Snort mailing list archives
Re: Bad Loopback Traffic
From: bclark () bwkip com
Date: Wed, 25 Feb 2004 13:15:22 -0500 (EST)
My new comments below:
The best summary of an explanation I have seen is attached below (From Dan of the Incidents list). Regards, Frank ---8<--- -----Forwarded Message-----=20 From: Dan Hanson <dhanson () securityfocus com> To: incidents () securityfocus com Subject: Administrivia: Are you seeing portscans from source 127.0.0.1 source port 80? Date: Tue, 28 Oct 2003 08:59:56 -0700 I am posting this in the hopes of dulling the 5-6 messages I get every day that are reporting port scans to their network all of which have a source IP of 127.0.0.1 and source port 80. It is likely Blaster (check your favourite AV site for a writeup, I won't summarize here). The reason that people are seeing this has to do with some very bad advice that was given early in the blaster outbreak. The advice basically was that to protect the Internet from the DoS attack that was to hit windowsupdate.com, all DNS servers should return 127.0.0.1 for queries to windowsupdate.com. Essentially these suggestions were suggesting that hosts should commit suicide to protect the Internet. The problem is that the DoS routine spoofs the source address, so when windowsupdate.com resolves to 127.0.0.1 the following happens. Infected host picks address as source address and sends Syn packet to 127.0.0.1 port 80. (Sends it to itself) (This never makes it on the wire, you will not see this part) TCP/IP stack receives packet, responds with reset (if there is nothing listening on that port), sending the reset to the host with the spoofed source address (this is what people are seeing and mistaking for portscans) Result: It looks like a host is port scanning ephemeral posts using packets with source address:port of 127.0.0.1:80 Solution: track back the packets by MAC address to find hte infected machine. Turn of NS resolution of windowsupdate.com to 127.0.0.1. Hope that helps D
Not sure that is it because the destination is port 80 not local host, but I do see the packet have a FIN flag. Most of the time the destinations are within the Class A that my class C belong too. Brian ------------------------------------------------------- SF.Net is sponsored by: Speed Start Your Linux Apps Now. Build and deploy apps & Web services for Linux with a free DVD software kit from IBM. Click Now! http://ads.osdn.com/?ad_id=1356&alloc_id=3438&op=click _______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://www.geocrawler.com/redir-sf.php3?list=snort-users
Current thread:
- Re: Bad Loopback Traffic bclark (Feb 25)