alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed DNS over HTTPS Domain (dns4me .net) in TLS SNI"; flow:established,to_server; tls.sni; bsize:15; content:".dns4me.net"; endswith; fast_pattern; pcre:"/^[a-z]{2}\d{2}\.dns4me\.net$/"; threshold:type both, count 1, seconds 600, track by_src; reference:url,github.com/curl/curl/wiki/DNS-over-HTTPS; classtype:misc-activity; sid:2052673; rev:3; metadata:created_at 2024_05_16, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, tag DNS_over_HTTPS, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_12_01, reviewed_at 2024_10_04, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1572, mitre_technique_name Protocol_Tunneling;)