blind XSS vulnerability that performs actions on behalf of the administrator.

🚀 Introduction

During one of my bug bounty sessions, I decided to test a feature that many researchers usually ignore: the Feedback Form.

Instead of treating my input as plain text, the application rendered my HTML payload directly, causing it to execute as JavaScript.

The payload I used was:

A few moments later, my server received the outbound request, confirming that the JavaScript had been executed successfully during the review process.

🔍 Hunting Process

Before reaching this point, I spent a long time testing common input fields without finding anything interesting.

So I changed my approach.

I started looking at areas that most bug hunters usually overlook because they receive much less attention during security testing.

One of those areas was the website's Feedback Form, where users can submit complaints or share their opinions about the service.

After submitting the payload, it wasn't displayed as normal text—it was later rendered and executed as JavaScript.

Sometimes, looking away from the obvious targets leads to the best discoveries.

⚡ What Actually Happened?

I submitted a normal feedback message containing the payload.

When the submitted content was later reviewed, the browser interpreted the HTML instead of displaying it as plain text.

As a result, the JavaScript inside the "onerror" attribute executed automatically and sent a request to my external server.

This type of issue is common in internal review panels because those interfaces are often hidden from regular users and may receive less security testing than public-facing pages.

📚 What Should You Learn to Master This?

If you want to become good at finding vulnerabilities like this, focus on the fundamentals before anything else.

Learn HTML & JavaScript

Understanding how browsers parse HTML and execute JavaScript is essential.

You should know exactly how user input is rendered, how events work, and why some payloads execute while others don't.

Learn at Least One Backend Programming Language

Whether it's PHP, Node.js, Python, Go, or another language, learning backend development helps you understand how applications sanitize user input and implement defenses against XSS.

You should also spend time learning HTTP Security Headers such as:

Content-Security-Policy (CSP)
X-Content-Type-Options
X-Frame-Options
Referrer-Policy

Understanding these headers will help you recognize both secure and insecure implementations.

Study Many XSS Scenarios

Don't memorize payloads.

Instead, study different XSS cases, understand why they work, and practice identifying new attack surfaces.

The more scenarios you study, the better your mindset becomes.

🤝 Need Help?

If you have any questions about Bug Bounty, Web Security, or your learning journey, feel free to send me a private message.

I'll do my best to help whenever I can.

❤️ Final Words

Don't forget to send blessings upon the Prophet Muhammad ﷺ.

Follow me if you enjoyed this article and found it useful.

May Allah forgive me and forgive you all.