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Re: Invalid WINS entries
From: Attonbitus Deus <Thor () HAMMEROFGOD COM>
Date: Wed, 17 Jan 2001 16:54:06 -0800

It doesn't work that way.  If you put a bogus BDC on the lan, the server
service won't even start unless its computer account is verified against the
dc based on the SID.  Same with putting a bogus PDC with the same domain
name...  A workstation won't even set up a secure channel in the first place
unless its account is verified which must happen before the
challenge/response take's place (insofar as NtLmSsp is concerned.)

Granted, you could screw with WINS a bit, but even then the IP stack will
fall back on broadcast to find a 'real' dc if you have properly configured
your node type to 0x8 (Hybrid).  If you are already on the LAN to the point
of doing all this stuff, just capture SMB packets over a few days---

---------------------------------
Attonbitus Deus
Thor () HammerofGod Com

----- Original Message -----
From: "Byrne, David" <dbyrne () TIAA-CREF ORG>
To: <BUGTRAQ () SECURITYFOCUS COM>
Sent: Wednesday, January 17, 2001 1:35 PM
Subject: Invalid WINS entries


After playing around with some WINS problems we were having, I discovered
something that doesn't seem to bother very many people. WINS does nothing
to
verify the 1Ch (domain controllers) registrations sent to it. This allows
an
attacker to overwrite some or all of the Domain Controllers in the record.
The new entries could be pointing at a box that will participate in the
logon process long enough to capture user names and passwords. If the
passwords are only hashed with LanMan (not NTLM), they can be easily
broken
with L0phtCrack. A less malicious problem can occur if someone brings up a
server that incorrectly thinks it is a Domain Controller. Although the
server cannot participate in the domain, it will register itself with WINS
in the 1Ch record and workstations will still send logon requests to it.

The best work around I could think of is to use static entries for records
that are sensitive (there are probably more besides 1Ch). Domain
Controllers
shouldn't be changed very often, so the management work would be minimal.
When I contacted Microsoft, I was told that they were aware of this, but
did
not consider it a significant problem. They confirmed that static records
were the best solution.

Attached is a PERL script that can demonstrate the problem. Use it
cautiously.


David Byrne, MCSE
TIAA CREF

 <<wins2.pl>>




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