OAuth2: Authorization Server XSS

In this course, we delve into the exploitation of an insecure OAuth2 Authorization Server, focusing on a Cross-Site Scripting (XSS) vulnerability. OAuth2 is notoriously difficult to implement correctly, making the detection and rectification of these vulnerabilities crucial. The lab guides you through registering an account, creating an OAuth application, and setting up a malicious redirect URL. By identifying the XSS vulnerability on the authorization page, you can bypass CSRF protection and automatically authorize your malicious application.

Once the victim visits your crafted URL, they are redirected back to your server, from which you can retrieve an authorization code. This code, combined with your client ID and secret, allows you to obtain an access token. The lab then demonstrates how to use this token to access the resource server and retrieve the key for the challenge. This exercise underlines the importance of securing OAuth2 implementations to prevent such exploits.