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RE: HTTP tunneling to bypass proxy filter
From: "Hayes, Ian" <ihayes () nvcancer org>
Date: Mon, 21 Apr 2008 15:57:26 -0700

This will work, but some devices will notice it. I did something similar
while doing some contract work for the Air Force. One of the first
projects I worked on was figure out how to bypass the content filters
they use at the bases. I set up a Linux box at home with SSHD listening
on port 443. The proxy they were using was a pain, it didn't really like
me trying to connect through it using SSH as a local SOCKS proxy.
Eventually, I had to wrap that all up in a HTTP tunneller. I had to
write an ACL to prevent access to port 443 from the outside except for
the base's outside address because if my provider were able to connect
to 443, they'd shut my connection down...

Eventually the guys further up the food chain noticed a good amount of
traffic going to a residential IP address, and looked into it. They were
very puzzled because they were seeing SSH traffic over an SSL port, and
made some phone calls to the base NOC where I was working. We worked on
reconfiguring their proxies to reject this kind of traffic. I'm not sure
of they were ultimately successful in preventing this or not.

--
Ian Hayes
Systems Engineer
Nevada Cancer Institute
Office:(702) 822-5156
email: ihayes () nvcancer org
http://www.nevadacancerinstitute.org

-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com]
On Behalf Of Brandon Louder
Sent: Monday, April 21, 2008 11:05 AM
To: uglyhunK; security-basics
Subject: RE: HTTP tunneling to bypass proxy filter

I am interested in hearing comments about this as well. I believe there
are some newer web security appliances that do deep inspection at the
application layer that would catch this, hopefully someone else can
contribute.

Another scenario in relation to your custom http tunnel client is a
socks based proxy to an SSH server. If you have an internet facing SSH
server and set it to listen on port 443 you should be able to tunnel
your web traffic over HTTPS. For instance with putty you can do:
putty -D 8080 -P 443 -ssh "ip address"

And then set your web browser to use socks proxy of localhost on port
8080.

All of the web traffic would then show up as https to the remote IP. If
you have a web security appliance that does HTTPS decryption and deep
inspection it may not work, similar as with the HTTP tunnel client.  

-brandon
-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com]
On Behalf Of uglyhunK
Sent: Saturday, April 19, 2008 8:39 AM
To: security-basics
Subject: HTTP tunneling to bypass proxy filter


Recently I was challenged by network admin to bypass corporate HTTP
proxy
filter. Easier option would have been to download one of many HTTP
tunnel
clients but that is ruled out as all the sites are blocked. I didn't
want to
email the installation file as there is a strict monitoring policy to
using
email and "leaving no traces" is one of the primary conditions.

Only option left was to write my own HTTP tunneling client and being a
developer I have access to JDK. Server component is written in PHP and
it
works like a charm; all the communication is encoded in base64 (though
not
the best way to obfuscate data). It took me just 10 days to successfully
bypass the proxy filter and access literally all the websites except
https
ones. Just for the info, this is @ one of the largest American banks.
So, I
won the first round and now I threw a challenge @ him to identify this
kinda
of tunneled data and block it successfully.

I'm not sure if he can do this, but, would like to know from you guys if
there is any way for the admin to block me from using custom tunnel
client.


-uglyhunK






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