Snort mailing list archives
Re: RE: BAD-TARFFIC Loopback traffic
From: Frank Knobbe <frank () knobbe us>
Date: Wed, 29 Oct 2003 12:24:03 -0600
On Wed, 2003-10-29 at 08:25, John Impallomeni wrote:
I was wondering if anyone else had seen a large number of alerts from the "BAD-TRAFFIC loopback traffic" rule. We had over 12,000 yesterday when we usually see none. When I try to ping the source addresses (total of 8108), I keep getting a loopback IP (127.0.0.1). There are only 2 outside internet address for the destination address. Also the destination port is varying but they are typical attack ports (21, 22, 23, 80...etc) Any ideas? Thanks
This question belongs to snort-users. I'm moving it. Yeah, several of us have been seeing this. These are indeed spoofed packets coming from the Internet but with a source address of 127.0.0.1. The best explanation I've seen summarized was posted yesterday to the Incidents list at SF. See the message below. Regards, Frank ---8<---[forwarded without permission]--->8--- 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 (MST) 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
Attachment:
signature.asc
Description: This is a digitally signed message part
Current thread:
- Re: RE: BAD-TARFFIC Loopback traffic Frank Knobbe (Oct 29)
- <Possible follow-ups>
- Re: RE: BAD-TARFFIC Loopback traffic JP Vossen (Dec 20)