you should use the correct configuration from the wiki
http://wiki.centos-webpanel.com/csflfd-firewall-configuration
But, in this rule if activated, blocked server http and mail traffic, ssh work ok.
Custom regex for mod security, file /etc/csf/regex.custom.pm :
#mod_security
if (($config{LF_MODSEC}) and ($globlogs{MODSEC_LOG}{$lgfile}) and ($line =~ /^\[\S+ \S+ \S+ \S+ \S+\] \[(\w*)?:error\] (\[pid \d+(:tid \d+)\]) \[client \S+:\S+\] \[client (\S+)\] ModSecurity:(( \[[^\]]+\])*)? Access denied/)) {
my $ip = $4;
$ip =~ s/^::ffff://;
if (split(/:/,$ip) == 2) {$ip =~ s/:\d+$//}
my $ruleid = "unknown";
if ($line =~ /\[id "(\d+)"\]/) {$ruleid = $1}
if (checkip(\$ip)) {return ("mod_security (id:$ruleid) triggered by","$ip","mod_security-custom","4","80,443","1")} else {return}
}