alert tcp $EXTERNAL_NET any -> $HOME_NET 110 (msg:"GPL POP3 USER format string attempt"; flow:to_server,established; content:"USER"; nocase; pcre:"/^USER\s+[^\n]*?%/smi"; reference:bugtraq,10976; reference:bugtraq,7667; reference:cve,2003-0391; reference:nessus,11742; classtype:attempted-admin; sid:2102250; rev:6; metadata:created_at 2010_09_23, signature_severity Unknown, updated_at 2019_07_26;)