RE: [fw-wiz] NTLM authentication from DMZ

From: Frank Knobbe (fknobbe@knobbeits.com)
Date: 09/19/02


From: Frank Knobbe <fknobbe@knobbeits.com>
To: Ben Nagy <ben@iagu.net>
Date: Thu Sep 19 17:16:01 2002


On Thu, 2002-09-19 at 02:13, Ben Nagy wrote:
> The key threat is that someone will hack your IIS box and then sit on it
> gathering valid password pairs for the LAN domain, and then just access
> C$ on whatever box they like as soon as anyone in the Domain Admins
> group checks their mail. We could argue about countermeasures to that,
> but believe me when I say that once someone has control over the DMZ box
> then you're in some pretty major schtuck unless you have an extremely
> smart IDS or Tingling Spider Senses.

Doesn't have to be that way. The OutlookWebAccess box only needs to have
access to the Exchange server and domain controllers. You could use a DC
in a third DMZ segment and only allow the OWA box to validate accounts
against it. That box in turn can talk to internal DC's. That way you
limit access from the OWA box to internal DC's. Yeah, doesn't prevent
password cracking, but it is still much harder to poke through to the
LAN.

RPC (and the two 'fixed' Exchange services) only need to be available to
the Exchange server not the whole network.

So the statement 'then just access C$ on whatever box they like' is only
valid if you drop the ball in the firewall config. Neatly tightened,
there is no c$ access.

I agree with the rest, such as:
> Note that I always recommend that Exchange boxen not talk SMTP to the
> outside world - setting up a secure mail relay in the DMZ is cheap, easy
> and can provide some good first-pass filtering / screening capabilities.

Regards,
Frank