Basics of API Security Testing

API Security Testing Basics

The API is a critical component of modern web and mobile applications, and SaaS. APIs, by definition, reveal business logic and confidential data such as Personally Identifiable Information (PII), and as a result, they have become a popular target for hackers. Rapid advancement would be difficult without secure and safe APIs.

Therefore, it becomes important to perform API security testing before a bad actor gets hold of it for you.

RESTful API Security Testing Fundamentals

There are just four basic guidelines to obey when it comes to performing security tests on RESTful APIs. However, as is the case for all good ideas, bringing them into reality can be difficult.

The below are the basic rules, which can be easily incorporated into a web server:

1. Discard Incorrectly Typed Inputs 

Where a null is undesirable, inputs that are null (empty) must be refused.

2. Refuse Incorrectly Sized Inputs

The more challenging concepts necessitate a thorough interpretation of the appropriate set of values and users, which can be difficult to deduce without first understanding how a REST API would be used.

3. For a Provided Input Value, the API should Deliver the Anticipated Output.

If the input realm and output range are minimal (e.g., Phone numbers, age), this can be easily tested. It turns out to be very tricky when developing permissive RESTful APIs that allow users to send their own content (e.g., in email and social networking sites).

4. Refuse Input values Beyond the Needed Domain

This is straightforward when the domain is simple (for example, date of birth should be greater than zero).  However, users furnishing the data complicates the process (e.g., providing a user to file upload endpoint may be a risky and an enormous challenge to secure).

5. API Must Provide Data to Authorized Users Only

This can be simple to enforce if permissions are already specified and resources are organized according to their permission level. However, authorization remains a difficult challenge to overcome, – with the presence of many multibillion-dollar firms (such as Okta) to help.

The majority of APIs are not thoroughly checked which ensures that they fulfill these requirements. Due to this, APIs breaches are common and there are organizations like OKTA that provide a shield on top of APIs.

Therefore, it is always best to perform effective security testing on APIs to defend them against attacks.

Elements of an API Security Testing

Security Testing

Security Testing helps in validating fundamental security requirements. You need to answer the following questions before performing the testing:

  • Exactly what sort of authentication is required to use the API, i.e. how do you determine an end user’s identity?
  • Identifying the kind of encryption being used on the data that is stored, and when is the data decrypted for transmission?
  • What are the conditions that enable users to gain access to resources?

This is the first step in securing APIs, and it will help avoid major security issues.

Penetration Testing

Penetration testing allows you to strengthen the exterior surface of your application from security weaknesses that may have crawled in during the development process. In this step, external facets of the API are attacked in a premeditated style in a controlled environment. This can be accomplished by using automated tools such as Netspark or Acunetix.

While performing API Penetration Testing, follow the steps below:

  • Make a list of potential security issues applicable to the application.
  • Arrange the items found in the above steps according to their risk. You can refer to the OWASP Top 10 list if you have any doubts about the risk a particular type of issue poses.
  • Create requests and sessions that include the test cases and deliver them to the server — preferably from both the internal and external to the network.
  • If an unauthorized user can gain access to the device, log and patch the issue.

Fuzz Testing

The final step in a security auditing phase is fuzz testing, which involves pushing an API to its limits. This can be accomplished by sending a large number of requests to it. Each request should have varying data in as many imaginative ways as possible to cover the risks arising due to sending an enormous number of requests. These flaws may lead to Denial of Service or Overflow attacks.

Performing Security Test on an API

Testing an API entails sending requests to an endpoint of the application being tested by using an HTTP client. There are tons of free HTTP clients available, but the most famous ones are Postman or Insomnia.

The DevOps lifecycle can be accelerated by automating parts of the Security Audit process. The Fuzz Test and the Security Test, covered in the previous section, are the simplest to automate.

Step 1: Determine Security Requirements

You must first consider the general specifications before planning a security test on an API. This entails answering questions such as:

  • Is API accessible via HTTPS and does the API require a TLS/SSL certificate?
  • What authorization classes exist for the application’s various resources?
  • How does the authentication process work? Is it using a third-party OAuth service?
  • What is the API’s attack surface?

It’s important to have a clear idea of what constitutes a pass or fail on your assessment while you’re answering the above questions.

Step 2: Setting Up a Testing Environment

It’s time to set up an application environment for testing once the scope of the test has been established. It’s fair to use the traditional staging environment for smaller applications. For bigger applications, it’s best to set up a different environment for testing bigger applications. It can be done by replicating the resources in the staging environment or by using a tool like WireMock for simulating.

Step 3: Performing a Sanity Check on Your API

Send off a couple of requests to the API to confirm that the whole thing has been properly set up.

Step 4: Assessing the Input Fields

It’s important to consider what each parameter does and the various combinations that each parameter will take, before creating individual test cases. This allows you to describe rare cases (values that are only slightly valid). Also, it helps to identify the parameters that are highly susceptible to injection attacks (such as SQL injections).

Step 5: Creating and Running the Test Cases

After you’ve set up the test environment and identified some potential edge cases, you can formulate and run tests, comparing the real output to the predicted output. You should group these according to the type of test being performed as a part of best practice.

Wrapping Up

Now, you will have a clear understanding of your application’s security status. It will also act as a toolkit for ensuring that no major security problems make it to production deployment. If this sounds too daunting, you can always take the help of security experts at Astra Security.