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Re: Question about dmz security
From: abretten () kroger com
Date: Fri, 14 Feb 2003 19:00:12 -0500

Jennifer, you are exactly right to be concerned.    When someone uses a
dual homed host to bridge a firewall, they are creating a huge potential
security hole....the first time a hacker exploits the ftp server, they have
free access to your entire internal network through that internal NIC on
the ftp server.

What people would consider the "best" or to put it a better way, the
"industry" standard way......you would have one NIC on the ftp server, and
place it on the DMZ. If you are a small company and all you have is a
firewall with two NICs and a router connected to the Internet, I would
recommend placing some ACL's on the Internet router to protect the ftp
server from common attacks (for example deny all the obvious ports like
telnet and echo and chargen).

The next step is to lock down the ftp server..........if all its doing is
ftp.......turn off all those "helpful" services that most OS's turn on by

If you have a little more resources a good design is build a firewall with
three NIC's........the outside is the DMZ, the inside is the inside, and
the 3rd NIC is referred to as a protected service network/screened subnet.

If you have more resources then you can follow a suspender and belts
design.........two firewalls one front of the other....the DMZ is at the
top, then a firewall, then the service network, the second firewall and
then your internal network.

Hope this helps a little bit.  I've barely scratched the surface of all the
things you can do to build a secure infrastructure.

if you haven't had chance to attend a class, every basic network security
course I've seen would cover what I've discussed.

Andy Bretten

                      Fountain"                To:       <security-basics () securityfocus com>                         
                      <JFountain () rbinc         cc:                                                                   
                      com>                     Subject:  Question about dmz security                                    
                      02/14/2003 02:42                                                                                  

I need an opinion on a current design implementation in place.  We have
an ftp server sitting in our dmz.  This box has two nics - one is
plugged into the dmz hub and one is plugged into our network.  I think
this is a security risk and we should just allow internal users access
to the box via the firewall by opening the port instead of having dual
nics.  they do not see a security risk. maybe i am just too new at this
and need some education.  what is the "best" way to implement this

Thank you
Jenn Fountain

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