[isalist] Re: [isapros] Re: Exchange Server 2010 Edge and TMG 2010 Integration
- From: Jerry Young <jerrygyoungii@xxxxxxxxx>
- To: isalist@xxxxxxxxxxxxx
- Date: Thu, 21 Jan 2010 15:58:21 -0500
I suppose for me the crux is what "security" represents. I currently see
security as a means for mitigating risks. While domain membership raises
the risks identified here, risks to external threats are what I'm looking to
mitigate. To get into my internal network, an external attacker would have
to compromise the server I have on the edge. In this particular case, there
is really only one way that could potentially happen - through SMTP (are
there others?). With TMG installed, use of the SMTP filter, and all other
ports closed (plus another firewall in front of it), how might an attacker
compromise the server?
Isn't that a better question to seek an answer to than attempting to address
principle and "just-in-case" scenarios?
I've never been able to win an argument from purely a principle or
"just-in-case" stance; I've always been required to have a concrete example.
On Thu, Jan 21, 2010 at 3:24 PM, Thor (Hammer of God)
<Thor@xxxxxxxxxxxxxxx>wrote:
> As always, you make excellent points. Indeed, design of structure
> without the business goals in mind could definitely bite the hand that
> feeds.
>
>
>
> I tend to boil these types of discussions down to the technical merit,
> particularly in the absence of states business goals and the presence of “to
> join, or not to join” questions.
>
>
>
> I would still assert that the same business goals could be met while
> meeting the security goals inherent in the question, but your more rounded
> “real life” approach is certainly valid.
>
>
>
> t
>
>
>
> *From:* isalist-bounce@xxxxxxxxxxxxx [mailto:isalist-bounce@xxxxxxxxxxxxx]
> *On Behalf Of *Jim Harrison
> *Sent:* Thursday, January 21, 2010 12:17 PM
>
> *To:* isalist@xxxxxxxxxxxxx
> *Subject:* [isalist] Re: [isapros] Re: Exchange Server 2010 Edge and TMG
> 2010 Integration
>
>
>
> Apparently, I postulated poorly.
>
>
>
> I don't use compliance as a security requirement, but as a business
> requirement (FSM help those who use it otherwise). Those who are tasked with
> the goal of "desigining a secure network path" must not determine network
> security goals and requirements without also considering the business goals
> and requirements. To do so is (IMHO) irretrievably stupid. invariably, the
> network design will be altered to satisfy some aspect of the business needs
> that were missed prior to the actual deployment. Reality (and Murphy)
> dictates that this is likely to happen anyway, but it's far worse if you
> miss them entirely in the initial design review.
>
>
>
> We also agree that if the business requirements dictate that you fire an
> 8-GA traffic shotgun at your DMZ firewall, then that DMZ is rendered
> effectively moot and the DMZ consequently represents nothing so much as
> additional network admin overhead.
>
>
>
> We agree that there is no such thing as "always" or "never" and that basing
> the deployment strictly on a single aspect of that deployment can only lead
> to disappointment and failure.
>
>
>
> My point in this discussion is to disabuse anyone that any single
> deployment model is "the best you can possibly do". All of them are
> contextual and will necessarily be limited by the business requirements OR
> that the security requirements will impose adjustments to the business
> requirements. It all depends on which requirement source weilds the bigger
> stick.
>
>
>
> HTH,
>
> Jim
>
>
> ------------------------------
>
> *From:* isalist-bounce@xxxxxxxxxxxxx [isalist-bounce@xxxxxxxxxxxxx] on
> behalf of Thor (Hammer of God) [Thor@xxxxxxxxxxxxxxx]
> *Sent:* Thursday, January 21, 2010 8:47 AM
> *To:* isalist@xxxxxxxxxxxxx
> *Subject:* [isalist] Re: [isapros] Re: Exchange Server 2010 Edge and TMG
> 2010 Integration
>
> The “outbound only policy” is only applies when it makes sense – nothing I
> say is ever put as a postulate. If you can do it, do it, if you can’t
> don’t. In regard to Exchange, as previously noted, the bi-directional
> properties of the rule are mitigated by the application filter, and I’m good
> with that.
>
>
>
> I think this is where our disconnect came last time… First, bringing in
> “compliance” in this discussion is non sequitur. “Compliance” has nothing
> to do with security or the technical aspects of the question; let’s not drop
> red herrings into this please. I still fail to understand how one can
> “manage and patch” so much easier in a domain than in the DMZ as a WG member
> – I’d really like for you to elaborate on that… If you are referring to
> push configurations and remote RPC based policy, then I would have to say
> that with the rules necessary to create a fully functional domain-based
> communications path to the system, you might as well not even have a DMZ, at
> least in respect to that system.
>
>
>
> If one must compromise the integrity of the DMZ structure to accommodate
> management goals, then someone has lost sight of the purpose of a DMZ. It
> would take a plethora of rules to deploy a fully managed domain member in
> the DMZ. One must treat the DMZ as a “when it is owned” set of assets. In
> this case, having systems fully managed from the internal network severely
> limits the strength of a DMZ. I have a production Exchange Edge box in my
> DMZ that is not a domain member. Once you configure the box, there isn’t
> any management one needs to do, really. Turn on auto updates and be done
> with it. Having rulesets in place 24/7 to allow for remote management is
> far more of a threat/risk than even an unpatched box would be in a “proper”
> DMZ.
>
>
>
> The main point is to start from a position of security, and design around
> that. If you find that you absolutely have to destroy the integrity of a
> DMZ structure by supporting domain members, well, that’s something you just
> have to do. But to start off with “management and patching might outweigh
> the need for security” is back-asswards, and obviates the purpose of a DMZ
> in the first place.
>
>
>
> t
>
>
>
> *From:* isalist-bounce@xxxxxxxxxxxxx [mailto:isalist-bounce@xxxxxxxxxxxxx]
> *On Behalf Of *Jim Harrison
> *Sent:* Wednesday, January 20, 2010 5:04 PM
> *To:* isalist@xxxxxxxxxxxxx
> *Subject:* [isalist] Re: [isapros] Re: Exchange Server 2010 Edge and TMG
> 2010 Integration
>
>
>
>
>
> I promise not to use references to thin cooking accoutrement headgear if
> you do... <oops; too late>
>
> Tim and I agree in principle - it's where implementation comes into play
> that we find ourselves reshaping our headgear.
>
>
>
> The question of domain vs. WG membership as a threat mitigation in and of
> itself typically ignores additional aspects of this question that an
> organization has to satisfy, such as compliance, management, patching, etc.
> Very frequently, the needs of the management outweigh the needs of the
> security or the traffic profile and its in these cases that you need to
> broaden your thoughts and do the "pro/con" checklist for yourself.
>
>
>
> Tim's arguments that a properly-defined and -managed traffic policy can do
> great things with mitigating this threat are absolutely correct (as I said;
> we agree in principle). Sadly, Tim's "outbound-only" traffic policy can't
> be used for Exchange SMTP connections because the Exchange team dropped
> such nice toys as TURN and ETRN in Exchange 2007 (shame, that). There are
> likely plenty of other examples where you have to adjust your traffic and
> deployment policies to meet the limitations of the applications and
> organizational requirements and you'll need to understand these before you
> make your final decision (or leave yourself some wiggle room afterwards)..
>
>
>
> Yes; absolutely seek opinions, options and technical thingies and weigh
> them all against your own requirements and limitations. You are the only
> one that can make the decision for your deployment and if it's based solely
> on "he said", then you haven't done your homework. None of the "reference
> folks" on this alias will intentionally steer you wrong, but neither can you
> base your decisions on these discussions alone.
>
>
>
> Security is not a goal; it's a repeating task. There is no "silver bullet"
> and the search for one can only end in unplanned cranial follicle freedom.
>
>
>
> ..we now return you to your irregularly-scheduled discussions...
>
> ..so there; thpthpthpthp :-)
>
>
>
> *From:* isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
> *On Behalf Of *Tim Mullen
> *Sent:* Wednesday, January 20, 2010 9:37 AM
> *To:* isapros@xxxxxxxxxxxxx
> *Subject:* [isapros] Re: Exchange Server 2010 Edge and TMG 2010
> Integration
>
>
>
> Jim and I recently had a rather “spirited” conversation around this.
> Hopefully we’ll leave out things like “tin foil hat” this time J (I had to
> Jim).
>
>
>
> My general though is to start with security in depth and least privilege in
> mind. As such, I begin the design of an Exchange Edge deployment with the
> mindset that I will not have them as domain members, but rather, simply
> stand-alone servers in a workgroup. I guess my first question would be,
> what makes you think it is more complex and that it requires a more
> difficult configuration?
>
>
>
> The role of the Exchange Edge is to accept SMTP mail for your domains, and
> presumably, to filter for spam and malware. This only requires SMTP to the
> perimeter and nothing else. If you choose to filter for recipient
> information, you can create an account for ADAM synchronization, however, I
> think you will find that the EE anti spam options are severely lacking in
> that respect – the logic is backwards; you can allow all main in TO someone,
> but not FROM someone, which totally defeats the purpose. I doubt you will
> use the feature at all, which means that ADAM sync is not necessary.
>
>
>
> Irrespective of that, the purpose of isolating the exchange edge box is to
> mitigate exposure should the server become compromised. If you DO make it
> domain member, then that box will have stored credentials for administrative
> access available to an attacker, as well as the necessary traffic rules to
> your DNS and domain controllers to fully compromise your entire network.
> My main rule in designing DMZ structures where there is anonymous access to
> the public for services (SMTP) is that “no credentials may live on that box
> which may be used on the internal network). Making that box a domain member
> breaks that.
>
>
>
> Now, that being said, am I to understand that you also wish to provide OWA,
> OA functionality via the Edge box? If so, I don’t see why – access to those
> services requires authentication, and can further be limited to
> certificates, so direct publication via TMG to your Exchange front end is
> acceptable. The EE box should only be used for SMTP inspection.
>
>
>
> Here’s how I do it:
>
>
>
> I begin with a 3 leg TMG box (UAG in my case): Internal, External, and
> DMZ. I publish SMTP (with the filter) to the DMZ to the Exchange Edge box.
> It does it’s thing. I then smart-host deliver mail via another publishing
> rule to the internal Exchange box. Yes, double publishing, with SMTP filter
> on both.
>
>
>
> OWA/OA is directly published via 443 to my Exchange box. The EE box is a
> stand alone server with different credentials. It is managed via a one-way
> RDP rule. If the EE box is compromised, the ONLY path to the internal
> network is via the SMTP publishing rule which is protected by the SMTP
> filter. I have full management capabilities, there is no internal
> credential exposure, and there is only a single protocol inbound to my
> network. To me, it is FAR more complex to securely publish and manage a
> domain member in the DMZ than a stand alone server, and increases the risk
> of exposure tremendously and really has little benefit. GPO need only be
> applied once on a role-based server, and can easily be applied via
> template.
>
>
>
> That’s my buck o’ five.
>
>
>
> t
>
>
>
> *From:* isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
> *On Behalf Of *Jerry Young
> *Sent:* Wednesday, January 20, 2010 9:01 AM
> *To:* isapros@xxxxxxxxxxxxx
> *Subject:* [isapros] Exchange Server 2010 Edge and TMG 2010 Integration
>
>
>
> I wanted to bounce a question off of the list regarding usage scenarios for
> integrating TMG 2010 with an Exchange 2010 Edge Server. My goal is to also
> install Forefront for Exchange on the boxes, too.
>
>
>
> My question, however, comes down to thoughts on domain membership and TMG
> utilization.
>
>
>
> My current thought is to make the Exchange 2010 Edge Servers domain
> members, install TMG on both of them in an array, and then use that same TMG
> array to provide reverse proxy access to other resources (like OWA, OMA, OA,
> CWA, etc.) through publishing rules.
>
>
>
> As in the past, the Exchange Product Group doesn't want the Edge Servers to
> be members of the forest in which the Exchange organization is hosted. I
> ran across postings on the Internet that indicate this can be done but was
> wondering what the list has seen deployed so far to date.
>
>
>
> While I could certainly dump the Edge Servers into their own perimeter
> network, that would require additional complexity, planning, and
> configuration for my client that they would like to avoid; they accept the
> risks presented by having the Edge Servers be domain members with the
> condition that TMG is used to mitigate those risks.
>
>
>
> Thoughts?
> --
> Cordially yours,
> Jerry G. Young II
> Microsoft Certified Systems Engineer
> Young Consulting & Staffing Services Company - Owner
> www.youngcss.com
>
--
Cordially yours,
Jerry G. Young II
Microsoft Certified Systems Engineer
Young Consulting & Staffing Services Company - Owner
www.youngcss.com
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