alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"GPL FTP PORT bounce attempt"; flow:to_server,established; content:"PORT"; nocase; ftpbounce; pcre:"/^PORT/smi"; classtype:misc-attack; sid:2103441; rev:2; metadata:created_at 2010_09_23, signature_severity Unknown, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)