alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed Network Tunneling Service Domain (burrow .io) in TLS SNI"; flow:established,to_server; tls.sni; dotprefix; content:".burrow.io"; endswith; fast_pattern; reference:url,github.com/anderspitman/awesome-tunneling?tab=readme-ov-file; reference:url,github.com/BadSamuraiDev/bs-lists/blob/main/living-off-trusted-tunnels.txt; classtype:misc-activity; sid:2066123; rev:1; metadata:affected_product Any, attack_target Client_and_Server, created_at 2025_12_05, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, tag Network_Tunneling, updated_at 2025_12_05, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1572, mitre_technique_name Protocol_Tunneling;)