Snort mailing list archives
Re: rule does not alert from nmap
From: Matt Kettler <mkettler () evi-inc com>
Date: Thu, 17 Aug 2006 14:15:42 -0400
repniksz () aviva co hu wrote:
Hi, I've written a very simply rule: alert tcp any any -> any 80 (msg: "SYN on 80 port" ; flags: S; ) I've started testing, first of all i used just a simply browser to get a page from there, and the rule was working. But after i've tried use Nmap in some way: nmap -sS -P0 -p 80 195.xxx.xxx.xxx nmap -P0 -p 80 195.xxx.xxx.xxx nmap -s-sacnflags syn -P0 -p 80 195.xxx.xxx.xxx All of them sent a SYN to the 80 port. I've checked with ethereal. But there was not any on the alert file. what's wrong?
If you are using the stream4 preprocessor, you need "flow:stateless" in order to detect this. Stream4 will suppress any tcp packets that don't wind up creating a successful tcp connection from being sent to normal rules. nmap -sS only sends a syn, so stream4 will suppress that packet from being scanned by ordinary rules. This is done to reduce overhead from pointless scanning of packets, as most rules are designed to examine the data content. If no connection is established, there can be no data... Adding "flow:stateless" will allow a rule to match any packets, even if a connection is not established. However, you should not use this on normal rules that are trying to look for server exploits in a session. You should only use this for rules that need to examine packets that do not result in a connection. (great for checking for single syn packet DoS exploits, like the classic "land" attack) ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ 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:
- rule does not alert from nmap repniksz (Aug 17)
- Re: rule does not alert from nmap Matt Kettler (Aug 17)