alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CastleRAT Malware Outbound Handshake M7"; flow:established,to_server; dsize:20; stream_size:server,=,1; content:"|74 6F D9 7F B5 48 F6 91 26 E0 16 5A 81 29 4F 35 21 6C 61 82|"; fast_pattern; depth:20; reference:url,tria.ge/250813-a7c3fadl7z; reference:url,assets.recordedfuture.com/insikt-report-pdfs/2025/cta-2025-1209.pdf; classtype:trojan-activity; sid:2066369; 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;)