alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Observed Malicious SSL Cert (Malicious Browser Ext CnC)"; flow:established,to_client; tls.cert_subject; content:"CN=*.liveupdt.com"; bsize:17; fast_pattern; tls.cert_issuer; content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; bsize:52; reference:url,darkreader.org/blog/attention/; reference:url,github.com/rainyrainyday/HomebrewOverlay; classtype:domain-c2; sid:2029922; rev:1; metadata:affected_product Web_Browsers, attack_target Client_and_Server, created_at 2020_04_15, deployment Perimeter, performance_impact Low, confidence High, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_04_15, mitre_tactic_id TA0042, mitre_tactic_name Resource_Development, mitre_technique_id T1587, mitre_technique_name Develop_Capabilities;)