alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (Cobalt Group/More_Eggs CnC)"; flow:from_server,established; tls.cert_subject; content:"CN=safesecurefiles.com"; nocase; endswith; tls.cert_issuer; content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; reference:url,medium.com/@quoscient/golden-chickens-uncovering-a-malware-as-a-service-maas-provider-and-two-new-threat-actors-using-61cf0cb87648; classtype:domain-c2; sid:2026703; rev:3; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2018_12_07, deployment Perimeter, malware_family Cobalt_Group, malware_family More_eggs, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_09_16, mitre_tactic_id TA0042, mitre_tactic_name Resource_Development, mitre_technique_id T1587, mitre_technique_name Develop_Capabilities;)