alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (BrushaLoader CnC) 2019-05-30"; flow:established,to_client; tls_cert_subject; content:"CN=halatest.info"; tls_cert_issuer; content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; reference:url,twitter.com/Racco42/status/1134214372996390913; classtype:domain-c2; sid:2027414; rev:3; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2019_05_31, deployment Perimeter, malware_family BrushaLoader, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_08_15, mitre_tactic_id TA0042, mitre_tactic_name Resource_Development, mitre_technique_id T1587, mitre_technique_name Develop_Capabilities;)