API Security Testing: Risks, Tools, and Best Practices

Key Takeaways

API security testing identifies vulnerabilities like broken authentication and data exposure by simulating attacks and analyzing API behavior under various conditions.
Combining testing (deep, contextual analysis) with scanning (broad, automated checks) enhances detection of both logic flaws and misconfigurations.
Integrating API security testing into CI/CD pipelines enables early detection of issues and aligns with DevSecOps practices to reduce manual effort.
Comprehensive testing across internal, external, and third-party APIs ensures consistent protection and reduces risk from indirect vulnerabilities.
Context-aware tools like Pynt help detect business logic flaws with high accuracy, minimizing false positives and streamlining developer workflows.

What is API Security Testing?

API security testing is the process of evaluating application programming interfaces to detect and resolve security weaknesses before they can be exploited. It involves simulating attacks, validating access controls, and assessing how APIs handle data, authentication, and input.

Unlike traditional application testing, API security testing addresses how APIs expose logic and data across systems. It focuses on identifying issues unique to API architecture, such as improper token handling, overexposed endpoints, and flawed access controls.

API Security Testing vs. API Security Scanning

Although they sound similar, testing and scanning serve different purposes. The best API security strategies should combine both.

API security testing encompasses both dynamic and static methods to identify deep-seated issues, such as broken authentication, data exposure, or logic flaws inherent to the API's design and implementation.
API security scanning prioritizes speed and coverage, leveraging automated tools to identify known issues such as misconfigured headers, insecure endpoints, or outdated components.

Why Is API Security Testing Important?

API security testing is essential due to the critical role APIs play in modern software architecture. APIs serve as gateways for accessing and manipulating data, making them attractive targets for attackers. Testing for security helps mitigate these risks in several ways:

Preventing Unauthorized Access: APIs often handle sensitive data, and security flaws can expose this data to unauthorized parties. By testing APIs, organizations can ensure that authentication, authorization, and access control mechanisms are robust and capable of thwarting unauthorized access attempts.
Preventing Service Disruption: Attackers can exploit vulnerabilities in APIs to perform denial-of-service attacks or cause underlying systems to crash, impacting service availability. Testing helps identify and address such issues, ensuring the reliability and availability of services that rely on APIs.
Protecting Against Data Manipulation and Loss: APIs can be manipulated to alter or destroy data, leading to data integrity issues. Security testing can reveal weaknesses in input validation and processing, preventing such manipulative attacks. This ensures that the data remains accurate and reliable.

Learn more in our detailed guide to API security scanning.

How Does API Security Testing Work?

API security testing follows a structured process that blends automation with manual inspection to uncover and resolve potential risks. This ensures that APIs handle requests securely, enforce access controls properly, and protect sensitive data from exposure or misuse. The process typically includes the following steps:

Understanding the API: Analyze the API’s design, documentation, and intended use cases to identify functionality, expected inputs, and high-risk operations that require closer scrutiny.
Creating a Testing Plan: Define what will be tested, such as authentication, authorization, rate limiting, input validation, and error handling. Prioritize test coverage based on risk and business impact.
Simulating Requests: Send various types of legitimate and malicious API requests. This includes malformed payloads, large volumes of queries, and attempts to bypass authentication, all aimed at evaluating how the API behaves under pressure or misuse.
Analyzing Responses: Review the API’s responses for indicators of security gaps, such as verbose error messages, data leakage, or inconsistent status codes that may expose sensitive implementation details.
Identifying Vulnerabilities: Use both manual techniques and automated tools (like DAST, SAST, and IAST solutions) to detect issues such as broken access controls, injection flaws, insecure authentication, and misconfigurations.
Remediating and Retesting: After vulnerabilities are identified, collaborate with development teams to patch the issues. Then, retest the same scenarios to confirm the fixes and ensure no regressions were introduced.
Integrating with CI/CD Pipelines: Incorporate automated API security tests into your CI/CD pipeline to catch regressions early and enforce secure coding practices throughout the development lifecycle.
Monitoring and Continuous Assessment: Go beyond one-time testing by continuously monitoring APIs in production environments to detect new threats, misconfigurations, or unauthorized access attempts as usage evolves.

Diagram showing the API Security Testing Lifecycle with six stages, including analysis, testing, CI/CD integration, and remediation.

Common Vulnerabilities Found in Various API Types

APIs differ in structure, protocol, and use case, and each type is prone to common API security risks. Understanding the most frequent API security vulnerabilities by API type helps prioritize testing efforts and tailor protections based on architecture. The table below provides a high-level overview of these risks for four widely used API types:

API Type	Common Vulnerabilities	Notable Traits
REST	- Missing or weak authentication - Injection attacks (e.g., SQL, command) - Unsecured endpoints - Data exposure due to improper filtering	Simple and widely adopted; uses HTTP methods; risk increases with poor access control
SOAP	- XML injection - XML External Entity (XXE) attacks - WS-Security misconfigurations - Denial-of-service (DoS) from large XML payloads	Protocol-heavy; uses XML and WS-Security; stricter schema but complex configuration
GraphQL	- Over-fetching of sensitive data - Deep query denial-of-service - Missing authorization checks - Query manipulation through batching or nesting	Single endpoint model, highly flexible, requires strong access control enforcement
JSON-RPC / XML-RPC	- Parameter tampering - Replay attacks - Insecure transmission if HTTPS is not enforced - Lack of input validation	Procedure-focused architecture, streamlined requests, vulnerable to logic-layer abuse.

REST APIs

REST APIs are commonly used in modern web applications due to their simplicity and scalability. However, they also present several security challenges:

Lack of Authentication and Authorization: One of the most common vulnerabilities in REST APIs is insufficient authentication and authorization mechanisms. Attackers can exploit weak or missing access control to gain unauthorized access to sensitive data or operations.
Injection Attacks: REST APIs are vulnerable to injection attacks, such as SQL injection or Command injection, where malicious input can be used to manipulate the backend systems or databases.
Insecure Endpoints: Unsecured API endpoints can expose the entire application to attacks. REST APIs often rely on HTTP methods (GET, POST, PUT, DELETE), and improper validation or poor endpoint security can lead to issues like data leakage or resource modification.
Data Exposure: Sensitive data can be exposed through REST APIs, especially if responses are not adequately filtered or sanitized. This can include personal information, API keys, or system configurations.
Rate Limiting: Lack of rate limiting can make REST APIs vulnerable to denial-of-service (DoS) attacks, where an attacker floods the API with excessive requests, leading to performance degradation or system crashes.

SOAP APIs

SOAP APIs, though more structured and protocol-driven than REST, have their own set of vulnerabilities:

XML Injection: SOAP APIs are prone to XML injection attacks, where attackers can inject malicious XML code into requests to manipulate the SOAP message processing and extract sensitive data.
WS-Security Misconfigurations: SOAP APIs often use WS-Security for message-level security. Improper configuration of WS-Security can lead to insufficient encryption or integrity checks, allowing attackers to tamper with messages.
XML External Entity (XXE) Attacks: SOAP APIs are vulnerable to XXE attacks, where an attacker can exploit poorly configured XML parsers to access internal files or execute malicious code on the server.
Complexity and Overhead: Due to the more complex nature of SOAP, APIs can suffer from higher overhead in terms of processing, making them susceptible to denial-of-service (DoS) attacks, especially if the API does not handle large payloads efficiently.

GraphQL APIs

GraphQL APIs, while more flexible and efficient in data fetching, introduce unique security concerns:

Excessive Data Exposure (Over-fetching): GraphQL allows clients to specify the exact data they need, but this flexibility can lead to over-fetching, where the API returns more data than necessary. Without proper restrictions, this can expose sensitive information.
Denial-of-Service (DoS) via Complex Queries: Due to GraphQL's query flexibility, attackers can craft overly complex or deeply nested queries, which can overwhelm the server, leading to performance issues or crashes.
Improper Authorization: GraphQL APIs often lack fine-grained access control mechanisms. Without proper authorization checks, attackers can gain access to unauthorized data or perform restricted operations.
Batching and Query Manipulation: Attackers can exploit GraphQL’s batching features by sending large query requests or altering the query structure to extract more data than intended, leading to data leaks.

JSON-RPC and XML-RPC

RPC-based APIs like JSON-RPC and XML-RPC focus on remote procedure calls but also face several vulnerabilities:

Parameter Tampering: In RPC APIs, parameters are often passed directly to backend systems. If these parameters are not properly validated, attackers can manipulate them to perform unauthorized actions or gain access to sensitive data.
Replay Attacks: RPC APIs are prone to replay attacks, where an attacker captures a valid request and resends it to the API to replicate actions, such as duplicating transactions or requests.
Insecure Transmission: If JSON-RPC or XML-RPC APIs do not use secure communication protocols (e.g., HTTPS), they are vulnerable to man-in-the-middle (MITM) attacks, where an attacker intercepts and manipulates requests and responses.
Lack of Input Validation: Improper input validation can lead to attacks such as injection (SQL, script, or command) where an attacker sends malicious payloads to compromise backend systems.

Did You Know?

Injection flaws ranked as the second most critical vulnerability according to Pynt's analysis of 100,000+ endpoints.

Benefits of API Security Testing

API security testing plays a critical role in reducing attack surface, ensuring compliance, and maintaining user trust. By proactively identifying and addressing weaknesses in how APIs handle requests, organizations can prevent security incidents before they occur. Key benefits include:

Early Detection of Security Flaws: Testing helps uncover logic flaws, weak authentication, and insecure configurations early in the development cycle, reducing the cost and impact of remediation.
Improved Protection of Sensitive Data: Security testing ensures APIs enforce proper access controls, helping prevent data leaks, unauthorized access, or unintentional exposure when users access data through the API.
Stronger Compliance with Regulatory Standards: Regular API testing supports compliance efforts for frameworks like GDPR, HIPAA, and PCI DSS, which require secure handling of personal and financial data.
Reduced Risk of Business Disruption: By identifying denial-of-service risks and critical vulnerabilities, testing helps maintain application uptime and service continuity.
Support for DevSecOps and Shift-Left Initiatives: Integrating testing into CI/CD pipelines enables security to be addressed earlier in development, improving agility without sacrificing protection.
Enhanced Customer Confidence and Trust: A well-tested API ecosystem strengthens user confidence by demonstrating a clear commitment to protecting data and maintaining reliability.

API Security Testing Checklist: How to Get Started

Establishing a reliable API security testing program requires planning, tooling, and coordination across development and security teams. The following steps offer a structured starting point for launching or improving your efforts, especially when formalizing workflows or scaling testing across services.

Step 1: Establish Who Has Responsibility for Testing API Security

Define clear ownership across teams. In a DevSecOps environment, API security testing may involve developers, QA engineers, security analysts, or SREs. Assign responsibilities for writing test cases, validating test coverage, and triaging results.

Step 2: Plan and Allocate Time and Resources

Include API security testing in your sprint cycles and resource planning. Allocate time for both automated and manual testing, as well as for remediation work. Successful testing requires organizational commitment, not just tooling.

Step 3: Define the Tools and Types of Tests to Run

Select a combination of scanning technologies based on your environment. Use SAST, DAST, and IAST tools where appropriate, along with specialized API security tools designed for modern application programming interfaces. Define your test strategy to include token handling, input fuzzing, authorization checks, and schema validation.

Step 4: Run Tests Early and Automate When Possible

Integrate automated testing into your CI and CD pipelines. Automated scans should run during code commits, pull requests, and staging deployments. Supplement automation with manual reviews to detect logic flaws that scanners cannot catch.

Step 5: Stay Current With Security Risks

Review the latest common API security risks from OWASP and industry advisories. As API threats evolve, so should your test cases. Revisit your threat model regularly to ensure it aligns with your API’s design and attack surface.

Step 6: Include Third-Party and Public API Dependencies

Third-party APIs often fall outside the scope of internal testing but introduce indirect risks. Review the documentation, scopes, and authentication models of every public API your platform consumes. Validate that integrations do not expose excess permissions or bypass your internal access controls.

Step 7: Track and Audit API Changes Over Time

APIs change rapidly, and each change introduces new potential issues. Keep changelogs and audit trails for all deployed versions. Use schema diffing tools to identify undocumented changes, and perform security testing consistently after each deployment to verify that protection remains intact.

Best Practices for API Security Testing

To maximize the effectiveness of API security testing, it’s important to approach it strategically, not just as a checklist exercise. The following best practices help ensure testing is thorough, repeatable, and aligned with modern development workflows.

Define the Scope of Testing: Identify which APIs need to be tested, what environments are in scope (development, staging, production), and which endpoints or data flows present the highest risk.
Test for Broken Authentication and Authorization: Prioritize tests that validate how the API handles identity, tokens, and permission boundaries. Broken access controls are among the most exploited API flaws.
Include Input Validation and Injection Checks: Simulate malicious inputs to detect injection risks (e.g., SQL, XML, or command injection) and confirm the API handles unexpected or malformed data safely.
Analyze Error Handling and Information Exposure: Test how APIs respond to failed or invalid requests. Look for verbose error messages or stack traces that may leak implementation details or sensitive information.
Use Both Manual and Automated Testing Techniques: Combine dynamic scanning tools and specialized API security tools with manual testing to uncover logic-level flaws, especially in APIs with complex workflows or business rules.
Integrate Security Testing into CI/CD Pipelines: Shift testing left by automating scans in your build process. This ensures that regressions and newly introduced risks are caught early.
Test for Rate Limiting and Abuse Prevention: Simulate excessive requests to confirm that APIs enforce throttling and handle denial-of-service attempts effectively.
Include Third-Party and Public APIs: Extend your testing to include third-party integrations, as they may introduce indirect security risks if misconfigured or overly permissive.
Keep Test Cases Updated: Regularly review and update your test suite to reflect changes in API design, new endpoints, or emerging threats. Also, perform security testing consistently across environments to ensure continuous protection.

Tzvika Shneider

CEO, Pynt

Tzvika Shneider is a 20-year software Security industry leader with a robust background in product and software management.

Expert Tip: Prioritize Contextual Testing to Catch What Tools Miss

Automated API scanners are essential for coverage, but they often miss flaws in business logic or access control rules.

That’s why I always recommend layering contextual, manual testing into your API security strategy. Here’s what works in real-world testing:

Test Privilege Boundaries Manually: Check if low-privilege users can access or manipulate high-privilege data by tweaking tokens or IDs.
Review Undocumented or Shadow Endpoints: Sometimes APIs expose dev routes or deprecated versions. Inspect network activity and API gateways closely.
Simulate Real Abuse Scenarios: Go beyond basic injection testing. What happens if someone scrapes massive data volumes or chains requests in a way that developers did not anticipate?

This hybrid approach reveals the most dangerous issues that automated tools often miss.

Takeaway: Real security comes from understanding how APIs behave in context, not just how they look on paper.

API Security Self-Assessment Questions

Before deploying or updating an API, security teams should step back and evaluate how well current practices hold up against modern threats. These self-assessment questions help identify common blind spots in API security posture and guide corrective actions that align with best practices. Use the table below as a practical reference during development, testing, or routine audits.

Question	Action
Do all your APIs require authentication and authorization?	Ensure only authorized users and systems can access your APIs.
Are you regularly testing APIs for vulnerabilities?	Incorporate both automated scans and manual testing into your workflow.
Is sensitive data encrypted in transit and at rest?	Use HTTPS and strong encryption standards such as TLS and AES.
Do you maintain up-to-date API documentation?	Keep documentation current to prevent misuse and support accurate security testing.
Are rate limits and throttling mechanisms in place?	Configure APIs to block abuse and prevent denial-of-service through rate-limiting policies.
Are tokens and session data configured with expiration policies?	Set appropriate token lifetimes and enforce re-authentication for long sessions.
Do you validate all input data from users and systems?	Implement strict input validation and sanitization to prevent injection attacks.
Are security logs monitored for unusual API activity?	Use centralized logging and automated alerts to detect suspicious behavior in real-time.
Are third-party APIs and integrations reviewed for security impact?	Audit third-party components and apply least-privilege access to reduce the risk of indirect threats.

Types of API Security Testing Tools ‍

An API is a software system, and so the same technologies used for application security testing can also be used for API testing. However, some testing tools are specifically designed to test important aspects of APIs.

The traditional methods of application security testing like SAST, DAST, and others can partially address API security concerns. However, API security testing requires more nuanced approaches due to unique challenges like understanding the specific business context of the application. These traditional methods need to be adjusted and complemented with additional techniques that are specifically designed for the complexities inherent in API security, ensuring a more comprehensive and effective security strategy.

1. Static Analysis Security Testing (SAST)

Static Analysis Security Testing, or SAST, involves analyzing the source code of the API. This analysis is performed without actually executing the code. SAST is designed to identify potential vulnerabilities in the code that could lead to security breaches.SAST tools scan the entire codebase to identify potential security issues. These could include coding errors, insecure coding practices, or the use of insecure libraries or dependencies. Once these issues are identified, they can then be rectified before the API is deployed.

2. Dynamic Application Security Testing (DAST)

Dynamic Application Security Testing (DAST) involves testing the API while it is running. DAST is designed to identify vulnerabilities that are only apparent when the API is in operation. This includes issues related to input validation, authentication, and session management, among others.DAST involves sending a series of requests to the API and observing its responses. These responses are then analyzed to identify any potential security issues. Once these issues are identified, they are fixed and the API is retested to ensure the issue has been resolved.

3. Software Composition Analysis (SCA)

Software Composition Analysis (SCA) focuses on identifying vulnerabilities in the libraries and dependencies used by the API. SCA involves analyzing the entire software stack to identify any potential security issues.SCA is an important complement to SAST and DAST because APIs often rely on a multitude of libraries and dependencies. If any of these components have security vulnerabilities, they could potentially be exploited, leading to a security breach.

4. Interactive Application Security Testing (IAST)

Interactive Application Security Testing (IAST) is a type of API security testing that combines elements of both SAST and DAST. IAST involves analyzing the API's source code while it is in operation, with some visibility into the underlying source code. This allows IAST to identify vulnerabilities that might be missed by either SAST or DAST alone.

5. Mobile Application Security Testing (MAST)

Mobile Application Security Testing (MAST) tests APIs used in mobile applications. MAST involves testing the API in the context of a mobile application to identify any potential security issues.MAST is important because mobile applications often have different security considerations compared to traditional web applications. This includes issues related to data storage, communication, and user authentication.

Types of API security testing tools: SAST, DAST, IAST, SCA, and MAST.

What to Look for in API Security Testing Solutions Integration Points

It's crucial to assess where the testing integrates within the SDLC. Solutions that embed in both AppSec and CI/CD pipelines offer more comprehensive coverage, ensuring security is maintained throughout the development process

Deployment Methods

The deployment method refers to how the solution is installed and used in your system. There are several deployment methods that you can choose from, including on-premises, cloud-based, and hybrid.On-premises solutions offer a higher level of control and security, but they can be more difficult and costly to maintain. On the other hand, cloud-based solutions are easier to deploy and manage, but they may not offer the same level of control.

Scan Quality and Accuracy

API security testing tools should perform detailed scans that cover as many possible vulnerabilities as possible while helping to identify and prioritize the most critical vulnerabilities. In addition, scans should be accurate, avoiding false positives or negatives. False positives are vulnerabilities erroneously detected by the tool, while false negatives are real vulnerabilities missed by the tool.

Context Awareness in API security testing solutions.

This involves the tool's ability to understand and adapt to the specific business logic and use cases of the APIs it tests. Such awareness is crucial to accurately identify and assess the real-world impact of potential vulnerabilities, ensuring that security measures are both effective and relevant to the API's operational context.

Scan Efficiency

Evaluate the duration and efficiency of scans. Optimal solutions should offer thorough yet time-efficient scans, balancing depth with speed to fit agile development environments

Reporting Capabilities

For reporting capabilities in API security testing solutions, look for a combination of reports that cater to different audiences. Reports should include developer-centric details that aid in resolving bugs effectively, using language and formats familiar to developers. Additionally, comprehensive penetration test reports are essential for security owners, providing a broader and more strategic view of the API's security posture. This dual approach ensures that both developers and security teams have the necessary information to address vulnerabilities effectively.

API Types Supported

You should consider the types of APIs that the solution supports. There are several types of APIs, including REST, SOAP, and GraphQL. The solution should support all the types of APIs you use, and provide specific security features adapted to the unique characteristics of each type of API.

API Categorization and Scope

This section delves into differentiating APIs based on their operational domain: internal, external, and third-party. Each type has unique security requirements:

Internal APIs: Focus on protecting sensitive internal data and functions. Implement strict access controls and regular audits to ensure safety within the organizational network.
External APIs: These are exposed to external users or services. Emphasize robust authentication, data encryption, and stringent input validation to safeguard against external threats.
Third-Party APIs: For APIs developed by external entities, conduct thorough security assessments and continuous monitoring. Ensure compliance with organizational security policies and consider the potential risks in data sharing and integration.

Understanding these distinctions is crucial for tailoring security measures effectively for each API type.

Explicit API Routes vs. Crawling for Discovery

Another important factor to consider is whether the API security testing solution uses explicit API routes or crawling for discovery. Explicit API routes involve manually defining the routes that the solution should test while crawling involves using an automated process to discover and test all possible routes. A combination of both provides the greatest flexibility.

Automated, Context-Aware API Security Testing with Pynt

Pynt addresses API security testing needs by providing an integrated, efficient solution tailored to modern B2B applications. It offers specialized tools that go beyond standard DAST and SAST, focusing on the unique aspects of API security.

Pynt supports automated security testing throughout the SDLC, distributing responsibility across developers, testers, and security teams. Its context-aware approach ensures vulnerabilities are identified early and accurately, streamlining the process and reducing the need for extensive manual effort. Pynt's effectiveness in API security makes it a vital tool in today's development landscape.

Learn more about Pynt

Conclusion

APIs are integral to modern digital ecosystems, but with their power comes heightened risk. API security testing isn’t just a technical necessity; it’s a strategic imperative that protects sensitive data, ensures compliance, and reinforces user trust. By combining manual and automated methods, integrating testing into CI/CD pipelines, and tailoring defenses to each API type, organizations can stay ahead of evolving threats.

Effective API security testing is continuous, context-aware, and embedded throughout the development lifecycle. When done right, it reduces attack surfaces, prevents service disruptions, and strengthens the entire application security posture.

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FAQs

Is API Security Testing Manual or Includes Automation?

API security testing includes both manual and automated techniques. Automated tools are used to scan for known issues, such as misconfigured headers, exposed endpoints, or outdated components. Manual testing is essential for detecting business logic flaws, improper access control, and complex misuse cases that automated tools may miss. A mature testing strategy combines both approaches to ensure full coverage.

What is an Example of an Insecure API?

An insecure API might expose sensitive user data without enforcing proper authentication. For example, an endpoint that allows access to account details using only a predictable user ID and no authorization checks could allow attackers to access data belonging to other users. This is commonly referred to as an insecure direct object reference (IDOR).

How to Perform API Assessment?

To perform an API assessment, begin by reviewing the API documentation and its intended functionality. Then, define a testing strategy that targets authentication, authorization, rate limiting, input validation, and error handling. Use API security tools to run automated scans and combine them with manual techniques to detect deeper issues. Assess the API’s response to invalid input, abuse scenarios, and access control boundaries. Finally, prioritize remediation and retest to validate fixes.

What is the Difference Between API Security and Application Security?

Application security is a broader discipline that covers all aspects of securing a software application, including frontend, backend, business logic, and infrastructure. API security focuses specifically on protecting application programming interfaces from abuse, misconfiguration, and unauthorized access. While both areas overlap, API security requires dedicated testing approaches due to the unique way APIs expose data and system functions.

What Are the Methods in API Security Testing?

API security relies on two key methods. One focuses on real-time threat protection through continuous monitoring of live API traffic to detect and respond to malicious activity. The other is shift left API testing, which simulates real-world attack scenarios early in the development cycle. This helps teams uncover issues such as excessive data exposure, broken authentication, and logic flaws before deployment. Using both methods helps reduce exposure and improve API security across the lifecycle.

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See Additional Guides on Key Application Security Topics

Together with our content partners, we have authored in-depth guides on several other topics that can also be useful as you explore the world of application security.

API Security

Authored by Pynt

Penetration Testing