RE: [fw-wiz] Single Exchange/OWA on LAN with Internet Access - a good
From: Ravdal, Stig (SRavdal_at_Quiznos.com)
To: "Behm, Jeffrey L." <BehmJL@bvsg.com>, <email@example.com> Date: Thu, 17 Nov 2005 10:42:44 -0700
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:
- It's a Web authentication application (easy to attack- lots of tools)
- It uses the user's domain credentials (easy to escallate to more
- 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).
From: Behm, Jeffrey L. [mailto:BehmJL@bvsg.com]
Sent: Thursday, November 17, 2005 10:32 AM
Cc: Ravdal, Stig
Subject: RE: [fw-wiz] Single Exchange/OWA on LAN with Internet Access -
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
*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>
[mailto:firstname.lastname@example.org] On Behalf Of Ravdal,
Sent: Thursday, November 17, 2005 9:50 AM
Subject: [fw-wiz] Single Exchange/OWA on LAN with Internet Access - a
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.
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