ET MALWARE Oyster Backdoor CnC Checkin M4

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET MALWARE Oyster Backdoor CnC Checkin M4";
    flow:established,to_server;
    http.method;
    content:"POST";
    http.uri;
    content:"/api/"; startswith;
    pcre:"/^(?:kcehc|[A-Za-z0-9]{15,})$/R";
    http.user_agent;
    content:"Mozilla/6.0"; startswith; fast_pattern;
    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:2064629; 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;
)