Re: DHCP in a corporate MS environment - Security Risk?

["Bill Royds" <Bill () royds net>]

I don't think there would be any real problem with DHCP. If you backup the DHCP
database regularly (daily if busy) with some kind of security checksum (MD5 or
SHA1), then you should have the ability to detect modifications that are not in
the activity logs.
  If you use the Microsoft DHCP software, the database is a SQL-server database
and can be reported on by many tools. It would allow you to monitor changes and
quickly find anomalies.
Since you are using Microsoft you are also using WINS or dynamic DNS with Active
Directory. Both  of these are similar to DHCP in structure so you already have
dynamic entries to worry about. Since Active Directory/Dynamic DNS and DHCP are
integrated, you have much better control of which users have which IPS with DHCP
than any static assignment.

Static assignment has security problems since you have to keep track manually of
all changes  and unless you are willing to have somebody spend their working
hours using arpwatch, they will soon get out of synch with reality. You are
likely to have assignment tables out of date and missing entries so you probably
will have more security problems with a static database than a DHCP. Since you
can assign static entries in the DHCP database for anything you want to monitor,
there is no reason to use complete static assignment at all.



----- Original Message -----
From: "Eye Am" <eyeam () optonline net>
To: <firewall-wizards () honor icsalabs com>
Sent: Monday, January 20, 2003 11:06 PM
Subject: [fw-wiz] DHCP in a corporate MS environment - Security Risk?


I'm looking for opinions, experiences and references on the subject. Downed
and searched the entire Firewall-Wizards list. Found little discussion
either
way. This may be a bit OT for the board except that some security may well
be set at the public-facing firewall as well as risks may be apparent there.

Our corporate network is reasonably well set up with private and public DNS,
no wireless IP connections and blocking all RFC1918 traffic in or out of the
public side. Some security consultants highly recommended static addressing
across the board for security and control reasons - i.e.. access-list
control and the potential for compromise of the DHCP database. I have
searched google etc and found a few articles and whitepapers.

We have historically configured static IPs on servers, routers, switches and
all outside-facing devices. We do have several multi-homed devices with
static, public IP and a second interface facing inside (these are being
migrated to DMZ where multi-homing will no longer be necessary.) However
this does get to be a pain when making across-the-board changes.
Documentation is a bear as well since we are a small company with little
resources available to keep detailed network drawings up-to-date.

Lately we are leaning towards regular lease-based DHCP for workstations and
reserved DHCP addresses on servers on the private side. This will, of
course, make life much easier when making widespread changes or additions
such as adding secondary DNS. I have been wavering back and forth.

Is there any experience with compromised DHCP databases in MS environments?
Any strong opinions or reasoning pro or con the use of DHCP? Any
recommendations for shoring up the service and it's traffic?

Much Appreciated In Advance
Chuck

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