Ever missed a critical bug because you didn’t chain vulnerabilities?

I almost did.

I stumbled upon an Insecure Direct Object Reference (IDOR) during a routine bug bounty hunt. At first, it seemed harmless — just another 403 error. But when I combined it with a Cross-Site Scripting (XSS) flaw, something terrifying happened:

I could access every user’s account.

This wasn’t just a “nice find.” It was a full-blown account takeover exploit. And the scary part?

Most developers wouldn’t even notice it.

Here’s exactly how I did it — step by step.

(Note: All testing was done ethically on authorized platforms. Always get permission before testing!)

Step 1: Finding the IDOR — From 403 Errors to Brute-Forcing IDs

The First Glitch

The target website had a simple user profile system. Each profile had a URL like:

https://example.com/profile?id=12345

I changed the id parameter to 12346—403 Forbidden.

“Okay, some protection,” I thought.