ET MALWARE Observed Malicious SSL Cert (ServHelper CnC)

alert tls $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET MALWARE Observed Malicious SSL Cert (ServHelper CnC)";
    flow:from_server,established;
    tls.cert_subject;
    content:"CN=almagel.icu"; nocase; fast_pattern; endswith;
    tls.cert_issuer;
    content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3";
    classtype:domain-c2;
    sid:2029604; rev:3;
    metadata:attack_target Client_and_Server, created_at 2020_03_10, deployment Perimeter, malware_family ServHelper, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_11_05, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;
)