ET SCAN Potential FTP Brute-Force attempt response

Query · suricata

flow:from_server,established;
dsize:<100;
content:"530 "; depth:4;
pcre:"/530\s+(Login|User|Failed|Not)/smi";
threshold:type threshold, track by_dst, count 5, seconds 300;
Raw source ET SCAN Potential FTP Brute-Force attempt response · 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 21 -> $EXTERNAL_NET any (
    msg:"ET SCAN Potential FTP Brute-Force attempt response";
    flow:from_server,established;
    dsize:<100;
    content:"530 "; depth:4;
    pcre:"/530\s+(Login|User|Failed|Not)/smi";
    threshold:type threshold, track by_dst, count 5, seconds 300;
    classtype:unsuccessful-user;
    sid:2002383; rev:12;
    metadata:created_at 2010_07_30, confidence Medium, signature_severity Informational, updated_at 2019_07_26;
)

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