alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"GPL FTP CWD ~ attempt"; flow:to_server,established; content:"CWD"; nocase; pcre:"/^CWD\s+~/smi"; reference:bugtraq,2601; reference:bugtraq,9215; reference:cve,2001-0421; classtype:denial-of-service; sid:2101672; rev:12; metadata:created_at 2010_09_23, cve CVE_2001_0421, signature_severity Unknown, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)