[Snort-users] help writing snort rule

Blake Hartstein bhartstein at ...4451...
Fri Jan 26 14:48:00 EST 2007

Bill Lopez wrote:
> which doesn’t produce an alert either – eventually I want to apply 
> this filter to just traffic from/to mail , telnet, ftp (etc) servers – 
> I can send any variance of xxx-xx-xxxx, xxxxxxxx or xxx xx xxxx via an 
> e-mail, text file attachment or file upload and still never see an 
> alert to the console. I have a simple rule to check for content using 
> a keyword and get alerted when sending that keyword with e-mail, 
> attachment and file upload (this was my test to see if snort was 
> actually alerting correctly) I am only running my test rules with an 
> out of the box snort.conf file.
> Why wouldn’t either of the above rules alert with (for example) an 
> e-mail sent with 555-55-5555 in the body?
Can you please paste how you are running snort on the command line, and 
if you changed anything in your snort.conf please post that information too.

This type of traffic should be seen by snort and the rules you created 
should alert.

Perhaps, snort isn't seeing the traffic you are expecting,

try running
# snort -vde -i eth0

to see what snort sees.

or if you are running from a pcap you might need to use
config checksum_mode: none
If you captured the file from the localhost.

Also, which port is this traffic intended for?
You might need to configure your flow_depth on http_inspect if you are 
seeing this deep within the packet, rather than just in the headers.


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