RE: Single Exchange/OWA on LAN with Internet Access - a good

["Ravdal, Stig" <SRavdal () Quiznos com>]

Hi Julian,

I think what you suggest is certainly an option.  I have seen it done both this way and where the traffic goes to the 
LAN via the firewall.  VPNs are sometimes terminated in this way.  

I believe that what you loose is the firewall "inspection" of the unencrypted traffic if the SSL connection is 
terminated on ISA.  If you pass the traffic back through the firewall to the LAN then the firewall could potentially 
block something bad or log it - but it depends on the capabilities of your firewall.  In some cases firewalls may not 
provide support for the twice-pass option.

In the case of ISA acting as the proxy it is at least a firewall and is capable of performing some inspection.  If all 
you have is a reverse-proxy and authentication you have created a bypass of the firewall at least for the allowable 
protocols, and to the firewall some traffic could be encrypted.

Thanks,

Stig

________________________________________
From: Julian M D [mailto:julianmd () gmail com] 
Sent: Monday, November 21, 2005 7:27 PM
To: Matt Bazan
Cc: Ravdal, Stig; firewall-wizards () honor icsalabs com
Subject: Re: [fw-wiz] Single Exchange/OWA on LAN with Internet Access - a good

Instead of placing the ISA box in PIX's DMZ, create a second DMZ by placing ISA between the  PIX's inside interface and 
the LAN, filtering the noise at the PIX level, and then just publish the Exchange services you need. You cold always 
use the RADIUS with any kind of secondary authentication (RSA cips) 
 
-------------------
|PIX ---DMZ1 |
-------------------
 |
 |-DMZ2
 |
 |
------------
|ISA      |
------------ 
|
|
|LAN
|
|
Exchange
 
Pros? Cons?
 
Thanks,

On 11/18/05, Matt Bazan <Mbazan () onelegal com> wrote: 
OWA front ended by ISA 2003 is solid.  Requires either port 80 or 443 or
one/other depending on your requirements.  Authentication is not handled 
by OWA box.

-----Original Message-----
From: firewall-wizards-admin () honor icsalabs com
[mailto: firewall-wizards-admin () honor icsalabs com] On Behalf Of Ravdal,
Stig
Sent: Thursday, November 17, 2005 9:43 AM
To: Behm, Jeffrey L.; firewall-wizards () honor icsalabs com 
Subject: RE: [fw-wiz] Single Exchange/OWA on LAN with Internet Access -
a good


Thanks Jeff & others,

No I won't let the admins have their insecure way about things.  What I
struggle with from time to time is having logical and factual reasons 
why this or that is more or less secure.

But I am starting to put together a list of issues from what I have seen
in the archives and some of the responses I have heard thus far.

A new challenge with OWA on Windows 2003 is that you cannot lock down 
the ports that the front-end server needs to talk to the back-end
system.  I saw a different comment on the list suggesting that MS has
done this to position ISA as the best (and only) solution for OWA in a
DMZ - it is designed to "publish" MS products including MS CRM.  We had 
another issue with that product and providing access to it via SSL-VPN
where the pages broke because of mangled activeX or something to that
effect - not very happy with MS approach to securing their products.

Here's what I have so far for good strong arguments & solutions:

> From Paul:
- It's a Web authentication application (easy to attack- lots of tools)
- It uses the user's domain credentials (easy to escallate to more 
attacks)
- Both of these are simple to do from a computer that's untrustworthy

Jeff & Manuel:
- CipherTrust's IronWebMail front end (that sits in a DMZ) or other
capable reverse proxy such as apache and do auth up-front there (combine 
that with Token and it's strating to get better).

Thanks guys,

Stig


-----Original Message-----
From: Behm, Jeffrey L. [mailto:BehmJL () bvsg com]
Sent: Thursday, November 17, 2005 10:32 AM 
To: firewall-wizards () honor icsalabs com
Cc: Ravdal, Stig
Subject: RE: [fw-wiz] Single Exchange/OWA on LAN with Internet Access -
a good

The DMZ server ( i.e. reverse proxy-type server) should be able to do
more than just port filtering and *shouldn't* require all those ports to
be open. It should be able to do various application level checks as
well, before the request makes it into your network. 

Look at CipherTrust's IronWebMail front end (that sits in a DMZ) for
example. It does more than just port filtering and doesn't require a ton
of open ports through the firewall, just normal web traffic. Other 
"reverse-proxy" front ends should behave similarly, although perhaps not
as robustly.

*DON'T* let your MS admins dictate the security of the network. If you
do, you'd be better off to just put the exchange servers directly on the 
Internet ;-)... <sarcasm>It'd be just as secure, faster (due to no
firewall latency), and less configuration issues.</sarcasm>

Jeff

-----Original Message-----
From: firewall-wizards-admin () honor icsalabs com
[mailto:firewall-wizards-admin () honor icsalabs com] On Behalf Of Ravdal,
Stig
Sent: Thursday, November 17, 2005 9:50 AM 
To: firewall-wizards () honor icsalabs com
Subject: [fw-wiz] Single Exchange/OWA on LAN with Internet Access - a
good

Hi everyone,

I hope that someone has been through this before and have some 
substantial arguments for/against:

Our MS admins are proposing to implement single OWA/Exchange servers
on the LAN and allow access directly to the server through the firewall.
The primary reason for doing it this way is to reduce the cost of the 
front-end server that would otherwise reside in a DMZ.   Their argument
is that with OWA 2003 you have to have a bunch of ports open anyway
and so what is the reason to put a front end server in the DMZ - if
that server were compromised they would practically have access to the
network anyway.  With the OWA/Exchange server inside the firewall
access from the Internet can be limited to 80 and/or 443 only.

My concern is that with the next OWA vulnerability someone will own 
the server in the DMZ through a single exploit.  However, I cannot
find anything that suggests that the front end server solution is
really any more secure.  Yeah it's another hop but it would be an easy
one as soon as the front end server is compromised. 

Thoughts?

Thanks,

Stig
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