Most companies ship APIs fast and secure them later. By then, it's already too late. Here are the 5 most common API vulnerabilities we find on almost every engagement:

1. Broken Object-Level Authorization (BOLA)

Your API lets User A access User B's data just by changing the ID in the URL. This is the #1 API vulnerability worldwide and most teams don't even test for it.

2. No Rate Limiting on Authentication

Without rate limiting, attackers can brute-force credentials or OTPs in minutes. We've cracked accounts on production apps in under 10 minutes during engagements.

3. Excessive Data Exposure

Your API returns the entire user object when the frontend only needs the name. That means internal IDs, email addresses, and sometimes even hashed passwords are leaking in every response.

4. Mass Assignment

Sending {"role": "admin"} in a signup request shouldn't work — but it does more often than you'd think. If your API blindly accepts all fields, attackers will find the ones that matter.

5. Missing TLS on Internal APIs

"It's internal, it doesn't need encryption." Until someone gets on the network. Internal APIs move sensitive data and deserve the same security posture as public ones.

If any of these sound familiar, your infrastructure probably has more issues underneath. We find them before attackers do.