Snort HTTP Pre-processor issues

[Sharath Hiremagalore <hssharath () gmail com>]

Hello,
I am trying to run Snort on a large set of pcap files with HTTP traffic to a web server. The pcap files contain only 
ingress packets to the web server and is missing the responses from the web server. I configured installed snort on two 
distros Ubuntu 12.04 and CentOS 6.3.  On the Ubuntu box, I installed Snort 2.9.2.2 from the repository packages;  on 
CentOS 6.3, I installed snort 2.9.3 from source. I downloaded the latest set of rules form snort web page and enabled 
only the web rules with HTTP_SERVERS as the destination. I used the snort configuration that came with the latest rule 
set for the experiments.

When I ran Snort on the Ubuntu server, the http_inspect shows the number of GET/POST request seen in the summary when 
snort finishes running. However, no alerts are generated on the pcaps. I have looked at the packets in one of the pcaps 
and see the /etc/passwd attack in the GET request. This should have been identified by the rule with sid:1122 in 
'web-misc.rules'. On repeating the same experiment on CentOS server, the http_inspect does not even report that 
GET/POST requests in the summary. Also, no alerts were generated on CentOS.

This rule sid:1122 (web-misc.rules) is triggered only when I remove 'flow:to_server,established' and 'http_uri' 
conditions from the rule. Does http_inspect require flows to parse the URI? Is there a way, I can configure 
http_inspect to work only on the ingress packets to the Web server?

Thanks,

Sharath
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