risks

There are numerous types of security threats that can compromise the security posture of APIs. When an API is under threat, it can lead to data breaches, unauthorized access, and several forms of misuse. Let’s explore some of the common API security risks. 

Injection attacks:

When the API requests contain infected codes, it can potentially lead an API to confront injection attacks. As a result, the database becomes accessible to attackers, who will proceed with malicious acts like cross-site scripting (XSS).

Unsafe communication:

Lack of encryption with the connections that are used for API data transmission may allow the attackers to intercept or alter the data. It can lead to a lack of safety in the communication between the client and the API. 

Insufficient input validation:

API inputs are the requests sent from it. These requests need to be validated to ensure that no attacker is intercepting and integrating malicious codes or data into them  to cause harm. 

Failure in validating forward input:

While using the APIs, the users must ensure that the system is configured to initiate input validation. When there is no proper validation mechanism, there is a high chance for attackers to interrupt the requests or replace them with malicious data. 

Broken authentication at the functional level:

 If there is no proper authentication at the functional level, the API environment can allow attackers to access it and exploit the situation for collecting identity data, session cookies, and other key information. 

Inadequate request monitoring and logging:

When there is no proper monitoring and logging of the requests coming from or going to the API, it becomes difficult to know whether the API is misused by an attacker for vested interests. 

Compromising API keys:

API keys are extremely sensitive. Only authorized systems or users should have them. If the keys get compromised, an attacker can easily use them to gain access to even a tightly secured API environment. 

Insufficient access control:

Lack of access control or insufficient access control to API resources would mean they are open to attackers. An attacker gaining access that way can figure out the vulnerabilities present and exploit them. 

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Jim Jacob

Jim Jacob is the founder of Cyberguard. He is an IT professional who has 21 years of professional experience in the tech field. Cybergurad is the product of his vision to share the knowledge gained from his career through the power of words. He is an expert at explaining complex tech concepts in simple language and has written numerous articles on IT and Cybersecurity.

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    API pentesting is the most fundamental step to safeguarding the security of an API environment. Before initiating a thorough pentest covering various aspects of the Application Programming Interface, it is important that you evaluate the interface carefully and ensure the following of the correct methods. Once the potential vulnerabilities are identified, appropriate steps need to be taken to address the risks. We hope that this blog provides you with an overview of what is involved in API pentesting.

    Frequently Asked Questions

    API pentesting is the process of assessing the security posture of an API (Application Programming Interface). The test involves scanning for vulnerabilities in an API by exploiting them through simulated attacks. It will allow the developers to figure out how immune the API is to resist those attacks. Following the testing, the testers report the vulnerability and  the various steps taken during the penetration testing. 

    API Penetration testing is a highly skilled process. It means, to perform it successfully; one must have the following basic requirements: 

    • Thorough knowledge of how HTTP/HTTPS protocols work
    • Strong understanding of web application architecture
    • Awareness of common security vulnerabilities present in the API

    API security testing consists of three different types of testing approaches. They are

    • Functional Testing
    • Performance Testing
    • Security Testing

    Ensuring that you start at the right point in API pentesting is essential for its success. So, start the testing by carefully going over the API documentation. It will help you identify the endpoints, and plan your test cases based on edge cases and functional requirements. 

    There are several API pentesting tools available, each of them differing in features, automation capabilities and other traits. The most common tools are Postman, Apache JMeter and Katalon Studio. 

    API penetration testing can be done both manually and through automation. However, it is recommended to combine both methods. Use automation for performing repetitive tasks and go with manual evaluation for complex edge cases. 

    The full form of API is Application Programming Interface.