OAuth2: Client Server XSS

This exercise covers the exploitation of a Cross-Site Scripting in the OAuth2 Client Server

1-2 Hrs.


The course details how an insecure OAuth2 Client, which uses OAuth2 as a pseudo-authentication mechanism, can be exploited due to a Cross-Site Scripting (XSS) vulnerability. By understanding how OAuth2 works, including the roles of the Resource Owner, User-Agent, Authorization Server, and Resource Server, learners will see how the lack of strict URL enforcement allows attackers to redirect victims to a malicious URL. This vulnerability can be exploited to leak the authorization code, enabling attackers to authenticate as the victim.

Through practical exercises, participants will register a malicious account on the Authorization Server, initiate an OAuth2 flow, and intercept the redirection to exploit the XSS vulnerability. By crafting a payload to leak the authorization code and using the correct state value, attackers can gain unauthorized access to resources. The course emphasizes the importance of detecting and fixing such vulnerabilities to protect against exploitation.

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