alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Oyster Backdoor CnC Checkin M3"; flow:established,to_server; http.method; content:"GET"; http.uri; bsize:6; content:"/login"; http.user_agent; bsize:11; content:"FingerPrint"; fast_pattern; http.header_names; content:"|0d 0a|x-amz-cf-id|0d 0a|"; content:"|0d 0a|Content-Encoding|0d 0a|"; content:"|0d 0a|Content-Length|0d 0a|"; reference:url,malpedia.caad.fkie.fraunhofer.de/details/win.broomstick; reference:url,www.cyberproof.com/blog/oyster-backdoor-the-malvertising-menace-masquerading-as-popular-tools/; reference:url,www.catonetworks.com/blog/cato-ctrl-oyster-malware-campaign/; classtype:trojan-activity; sid:2064628; rev:1; metadata:attack_target Client_and_Server, created_at 2025_09_12, deployment Perimeter, malware_family Oyster_Backdoor, performance_impact Low, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_09_12, mitre_tactic_id TA0037, mitre_tactic_name Command_And_Control, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel; target:src_ip;)