alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Win32/Ketrican CnC Activity"; flow:to_server,established; http.method; content:"POST"; http.uri; content:".aspx?a1="; fast_pattern; pcre:"/^[a-f0-9]{8}$/R"; http.request_body; content:"AA"; depth:2; pcre:"/^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/"; http.content_len; content:"88"; reference:url,www.welivesecurity.com/wp-content/uploads/2019/07/ESET_Okrum_and_Ketrican.pdf; reference:md5,e46d8f510c09f09e2e6b958b84190d8b; reference:md5,03a2f5ea0cea83e77770a4018c4469ab; classtype:command-and-control; sid:2027728; rev:3; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2019_07_18, deployment Perimeter, deployment SSLDecrypt, malware_family Win32_Ketrican, confidence High, signature_severity Major, tag Ketrican, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_08_31;)