Level 3 - Level 4

Username: natas4
Password: tKOcJIbzM4lTs8hbCmzn5Zr4434fGZQm
URL:      http://natas4.natas.labs.overthewire.org

This time the target website stated that we have to come from http://natas5.natas.labs.overthewire.org to access the content of the page.

So I intercepted the request using burpsuite and modified the Referer URL from http://natas4.natas.labs.overthewire.org to http://natas5.natas.labs.overthewire.org and then sent the request and got the password for the next level in the response.