alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed DNS over HTTPS Domain in TLS SNI (basic .rethinkdns .com)"; flow:established,to_server; tls.sni; content:"basic.rethinkdns.com"; bsize:20; fast_pattern; threshold:type both, count 1, seconds 600, track by_src; reference:url,rethinkdns.com; classtype:misc-activity; sid:2048507; rev:3; metadata:created_at 2022_02_09, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, tag DoH, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_12_01, former_sid 2851065, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1572, mitre_technique_name Protocol_Tunneling;)