alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CROSSWALK CnC Checkin"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/QUERY/"; http.header; content:"dCy|3a 20|"; fast_pattern; pcre:"/^(?:[A-Z0-9+/]{4})*(?:[A-Z0-9+/]{2}==|[A-Z0-9+/]{3}=|[A-Z0-9+/]{4})\d(?:\r\n)?$/RHmi"; http.header_names; content:!"User-Agent"; classtype:command-and-control; sid:2029570; rev:2; metadata:created_at 2020_03_04, deployment Perimeter, malware_family CROSSWALK, performance_impact Low, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_03_04;)