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RE: Bypassing Firewalls
From: "Lars Troen" <Lars.Troen () sit no>
Date: Sat, 8 Apr 2006 19:27:13 +0200

I guess I understand, first you need to scan for any openings 
on the network (what is allowed through the firewall).  Then 
scan IP addresses on those ports for alive machines.  Once 
that is complete, try to gain root/admin privilege on 
one/many inside machines to launch your system(s), or I guess 
you could install your tools on the compromised host (if 
permitted) to further your scanning/testing.

Please understand, I am very new to this and am looking to 
get as much advice as possible, so I can become an expert. 

For scanning port and IP's on internal networks: The way you outline it
is not optimal. Different hosts often have different ports open if
they're offering different services. A clustered service will have the
same ports open on all these hosts that are part of the same cluster.
The same also applies for other types of "farms". But you normally
figure this out. When doing port scans, I feel that you get a better hit
rate when first scanning "often used ports" or a ping sweep to get a
picture of the landscape. 

Be however aware that a portscan is like a light house to any IDS/IPS
system and some firewalls might also have counter measures to this. This
depends completely on the environment you're testing and you risk having
your ip/switch port blocked out automaticly. It's important to make such
things clear with the customer before you begin and try to get as much
information as possible about subnets and services in order be able to
do a good pen test that gives an as accurate picture as possible of the

Trying to find a way out of the network? Do you have access to an
existing client pc? It would help you a lot to see what methods a normal
user uses for contact with external networks. Typically these accesses
involves http(s), smtp, icmp. In most cases (for larger environments)
these services (except icmp) are proxied and you can only gain access
through authenticated access.

If you can ping hosts on the internet, the icmp requests are in many
cases not masked/proxied.

If you can't gain access to a client pc, then maybe you're connected to
the same switch as a client pc that is being used? Then you can put the
switch into "hub mode" and sniff it's activity and see how it
communicates with the world.

If you can gain access through any of these (or other) services you can
setup a tunnel through these protocols.

If you know what kind of firewalling technology (brand/version) they're
using there are several default setups that you might want to check.

If you don't know anything about the customer setup, and you're
completely on your own it will be a much more time consuming task to
locate the relevant values that can take you further (but still very

Good luck!


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