This lab involves a front-end and back-end server, and the front-end server doesn't support chunked encoding. The front-end server is caching static resources.
To solve the lab, perform a request smuggling attack such that the next user's request causes their API key to be saved in the cache. Then retrieve the victim user's API key from the cache and submit it as the lab solution.
You have an account on the application that you can use to help design your attack. The credentials are: carlos / montoya.
The lab simulates the activity of a victim user. Every few POST requests that you make to the lab, the victim user will make their own request. You might need to repeat your attack a few times to ensure that the victim user's request occurs as required.
Manually fixing the length fields in request smuggling attacks can be tricky. Our HTTP Request Smuggler Burp extension was designed to help. You can install it via the BApp Store.