Polluting My Way to Victory: How I Found HTTP Parameter Pollution (HPP) and Exploited It Like a Pro

Have you ever stared at a web application and thought, What happens if I send two of the same parameters? Most hunters don’t give this a second thought. But what if I told you that something as simple as duplicating a parameter could lead to bypassing authentication, manipulating business logic, or even stealing sensitive data?

Hi, I’m Akash (myselfakash20), a bug bounty hunter who loves uncovering the hidden gems of vulnerabilities. During a recent hunt, I stumbled upon a fascinating bug: HTTP Parameter Pollution (HPP). What started as routine testing ended up in a treasure trove of exploits. With just a few tweaks to GET and POST requests, I bypassed restrictions, tampered with sensitive data, and uncovered how poorly designed systems crumble when overloaded with duplicate parameters.

Here’s how I did it.

The Discovery —

The target was a financial services platform, boasting a sleek UI and robust-looking APIs. During recon, I noticed something interesting: their account update endpoint allowed multiple POST parameters like username, email, and balance.

My recon began with this normal request: