alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed Tunnel/Reverse Proxy Service (btunnel .in) in TLS SNI"; flow:established,to_server; tls.sni; dotprefix; content:".btunnel.in"; endswith; fast_pattern; reference:url,www.btunnel.in; classtype:misc-activity; sid:2063124; rev:1; metadata:affected_product Any, attack_target Client_and_Server, created_at 2025_06_20, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, updated_at 2025_06_20, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1665, mitre_technique_name Hide_Infrastructure;)