HTTP request smuggling

HTTP request smuggling is a security exploit on the HTTP protocol that uses inconsistency between the interpretation of codice_1 and/or codice_2 headers between HTTP server implementations in an HTTP proxy server chain. It was first documented in 2005, and was again repopularized by PortSwigger's research.
Types.
CL.TE.
In this type of HTTP request smuggling, the front end processes the request using Content-Length header while backend processes the request using Transfer-Encoding header.
TE.CL.
In this type of HTTP request smuggling, the front end processes request using Transfer-Encoding header while backend processes the request using Content-Length header.
Prevention.
HTTP/2 should be used for backend connections and web server accepting same type of HTTP header should be used. 