alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE CastleLoader User-Agent Observed (GoogBot)"; flow:established,to_server; http.user_agent; bsize:8; content:"GoogeBot"; threshold:type limit,count 1,seconds 300,track by_src; reference:md5,1a3896a986195c277f1547706dbdea08; reference:md5,f75bb2393f80bf30c4788c82f3a7dadf; reference:url,ibm.com/think/x-force/dissecting-castlebot-maas-operation; classtype:trojan-activity; sid:2064205; 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; target:src_ip;)