alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CastleRAT Malware Outbound Handshake M4"; flow:established,to_server; dsize:20; stream_size:server,=,1; content:"|56 EA 59 DB 6B DD 36 81 42 01 C6 84 DF 5A 6B E8 38 14 8D 07|"; fast_pattern; depth:20; reference:url,tria.ge/250505-wmbvjabk3t; reference:url,assets.recordedfuture.com/insikt-report-pdfs/2025/cta-2025-1209.pdf; classtype:trojan-activity; sid:2066366; 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_18, deployment Perimeter, deployment SSLDecrypt, malware_family CastleRAT, performance_impact Moderate, confidence Medium, signature_severity Major, updated_at 2025_12_18, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel; target:dest_ip;)