Authentication Bypass leads to PII = ($$$)

Hello folks, Ramadan Kareem !

I hope you’re doing well! I want to share a recent scenario from one of my latest findings. As we know, most websites return a 403 Forbidden status when access is restricted, displaying messages like “Unauthorized” or “Access Denied.” However, in this particular case, the target responded with 200 OK, but with a message saying, “You do not have access to view this page.”

This type of response can sometimes be a goldmine when paired with fuzzing techniques whether for directories, parameters, or headers. In my case, I fuzzed for headers and discovered that this page was meant for internal employees. The authentication mechanism relied on the X-Forwarded-For: 127.0.0.1header, which returned a response with a different size than usual. This anomaly caught my attention, prompting me to browse the page using that header. So I gained access to a panel containing Personally Identifiable Information (PII) of users.

Bypassing Authentication with Header Manipulation

Most automated tools detect authentication bypass by checking for status code differences; if a normal request…