ET MALWARE Observed Malicious SSL Cert (Cobalt Group/More_Eggs CnC)

alert tls $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET MALWARE Observed Malicious SSL Cert (Cobalt Group/More_Eggs CnC)";
    flow:from_server,established;
    tls.cert_subject;
    content:"CN=safesecurefiles.com"; nocase; endswith;
    tls.cert_issuer;
    content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3";
    reference:url,medium.com/@quoscient/golden-chickens-uncovering-a-malware-as-a-service-maas-provider-and-two-new-threat-actors-using-61cf0cb87648;
    classtype:domain-c2;
    sid:2026703; rev:3;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2018_12_07, deployment Perimeter, malware_family Cobalt_Group, malware_family More_eggs, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_09_16, mitre_tactic_id TA0042, mitre_tactic_name Resource_Development, mitre_technique_id T1587, mitre_technique_name Develop_Capabilities;
)