RE: AD in the DMZ . . . OK?

From: Dieter Sarrazyn (dsr_at_ascure.com)
Date: 07/30/04

  • Next message: Sabo, Eric: "RE: Network spyware detection" 
    Date: Fri, 30 Jul 2004 07:09:10 +0200
To: <security-basics@securityfocus.com>

    Wouldn't using LDAP be a solution here? Every AD system is in fact also
    an ldap server.

    If the only thing needed is authentication with userid/password, then
    this is fairly simple to do. A special group could be created containing
    all users that are allowed to use this type of authentication. Using a
    "ldap-read" user which has only read access to this group is pretty
    secure I guess.

    Regards,
    Dieter

    > -----Original Message-----
    > From: Roger A. Grimes [mailto:roger@banneretcs.com]
    > Sent: donderdag 29 juli 2004 4:51
    > To: karl; security-basics@securityfocus.com
    > Subject: RE: AD in the DMZ . . . OK?
    >
    > Karl, why I can't say I'm an expert on the subject, all I can
    > say is to use caution and think about the risks that are
    > involved (which you are already doing by sending out this
    > email). If I were to expose any AD domain to the DMZ, I
    > would take great pains to secure it using additional methods
    > (i.e. IPSec, SSL with client authentication certificates,
    > VPN, RRAS, Network Access Quarantine Control, etc.) to secure
    > and authenticate the communication channel. For a couple of
    > reasons:
    >
    > 1. First AD with W2K and above, likes to use Kerberos as the
    > default user authentication protocol. Kerberos is
    > significantly stronger than its predecessors (LM, NTLM, and
    > NTLMv2). If users connect to your AD on the DMZ and don't
    > have a secure VPN tunnel that supports Kerberos, then they
    > will connect using one of the earlier protocols, all of which
    > have been successfully attacked using brute force methods.
    > Unless you have LM hashing turned off, I maybe able to
    > capture LM password hashes in the traffic and compromise passwords.
    >
    > 2. Unless you have SID filtering turned on, it may be
    > possible for a lesser authenticated security principal
    > account (other requirements
    > apply) to elevate their privileges using the SID History trick.
    >
    > 3. Unless you have your anonymous enumeration permissions
    > set securely, a remote hacker may be able to enumerate your
    > AD objects.
    >
    > 4. If I was a malicious hacker and I knew you were
    > authenticating your network user accounts on your DMZ, I
    > would try my best to successfully compromise your DMZ and
    > sniff traffic.
    >
    > This is just a few things I would worry about. A secure
    > communication's tunnel and/or a properly designed .NET app
    > can minimize the risk. So the real answer is that yes,
    > putting AD on the DMZ elevates your risk of compromise, but
    > that elevated risk can be minimized by taking additional
    > countermeasures. And security risk is always just a
    > cost/benefit trade off.
    >
    > Roger
    >
    > **************************************************************
    > **********
    > ***
    > *Roger A. Grimes, Banneret Computer Security, Computer
    > Security Consultant *CPA, CISSP, MCSE: Security
    > (NT/2000/2003/MVP), CNE (3/4), A+
    > *email: roger@banneretcs.com
    > *cell: 757-615-3355
    > *Author of Malicious Mobile Code: Virus Protection for
    > Windows by O'Reilly *http://www.oreilly.com/catalog/malmobcode
    > *Author of upcoming Honeypots for Windows (Apress)
    > **************************************************************
    > **********
    > ****
    >
    > -----Original Message-----
    > From: karl [mailto:opium@runningriver.co.uk]
    > Sent: Wednesday, July 28, 2004 6:49 AM
    > To: security-basics@securityfocus.com
    > Subject: AD in the DMZ . . . OK?
    >
    > Hello
    >
    > One of the developers I work with has come up with a wild and
    > crazy notion to write a .NET app that sits on a DMZ Web
    > server but gets user information from the Active Directory on
    > the other side of the firewall..
    >
    > I'm inexperienced with this, so did some research and found
    > that this kind of thing is possible (plenty of articles on
    > putting Exchange servers in the DMZ), but found myself
    > wondering if this ever happens, i.e. do people actually have
    > their networks set up this way? Do folk expose/replicate AD
    > to the DMZ in practice?
    >
    > It's all very well that this stuff is possible, but if it's
    > perceived as insecure and not implementable in the real world
    > . . . . . . .
    >
    > Thanks for any advice . . . . .
    >
    > Karl
    >
    >
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  • Next message: Sabo, Eric: "RE: Network spyware detection"

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