[Dshield] Weird scanning, weird ports, weird TCP flags..

Nick Harley nickharley at bcbsal.org
Thu Oct 23 18:21:26 GMT 2003


This is a bit of a newbie question but I don't understand your range
notation: "private address space and ranges like: 0/8, 1/8, 126/8, etc."
Can anyone tell me how this works? I've seen it in other places as well
but no one's really been able to give a good explanation.

>>> Jon.Kibler at aset.com 10/23/2003 11:20:33 AM >>>
Tom Liston wrote:
> 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> It sounds like you're seeing is what is known as "back-scatter."
> 
> This is caused when someone attacks a machine on the internet using
your
> IP address as a source on a spoofed packet.  Normally this is part of
a
> denial of service attack.  The attacked machine is responding back to
your
> IP address with a SYN-ACK or RST-ACK in response to a spoofed inbound
SYN.
> 
> - -TL

We too have been seeing a lot of apparent scanning on 'strange' TCP and
UDP ports (ports > 32k) and thought that it was backscatter. However,
upon closer analysis, most of these garbage packets are coming from
bogus IPs (private address space and ranges like: 0/8, 1/8, 126/8, etc.)
and we are only seeing a few per port.

The amount of the garbage traffic has grown in the past week or two
from one or two a day ports per day (fairly constant for the past few
years) to now we are seeing dozens or more a day. A few are from legit
IPs and are probably backscatter -- but anyone have any ideas about the
rest coming from bogus IPs?

Jon R. Kibler
Chief Technical Officer
A.S.E.T., Inc.
Charleston, SC  USA
(843) 849-8214




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