Snort mailing list archives
Re: DOS rules for Nimda
From: "Richard Ellerbrock" <richarde () eskom co za>
Date: Thu, 26 Sep 2002 17:17:43 +0200
Ah, I think you understand what I am after, probably because you wrote the book on this kinda stuff - thanks for a great tool! No, SEQ number not the same. Only thing that is constant is that for each SYN to a destination there are EXACTLY two of the EXACT same packets (Flags, SEQ, Source Port and WIN). So here is an example trace: 10.201.151.40 -> 10.201.18.154 D=80 S=4147 SYN SEQ=2132994334 LEN=0 WIN=16384 10.201.151.40 -> 10.201.18.154 D=80 S=4147 SYN SEQ=2132994334 LEN=0 WIN=16384 10.201.151.40 -> 10.201.84.107 D=80 S=4148 SYN SEQ=2147466592 LEN=0 WIN=16384 10.201.151.40 -> 10.201.84.107 D=80 S=4148 SYN SEQ=2147466592 LEN=0 WIN=16384 10.201.151.40 -> 10.201.58.47 D=80 S=4149 SYN SEQ=2147500852 LEN=0 WIN=16384 10.201.151.40 -> 10.201.58.47 D=80 S=4149 SYN SEQ=2147500852 LEN=0 WIN=16384 . . . (copied from sniffer trace, these packets are 0.002 seconds apart!) For some hosts the WIN size is 8192, but I think this depends on the MS version and nothing else. What snort really needs to be able to do is detect a constant source address with a rapidly changing destination address doing a port scan, something along the lines of a TCP verion of a ICMP smurf detector. I will also check out 1.9 for the threshold option. Richard http://iptrack.sourceforge.net
Martin Roesch <roesch () sourcefire com> 2002/09/26 04:27:38 >>>
Is the seq number constant for every connection? If so you could do a simple detection rule looking for the seq + window with the SYN flag set. If you use version 1.9 you can even use the new threshold keyword to only get one event notification for every X alerts.... -Marty On 9/26/02 7:11 AM, "Richard Ellerbrock" <richarde () eskom co za> wrote:
I am trying to help a very large site that is being killed by denial
of
service due to a large number of MS type workstations infected by
Nimda.
The standard snort rules are no good as no connection is actually
made,
just a HUGE SYN flood looking for open Web servers to infect.
Traffic
looks like this: Each host sends 2x SYN packets exactly the same (same source port,
SEQ
and WIN size) to a remote host on port 80. Obviously never gets a
reply.
Within a couple of milliseconds, tries another randon destination. Now my understanding of snort points to the stream4 processor to
catch
this stuff, but how to configure. The docs are a little unclear to
this
snort newbie. I do get TTL evasion on stream4, but this does not indicate much. Any help with rules/setup for this would be great. ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ 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
-- Martin Roesch - Founder/CTO Sourcefire Inc. - (410) 290-1616 Sourcefire: Professional Snort Sensor and Management Console appliances roesch () sourcefire com - http://www.sourcefire.com Snort: Open Source Network IDS - http://www.snort.org ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ 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:
- DOS rules for Nimda Richard Ellerbrock (Sep 26)
- Re: DOS rules for Nimda Chris Green (Sep 26)
- Re: DOS rules for Nimda Martin Roesch (Sep 26)
- <Possible follow-ups>
- RE: DOS rules for Nimda McCammon, Keith (Sep 26)
- RE: DOS rules for Nimda Tudor Panaitescu (Sep 26)
- RE: DOS rules for Nimda Richard Ellerbrock (Sep 26)
- Re: DOS rules for Nimda Richard Ellerbrock (Sep 26)
- RE: DOS rules for Nimda Madziarczyk, Jonathan (Sep 26)
- RE: DOS rules for Nimda Richard Ellerbrock (Sep 26)