Let me be straight with you: if you're not testing your APIs for security vulnerabilities, you're basically leaving your digital front door unlocked. I've seen startups lose customer data, e-commerce sites get drained, and SaaS platforms go down for days—all because of API security holes that were completely preventable.

The scary part? Most of these companies thought their APIs were secure. They'd implemented HTTPS, used API keys, maybe even added rate limiting. But security isn't about ticking boxes—it's about thinking like an attacker. And that's exactly what I'm going to teach you today.

We'll use our new API Tester to walk through real vulnerabilities. By the end, you'll know how to find and fix the most dangerous API security issues yourself.

1. Think Like a Hacker (It's Not What You Expect)

Your Testing Checklist

2. Broken Authentication: The #1 API Killer

I can't tell you how many APIs I've broken into simply by messing with authentication. It's usually the weakest link. Here's what to test:

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// Testing JWT "none" algorithm vulnerability
const maliciousJWT = 'eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.';

// Send request with "none" algorithm JWT
fetch('/api/user/profile', {
    headers: {
        'Authorization': `Bearer ${maliciousJWT}`
    }
})
.then(response => {
    if (response.ok) {
        console.log('🚨 VULNERABLE: JWT "none" algorithm accepted!');
    }
});

3. Injection Attacks: Not Just for SQL Anymore

Everyone knows about SQL injection, but APIs open up new injection vectors. Here are the ones I find most often:

4. Missing Rate Limits: The Brute Force Dream

How to Test Rate Limiting

// Test rate limiting
async function testRateLimit() {
    const requests = [];
    
    // Send 100 rapid requests
    for (let i = 0; i < 100; i++) {
        requests.push(
            fetch('/api/login', {
                method: 'POST',
                body: JSON.stringify({username: 'test', password: 'guess'})
            })
        );
    }
    
    const responses = await Promise.all(requests);
    const successCount = responses.filter(r => r.ok).length;
    
    if (successCount > 10) {
        console.log(`🚨 VULNERABLE: ${successCount}/100 requests succeeded`);
    } else {
        console.log('✅ Rate limiting appears to be working');
    }
}

5. Putting It All Together: Your API Security Workflow

Testing APIs manually is painful. That's why we built our API Tester with security in mind. Here's how to use it effectively:

pm.test("No rate limiting", function () {
    // Send 50 rapid requests
    // Expect less than 5 successes
});

pm.test("JWT validation", function () {
    // Test with "none" algorithm
    // Should return 401
});