varnish -- Request Smuggling Vulnerability

Varnish Cache Project reports:

A request smuggling attack can be performed on Varnish Cache servers by requesting that certain headers are made hop-by-hop, preventing the Varnish Cache servers from forwarding critical headers to the backend. Among the headers that can be filtered this way are both Content-Length and Host, making it possible for an attacker to both break the HTTP/1 protocol framing, and bypass request to host routing in VCL.

[source]