alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"GPL SMTP vrfy decode"; flow:to_server,established; content:"vrfy"; nocase; content:"decode"; distance:1; nocase; pcre:"/^vrfy\s+decode/smi"; reference:arachnids,373; reference:bugtraq,10248; reference:cve,1999-0096; classtype:attempted-recon; sid:2100672; rev:10; metadata:created_at 2010_09_23, cve CVE_1999_0096, signature_severity Unknown, updated_at 2019_07_26;)