alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CastleBot CnC Checkin (GET)"; flow:established,to_server; urilen:82; http.method; content:"GET"; http.uri; content:"/service/settings/"; startswith; fast_pattern; pcre:"/^[a-z0-9]{64}$/R"; http.header; content:"cache|2d|control|3a 20|no|2d|cache"; nocase; content:"pragma|3a 20|no|2d|cache"; nocase; http.header_names; content:!"|0d 0a|referer|0d 0a|"; nocase; reference:md5,835ab1cf597812b0e6464c2e8f100678; classtype:trojan-activity; sid:2064004; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, tls_state plaintext, created_at 2025_08_13, deployment Perimeter, malware_family CastleBot, confidence High, signature_severity Major, tag c2, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_08_13, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol; target:src_ip;)