alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE TA421/YTTRIUM/APT29 TLS Certificate M3"; flow:established,to_client; tls.cert_subject; content:"C=US, O=GMO GlobalSign, Inc"; startswith; fast_pattern; tls.cert_issuer; content:"C=US, O=GMO GlobalSign, Inc, CN=*"; bsize:33; reference:url,community.riskiq.com/article/642d186e; classtype:domain-c2; sid:2033634; rev:2; metadata:attack_target Client_and_Server, created_at 2021_07_31, deployment Perimeter, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_07_04, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;)