alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (OilRig QUADAGENT CnC)"; flow:from_server,established; tls.cert_subject; content:"CN=cpuproc.com"; tls.cert_issuer; content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; reference:md5,d51c2ffce844d42bab2f2c3131e3dbd4; reference:url,researchcenter.paloaltonetworks.com/2018/07/unit42-oilrig-targets-technology-service-provider-government-agency-quadagent/; classtype:domain-c2; sid:2025892; rev:4; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2018_07_25, deployment Perimeter, malware_family QuadAgent, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_10_30, mitre_tactic_id TA0042, mitre_tactic_name Resource_Development, mitre_technique_id T1587, mitre_technique_name Develop_Capabilities;)