alert tcp-pkt $HOME_NET any -> $EXTERNAL_NET 1024: (msg:"ET MALWARE SainboxRAT CnC Checkin"; flow:established,to_server; dsize:<45; content:"HELLO|7c|"; startswith; fast_pattern; content:"|7c|SYSTEM|0a|"; endswith; reference:md5,f5aea239fa2f9d52d6e2bb43c75533ed; classtype:command-and-control; sid:2069284; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, tls_state plaintext, created_at 2026_05_14, deployment Perimeter, malware_family Sainbox, confidence High, signature_severity Critical, tag c2, updated_at 2026_05_14, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel; target:src_ip;)