Snort mailing list archives
Re: Question on port lists and negation
From: Jason <security () brvenik com>
Date: Mon, 08 Oct 2007 20:55:38 -0400
Richard Bejtlich wrote:
On 10/8/07, Matthew Watchinski <mwatchinski () sourcefire com> wrote:Richard Bejtlich wrote:Say I create this snort.conf: portvar MY_HTTP_PORTS [80,81,82,83,88,8000,8008,8080] alert tcp any any -> any !$MY_HTTP_PORTS (msg:"Example Not"; sid:4;)It alerts because 192.168.2.105:50970 -> 192.168.2.103:8000 is no different than 192.168.2.103:8000 -> 192.168.2.105:50970 cause you are running with any any -> any !PORTS any any matches both 192.168.2.105:50970 -> 192.168.2.103:8000 and 192.168.2.103:8000 -> 192.168.2.105:50970Hi Matt, Thanks for your comments. I don't understand why these packets are "no different". The MY_HTTP_PORTS variable includes 8000. If I negate MY_HTTP_PORTS in my rule, why do I get an alert on 192.168.2.105:50970 -> 192.168.2.103:8000? Is it because port 8000 in the packet is not other ports in the variable, like 80, 81, etc.?
NOTE: I've not had a chance to look at the code, I could be wrong, please verify. I think there may two issues working together. 1) not(80 and 81 and 82...) is different than (not 81 and not 81...) 2) not(80 and 81 and 82...) will always be true I would expect the same behavior if you ran $ nc -v 192.168.2.103 8001 as the command you are testing $ nc -v 192.168.2.103 8000 because not (80 and 81 and 82 and 83 and 88 and 8000 and 8008 and 8080) is always true, it is not possible for a single port to be both 81 and 82 and thus when you negate the negative you get a positive. Same rules apply when dealing with ip addresses IIRC. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ 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:
- Question on port lists and negation Richard Bejtlich (Oct 08)
- Re: Question on port lists and negation Matt Kettler (Oct 08)
- Re: Question on port lists and negation Scott Dexter (Oct 08)
- Re: Question on port lists and negation Jeffrey Denton (Oct 08)
- Re: Question on port lists and negation Matthew Watchinski (Oct 08)
- Re: Question on port lists and negation Richard Bejtlich (Oct 08)
- Re: Question on port lists and negation Jason (Oct 08)
- Re: Question on port lists and negation Matt Kettler (Oct 09)
- Re: Question on port lists and negation Jason (Oct 09)
- Re: Question on port lists and negation Matt Kettler (Oct 09)
- Re: Question on port lists and negation Jason (Oct 09)
- Re: Question on port lists and negation Richard Bejtlich (Oct 08)
- Re: Question on port lists and negation Matt Kettler (Oct 08)
- Re: Question on port lists and negation John Curry (Oct 08)
- Re: Question on port lists and negation Richard Bejtlich (Oct 09)