API Security Testing: Importance, Risks and Checklist

Posted DateAugust 14, 2023
Posted Time 8   min Read

Many API-related breaches do not result from sophisticated attackers or diligent security researchers but stem from improper API design and implementation. Recent incidents at Clubhouse, John Deere, and Experian serve as examples, highlighting the consequences of neglecting basic API security best practices.

To safeguard against security risks, comprehensive API security testing becomes essential, ensuring APIs align with published specifications and are resilient to malicious inputs and attacks.

What is API Security Testing?

API security testing involves a comprehensive evaluation of API endpoints to uncover any weaknesses cybercriminals could exploit. The aim is to detect potential vulnerabilities such as injection attacks, fuzzy inputs, tampered parameters, authentication and authorization flaws, sensitive data exposure, and more. These vulnerabilities can allow attackers to gain unauthorized access, manipulate data, or even disrupt critical business functions.

By identifying these risks proactively, organizations can prevent security breaches, financial losses, and reputational harm.

One of the key aspects of security testing is the utilization of specialized tools designed to identify vulnerabilities within APIs. These tools can automatically scan API endpoints for common vulnerabilities and security misconfigurations.

Simultaneously, manual pen testers also play a critical role in the process by applying their expertise to analyze API responses for unexpected behaviours and anomalies that automated tools might overlook.

For instance, verifying whether an API returns accurate data not only concerns its functionality but also relates to its security – inaccurate or manipulated data could potentially indicate a security breach.

Benefits of API Security Testing

  • Discover all API endpoints, including proprietary and third-party APIs, using API-specific rules
  • Detect shadow, rogue, zombie, and other undocumented APIs. It ensures they don’t blindside you
  • Identify all known API vulnerabilities, weaknesses, and flaws, including OWASP Top 10 API risks
  • Identify and analyze unknown, logical, and zero-day API vulnerabilities using automated and manual pen testing
  • Use comprehensive API endpoint scanning reports to fix/ remediate/ manage vulnerabilities effectively
  • Understand the protection status of vulnerabilities via centralized dashboards
  • Prevent a wide range of known and unknown API threats. Fix flaws and vulnerabilities proactively through intelligent scanning
  • Understand your risks and harden your security posture

4 Reasons Why API Security Testing Needs Special Attention

1. Surge in API Adoption and Attacks

API attacks are rapidly rising in size and complexity, mirroring the growth of APIs themselves. The cost to address and mitigate such attacks is also on the upswing.

For example, consider the case of Twitter breach, which shows how serious the problems from API issues can be. Due to an unpatched API vulnerability, unauthorized access was granted to email addresses and phone numbers associated with user accounts. Unfortunately, this flaw went unnoticed for seven months, giving attackers ample time to exploit it and disclose the account information of 235 million users. Here is a detailed blog on diverse API security vulnerabilities and breaches.

2. Lack of API Visibility

A study conducted by Ping Identity revealed that 51% of the companies surveyed are uncertain if their security teams have complete visibility into all the APIs used within their organization.

3. Poorly Documented APIs

In practice, the need to introduce new features and speed up time to market often leads to restricted documentation. Without comprehensive API documentation, which includes definitions and specifications, QA and security teams are left to make assumptions about various use and misuse scenarios, including usage constraints.

4. Inability of Traditional Web Application Scanners

Web application security employed in conventional ways offers only partial solutions. Regarding API security, static analysis tools primarily focus on source code examination. Although they can detect certain API-related issues, their limitations in understanding the intended functionality hinder their completeness.

DAST scanners may not be well-suited for testing API security, lacking the capability to enumerate API endpoints. Although some DAST tools can utilize an OpenAPI/Swagger file for the spidering process, they still lack a deeper understanding of API endpoints, limiting their ability to provide an intelligent assessment of API security.

For instance, identifying Broken Object Level Authorization (BOLA) issues would require knowledge of the parameter value used to identify the object and the ability to interpret the response to assess attack success or potential errors.

The Indusface Infinite API Scanner offers a comprehensive identification of API and business logic vulnerabilities by combining a DAST scanner with manual penetration testing.

API Security Testing Checklist

When performing security testing for your organization, there are various factors you need to consider. The following are the essential best practices in API security testing to identify weaknesses, safeguard sensitive data, and protect against cyber-attacks.

Understanding the API Environment

The first step in API security testing checklist is understanding the API environment comprehensively. This involves identifying all APIs utilized within the application, including internal and third-party ones. Understanding the business logic, data flow, and user roles associated with each API is crucial for formulating an effective testing strategy.

API Threat Modeling

API threat modeling involves identifying potential threats and risks specific to the API and the application it supports. This step helps prioritize the focus of security testing efforts and ensures that critical vulnerabilities are addressed first.

OWASP API Top 10 is a foundational resource for understanding the most common and damaging API vulnerabilities. Many of these vulnerabilities are related to identity and access management issues.

Here is a comprehensive compilation of the OWASP API Top 10 2023 security threats and vulnerabilities that organizations must consider when conducting API testing:

  • API1:2023 Broken Object Level Authorization
  • API2:2023 Broken Authentication
  • API3:2023 Broken Object Property Level Authorization
  • API4:2023 Unrestricted Resource Consumption
  • API5:2023 Broken Function Level Authorization (BFLA)
  • API6:2023 Unrestricted Access to Sensitive Business Flows
  • API7:2023 Server-Side Request Forgery (SSRF)
  • API8:2023 Security Misconfiguration
  • API9:2023 Improper Inventory Management
  • API10:2023 Unsafe Consumption of APIs

There are multiple similarities between the list and the OWASP API Top 10 2019 index, featuring some reordering and redefining alongside the introduction of original concepts.

Beyond strong authentication controls, proper authorization at both the object level and function level is crucial, as highlighted in the OWASP API Security Top 10. Additionally, input validation is essential to prevent injection flaws, and rate limiting is necessary to restrict the number of lookups a single user can perform within specific timeframes, such as minutes, hours, or days. Adequate logging and monitoring are pivotal in promptly detecting and exposing attacks.

Discover key strategies for API security, including authorization, rate limiting, and twelve effective ways, here.

API Discovery

Enterprises require an automated solution to detect and categorize all APIs, encompassing both shadow and rogue ones.  API discovery involves identifying and cataloging all the APIs an application exposes, along with their functionalities, endpoints, and associated data flows.

API discovery acts as a critical first step in API security testing, providing insights into the attack surface and aiding in identifying and mitigating potential vulnerabilities.

Visualize APIs Using API Definitions

API definitions are also known as API specifications or description formats. They are language-agnostic baseline guides for machine consumption. By leveraging API definitions, automated tools generate API documentation, monitor APIs, and test.

API definitions are key for API scanning. API definitions tell automated tools the following details:

  • How is the API organized and structured?
  • How does it function and behave?
  • How does it link with other APIs?

In other words, the definitions help tools better visualize the API. API security scanning tools leverage the API definitions and predefined rules to detect vulnerabilities.

Prioritize Early and Automate API Security Tests

By incorporating API endpoint scanning early, potential vulnerabilities and weaknesses can be identified and addressed before they escalate into major issues. Automating these tests streamlines the process, enabling continuous monitoring and faster feedback to developers.

This proactive approach enhances the overall security posture, reduces the chances of security breaches, and saves time and resources in the long run. Emphasizing early and automated API security testing empowers organizations to deliver secure and reliable APIs to their users.

False Positive Management

The accuracy of security tests is paramount, as false positives can lead to unnecessary burdens on engineering and security teams, eroding trust in the testing process. Many companies have initiated security testing endeavors but abandoned the tools due to overwhelming false positives, resulting in a poor signal-to-noise ratio.

When choosing a security testing vendor, it is crucial to ensure they are well-equipped for modern application architecture, and API security testing.

Manual API Penetration Testing

While automated API security testing tools have limitations in testing custom business logic and specific application features, manual penetration testing becomes crucial. Security teams can uncover and mitigate API vulnerabilities through simulated attacks from internal or external sources.

Define the Types of Tests to Run

Running a comprehensive set of security tests is vital to identifying and mitigating vulnerabilities in APIs. A crucial aspect of this process is understanding how to test API security appropriately.

Here are the key API security test cases that should be performed during API security testing:

Authentication and Authorization Testing

Authentication verifies the identity of users or applications accessing the API, while authorization ensures they have the necessary permissions to perform specific actions. Testing the strength of authentication mechanisms and verifying proper authorization controls is crucial to prevent unauthorized access.

Input Validation Testing

Input validation ensures the API correctly handles and sanitizes user inputs to prevent common injection attacks, such as SQL injection and Cross-Site Scripting (XSS). Validating inputs helps prevent attackers from exploiting vulnerabilities by injecting malicious code.

Parameter Tampering Testing

Parameter tampering testing checks if an attacker can modify API parameters to manipulate data or perform unauthorized actions. This test validates that the API correctly detects and rejects tampered parameters.

Error Handling Testing

Error handling testing assesses how the API responds to various error conditions. Proper error handling ensures that sensitive information is not leaked in error messages and helps prevent information disclosure.

Security Misconfiguration Testing

Security misconfigurations occur when APIs are set up with incorrect or insecure configurations, leaving them vulnerable to exploitation. This test checks for misconfigurations in the API’s settings, permissions, and access controls.

Rate Limiting and Throttling Testing

Rate limiting and throttling are essential to prevent abuse and potential denial-of-service (DoS) attacks on the API. This test verifies that rate limiting is correctly implemented to restrict the number of requests per user or IP address.

Session Management and Token Testing

This test evaluates how the API manages user sessions and authentication tokens, such as JSON Web Tokens (JWTs). It ensures that sessions are appropriately managed and tokens are securely handled to prevent session-related vulnerabilities.

Business Logic Testing

The business logic testing assesses the API’s response to various business-specific scenarios. This test helps identify any security issues arising from improper handling of business logic, such as authorization checks or data validation.

Third-Party Integration Testing

APIs often integrate with third-party services or APIs. Testing these integrations ensures secure and properly configured data exchange and communication between the API and external services.

Compliance and Regulatory Testing

Compliance and regulatory testing ensure that the API adheres to relevant security standards and industry-specific requirements for APIs handling sensitive data or operating in regulated industries.

Take advantage of our all-inclusive API penetration testing checklist to craft a robust and thorough testing plan for your APIs. This checklist provides comprehensive API security testing test cases, aligning with the OWASP API Top 10, to ensure thorough coverage of potential vulnerabilities.


In API security testing, when tests fail, it is essential to fix the identified issues promptly and retest the API. Addressing vulnerabilities and weaknesses ensures a more resilient and secure API, reducing the risk of potential threats and data breaches. Continuous testing and remediation lead to a robust and trustworthy API environment.


API scanning is incomplete without proper reporting and documentation of the findings. The insights the scan reports provide are central to effectively managing security risks.

The API security testing report provides comprehensive details about the API’s security posture, including identified vulnerabilities, potential risks, and recommended remediation measures. It offers stakeholders valuable insights to enhance the API’s security and mitigate potential threats effectively.

Test your APIs with Infinite API Scanner

Indusface Infinite API scanner seamlessly navigates the complexities of API security. With plug-in-based architecture penetration testers and internal security teams can develop scripts to automate security test scenarios. With zero false positives, you can fix vulnerabilities accurately. It does not just perform input validation from the front end. With built-in manual pen testing, it covers all the business logic flaws scanners may miss.

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