alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE TA450 CnC Victim Checkin"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"|2f|content|3f|id|3d|"; startswith; fast_pattern; pcre:"/^\d{1,4}$/R"; http.user_agent; bsize:11; content:"application"; threshold:type limit,count 1,seconds 300,track by_src; classtype:command-and-control; sid:2068002; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, tls_state TLSDecrypt, created_at 2026_02_17, deployment Perimeter, deployment SSLDecrypt, confidence High, signature_severity Critical, tag MuddyWater, tag c2, tag TA450, updated_at 2026_03_04, former_sid 2866181, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol; target:src_ip;)