alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed FUNNULL CDN Domain (funnull .com in TLS SNI)"; flow:established,to_server; tls.sni; dotprefix; content:".funnull.com"; endswith; fast_pattern; threshold:type limit, count 1, seconds 120, track by_src; reference:url,www.silentpush.com/blog/triad-nexus-funnull/; reference:url,silentpush.com/blog/infrastructure-laundering/; classtype:bad-unknown; sid:2061966; rev:1; metadata:attack_target Client_Endpoint, created_at 2025_04_29, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, updated_at 2025_04_29, mitre_tactic_id TA0001, mitre_tactic_name Initial_Access, mitre_technique_id T1189, mitre_technique_name Drive_by_Compromise;)