ET MALWARE CastleBot CnC Exfil (POST)

Query · suricata

flow:established,to_server;
urilen:14;
http.method;
content:"POST";
http.uri;
content:"/service/tasks"; fast_pattern;
http.user_agent; bsize:<26;
pcre:"/^(?:[a-zA-Z0-9]{20,25})$/";
http.request_body;
content:"Content|2d|Disposition|3a 20|form|2d|data|3b 20|name|3d 22|data|22|";
target:src_ip;
Raw source ET MALWARE CastleBot CnC Exfil (POST) · Suricata
Esc
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 -> $EXTERNAL_NET any (
    msg:"ET MALWARE CastleBot CnC Exfil (POST)";
    flow:established,to_server;
    urilen:14;
    http.method;
    content:"POST";
    http.uri;
    content:"/service/tasks"; fast_pattern;
    http.user_agent; bsize:<26;
    pcre:"/^(?:[a-zA-Z0-9]{20,25})$/";
    http.request_body;
    content:"Content|2d|Disposition|3a 20|form|2d|data|3b 20|name|3d 22|data|22|";
    reference:md5,1a3896a986195c277f1547706dbdea08;
    reference:md5,f75bb2393f80bf30c4788c82f3a7dadf;
    reference:url,ibm.com/think/x-force/dissecting-castlebot-maas-operation;
    classtype:command-and-control;
    sid:2064208; 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 CastleBot, confidence High, signature_severity Critical, tag c2, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_08_28, 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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