OSEC

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Bugtraq archives for 4th quarter (Oct-Dec) 1998: Re: [NTSEC] By-passing MS Proxy 2.0 and others packet filtering

Re: [NTSEC] By-passing MS Proxy 2.0 and others packet filtering

Gus (angusINTASYS.COM)
Tue, 13 Oct 1998 11:18:23 +0100 

So to summarise:

"Proxy servers can be abused. Ensure that only authorised users can
connect"

Exactly how you do this will depend on your circumstances and software.
Binding the server to the inward-facing NIC in a 'bastion host' config,
ensuring access control features are enabled by default if you are a
vendor and blocking inward traffic to proxy port if you run a firewall or
filtering router.

Perhaps Squid's "X-Forwarded-For: " header is a solution that could be
applied for situations where limiting the access to the server is not a
viable proposition.

A portscanner that bounces through a proxy server, in the style of the
ftp 'bounce' attack is at http://www.intasys.com/~angus/pbs.c

It goes without saying that 90% of "ftp bounce attack" code will only need
very small mods to be used on a WWW proxy.

Regards
        Gus

--
                                angusintasys.com