RE: spoofed packets to RFC 1918 addresses

["Kent Hundley" <kent.hundley () prodigy net>]

Dirk,

I'm not aware of such a tool, but there has been at least one bug in IIS
that allowed someone to obtain the actual address used by a server, so there
may be other ways to obtain this information not generally known.

However, if the packets have a destination address in the RFC1918 space, I
think you can conclude that they are in fact originating from the segment on
the outside of your firewall.  Unless something is seriously fubar'd on your
router _and_ your upstream ISP's router, there's no way short of source
routing to have packets with destination addresses in those ranges get to
your network from the Internet.

I would suspect either a misconfiguration of something on the outside of
your firewall or a compromise of something on the outside of your firewall.
Probably time to do some investigating of whatever devices you have on the
outside.  I'd also start looking at the source MAC of the packets and see
what ports on your switch are seeing that source MAC.

HTH,
Kent



-----Original Message-----
From: Dirk Koopman [mailto:djk () tobit co uk]
Sent: Wednesday, June 26, 2002 8:49 AM
To: Incidents Mailing List
Subject: spoofed packets to RFC 1918 addresses


There seems to be a "tool" about, which is somehow able to
detect valid rfc1918 addresses behind a NATed firewall and is spoofing
from addresses using random (usually non-existant) addresses from the
class C on the internet side of that firewall.

It isn't doing them any good as the packets are being dumped before they
get to the 'visible' class C (as I am making sure that packets from that
class C emanate only from the interface attached to that class C).

However, I am interested to know:

a) how the attackers are able to "guess" correct (ie existing) rfc1918
addresses as, AFAIK, these are not being leaked thru the firewall.

b) how these packets are getting to me in the first place as they don't
seem to be source routed.

c) which "tool" is doing this anyway.

Regards

Dirk Koopman
--
Please Note: Some Quantum Physics Theories Suggest That When the
Consumer Is Not Directly Observing This Product, It May Cease to
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