This lab involves a front-end and back-end server, and the back-end server doesn't support chunked encoding. The front-end server rejects requests that aren't using the GET or POST method.
To solve the lab, smuggle a request to the back-end server, so that the next request processed by the back-end server appears to use the method
In Burp Suite, go to the Repeater menu and ensure that the "Update Content-Length" option is unchecked.
Using Burp Repeater, issue the following request twice:
POST / HTTP/1.1
GPOST / HTTP/1.1
You need to include the trailing sequence
\r\n\r\n following the final
The second response should say:
Unrecognized method GPOST.