alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"ET POLICY Nginx Server with modified version string - Often Hostile Traffic"; flow:established,from_server; content:"HTTP/1."; depth:7; content:"|0d 0a|Server\: nginx/"; nocase; pcre:"/Server\: nginx/[a-zA-Z]/i"; threshold:type limit, seconds 60, count 3, track by_src; classtype:bad-unknown; sid:2008065; rev:1;)

Added 2008-03-28 13:33:34 UTC

Many malware instances of nginx use (rbn, etc) have a modified server string. It should be nginx/0.x.x. This will catch violations of that which may be more likely to be hostile.

-- MattJonkman - 28 Mar 2008