Dirk, You are NATing.... Do you have any static NATs assigned to a webserver for instance? If someone were to plugin to your network and get a DHCP address and type in http://www.yourserver.com they would recieve your public address assigned to a static NAT. Then you would ship off packets with a source address from your private network 10.x.x.x it would hit what ever device you are NATing with. The device would think it is being spoofed and drop the packet and log it.... I've seen this while using a Watchguard firewall. To make a long story short it could be someone trying to get from you internal network to your public website... but the router or firewall thinks it is being spoofed... what ports are being sent from with the spoofed addreses? Regards-- Shane -----Original Message----- From: Kent Hundley [mailto:kent.hundleyat_private] Sent: Thursday, June 27, 2002 1:54 PM To: 'Dirk Koopman'; 'Incidents Mailing List' Subject: RE: spoofed packets to RFC 1918 addresses 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:djkat_private] 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 Exist or Will Exist Only in a Vague and Undetermined State. ---------------------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com ---------------------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com **************************************************************************** This e-mail is intended only for the addressee named above and may contain confidential, proprietary or privileged information. If you are not the named addressee or the person responsible for delivering the message to the named addressee, please inform us promptly by reply e-mail, then delete the e-mail and destroy any printed copy. The contents should not be disclosed to anyone and no copies should be made. We take reasonable precautions to ensure that our emails are virus free. However we accept no responsibility for any virus transmitted by us and recommend that you subject any incoming e-mail to your own virus checking procedures. ---------------------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com
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