[isapros] Re: ISA, Exchange 2007 and Perimeter Networks

  • From: "Jim Harrison" <Jim@xxxxxxxxxxxx>
  • To: <isapros@xxxxxxxxxxxxx>
  • Date: Wed, 10 Jan 2007 19:36:36 -0800

..to clarify further...

"using secure Exchange RPC publishing is the best security solution" -
pure, unadulterated BS.

You can't pre-auth server publishing rules; thus any auth attacks (and
there are *many*) must then be absorbed by the Exch server.

Yeh - that's secure.

 

While its true that ISA doesn't examine the "RPC" (it isn't really - not
at this stage of the game) within the RPC/HTTP stream, you can severely
limit the HTTP traffic is allowed through this rule via some very clever
HTTP Filter settings provided by the Exch team.

Even with the default settings, anyone who can reach your Exch server
via a *properly deployed* RPC/HTTP path through ISA is:

1.       An internal malcontent

2.       Smarter than you anyway

 

Let's not confuse the question of a member of the internal domain
residing across a firewall boundary with that of a member of a
completely separate (and untrusted) DMZ domain.

 

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Jim Harrison
Sent: Wednesday, January 10, 2007 7:14 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

 

"- me thinks not!" - I'll agree with that.

ISA RPC publishing protected every swingin' Exch server that was
published thusly from that nasty beasty known as Blaster.

Literally No Other "firewall" can truthfully make that claim.

 

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Jason Jones
Sent: Wednesday, January 10, 2007 4:56 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

 

"It's as safe in the domain as in the DMZ if it's being protected by a
properly configured ISA box....."

 

Hmmm...so what if your FE *does* gets compromised? ISA is impressive,
but it can't always protect against published server application
vulnerabilites.

 

As an example - does ISA protect FE servers against RPC attacks when
publishing RPC over HTTP using web publishing then?? - me thinks not!

When ISA is protecting RPC over HTTP all filtering is in the HTTP
domain, so ISA has no way of knowing if the RPC data being tunnelled is
valid or not. Once the packets reach the FE they are then decapsulated
by the RPC proxy, and could in theory, be malicious. This is why using
secure Exchange RPC publishing is the best security solution, but most
people just publish RPC/HTTP and hence only really inspect HTTP data. 

 

Don't forget, we are talking about Internet connections to Exchange
services on a FE/CAS - even with ISA in place, there will still be ways
to attack the FE. Yes they are greatly limited, but still there.  

Jason Jones | Silversands Limited | Desk: +44 (0)1202 360489 | Mobile:
+44 (0)7971 500312 | Fax: +44 (0)1202 360900 | Email:
jason.jones@xxxxxxxxxxxxxxxxx <mailto:jason.jones@xxxxxxxxxxxxxxxxx> 

 

 

________________________________

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Steve Moffat
Sent: 11 January 2007 00:36
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Oooohh......we're talking Exchange here......not SQL....

 

It's as safe in the domain as in the DMZ if it's being protected by a
properly configured ISA box.....

 

J

 

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Thor (Hammer of God)
Sent: Wednesday, January 10, 2007 8:26 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

 

Because it's safer that way, that's why... That's what an authenticated
access DMZ perimeter is for- with a CAS server that presents logon
services to any Internet user, I would (and, in fact, require) that the
server be in a least-privileged authenticated access perimeter network
that limits that servers communications to the minimum required for
required functionality - and only to the hosts it needs to talk to.

Let's say there is a front-end implementation issue or coding
vulnerability: the CAS on the internal network would allow unfettered,
full-stack access to the internal network.  A CAS in a perimeter DMZ
would mitigate potential exposure in the event of a 0day or
configuration issue. 

"Safer on the internal network" is a complete misnomer when it comes to
servers presenting services to an untrusted network. 

t


On 1/10/07 3:04 PM, "Jim Harrison" <Jim@xxxxxxxxxxxx> spoketh to all:

Why would you want to place a member of your internal domain in your
DMZ, fer chrissakes?!?
Hosting any domain member in the DMZ is a difficult proposition;
especially where NAT is the order of the day.
You can either use a network shotgun at your firewall or attempt to use
your facvorite VPN tunnel across the firewall to the domain.

Jim

________________________________

From: isapros-bounce@xxxxxxxxxxxxx on behalf of Jason Jones
Sent: Wed 1/10/2007 2:35 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

From what I can gather, the new CAS role now uses RPC to communicate
with the back-end (not sure of new name!) servers so I am guessing that
this is an "RPC isn't safe across firewalls" type stance. Which I guess
for a PIX, is a pretty true statement.

Just think how much safer the world will be when firewalls can
understand dynamic protocols like RPC...maybe one day firewalls will
even be able to understand and filter based upon RPC interface...maybe
one day... :-D ;-)

Shame the Exchange team can't see how much ISA changes the traditional
approach to DMZ thinking...kinda makes you think that both teams work
for a different company :-(
Jason Jones | Silversands Limited | Desk: +44 (0)1202 360489 | Mobile:
+44 (0)7971 500312 | Fax: +44 (0)1202 360900 | Email:
jason.jones@xxxxxxxxxxxxxxxxx <mailto:jason.jones@xxxxxxxxxxxxxxxxx>
<mailto:jason.jones@xxxxxxxxxxxxxxxxx>  

 

________________________________

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Greg Mulholland
Sent: 10 January 2007 22:07
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

I seriously hope that they have take different paths and these are not
limitations on the software or it is going to mean a nice little
redesign and break from custom..

Greg

----- Original Message ----- 
From: Jason Jones <mailto:Jason.Jones@xxxxxxxxxxxxxxxxx>
<mailto:Jason.Jones@xxxxxxxxxxxxxxxxx>   
To: isapros@xxxxxxxxxxxxx 
Sent: Thursday, January 11, 2007 8:25 AM
Subject: [isapros] ISA, Exchange 2007 and Perimeter Networks


Hi All, 

I heard today from an Exchange MVP colleague that members of the
Exchange team (Scott Schnoll) are saying that they (Microsoft) do not
support placing the new Exchange 2007 Client Access Server (like the old
Exch2k3 FE role) role into a perimeter network. Has anyone else heard
the same? This sounds very similar to Exchange admins of old when they
didn't really understand modern application firewalls like ISA could do
- RPC filter anyone???
http://groups.google.co.uk/group/microsoft.public.exchange.design/browse
_thread/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&q=cas+dmz+isa&rn
um=2&hl=en#4db165c21599cf9b
<http://groups.google.co.uk/group/microsoft.public.exchange.design/brows
e_thread/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&amp;q=cas+dmz+i
sa&amp;rnum=2&amp;hl=en#4db165c21599cf9b>
<http://groups.google.co.uk/group/microsoft.public.exchange.design/brows
e_thread/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&q=cas+dmz+isa&r
num=2&hl=en#4db165c21599cf9b>  

I have just about managed to convince Exchange colleagues (and
customers) of the value of placing Exchange FE servers in a separate
security zone from BE servers, DC's etc and now I here this...

Are the Exchange team confusing the old traditional DMZ's with what ISA
can achieve with perimeter networks? 

From what I believe, it is good perimeter security practice to place
servers which are Internet accessible into different security zones than
servers that are purely internal. Therefore, the idea of placing
Exchange 2003 FE servers in an ISA auth access perimeter network with
Exchange 2003 BE servers on the internal network has always seemed like
a good approach. It also follows a good least privilege model. 

Is this another example of the Exchange and ISA teams following
different paths???? 

Please tell me that I am wrong and that I am not going to have to start
putting all Exchange roles, irrespective of security risk, on the same
network again!!!!

Comments? 

Cheers 

JJ 

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