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Guide To API Security Testing: Software and Trends

Application Programming Interface (APIs) have been around for a long time. Their widespread adoption in everyday application development has made them one of the most sought-after targets among cybercriminals. 

According to recent research on leading software giants, APIs witnessed a massive 168% increase in overall traffic as the attacks on them increased by 117%!

API vulnerabilities can lead to severe outcomes like data breaches, unauthorized access to critical systems, etc. If not attended to in due time, these vulnerabilities can cost your business millions, not to mention the reputational damage.

In this guide post, we will look at some critical API vulnerabilities and what your business can do to test your APIs effectively and keep the vulnerabilities at bay.

What Does an API Mean?

An API is a way for two different computer systems to share information. Depending on whether the two systems are running on the same machine, an API can be set up either at the code level or network level. An API is almost always a web interface, the most common way to link different computer systems in the business world.

API Security Testing ChecklistRESTful APIs have become an important part of building modern web apps in recent years. The RESTful method is much easier and more scalable than the older versions of web API that came before it, like SOAP (Simple Object Access Protocol).

REST can only be used on top of HTTP, the protocol that makes the web work. This means that insecure REST APIs pose the same risks as traditional websites and apps but are harder for automated web security scanners to test.

Why Do We Need API Security?

When an application's API fails, it is often assumed that the application is at fault. However, sometimes the bugs are in the API. Any information that the API shares with a third-party app is sent back to the internet in the end. So, APIs can reveal private and sensitive financial, medical, and personal information, potentially harming a company's finances and reputation.

In the past 12 months, about 95% of businesses have had at least one API security incident, according to the recent Salt Labs State of API Security report

Also, many businesses, including Facebook, Experian, Starbucks, and Peloton, have had public API incidents in the past few years. APIs need more security against vulnerabilities than the present generation of application security approaches can provide.

What are Some Key API Vulnerabilities?

Security issues and Vulnerabilities in APIs typically fall into a few distinct categories. Some of the key API vulnerabilities include:

1. Access Control Vulnerabilities

Authentication: Similar to how doors have multiple types of locks, APIs can have several authentication mechanisms. API keys supplied as headers or query parameters, HTTP Basic Authentication using a username and password, and OAuth 2.0 Bearer Access Tokens are all common authentication methods.

Authorization: Authorization is the process of figuring out if a user or machine can access data or do actions with or without authentication. Access control policies and privileges can be used together to make this happen. Authorization is a bit harder to set up than authentication because it requires setting up complex chains of multiple rules and policies that must be evaluated securely to allow or block actions.

Access control policies frequently have a pattern. When a client requests access to a resource that needs authentication, the server examines the request for authorization and authentication and looks for items like:

  • If the account is present
  • Whether the requested resource falls under the client's access scope
  • If the request included any cookies or tokens from the past, etc.

The server may return a token, session id, or other identifiers to mark the session if the attempt is successful. Throughout the session, additional authenticated requests will proceed similarly.

2. Input Validation

Input validation is always essential to consider while searching for bugs in your API. Understanding that input includes everything the server receives from the user, third-party applications, and internal procedures are vital. Common areas to test for input attack vectors in an API include:

  • Within the requested header
  • Parameters within the request
  • Parameters within the URL
  • Different request methods
  • File uploads (PUT/DELETE requests)

3. Rate Limiting Vulnerabilities

APIs are designed for applications anticipating a high volume of random requests. This feature can be exploited to enumerate the API endpoints in unforeseen ways rapidly. If an API's rate limiting isn't set up right, it could be used to send a lot of requests to enumerate the application and cause other issues.

4. HTTP Vulnerabilities

APIs support a variety of HTTP methods. When testing the API, it's crucial to understand what the application expects and what it supports. Sometimes using HTTP methods can force a user to execute prohibited operations like PUT, POST, DELETE, etc. Even if these are not incorporated into the application logic, bizarre things can happen if the program is sloppy and lacks any logic to parse.

5. Cross-Site Scripting Attacks

Cross-site scripting, or XSS, occurs when malicious code is inserted into a website. These codes have the power to force the user to take any action, including unauthorized access and data breaches. The attacker's intentions will wholly determine its actions.

6. SQL Injection

In this vulnerability, a user enters a SQL query instead of valid data, which can change the way your API works.

How to Test API Security?

To test an API, client software is used to send requests to an endpoint of the application being tested. Almost always, this is an HTTP client, and there are many free ones to choose from.  

Postman or Insomnia are the most well-known clients. Small APIs should use Insomnia because it is easy to work with and doesn't need many configurations. Postman is better for APIs that are more complicated because it stores authentication parameters and lets you make groups of requests. Postman can also automate testing with "monitors," which is helpful if the application it is testing is constantly changing.

The DevOps lifecycle can move along faster if some parts of the Security Audit process are automated. The Fuzz Test and the Security Test are the two parts that are easiest to automate.

Step 1: Outline the Security Requirements

Before planning a security test for an API, you need to know the basic requirements. This means asking questions like: 

  • Should the API use a TLS/SSL certificate and be accessed through HTTPS?
  • What permission groups are there for the different types of application resources?
  • How does the process of logging in work? Is there an outside OAuth provider?
  • What is the API's attack surface? Where could someone do something bad to the app?

As a part of asking the above questions, it's essential to understand beforehand what makes a test pass or fail based on the outlined requirements.

Step 2: Organize Your Testing Environment

After figuring out the scope of the test, it's time to set up an application environment for testing. Using the standard staging environment for smaller applications is a good idea. It is best to set up a separate test environment for more extensive applications with many internal states. You can do this by duplicating all resources in the staging environment or simulating them with a tool like Wire Mock.

Step 3: Do a Sanity Check of Your API

After you have scoped out your requirements and organized your testing environment, make sure you send your API a few requests to ensure everything is set up correctly.

Step 4: Define the Input Domain

Before generating individual test cases, it is vital to have a solid understanding of what each parameter is responsible for and the various combinations that can be used for each parameter. This allows you to establish edge cases, which are just barely legitimate values, and figure out which parameters are the most susceptible to injection attacks (like SQL injections).

APIs should set limits on what can be put in, like the types and ranges of data (for example, a particular parameter could only be valid as an integer between 1 and 100). With JSON Schema in OpenAPI, you can write down these rules and use them to check if they are correct. Always make test cases that go beyond the limits and have your test runner ensure they lead to a 400 Bad Request error.

Step 5: Develop and Execute the Test Cases

When the test environment is ready, and you are aware of any potential edge situations, you can develop and run tests to compare the results with anticipated ones. Best practices dictate that you should categorize these according to the sort of test being administered. Here are a few instances:

  • Can both HTTP and HTTPS be used to access resources?
  • Does authentication apply to all endpoints?
  • What happens if you submit a potentially dangerous file with the mime type that the program expects if you support file upload?
  • What happens if you provide an HTML/JS element instead of user-supplied data if the web app that consumes the API embeds user-supplied data (for example, a name) on the page?
  • Are there any resources you can access that your token isn't allowed to?

If you adhere to these guidelines, you need a solid grasp of your application's security posture and a toolkit to ensure that no severe security flaws make it into a production deployment.

What is the Timeline for API Security Testing?

Ideally, the time required for API security testing depends on the project's scope and infrastructure. Depending on the number of test cases, the time can vary from a few hours to a few days. If you are going for the Appknox Mobile App Security Testing suite, the entire process will finish in less than 60 minutes with more than 130+ test case coverage and less than 1% false positives!

How Much Does API Security Testing Cost?

To have a secure website, you need to find the right API security testing provider that can find all your API's hidden flaws. Depending on the size and complexity of an API security test, the price might range from $500 to $6,000 per scan. However, several customized plans are available in the market, which caters to your application specifically, and the price is decided flexibly. 

The most popular Appknox Profesional testing plan, which offers unlimited vulnerability assessment and dedicated call and chat support, comes at unbelievably affordable prices!

API Security Testing Checklist: 7 Best Practices

The best practices below will help make sure that an API security testing program is complete and thorough. 

API Security Testing Checklist-1

1. Determine Who Oversees API Security Testing and Upkeep Overall

An API's lifespan involves numerous teams, and as it moves forward, numerous quick modifications and iterations will occur. It's crucial to assign someone responsible for documenting every API, and ensuring all tests are finished and the findings are used. 

2. Always Take Money and Time Into Consideration

Organizations must take time and money into account when beginning a new project because security testing requires both. Threat modelling will identify potential API risks and vulnerabilities that require mitigation. However, a budget for maintaining and updating API tests will also be required after the project is live. 

3. The Function and Intended Use of Each API Should Be Registered, Classified, and Documented

It is crucial to describe APIs and how to utilize them. Tests can determine whether an API can handle both acceptable actions and valid data and unacceptable actions or incorrect data using the information from these papers. Both humans and machines can learn about and comprehend API capabilities thanks to standards like the OpenAPI Specification, AsyncAPI, and GraphQL Introspection. Several API tools use these specs to accelerate the creation of APIs.

4. Start Your Test Runs Early and Automate As Much as You Can

Everyone saves time and money if security issues are discovered early in the development lifecycle. Several API security tools are available, both commercial and open source, that may be included in current processes and pipelines for continuous integration and delivery. Building exact replicas of production systems are no longer necessary, thanks to tools that offer mimicking services. 

Determine who will do the tests, such as developers, the security team, or outsourced pen testers, if the internal team lacks the necessary expertise. Tests ought to be executed on each build of the application, ideally.

5. Define the Types of Tests To Run

The following tests should be performed on every API:

  • Invalid inputs: Inputs from an API should be cleaned and checked as if they came from a source that can't be trusted. Fuzzing is a way to test an API's ability to handle unexpected data without crashing by sending it random data.

  • Injection attacks: Use these test attacks to ensure that the API rejects requests that attempt to alter back-end databases or run OS commands on the server without revealing any sensitive information.

  • Parameter tampering: An attacker can easily modify parameters sent through an API request, like the price of an item in a shopping cart. Check to see if the API verifies and makes sure the parameters make sense before it uses them.

  • Restricted HTTP methods: Send requests using all eight HTTP methods to make sure that methods like CONNECT, DELETE, PUT, and TRACE, which aren't needed or allowed on the server. This is a security risk if these methods return a valid response instead of an error. If an application needs to use one of these methods, make sure that only trusted users can use it.

  • Business logic vulnerabilities: Because of flaws in how an API was designed and built, an attacker might be able to make it do things developers never intended. For example, they can finish a transaction without going through the intended purchase workflow. Automated tools often have trouble testing for this kind of vulnerability because the vulnerability is usually unique to the application and how it works. This vulnerability can be avoided by having clear design and data flow documents that describe transactions and workflows and list the assumptions made at each step.

  • Controls for authentication, access, and encryption: Ensure that the person making a request is known to the server and has permission to use the requested resources. Identity and authorization protocols like OpenID Connect and OAuth can take a lot of work to set up and manage the keys and tokens that go with them. More time needs to be set aside to test these security controls.

  • Excess Loads: Rate limit controls, which say how many times an API can be called each time, help stop unauthorized connections and protect against DDoS. Make sure these limits are set for the best results. 

Lastly, error messages, log entries, and handling a failover are essential parts of testing. After each test, check the messages and logs to ensure the right information is recorded. 

6. Stay Current With Security Risks and Update Documentation

Everyone who builds APIs needs to know the latest ways that hackers attack APIs so that they can update code, security controls, and tests. The security team should regularly update everyone in the project on new threats and best practices. 

Final Thoughts

Application Programming Interfaces (APIs) serve as the conduits for data transfer between distinct programs and (micro)services. Data leakage can be prevented if adequate safeguards are implemented before, during, and after use. 

APIs serve a vital role within modern technology-driven ecosystems where they are essentially portals into your software and applications; these are where hackers will most likely try to break in. Utilizing the information provided in this guide, you can not only safeguard your APIs from critical security vulnerabilities but also enhance the reputation of your product in the market considerably.

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