ET MALWARE CastleRAT Malware Outbound Handshake M3

Query · suricata

flow:established,to_server;
dsize:20;
stream_size:server,=,1;
content:"|6B 13 5C 08 BD 49 59 75 79 62 4E EA 2F DE 57 F4 6E 08 8B 6B|"; fast_pattern; depth:20;
target:dest_ip;
Raw source ET MALWARE CastleRAT Malware Outbound Handshake M3 · Suricata
Esc
Published by Emerging Threats Open ↗, licensed under BSD 3-Clause ↗. Line breaks added for readability; the rule is otherwise unchanged. 
alert tcp $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET MALWARE CastleRAT Malware Outbound Handshake M3";
    flow:established,to_server;
    dsize:20;
    stream_size:server,=,1;
    content:"|6B 13 5C 08 BD 49 59 75 79 62 4E EA 2F DE 57 F4 6E 08 8B 6B|"; fast_pattern; depth:20;
    reference:url,tria.ge/250219-nsbsqazpep;
    reference:url,assets.recordedfuture.com/insikt-report-pdfs/2025/cta-2025-1209.pdf;
    classtype:trojan-activity;
    sid:2066364; rev:1;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, affected_product Mac_OSX, attack_target Client_Endpoint, tls_state TLSDecrypt, created_at 2025_12_18, deployment Perimeter, deployment SSLDecrypt, malware_family CastleRAT, performance_impact Moderate, confidence Medium, signature_severity Major, updated_at 2025_12_18, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;
    target:dest_ip;
)

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