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Re: Question for DNS pros
From: Dave Yingling <loser_313 () yahoo com>
Date: Sun, 25 Jul 2004 02:48:15 -0700 (PDT)

This might not be exactly what you want, but you can register with
verisign and download the root zone file that contains the com and net
TLD's.  I think the org TLD is done by someone else.  Anyway, there are
some weird restrictions, such as IP access lists and what not, but if
you get the zone file you could grep for it. :)  If that doesn't work a
perl or shell script might work.  But I doubt you want to write the
script for something that might not even work.  It's just an idea you
could maybe try.

The verisign link:
then just click around till you find it.


--- Nick FitzGerald <nick () virus-l demon co uk> wrote:
Paul Schmehl wrote:

Well, no, because that wouldn't solve the problem.

A host on our network is being queried quite regularly on udp/53 by
hosts. A review of the packets reveals that these other hosts
believe that 
our host is a dns server.  (AAMOF the IP address isn't even in use
at the 
present time.)

OK, given this extra information, I see you are making one huge 

Now, if you do a reverse lookup for that IP, *our* DNS servers,
which are 
authoritative for our network will tell you what the hostname is. 
But that 
isn't what I want to know.  Obviously, a simple dig -x IP will tell
me that.

What I want to know is *why* do these "foreign" hosts think an IP
on my 
network is serving DNS when there's not even a host at that

I think you're assuming that a remote host should only consider this
of yours as a DNS server _if_ that information is _in the DNS, 
somewhere_, hence your query -- you're trying to work out how to find

out what part of the DNS thinks this IP of yours is a DNS server.

I can think of two possibilities:

1) At some time in the past, a host *was* serving DNS at that
address and 
some "foreign" hosts have cached the address.
2) Someone somewhere has registered a domain and used our IP
address for 
one of their "nameservers" in the registration.

(If anyone can think of other explanations, please let me know.)

I can think of another...

Several recent malwares (mostly mass-mailing viruses, but some others

too) have hard-coded lists of various servers to fall back on if
(i.e. local to the compromised/victim host) fails.  When we first 
started to see this tactic (several years ago) it tended to be SMTP 
servers running open relays (or at least, the largest internal-to- 
external-relaying SMTP servers at the largest ISPs).  Usually these 
lists were used if MX lookup for a target address failed or other 
transmission difficulties presented themselves (outgoing connections
port 25 failed because of firewall rules, etc), or (particularly
the mass-mailers did MX) if simply guessing "smtp.<domain>", 
"mail.<domain>", etc as the likely MX of a target domain failed. 
recently, as proper MX resolution has become more common in these 
malwares' mailing engines, so has inclusion of lists of "known 
promiscuous" DNS servers, presumably in the expectation that MX for 
more target domains will be resolved than simply relying on the 
victim's default DNS.

If your IP was in one of these lists (perhaps because of a typo or
nefarious inclusion in some commonly distributed list of promiscuous 
DNS servers) you could see requests from all over the place asking
all manner of target hosts (assuming that the malware writers
get their DNS querying code right!).  If the malware in question were

doing this for MX reasons (by far the most common use to date) you 
would, of course, expect to see whatever DNS query or sequence of 
queries is normal for getting MX information, but now we are getting 
out of area fo expertise.  Of course, all manner of other nefarious 
malware-related purposes besides self-mailing could be tied into such

behaviour, so not seeing MX requests does not mean that this type of 
explanation is incorrect...

Nick FitzGerald
Computer Virus Consulting Ltd.
Ph/FAX: +64 3 3529854

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