ET MALWARE Observed Malicious SSL Cert (Sidewinder CnC)

alert tls $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET MALWARE Observed Malicious SSL Cert (Sidewinder CnC)";
    flow:from_server,established;
    tls.cert_subject;
    content:"CN=trans-can.net"; nocase; fast_pattern; endswith;
    tls.cert_issuer;
    content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3";
    reference:url,www.secrss.com/articles/13390;
    classtype:domain-c2;
    sid:2028568; rev:3;
    metadata:attack_target Client_and_Server, created_at 2019_09_10, deployment Perimeter, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Sidewinder, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_09_17, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;
)