API Pentesting: Types, Common Flaws & Testing Tools
API Pentesting: Types, Common Flaws & Testing Tools
What are APIs?
API, Application Programming Interface, is a set of rules that allows two systems to communicate with each other. More than 80 to 90% of modern web applications use at least one, and sometimes more than one, API. Large platforms like Facebook, Google, Twitter, Shopify, and Amazon heavily rely on API internally and externally. Even small SaaS applications, such as those for payment, maps, analytics, and email, are communicating through APIs. Securing APIs and web application interfaces is more important than preventing your website from other attacks.
The origin of API is the first widely recognized API, which was a remote procedure call (RPC) concept introduced by Sun Microsystems in 1980, allowing programmers to communicate over the network and invoke functions on remote systems. This small change revolutionized tech history and went viral in no time.
The importance of API security
API security is crucial for any business, regardless of its size or level of operation. Not implementing API security can cause several issues, including unauthorized access to sensitive data, such as financial information and property details, which can be stolen, enabling unauthorized actions, and allowing attackers to manipulate systems or perform unauthorized actions. Expose internal systems. Poorly secured APIs can reveal the internal infrastructure of any application, including web, mobile, or desktop applications, which can damage trust and compliance and become a major cause of data breaches.
The objective of API penetration testing
The objective of API penetration testing is to evaluate the potential vulnerability and security that can be later exploited by hackers and hacktivist groups. This includes accessing the API’s authentication, data handling, input validation, and much more. The main aim is to find broken authentication, object-level authorization, or any kind of malicious activity or misconfiguration.
Common API vulnerabilities
API can have multiple levels of normal to severe API vulnerabilities, including broken authentication, escalated privileges, missing role validation, SQL injection, NoSQL injection, command line injection, and sometimes these vulnerabilities can lead to object-level authorization to remote code execution.
Types of API penetration tests
- Black Box Testing
- White Box Testing
- Gray Box Testing
- Authentication Testing
- Authorization Testing
- Input Validation Testing
- Business Logic Testing
- Rate Limiting Testing
- Data Exposure Testing
- Injection Testing
- Session Management Testing
- Error Handling Testing
Mobile Application Penetration vs web application Penetration Testing
Testing a mobile application and testing a web application architecture are quite different. However, the Android mobile application sometimes defaults to encryption in binaries, and attackers have a solution that allows them to decode the mobile application using various techniques and tools. However, developers often overlook weak authentication points in mobile applications, leaving API keys in variables and other sensitive data, which later become critical vulnerabilities. Sometimes exploiting a mobile application can help identify potential vulnerabilities, such as authorization bypass, data exposure, and API endpoints, among others.
Attackers Can Find in Mobile Apps (Related to API Security):
- Hardcoded API keys and secrets
- Insecure storage of sensitive data
- Weak or missing authentication
- Insufficient authorization checks
- Exposure of API endpoints
- Lack of certificate pinning (enables MitM attacks)
- Insecure data transmission (e.g., using HTTP instead of HTTPS)
- Debug information and verbose error messages.
- Inadequate rate limiting
- Outdated libraries and dependencies(which can be exploit latter )
Tools and techniques for API pen testing
There are multiple tools that help to test APIs. Some of them are highly paid, and some of them are open source for testing. Fuzz, Burp Suite, Dersearch, and tools like these are freely available in the marketplace to test. However, there are third-party organizations that do manual testing for you. Manually testing can be more beneficial than testing through automation. Sometimes testing through automation can leave many vulnerabilities behind.
How much investment is typically required for effective API security and testing?
There are various organizations in the market that currently provide manual and automated API testing, including both black box and white box testing. The cost depends on the business. If the business is a smaller-scale operation with minimal web infrastructure, it can incur a cost of $100 to $500 for the API section, which includes 500 parameters. The cost can then range from $5,000 to $100,000, depending on the infrastructure and the number of in-scope domains.
How often should API penetration testing be performed?
Regular penetration testing is recommended because it helps identify (Medium, High Critical) level security weaknesses, misconfigurations, and overlooked vulnerabilities before they can be exploited by attackers or hacktivist groups.
While it may not always uncover true zero-day vulnerabilities, it is highly effective at detecting known issues, business logic flaws, and insecure implementations. By continuously assessing applications and systems, organizations can reduce their attack surface, validate the effectiveness of security controls, and proactively mitigate risks before they lead to real-world breaches.