API Penetration Testing: An In-Depth Overview

To accurately understand real-world hacker habits, cybersecurity experts use penetration testing tools and services to mimic typical injection attacks and exploits. In fact, penetration testing comes in several different styles and types depending on the needs of the company involved.

API penetration testing, for example, helps businesses and developers find vulnerabilities in web application interfaces and the connections between different software. It’s a practice that, when carried out properly by professional testers, can boost your outward security posture.

We’ll walk through the basics of penetration testing as it applies to API security, why it’s important, and how professional experts carry out such tests.

What is an API Penetration Test?

An API penetration test is a controlled hack or attack on an Application Programming Interface, or API, used to find security vulnerabilities.

Testing also explores how attackers exploit these weaknesses to harvest sensitive data, harm users, and damage developer reputation.

APIs help you deliver specific types of services to your end users. It’s a middleman or intermediary, a mechanism that ensures smooth communication between different applications.

For example, a maps app on your phone will use APIs to communicate with software that pulls GPS data and translates it into a user-friendly format.

Unfortunately, as with all networks, programs, and infrastructures, there is always a risk of security vulnerabilities.

Potential vulnerabilities in APIs might include functionality problems, security misconfigurations, or poor defense against common Sequence Query Language (SQL) injection and brute force attacks.

Essentially, a thorough API penetration test helps to limit data exposure and offers developers advice on remediation and how to fortify APIs against genuine attacks. Think of it as a "dry run" before hackers try to gain unauthorized access for real.

What Vulnerabilities can API Penetration Testing Identify?

Common API vulnerabilities that this penetration test can identify include:

• SQL injection and NoSQL injection vulnerability
• Command injection vulnerability
• Faulty or broken access control
• Login form vulnerabilities
• Server-Side Request Forgery (SSRF) attack weaknesses
• IDOR (insecure direct object reference) or URL weaknesses
• Sloppy asset management
• Poor control of API endpoints
• Query string data exposure
• DOS (denial of service) attack weaknesses
• Obsolete versions
• Broken object level authorization

These, of course, are just some of the specific errors in the programming, deployment, and management of APIs that could lead to malicious attacks.

However, many penetration testers refer to the Open Web Application Security Project, or the OWASP, to learn more about the most common faults and vulnerabilities in API development.

OWASP produces a "Top Ten" that professional testers use as a springboard to build a penetration methodology on.

For example, alongside the above, OWASP recommends that developers look for forgery of server-side requests when managing APIs. It also suggests that poorly secured design elements and general integrity failures can lead to data leakage.

Resources such as the OWASP API Top Ten help testers manage a target API by keeping them up to date on the biggest threats in the current landscape, too. For instance, testers might learn that they need to focus on cross-site scripting (XSS) or injections into user input forms.

Best Practices for API Security

To prevent many of the threats that can arise through API requests, our cybersecurity experts and testers recommend the following practices to tighten up your security posture.

Authentication and Authorization

Hackers frequently attack APIs by focusing where people request access to such services through forms and login screens.

Here, attackers might use brute force attacks (where they guess credentials countless times using specific tools), or manipulate JSON web tokens so they mimic users with advanced access privileges.

We typically suggest using a separate, dedicated 0Auth server if you need to provide access tokens to users.

Token issuing is where you authenticate and authorize users – and leaving these tasks to frontend gateways or APIs themselves can open up security issues that are difficult to manage.

A single 0Auth server can, in our experience, provide a more streamlined, manageable, and secure authentication and authorization process.

We also recommend using multi-factor authentication, or MFA, to ensure anyone requesting access needs to do so through several accepted devices. If in doubt, offer zero permissions unless you can be absolutely sure you know who’s trying to gain access.

Use HTTPS

HTTPS is the secure standard for data transfer online. Using HTTPS to encrypt data shared via API effectively cloaks it so no external parties can sniff it out. It's an extra layer of protection that ensures you screen everyone and everything that demands access.

Beyond this, always store encrypted passwords in secure vaults or databases. Just because it’s encrypted data doesn’t mean you should store it out in the open. You could use HTTPS headers or query strings, for example, for extra security in your API.

Input Validation

A strict input validation process ensures that you can restrict against unexpected values and text being entered into public-facing forms. This can, for instance, protect your API against common injection vulnerabilities, where attackers insert malicious code to gain unauthorized access.

We often recommend that our clients use specific tools and commands to whitelist the values they expect to see, and the range of characters that can be used.

API Request Limitation

Rate limiting and request limiting can prevent brute force attackers from trying to gain access to APIs. This essentially helps to prevent flooding and crashing, too.

Penetration testers might find that there are few limit controls in place – in which case, a primary point of remediation will be to simply apply a set number of strikes before user access is blocked.

Logging and Monitoring

Logging and monitoring is extremely important during penetration testing. It’s where testers keep detailed records of what they’ve tried and the outcomes of certain experiments.

However, it’s just as important to set up detailed error logging on the server side of your operation. Doing so records every action taken via your API and when it was used. It’s extremely useful in helping to filter out potentially suspicious usage patterns.

Consulting a detailed error log could make all the difference in addressing potential data breaches early on, or leaving your applications and web services to fester.

Using error logs in a simplified format for end users can be helpful, too – particularly if they want to troubleshoot API problems independently.

How is an API Pentest Conducted?

A typical API pen test includes:

1. Outlining which APIs are to be tested and which methodologies are most appropriate
2. Deciding which tools are to be used when researching weaknesses and exploiting them
3. Confirming the scope of vulnerabilities searched for during said testing
4. Drawing up the types of reports and remediation advice to be given to end users at the end of tests

Testers then start to explore the APIs within the scope of their project and record any notable weaknesses or flaws that could be exploited. They might send requests to APIs and, working alongside the client, build a list of priorities.

Once this record is built, testers can work using a range of tools to investigate and actively attack a client’s APIs in a controlled environment. They go as far as carrying out a hack without leaking the data.

Again, the results of these tests are recorded carefully. Testers then analyze this data and provide detailed reports to the client, with advice on improving their API security in the face of future threats.

Like general penetration testing, we recommend running these analyses twice a year, or as soon as significant changes are made to APIs. This is to ensure your APIs are robust against the latest threats in the landscape.

How Long Does API Pen Testing Take?

API pen testing might take as quickly as 24 hours to initiate and get underway, but taking full attacks and reporting into account, it could take up to ten working days.

This, however, depends largely on the scope of the project in question, the tools used, and the expertise involved in the testing.

It’s why we always advise customers to consult with us before we can set transparent budgeting and timescales. It’s a fair way to ensure you know exactly what to expect from our process.

API Penetration Testing Tools

The tools an API pen tester might use will, again, vary wildly depending on project scope and demands. However, some of the most commonly used API penetration testing tools include:

• Jwt_tool, an open-source tool that can emulate token manipulation attacks
• Postman, a general API builder and manipulator
• GraphQL, a type of API language used to build APIs in other languages
• Burp Intruder, or the Burp Suite, which testers use to mimic brute force attacks
• Swagger, a tool that helps to build and break down API documentation
• Probely, an automated vulnerability scanning tool built for APIs

Of course, in some cases, testers might not use any of the above, or might use them all – and more besides.

Conclusion

API penetration testing is a reliable way to ensure the security of your software and the communication bridges between them. However, it's always important to hire a professional team with the right certifications.

That way, you can ensure you have an appropriate attack surface to evaluate the effectiveness of your firewall, error handling practices, user accounts security, and more.

At VikingCloud, we offer penetration testing that puts your sensitive information under safe scrutiny. It’s as close to real-world hacking as you can get without causing any legitimate harm.

Struggling to understand the meaning of business logic, payloads, and debug modes? Let our team handle the complex side of testing so you and your own customers can rest a little easier – with more robust, secure APIs. We’re the only penetration testing providers you’ll ever need.