This exercise covers how insecure calls to the JavaScript function postMessage() can be used to leak sensitive information

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In this comprehensive course, you will explore the intricacies of exploiting an application that uses the `postMessage` method without setting a destination. The course is based on real-world scenarios and provides step-by-step guidance on how to craft a malicious page to extract sensitive information. By following the detailed instructions, you will learn to identify the vulnerabilities, write a malicious HTML page, and leak data back to your server.

The course begins with an introduction to the `postMessage` method and its usage in cross-origin communication. It then delves into the exploitation process, where you will create a malicious page to open the vulnerable application and listen for events. The final part of the course demonstrates how to use an event listener to dynamically create an image tag that leaks the sensitive information back to your server. By the end of this course, you'll have a solid understanding of how to exploit `postMessage` vulnerabilities and protect against them.

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