alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Suspicious Domain (*.icu) in TLS SNI"; flow:established,to_server; threshold:type limit, count 1, track by_src, seconds 120; tls.sni; content:".icu"; endswith; fast_pattern; nocase; classtype:bad-unknown; sid:2026889; rev:4; metadata:attack_target Client_Endpoint, created_at 2019_02_06, deployment Perimeter, confidence High, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_11_21;)