alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed External IP Lookup Domain (ip .cn in TLS SNI)"; flow:established,to_server; tls.sni; bsize:5; content:"ip.cn"; fast_pattern; classtype:external-ip-check; sid:2047080; rev:1; metadata:attack_target Client_Endpoint, created_at 2023_08_08, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, updated_at 2023_08_08, reviewed_at 2024_03_05, mitre_tactic_id TA0007, mitre_tactic_name Discovery, mitre_technique_id T1614, mitre_technique_name System_Location_Discovery;)