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Re: Can anyone identify this possible backdoor?

From: Greg Owen (gowen-incidentsswynwyr.com)
Date: Sat Aug 23 2003 - 19:51:05 CDT

Greg Owen wrote:
> Investigating a machine which is spewing SoBig.F and may be compromised,
> I'm seeing the following response on port 2001/tcp:
> % nc 2001
> <
> > Unrecognized command or Invalid argument received
> % nc 2001
> helo
> <helo> Unrecognized command or Invalid argument received
> %

Sorry, I should have been a bit more explicit.

1) The command line above 'nc 2001' is me investigating,
not anything running on or printed by the victim machine. Netcat may or
may not be in use on the victim machine, but that's not really my point;
I'm wondering what is sending back the error message here (and it isn't
netcat, I've grepped the source).

2) The first time I connected, I hit 'return', at which point whatever
is listening printed "<\n> Unrecognized command or Invalid argument
received" where \n was an actual CRLF.

3) The second time I connected, I typed 'helo' and hit 'return', at
which point whatever is listening printed "<helo> Unrecognized..."

4) 'helo' is SMTP, but that was just what I used to probe, on the off
chance this might be a spam relay. It should not be interpreted as
meaning anything in identifying the listener.

5) My point is, there's something there that spits back "<CMD>
Unrecognized command or Invalid argument received" when it gets input it
doesn't recognize. Google doesn't show anything for that string, which
makes it likely (to my mind) that it is some sort of backdoor that isn't
widely available. I'm curious if anyone has run across something that
spits this string out, that's all.

6) Again, I don't have physical access, so a standard forensic
investigation is unlikely. Thus my asking.

         gowen -- Greg Owen -- gowen-incidentsswynwyr.com
         GCFA, GCIH, GCWN
         79A7 4063 96B6 9974 86CA 3BEF 521C 860F 5A93 D66D

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