Snort mailing list archives
Re: Bad Loop Back Traffic
From: Frank Knobbe <frank () knobbe us>
Date: Tue, 24 Feb 2004 13:17:08 -0600
On Tue, 2004-02-24 at 11:01, bclark () bwkip com wrote:
I have also seen this type of traffic about 200,000 alerts last night. I am not sure but I think it is a clients Windows machine.
The best summary of an explanation I have seen is attached below (From Dan of the Incidents list). Regards, Frank ---8<--- -----Forwarded Message----- 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 --------------------------------------------------------------------------- -- Warning at the Gates of Bill: Abandon hope, all ye who press <ENTER> here...
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Current thread:
- Bad Loop Back Traffic Scott Elgram (Feb 24)
- <Possible follow-ups>
- Re: Bad Loop Back Traffic bclark (Feb 24)
- Re: Bad Loop Back Traffic Mat Harris (Feb 24)
- Re: Bad Loop Back Traffic Frank Knobbe (Feb 24)
- Re: Bad Loop Back Traffic Scott Elgram (Feb 25)
- RE: Bad Loop Back Traffic Finney Charles E (Feb 24)
- Re: RE: Bad Loop Back Traffic Scott Elgram (Feb 25)
- Re: RE: Bad Loop Back Traffic James Nonya (Feb 24)
- Re: Bad Loop Back Traffic SN ORT (Feb 25)
- Re: Bad Loop Back Traffic Scott Elgram (Feb 27)
- Re: Bad Loop Back Traffic Mark . Schutzmann (Feb 27)