ET MALWARE CastleLoader User-Agent Observed

Query · suricata

flow:established,to_server;
http.user_agent; bsize:20;
content:"400yBAXUg5BGosOCwsmv";
target:src_ip;
Raw source ET MALWARE CastleLoader User-Agent Observed · Suricata
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Published by Emerging Threats Open ↗, licensed under BSD 3-Clause ↗. Line breaks added for readability; the rule is otherwise unchanged. 
alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET MALWARE CastleLoader User-Agent Observed";
    flow:established,to_server;
    http.user_agent; bsize:20;
    content:"400yBAXUg5BGosOCwsmv";
    reference:md5,835ab1cf597812b0e6464c2e8f100678;
    classtype:trojan-activity;
    sid:2064003; rev:1;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, tls_state plaintext, created_at 2025_08_13, deployment Perimeter, malware_family CastleLoader, confidence High, signature_severity Major, tag c2, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_08_13, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol;
    target:src_ip;
)

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