Hi,
In favor of better performance, you can use a negative look behind
instead of a direct negative match as the first check in a pcre. This
allows the pcre check to finish quicker. I felt this was particularly
important if you want to use this rule, since it happens to look on any
port.
Before: (avg/check 427.9 microseconds)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
ver command"; flow: established; flowbits:isset,community_is_proto_irc;
content:"ver"; pcre:"/[^a-zA-Z0-9\x3A\s]ver/"; classtype:
trojan-activity; sid:100000272; rev:2;)
After: (avg/check 28.3 microseconds)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
ver command"; flow: established; flowbits:isset,community_is_proto_irc;
content:"ver"; pcre:"/(?<![a-zA-Z0-9\x3A\s])ver/"; classtype:
trojan-activity; sid:100000272; rev:3;)
This improvement applies to :
100000272 "/[^a-zA-Z0-9\x3A\s]ver/"
100000273 "/[^a-zA-Z0-9\x3A\s]info/"
100000274 "/[^a-zA-Z0-9\x3A\s]scan/"
100000275 "/[^a-zA-Z0-9\x3A\s]portscan/"
100000276 "/[^a-zA-Z0-9\x3A\s]stopscan/"
100000277 "/[^a-zA-Z0-9\x3A\s]packet/"
100000278 "/[^a-zA-Z0-9\x3A\s]bnc/"
The new rules are:
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
ver command"; flow: established; flowbits:isset,community_is_proto_irc;
content:"ver"; pcre:"/(?<![a-zA-Z0-9\x3A\s])ver/"; classtype:
trojan-activity; sid:100000272; rev:3;)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
info command"; flow: established; flowbits:isset,community_is_proto_irc;
content:"info"; pcre:"/(?<![a-zA-Z0-9\x3A\s])info/"; classtype:
trojan-activity; sid:100000273; rev:3;)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
scan command"; flow: established; flowbits:isset,community_is_proto_irc;
content:"scan"; pcre:"/(?<![a-zA-Z0-9\x3A\s])scan/"; classtype:
trojan-activity; sid:100000274; rev:3;)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
portscan command"; flow: established;
flowbits:isset,community_is_proto_irc; content:"portscan";
pcre:"/(?<![a-zA-Z0-9\x3A\s])portscan/"; classtype: trojan-activity;
sid:100000275; rev:3;)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
stopscan command"; flow: established;
flowbits:isset,community_is_proto_irc; content:"stopscan";
pcre:"/(?<![a-zA-Z0-9\x3A\s])stopscan/"; classtype: trojan-activity;
sid:100000276; rev:3;)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
packet command"; flow: established;
flowbits:isset,community_is_proto_irc; content:"packet";
pcre:"/(?<![a-zA-Z0-9\x3A\s])packet/"; classtype: trojan-activity;
sid:100000277; rev:3;)
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"COMMUNITY BOT GTBot
bnc command"; flow: established; flowbits:isset,community_is_proto_irc;
content:"bnc"; pcre:"/(?<![a-zA-Z0-9\x3A\s])bnc/"; classtype:
trojan-activity; sid:100000278; rev:3;)
-Blake
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