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

From: "Thor (Hammer of God)" <thor@xxxxxxxxxxxxxxx>
To: "isapros@xxxxxxxxxxxxx" <isapros@xxxxxxxxxxxxx>
Date: Fri, 12 Jan 2007 09:22:24 -0800
I can¹t yet comment on what protocols will be necessary for CAS to perform
particular functions as I have not yet analyzed the required traffic, but
even with Ex2k3, ³full time² intradomain protocol support is totally
unnecessary for the FE to act as the OWA front end once it has been properly
initiated into the Exchange organization  I mentioned this in a past post,
but as part of my ³least privileged² configuration, CIFS and RPC (All
interfaces) are disabled, and only Kerberos-UDP, LDAP, LDAP GC, Ping and DNS
are enabled from the FE to my DC¹s object, and only HTTP from the FE to the
BE.  This works perfectly.  But, if I need to log on to the FE perimeter box
box or use System Manager from that box, then I enable the CIFS/RPC rule to
the DC¹s, get ?er done, and disable again.  This is completely different
than the ³official² Exchange documentation, but it is about as secure as you
could hope for in such an easily maintained configuration.  This is because
I think the Exchange group is not necessarily explicitly aware of the
authentication negotiation process, and just assumes that CIFS is required
for authentication  but, if the client can¹t establish a standard SMB
channel, it will fall back to Kerberos UDP.  Given what one can do with an
established authenticated CIFS connection, I choose to disable it for
security reasons.  

My guess (again, I¹m not sure) is that different operations will require
different protocol support.  For standard OWA access, I¹m sure we can get
away with similar limited protocols.  If you want to be able to map drives
via the OWA interface (which CAS will let you do) you¹ll most probably need
to allow CIFS to the host (but ONLY to that host).  Even so, it¹s a far
better configuration considering the ³universal access² to the FE.

When I deploy this, I¹ll know better.  And even if PSS gives me crap about
it not being supported, I just won¹t tell them.  I¹ll put the CAS ³behind
ISA² like they say and keep my perimeter DMZ configuration to myself.

t


On 1/12/07 3:56 AM, "Jason Jones" <Jason.Jones@xxxxxxxxxxxxxxxxx> spoketh to
all:

> From what I have read, the CAS is similar to the FE but with the addition some
> new features - I would *imagine* it would use very similar protocols, and if
> anything hopefully it will use less protocols for more efficient
> communications. I am sure it will still need to core intradomain protocols as
> it will be a domain member, but I think they have moved away from the FE>BE
> HTTP, POP3, IMAP model.
>  
> Need to lab it really to get a good idea.
> 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 Thomas W Shinder
> Sent: 12 January 2007 04:23
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> 
> WORD!
>  
> I¹ll gladly joining you in that public nut-kicking when the time comes. What I
> want to understand first is what are the protocol requirements for the CAS to
> the back-end components, and what their rationale is for making the statements
> that have been reported so far. They might have a good point, and if they have
> it, I want to hear it. But if the point is ?it¹s too hard² or ³I don¹t
> understand network security, I just say what my boss tells me to say² or ³I¹m
> on the take with Syphco² then those aren¹t valid and body parts will deserve
> some shaking up in the public square. The least they can do is state ³we don¹t
> have the time or inclination to show you have to provide the highest level of
> network security, but it is possible to do it right, we¹re just not going to
> show you how to do it² as a disclaimer. With that, we can then go ahead and
> help those who want to be helped J
>  
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Thor (Hammer of God)
> Sent: Thursday, January 11, 2007 6:40 PM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
>  
> It may be just this type of ³beating it to death² that is required to get the
> Exchange group¹s attention.  I don¹t really care if they don¹t support
> ³perimeter network² deployments as long as ISA is an exception.  I have every
> intention to ensure that an ISA authenticated perimeter network DMZ segment
> ³in front² of the CAS server is fully supported if the proper protocols are
> allowed.  I will make sure to press them into officially stating why it is not
> supported.  Even so, if they try that, I will publicly kick them in the nuts.
> 
> t
> 
> 
> On 1/11/07 4:15 PM, "Jason Jones" <Jason.Jones@xxxxxxxxxxxxxxxxx> spoketh to
> all:
> Hi Amy,
> 
> I am not really sure for their reasoning, but think it is based around the
> "Swiss cheese", don't pass intradomain traffic across a normal firewall
> argument.
> 
> Sorry, my bad for using the term DMZ, the exact phrase used by Scholl is "It's
> true. The Client Access Server (CAS), which among other things includes the
> OWA feature, is not supported in a perimeter network (aka a DMZ).  Instead
> you'll deploy one or more CASs inside your organization and put a robust
> firewall such as ISA 2006 in front of it." I am guessing from experience of
> other Exchange team recommendations that when they say perimeter network they
> really mean a traditional DMZ which is created using traditional packet filter
> firewalls. The recommended deployment is to put the CAS on the internal
> network e.g. on the same network as the Exchange back-end servers. Once the
> CAS is on the internal network, it should then be published to the Internet
> using ISA.
> 
> This design if fine if you want a simple open network where all servers exist
> in the same security zone and hence all trust each other, but many people are
> now trying to better this design by placing different types of servers into
> different security zones based upon their risk level and internet presence -
> say hello to the ISA auth access perimeter network! ;-)
> 
> Basically I think it all harks back to the "don't put domain members in a DMZ"
> mantra which is a pretty fair statement when using PF firewalls like PIX, but
> things have moved on as least privilege authenticated access perimeter
> networks with ISA are now getting advanced enough to challenge this argument.
> Maybe the difference between a PIX firewall and ISA firewall is just too
> subtle for some people???
> 
> Think we have now done this to death now!! - be very surprised if the Exchange
> team go back on these type of statements though. I remember Tom banging his
> head against a brick wall with Henrik based upon one of his MSExchange.org
> articles which said "not in the DMZ" type statements.
> 
> JJ 
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Amy Babinchak
> Sent: 11 January 2007 23:15
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> 
> Jason,
>  
> What¹s the reasoning behind CAS not in the DMZ? Where to they want it? Handing
> nude off the router? Behind a firewall?
>  
> If the later, then just drop the out dated DMZ language. Most firewall admins
> think that DMZ means nude off the other port on my nat box. Your least priv
> design puts CAS safely behind a firewall.
>  
> 
> Amy Babinchak
> Harbor Computer Services
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Jason Jones
> Sent: Thursday, January 11, 2007 5:58 PM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> 
> Thanks Amy - maybe I am being a little oversensitive, just didn't expect some
> of the initial responses.
> 
> I tend to avoid most of the main mailing lists, probably for similar reasons
> as others, and I tend to hang out at isaserver.org 95% of the time. Hence
> maybe why only Tom (and Stefan) tend to see my input and views on stuff.
> 
> Tom invited me to this list as he felt it would be a good place for me to pose
> all the questions that he can't answer or go unreplied on isaserver.org
> 
> I really do value the combined "ISA brain power" here, but just think it could
> be a little more forgiving and friendly at times...having said that I have
> found answers here that I just couldn't get elsewhere, so don't misunderstand
> me as ungrateful.
> 
> Anyhow back to the "core issue", from what I hearing from Exchange MVP
> contacts, MS are playing the "CAS in a DMZ is totally unsupported" tune very
> strongly. This is a real shame as it looks like I will never be able to deploy
> the existing least privilege design with Exchange 2007 without fear of
> customers coming back to us after trying to log PSS calls or getting other
> non-ISA firewall guys in who slate the design...oh well, at least ISA will
> still involved to some degree, just not as cool as it could be...
> 
> JJ  
> 
> 
>   
> 
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Amy Babinchak
> Sent: 11 January 2007 15:09
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> Jason don¹t get discouraged. The changes in Exchange are monumental so there
> are bound to be disagreements and changes of opinion on how to best secure it.
> The concept of an authenticated access DMZ in a separate security zone
> allowing only a very minimal set of protocols is a completely foreign concept
> to 99% of firewall admins out there. That fact you are even thinking about
> this stuff put you in an elite class. The rest are still poking holes and
> setting up VLANs.
>  
> Tom, Thor and Jim can be a bit clubby and a little overly poky to new comers.
> It¹s a twitch they developed after participating on the ISA server mailing
> list. It got worse when they decided to join a general purpose SBS list. I¹m
> not sure that they¹ll ever completely recover.
>  
> 
> Amy 
>  
> 
>  
>  
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Jason Jones
> Sent: Thursday, January 11, 2007 5:47 AM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> 
> Wish I had never asked now...sometimes, some of you guys really don't make it
> easy for new people to try express their views and pose questions for comment
> without being slapped down. One minute I am being labelled as an "idiot" for
> my comments/views, the next minute someone else who says the same thing as me
> is now right and not challenged. What gives?
> 
> I know many of you guys don't know me from Adam, but kinda unfair to just
> assume I know jack about ISA and secure network design just because I'm not
> "part of the club".
> 
> 
> Anyhow, thanks to Tim and Tom for seeming to share my disappointment with the
> decision made by the Exchange 2007 team...I think I need to try and find out
> how "official" their lack of support with 2k7 is going to be before I can
> continue recommending the least privilege model I have been using for Exchange
> 2003.
> 
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Jim Harrison
> Sent: 11 January 2007 04:30
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> ..maybe I¹m just tired?
> I spent two hours trying to get home tonight and I¹m clearly not in my mind
> (right or otherwise).
> Forget I wrote and we¹ll start over tomorrow?
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
> Behalf Of Thor (Hammer of God)
> Sent: Wednesday, January 10, 2007 8:18 PM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
> 
> That¹s exactly what I¹m talking about.  And precisely the configuration I
> deploy:
> 
> My FE is in the authenticated segment of the DMZ  and a member of my internal
> domain; however, the ³recommended protocols² the Exchange group recommends are
> not necessary- and thus, Steve¹s contention that ³CIFS and all that other
> stuff... Might as well just be internal² I reject.  I only allow Kerberos-Sec,
> LDAP, LDAP GC, Ping and DNS only from my FE to the internal DC¹s.  And only
> HTTP to the BE¹s.
> 
> Even if the other prots WERE required, it would still be far smarter to deploy
> the FE in the authenticated DMZ with limited access than to just give full
> stack access to the ENTIRE internal network.   This is a deployment of a
> services made available (initially) to a global, anonymous, untrusted network.
> 
> Maybe I¹m not properly articulating my point, but I have to say I¹m really
> surprised that we are having this conversation...
> 
> t
> 
> 
> On 1/10/07 7:10 PM, "Jim Harrison" <Jim@xxxxxxxxxxxx> spoketh to all:
> C¹mon, Tim; I know what your deployment recommendations are; this isn¹t it.
> He wants to extend his domain via ³remote membership²; not create a separate
> domain.
>  
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
> <mailto:isapros-bounce@xxxxxxxxxxxxx%5d>  On Behalf Of Thor (Hammer of God)
> Sent: Wednesday, January 10, 2007 4:26 PM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
>  
> Because it¹s safer that way, that¹s why... That¹s 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.
> 
> Let¹s 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.
> 
> ³Safer on the internal network² 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>
> 
>   
> 
> 
> 
> From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
> <mailto:isapros-bounce@xxxxxxxxxxxxx%5d>  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>
> 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_threa
> d/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&q=cas+dmz+isa&rnum=2&hl=en#4
> db165c21599cf9b 
> <http://groups.google.co.uk/group/microsoft.public.exchange.design/browse_thre
> ad/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&amp;q=cas+dmz+isa&amp;rnum=
> 2&amp;hl=en#4db165c21599cf9b>
> <http://groups.google.co.uk/group/microsoft.public.exchange.design/browse_thre
> ad/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&amp;q=cas+dmz+isa&amp;rnum=
> 2&amp;hl=en#4db165c21599cf9b>
> <http://groups.google.co.uk/group/microsoft.public.exchange.design/browse_thre
> ad/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&amp;q=cas+dmz+isa&amp;rnum=
> 2&amp;hl=en#4db165c21599cf9b>
> <http://groups.google.co.uk/group/microsoft.public.exchange.design/browse_thre
> ad/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&amp;q=cas+dmz+isa&amp;rnum=
> 2&amp;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 
> 
> All mail to and from this domain is GFI-scanned.
> 
> 
> 
>  
> 
>   
> 
> All mail to and from this domain is GFI-scanned.
> 
> 
> 
> 
> All mail to and from this domain is GFI-scanned.
> 
>  
> 
>  
>
[isapros] Re: ISA, Exchange 2007 and Perimeter Networks

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