alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CastleLoader Malware Outbound Checkin"; flow:established,to_server; urilen:82; http.method; content:"GET"; http.uri; content:"|2F|service|2F|settings|2F|"; fast_pattern; http.header; content:"cache-control|3d 20|no-cache|0d 0a|connection|3a 20|keep-alive|0d 0a|pragma|3a 20|no-cache|0d 0a|user-agent|3a 20 0d 0a|"; content:"host|3a 20|"; distance:0; content:!"accept|3a 20|"; nocase; reference:url,catalyst.prodaft.com/public/report/understanding-current-castleloader-campaigns/overview; classtype:trojan-activity; sid:2066299; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, affected_product Mac_OSX, attack_target Client_Endpoint, tls_state TLSDecrypt, created_at 2025_12_12, deployment Perimeter, deployment SSLDecrypt, malware_family CastleLoader, performance_impact Moderate, confidence Medium, signature_severity Major, updated_at 2025_12_12, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel; target:dest_ip;)