alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE MaskGramStealer CnC initial Victim Checkin"; flow:established,to_server; http.method; content:"POST"; http.user_agent; bsize:10; content:"Client/1.0"; fast_pattern; http.request_body; bsize:<30; content:"user_"; startswith; pcre:"/^[a-zA-Z0-9]{21,24}$/R"; reference:md5,25041e230c55fd46e5ef52ab02b3bc6c; classtype:command-and-control; sid:2066623; 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_01_08, deployment Perimeter, deployment SSLDecrypt, malware_family MaskGramStealer, confidence High, signature_severity Critical, updated_at 2026_01_08, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol; target:src_ip;)