alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Observed DCRat Related Domain (crystalfiles .ru in TLS SNI)"; flow:established,to_server; tls.sni; content:"crystalfiles.ru"; bsize:15; fast_pattern; reference:url,blogs.blackberry.com/en/2022/05/dirty-deeds-done-dirt-cheap-russian-rat-offers-backdoor-bargains; classtype:domain-c2; sid:2036640; rev:1; metadata:attack_target Client_Endpoint, created_at 2022_05_20, deployment Perimeter, malware_family DCRat, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_05_20, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;)