alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Oyster Backdoor CnC Checkin M5"; flow:established,to_server; urilen:<30; http.method; content:"GET"; http.uri; content:"/api/"; startswith; http.user_agent; content:"Mozilla|2f|6|2e|0|20 28|"; startswith; fast_pattern; http.header_names; content:!"|0d 0a|auth|0d 0a|"; nocase; content:!"|0d 0a|x-"; nocase; content:!"|0d 0a|referer|0d 0a|"; nocase; reference:md5,5c44fcd4914bd2114c9f150284111f4d; classtype:command-and-control; sid:2065047; 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_10_03, deployment Perimeter, deployment SSLDecrypt, malware_family Oyster_Backdoor, performance_impact Moderate, confidence High, signature_severity Critical, tag c2, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_10_03, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol; target:src_ip;)