alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (Quasar CnC)"; flow:from_server,established; tls.cert_subject; content:"CN=Quasar Server CA"; nocase; fast_pattern; endswith; reference:url,sslbl.abuse.ch/ssl-certificates/sha1/f87d2aff4148f98f014460ab709c77587ea1e430/; classtype:domain-c2; sid:2027619; rev:3; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2019_06_27, deployment Perimeter, malware_family Quasar, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag RAT, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_09_17, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;)