What if I told you that a simple Cross-Site Scripting (XSS) vulnerability could be the golden ticket to a full Account Takeover (ATO)? No malware, no phishing — a few lines of JavaScript.

If you’re into ethical hacking or bug bounty hunting, you’ve probably heard of XSS.

But have you ever thought about how dangerous it can be when combined with session hijacking or cookie theft?

In this article, we’ll break down how XSS can lead to ATO, share a real-world bug bounty writeup, and reveal some clever tricks like Base64 bypass and using Param Spider to find hidden parameters.

By the end, you’ll see why XSS isn’t a ‘low-risk’ bug — it’s often the hidden key to stealing accounts.

What Is XSS, and Why Should You Care?

Cross-site scripting (XSS) is a vulnerability that lets attackers inject malicious scripts into web pages viewed by other users.

Most people think of XSS as just popping an alert box, but in reality, it can be much worse.

There are three main types:

1. Reflected XSS (RXSS) — The payload is in the URL or input and gets executed immediately.
2. Stored XSS — The malicious script is saved on the server (e.g., in a…