alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CastleLoader Bot Download (GET)"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/service/download/"; startswith; fast_pattern; pcre:"/\x2e(?:exe|bin|zip|msi|docx?|msi|xlsx?|dll)$/"; http.header_names; content:!"|0d 0a|referer|0d 0a|"; nocase; reference:md5,1a3896a986195c277f1547706dbdea08; reference:md5,f75bb2393f80bf30c4788c82f3a7dadf; reference:url,ibm.com/think/x-force/dissecting-castlebot-maas-operation; classtype:trojan-activity; sid:2064197; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, tls_state TLSDecrypt, created_at 2025_08_28, deployment Perimeter, deployment SSLDecrypt, malware_family CastleLoader, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_08_28, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1105, mitre_technique_name Ingress_Tool_Transfer; target:src_ip;)