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Invalid WINS entries
From: "Byrne, David" <dbyrne () TIAA-CREF ORG>
Date: Wed, 17 Jan 2001 16:35:49 -0500

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

David Byrne, MCSE


Attachment: wins2.pl

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