DOM XSS via Web Messages: Exploits unsafe postMessage handling and innerHTML injection to execute arbitrary JavaScript.
Write-Up by Aditya Bhatt | DOM-Based XSS | Web Message Injection | BurpSuite
Lab: DOM XSS using web messages
Lab Link: https://portswigger.net/web-security/dom-based/controlling-the-web-message-source/lab-dom-xss-using-web-messages
My GitHub Repository Link: https://github.com/AdityaBhatt3010/DOM-XSS-using-web-messages-and-JavaScript-URL
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⭐ TL;DR
This PortSwigger lab demonstrates a DOM XSS vulnerability via web messages. The webpage listens for postMessage events and directly injects received data into innerHTML without validating origin or sanitizing content. By abusing an iframe and sending a crafted message containing an <img> tag with an onerror handler, we trigger JavaScript execution and solve the lab.
🔥 Introduction
Web messaging (window.postMessage) is a powerful API intended for secure cross-origin communication. However, when developers fail to validate…