alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (ColdRiver APT DNSpionage MITM)"; flow:from_server,established; tls.cert_subject; content:"CN=mail.apc.gov.ae"; nocase; endswith; tls.cert_issuer; content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; reference:url,www.lastline.com/labsblog/threat-actor-cold-river-network-traffic-analysis-and-a-deep-dive-on-agent-drable/; classtype:domain-c2; sid:2026802; rev:3; metadata:attack_target Client_and_Server, created_at 2019_01_12, deployment Perimeter, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag APT, tag ColdRiver, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_09_16, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;)