postMessage() III

This exercise covers how insecure calls to the JavaScript function postMessage() can be used to trigger a Cross-Site Scripting

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In this course, you'll delve into the security implications of using `addEventListener()` without verifying the origin of messages in web applications. By exploiting this vulnerability, you can craft a malicious HTML page that loads the vulnerable page in an iframe and uses postMessage() to send a Cross-Site Scripting (XSS) payload. This approach is particularly effective against applications that rely on cookies for authentication and do not implement adequate origin checks.

The course provides a step-by-step guide, starting with understanding how postMessage is used and how authentication works within the application. You'll then learn how to write a malicious page that can send your XSS payload to the vulnerable application, retrieve the victim's cookies, and gain unauthorized access to their session. The video transcript complements the course content by offering practical insights and a live demonstration of the attack, making it easier to grasp the concepts and techniques discussed.

You'll also gain an understanding of how to mitigate such vulnerabilities by ensuring that the frontend checks the origin of events and properly encodes any information provided. This course is based on real-world research and examples, ensuring that you are learning practical and applicable skills.

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