APIs power nearly every modern digital experience. Every time you book a cab, scroll through social media, or make a payment online—there’s an API working behind the scenes, connecting systems and moving data in real-time. They’re fast, efficient, and absolutely essential in today’s digital world.
But here’s the catch—APIs are also one of the easiest ways for attackers to sneak in.
From broken authentication to exposed sensitive data, poorly secured APIs have caused some of the biggest security breaches in recent years. That’s why API security can’t be an afterthought—it has to be built in from the start.
To help teams stay ahead, OWASP (the global leader in application security) created a list of the Top 10 API Security Risks—a go-to framework that shows where APIs usually go wrong.
In this blog, we’ll break down what OWASP API Security is all about, highlight the top 10 vulnerabilities, and show you how to catch them early using automated testing. Whether you’re building APIs or testing them, this guide will help you secure your endpoints like a pro—before attackers get a chance.
What Is OWASP API Security?
When it comes to securing APIs, OWASP (Open Worldwide Application Security Project) is the name you need to know. It’s a global, non-profit organization that creates free resources to help improve software security—and their API Security Top 10 is one of the most trusted references in the industry.
While the traditional OWASP Top 10 focuses on general web application threats, the OWASP API Security Top 10 is tailored specifically for the unique vulnerabilities that affect APIs.
So, what does that mean for you?
APIs behave differently than regular web apps. They expose endpoints, handle structured data, and often lack user interfaces—all of which create new attack surfaces. The OWASP API Security list identifies the most common mistakes developers and teams make when designing or deploying APIs, such as:
- Weak authentication
- Broken access controls
- Excessive data exposure
- Lack of proper rate limiting
- Insecure integrations with third-party APIs
These are not just theoretical risks—they’re vulnerabilities that attackers are actively exploiting in the wild.
OWASP API Security Top 10
1. Broken Object Level Authorization (BOLA)
What it is:
When an API allows users to access data objects (like user profiles or orders) without checking if they’re authorized.
Real-world example:
A user changes the endpoint /orders/101 to /orders/102 and sees someone else’s order details.
Why it matters:
BOLA is widely recognized as one of the most frequently exploited and dangerous API vulnerabilities. It can expose sensitive user data and lead to massive data leaks.
2. Broken Authentication
What it is:
Weak authentication mechanisms allow attackers to gain unauthorized access to user accounts or systems.
Real-world example:
The API accepts an expired token or doesn’t lock out users after multiple failed login attempts.
Why it matters:
Attackers can log in as legitimate users, hijack sessions, or even escalate to admin access.
3. Broken Object Property Level Authorization
What it is:
Users are able to access or modify specific fields within an object they shouldn’t have access to.
Real-world example:
A regular user is able to modify or access specific object properties (e.g., userRole, accountType) without proper authorization checks in place.
Why it matters:
This can result in privilege escalation or leakage of sensitive system configurations.
4. Unrestricted Resource Consumption
What it is:
APIs allow excessive use of system resources (like memory, bandwidth, or CPU) without limits.
Real-world example:
A user sends thousands of large file uploads, slowing down the entire server.
Why it matters:
This opens the door to DoS (Denial of Service) attacks, affecting system performance and availability.
5. Broken Function Level Authorization
What it is:
Users can access privileged functions (like admin actions) due to missing or weak access controls.
Real-world example:
A normal user accesses an admin API endpoint like /deleteUser and it works.
Why it matters:
Attackers can perform high-impact actions like deleting data, modifying user roles, or changing system settings.
6. Unrestricted Access to Sensitive Business Flows
What it is:
Key business operations (like password resets or checkouts) can be accessed or automated without restrictions.
Real-world example:
A bot floods the password reset API to lock out thousands of user accounts.
Why it matters:
This can lead to account lockouts, abuse of promotions, fake traffic, and fraud.
7. Server-Side Request Forgery (SSRF)
What it is:
APIs fetch external URLs without validating them, allowing attackers to target internal systems.
Real-world example:
A user provides a URL like http://localhost/admin and the server makes the request internally.
Why it matters:
SSRF can expose internal files, access cloud metadata, or reach services not meant for public access.
8. Security Misconfiguration
What it is:
APIs are deployed with insecure settings—like default configurations, overly verbose error messages, or open CORS policies.
Real-world example:
The API returns full stack traces or allows all domains via Access-Control-Allow-Origin: *.
Why it matters:
These issues provide attackers with valuable insights and can be used as stepping stones for further attacks.
9. Improper Inventory Management
What it is:
Teams lose track of exposed API endpoints, especially older versions or test environments.
Real-world example:
An outdated /v1/payment endpoint still works and lacks the security updates applied to /v3/payment.
Why it matters:
Unused or undocumented APIs often go untested and can be easily exploited.
10. Unsafe Consumption of APIs
What it is:
Trusting data from third-party APIs without proper validation or error handling.
Real-world example:
An app relies on a weather API and uses the data directly, even if the response is tampered or malformed.
Why it matters:
This can cause unexpected behavior, data corruption, or introduce malicious payloads into your system.
How to Test APIs for Vulnerabilities?
Now that you understand the top risks from the OWASP API Security Top 10, the next question is:
How do you actually test your APIs for these vulnerabilities—consistently and efficiently?
The answer lies in a mix of automated testing, manual validation, and secure design practices. Here’s a step-by-step breakdown to help you get started:
1. Use API Security Testing Tools
Leverage tools designed specifically for scanning APIs for security issues. These tools simulate attacks and check for common vulnerabilities based on OWASP’s recommendations.
Popular tools include:
- OWASP ZAP – Best suited for traditional web apps and REST APIs with scripting. Limited support for GraphQL unless extended with custom scripts.
- Burp Suite – Widely used for penetration testing and request manipulation.
- Postman with Security Assertions – Postman is excellent for scripting functional security assertions but doesn’t simulate advanced attack vectors (e.g., SSRF, fuzzing). Supplement with DAST tools.
- Insomnia, Fiddler, or REST-assured – For manual inspection and automated test scripting.
2. Automate Vulnerability Scans in CI/CD Pipelines
Integrate API vulnerability scanners into your CI/CD pipeline so that security tests run automatically with every code push.
Benefits:
- Catch issues early before they hit production.
- Shift security testing left in the development process.
- Save manual testing effort.
Tip: Use tools like ZAP CLI, GitHub Actions, or Jenkins plugins to automate scans post-deployment.
3. Test Authentication and Authorization Thoroughly
Broken authentication and access control flaws (like BOLA or Function Level Authorization) are hard to catch with functional tests.
Here’s what to check:
- Can a user change object IDs and access someone else’s data?
- What happens if you use an expired or invalid token?
- Can a regular user access admin endpoints?
Automate these using:
Custom scripts in Postman, Karate, or security-focused test suites in your framework.
4. Check for Input Validation and Data Exposure
APIs should never trust user input or expose more data than needed.
Your tests should try:
- Injecting scripts (XSS, SQLi) into input fields
- Requesting full object details and observing what’s returned
- Uploading oversized files or unexpected formats
Look for:
- Sensitive fields in responses (passwords, tokens)
- Inconsistent error messages or stack traces
- JSON/XML injection possibilities
5. Simulate Abuse Scenarios
Many vulnerabilities arise not from broken functionality, but abuse of intended behavior.
Try these test scenarios:
- Repeating password reset or checkout APIs rapidly
- Uploading huge payloads to test rate limits
- Using bots or scripts to brute-force tokens or login
Tools to help:
- Locust, JMeter, or k6 – For load testing and abuse simulation
- OWASP Amass – For API discovery and recon
6. Test for Versioning and Shadow APIs
Many breaches occur because of forgotten or undocumented APIs.
How to test:
- Use tools like Amass or API Fuzzer to discover unexpected endpoints.
- Check older versions like /api/v1/ that may still be exposed.
- Validate all discovered endpoints have authentication and security checks.
7. Include Security Assertions in Functional Tests
Add simple security checks to your existing test scripts.
Examples:
- Assert Authorization headers are required
- Check if server responds with correct error codes (401/403 vs 200)
- Validate rate limiting headers and limits
Why it helps:
It brings security closer to the developer’s workflow and improves coverage without much extra effort.
How to Secure Your APIs with Automated Testing Based on OWASP Top 10 Risks
1.Automated Authorization Checks (for BOLA and Function-Level Flaws)
Write automated tests to simulate unauthorized access by:
-> Changing object IDs (e.g., /users/123 → /users/124)
-> Accessing restricted endpoints as a normal user
Tools you can use:
-> Postman (with scripts)
-> Cypress or Playwright (for front-end driven API access)
-> Custom scripts in Python or JavaScript
Pro Tip: Automate these tests in your CI pipeline to catch broken access control early.
2. Authentication Validation Scripts
Automate testing for:
-> Invalid, expired, or missing tokens
-> Reuse of tokens after logout
-> Token tampering
Integrate into:
Your Postman collections, Newman CLI, or REST-assured test suites.
Automation Goal: Ensure only valid tokens work, and sessions can’t be hijacked or reused.
3. Static and Dynamic Security Scans
Use SAST (Static Application Security Testing) for code-level flaws and
DAST (Dynamic Application Security Testing) for runtime issues.
Tools to automate with CI/CD:
-> OWASP ZAP (DAST) – for automated vulnerability scans
-> SonarQube + plugins – to detect insecure coding patterns
-> Semgrep – to detect misconfigurations and secrets in code
These tools can flag:
-> SSRF risks
-> Insecure deserialization
-> Security misconfiguration
4. Rate Limiting and Abuse Tests
Simulate:
-> Flooding APIs with requests
-> Uploading oversized files
-> Repeating sensitive actions like password reset
Automation tools:
-> JMeter, k6, or Locust to check rate limits
-> Newman or Postman Runner to loop requests and assert error codes (like 429 Too Many Requests)
5. Sensitive Data Exposure Validation
Automate checks to inspect:
-> Fields returned in API responses
-> Whether any sensitive or internal info is exposed
-> Unfiltered stack traces or debug info
Scripted checks can validate:
-> API responses must not contain sensitive fields like passwords, secrets, or tokens—masked or otherwise. These should be omitted entirely.
-> Error messages are generic
-> Only allowed fields are in the response schema
Tools: Postman + scripting, REST-assured, or custom API test validators.
6. Automated Input Validation Testing
Use automation to test for:
-> SQL injection, XSS payloads, or command injections in API fields
-> Malformed JSON/XML payloads
-> Unicode or unexpected input formats
How:
Run input fuzzing tools or build test cases using OWASP ZAP’s automation framework or custom scripts.
7. Version & Shadow API Scanning
Use automation to:
-> Scan for outdated or undocumented APIs
-> Test /v1/, /v2/, /test/, /internal/ endpoints
Automated tools to explore:
-> Amass, Nuclei, or API security fuzzers
-> Swagger/OpenAPI diffing tools to catch undocumented changes
8. Security Assertions in Unit/API Tests
Embed security logic in test cases:
-> Check for presence of security headers
-> Assert CORS policy
-> Validate cookie flags (HttpOnly, Secure)
Why this works:
Developers stay security-aware from the start, and security becomes part of “done”.
End note:
APIs are the core of today’s digital applications—and that makes them a prime target for attackers. As we’ve seen, the OWASP API Security Top 10 (2025) outlines the most critical threats, many of which go undetected in traditional testing.
But the good news is: You don’t need to wait until production to catch them.
By embedding automated API security tests early into your CI/CD pipelines, and validating against common risks like broken authorization, data leaks, and SSRF, you build a system that’s not just functional—but resilient.
At Testrig Technologies, we help companies around the world implement continuous API security testing services—powered by automation and aligned with the latest OWASP guidelines.
Want to safeguard your APIs without slowing down delivery? Let’s talk about how we can strengthen your API security strategy—end-to-end.
