Application programming interfaces (APIs) foster information sharing by allowing different software services to interact. Although APIs have become important in developing web applications with ease, they can also share security vulnerabilities.

That’s why developers need to test early and often for API security threats. One way of correctly handling API security issues is by first testing to know if any issues are present and then employ industry best practices to remedy the detected bugs.

In this article, we’ll explore how to begin testing an API, what you need to have in mind when defining an API test, how to go about testing an API, and, finally, how to fix related bugs that cause API security weaknesses and risks.

API Security Testing at Work

API security testing at its root is the process of checking API endpoints for security and reliability to uncover possible security issues and bugs. It’s a software testing type that validates how APIs are built before they go into production. In testing an API, you send calls through the API, get an output, and note the system’s response. This lets you know if the test passed or failed. 

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Types of API Security Testing

There are three major types of API security tests. Let’s explore them. 

Static API Security Testing (SAST)

This kind of language-specific API testing utilizes tools that look at the code pattern of the application to identify potential vulnerabilities by looking at the application code. Because it’s language-specific, you have to use a tool that matches the language of your API. An example of SAST is penetration testing, a progressive static security test method.

API security testing cameras

Dynamic API Security Testing (DAST)

Dynamic API security testing introduces real attacks on APIs to detect any vulnerabilities. This kind of testing runs active tests against your API endpoints. It is the best form of API testing compared with SAST. Although there are a lot of DAST tools out there, you should always choose tools that are built for APIs. 

An example of a dynamic API security test is a fuzz test. In a fuzz test, the developer adds random parameters into the application and watches its output. If there’s an error, the developer tries to address the error or vulnerability.

Software Composition Analysis

This type of API testing method explores the composition of the API, such as the frameworks and libraries. It does so to expose known vulnerabilities by matching the application’s dependency with a database of known vulnerabilities. This is an important method since there are a lot of open-source libraries developers can utilize. 

However, developers need to note that SCA testing does not surface vulnerabilities if the vulnerability is exploitable within the API.  Also, SCA testing does not capture a vulnerability from bugs in the application’s code except if it’s a dependency vulnerability.

Steps to Start Testing an API

To successfully test an API for vulnerabilities, you must apply the following steps:

Understand Basic API Requirements

You need to understand the basic requirements of the API. This will help you set a proper output to determine the result of the test. To understand these basic requirements, ask the following questions: 

  1. Is the API required to have a TSL/SSL certificate? For example, this is necessary if you’ll need to access the API via HTTP requests.
  2. What is the authentication flow in the API?
  3. What permission grants what privilege to which user?

If you can answer the questions above properly, then you’ll be able to determine what constitutes the passing or failing of an API for your test.

Set Up the Environment for Testing the API

After understanding the API’s requirement, the next thing we’ll do is set up a test environment. Setting up the testing environment for an API is different from setting up a testing environment for a GUI test. You’ll need the following settings for testing an API: 

  1. The environment should have a set of parameters that invokes the API and examines the test result.
  2. A database and server configuration should meet the application’s needs.
  3. After the installation, the API function should check if the API is working.
  4. For smaller applications, you can use a standard staging environment. However, in larger applications, you’ll need to stage the testing in a separate environment.

Define Input Parameters

The next step is to define and understand what each input parameter in the API does. This will help understand parameters that are most vulnerable to injection attacks. 

Finally, after defining and properly understanding the function of each parameter in the API, you can now develop and execute the tests. Above all, you compare the actual output given by the API test and the output that you expected. 

Ways to lock and protect APIs

How to Fix Potential API Security Issues

Acknowledging the existence of a security flaw in an API is the first step in keeping the application safe. After finding the flaws, it’s advisable to secure the API. Some of the best practices for fixing potential API security issues are as follows:

  1. Utilize an API gateway to implement authorization checks. This way, accessing grants should require access tokens. Therefore, only those with proper access should get access to certain data.
  2. To prevent broken authentication vulnerabilities, you’ll need to go beyond API keys. For instance, OAuth flows to ensure that user authentication is secured.
  3. For excess data exposure, it’s a good industry practice to always filter data at the server side of an application. In addition to this, you should make use of OAuth scopes and claims to determine who’s eligible to access which data.
  4. Putting rate limits and restrictions on the amount of data that the API can share will prevent the flow of sensitive data from the API responses.
  5. As much as possible, try not to rely solely on default configurations.

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The use of APIs in modern software is growing faster and, in recent times, APIs have helped build a lot of robust applications by sharing data between software. Most times, APIs are used for sharing sensitive data of organizations that need to be protected. Therefore, the need to understand how to protect APIs is an important topic to discuss.

Although setting and staging a manual API will help surface vulnerabilities, this won’t be helpful in cases where you need to perform API testing regularly. This is where the use of automated API testing comes into play. Automated testing helps in the creation of tools that can be used to automatically test APIs to prevent the API from breaking whenever there are a few changes.

You can perform automated API testing in association with API security tools like Traceable AI. Traceable AI can be used to gain visibility, real-time protection, and threat analysis for modern APIs and cloud-native applications. It doesn’t require changes in the application. It also helps you know where you’re exposed by giving you insights on APIs, monitoring APIs for risks, and tracking users’ activity.

You can learn more about Traceable AI and how it helps test automation. Depending on your role and the needs at your organization, there are multiple options to get started with Traceable AI and its many options for observability and API security:

  • If you’re a CISO or DevSecOps security leader and want to evaluate your API security risks, try the API Security Posture Assessment
  • To start your journey, sign up for a Free Tier and learn all about your APIs — internal, external, third-party, and even the shadow or rogue APIs you may not even be aware of.
  • If you want to compare different API security solutions in the market, check out the API Security Tools comparison guide.
  • You can also view a demo or book a meeting to learn more and ask your questions on how Traceable can meet your API observability and security requirements. 

This post was written by Ukpai Ugochi. Ukpai is a full stack JavaScript developer (MEVN), and she contributes to FOSS in her free time. She loves to share knowledge about her transition from marine engineering to software development to encourage people who love software development and don’t know where to begin.

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