alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (ServHelper RAT CnC)"; flow:from_server,established; tls.cert_subject; content:"CN=checksolutions.pw"; tls.cert_issuer; content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; reference:md5,43e7274b6d42aef8ceae298b67927aec; classtype:domain-c2; sid:2026767; rev:4; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2018_11_09, deployment Perimeter, malware_family ServHelper, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag RAT, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_08_27, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;)