Monday, May 27, 2013

Bypassing the Corporate Proxy

This is a post in Spanish that explains how to bypass a corporate web proxy (and its filters) by using standard (not true 100%) Unix tools. In this scenario, the user wants to bypass a proxy (a Windows Proxy) that is using NTLM authentication in order to visit forbidden pages and/or for for privacy reasons.


The following tools are used:
  • cntlm is proxy that let our tools go through the proxy by doing the NTLM authentication bits. It will be listening in localhost and behaving like a common HTTP proxy.
  • corkscrew to tunnel SSH traffic over HTTP proxies
  • An ssh client to open a Socks proxy in localhost and an ssh server listening on 443.
  • A web browser that supports Socks proxies (e.g. Firefox)

The traffic will flow as follows:

Firefox -> ssh client -> corkscrew -> CNTLM -> Corporate Proxy -> SSH server -> Inet.

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