alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed APT41 Malicious SSL Cert (ColunmTK Campaign)"; flow:established,to_client; tls.cert_fingerprint; content:"b3:03:81:01:fd:0e:8b:11:c5:19:f7:39:f1:2c:7e:9b:60:23:4d:3b"; classtype:domain-c2; sid:2033140; rev:3; metadata:attack_target Client_and_Server, created_at 2021_06_11, deployment Perimeter, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2023_05_05, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;)