How to understand `the socks can fool the internal http proxy server`?

Question

A server's firewall only allows some ports (such as http port 80) to communicate, then you can use the socks5 protocol to connect to a socks5 server that opens 80 ports to connect to other servers on the public network. With some additional technical means, you can even fool the internal http proxy server. In this environment, you can use the network service without restrictions in the environment of using the intranet http proxy. This is called socks over HTTP (we often say Through the wall).

How to understand this meaning:

With some additional technical means, you can even fool the internal http proxy server. In this environment, you can use the network service without restrictions in the environment of using the intranet http proxy. This is called socks over HTTP

Answer 1

It looks like it might perhaps be part of (a poor translation of?) some text that is heavy on assumptions but light on details, or perhaps relying heavily on context not included in the quoted text.

It seems to be attempting to describe a SOCKS over HTTP technique but glosses over the details.

SOCKS over HTTP is typically implemented using the HTTP CONNECT method. Of course, an intranet HTTP proxy has the option to restrict which sources are allowed to use this option, and the allowed destinations of requests using such a method.

If you are in a (supposedly) restricted intranet that allows outgoing connections to port 80 only, and only through a HTTP proxy, and that proxy allows the use of the CONNECT method to a destination server under your control, and you make that destination server a SOCKS server in port 80, you can use the resulting tunnel to have effectively unrestricted network connectivity to the outside internet.

The SOCKS protocol also includes a reverse port forwarding feature, so you can also use the tunnel to allow incoming connections through the SOCKS server to the "restricted" intranet, bypassing the restrictions.