alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET INFO Observed DNS over HTTPS Domain in TLS SNI (ada .openbld .net)"; flow:established,to_client; tls.cert_subject; content:"ada.openbld.net"; fast_pattern; pcre:"/CN=(?:[^\r\n]+?\.)?ada\.openbld\.net(?!\.)/"; reference:url,github.com/curl/curl/wiki/DNS-over-HTTPS; classtype:misc-activity; sid:2045865; rev:2; metadata:created_at 2023_05_25, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, tag DoH, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_12_01, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1572, mitre_technique_name Protocol_Tunneling;)