Unauthorized Access to Internal Panel via Response Manipulation

Hi everyone,
I’m Ahmed Ehab, but many in the security community know me as Nopr. Today, I’d like to share an interesting bug I discovered during testing a bug bounty program. While I’m using example.com as a placeholder to protect sensitive details, the underlying issue offers valuable insights for fellow bug hunters.

Overview of the Bug

While I was hunting with my friend soliman we found an internal login panel that, despite having no registration function, allowed a user to bypass authentication in an unexpected way. Under normal circumstances, when invalid credentials are submitted, the server responds with a 401 Unauthorized status, denying access. However, I discovered that by intercepting the response and changing the status code from 401 to 200 OK, I could trick the client into accepting the login as successful.

What’s Happening Here?

This is a classic case of response manipulation. Typically, a 401 status code signals that the authentication has failed, and the client-side logic should treat this as a denial of access. By modifying the response, I bypassed this check. The client, seeing a 200 OK, assumed that the authentication was successful — even though the server originally intended to reject the credentials.

For those unfamiliar with the term, response manipulation refers to intercepting and altering the data that flows between the client and the server. Tools like Burp Suite or similar proxies allow us to modify requests or responses in real-time, revealing potential security oversights in how applications handle authentication and session management.

Steps to Reproduce:

1. Navigate to: https://example.com
2. Enter any random username and password into the login form.
3. Intercept the login request using your preferred proxy tool.
4. Notice that the server responds with a 401 Unauthorized status.
5. Change the response status from 401 to 200 OK and forward the modified response.
6. Observe that the application treats you as logged in, bypassing the intended authentication mechanism.

Key Takeaways for Bug Hunters

• Server-Side Validation is Crucial: Never rely solely on client-side checks or response codes for authentication. Always ensure that critical validations occur on the server side.
• Understand Your Tools: Familiarize yourself with features like Match and Replace Rules in your proxy tools. These can be powerful for both testing and demonstrating vulnerabilities.

This vulnerability serves as a reminder that every layer of an application must be robust against tampering. By understanding techniques like response manipulation, we can better identify and mitigate such risks, ultimately making our digital environments safer.

Sadly It was duplicated:

Thanks for reading, and I hope this write-up provides useful insights for your own security research. If you have any questions or thoughts, feel free to reach out!

Stay safe and keep hunting,
Ahmed Ehab (Nopr)