GPL SMTP AUTH LOGON brute force attempt

Query · suricata

flow:from_server,established;
content:"Authentication unsuccessful"; offset:54; nocase;
threshold:type threshold, track by_dst, count 5, seconds 60;
Raw source GPL SMTP AUTH LOGON brute force attempt · Suricata
Esc
Published by Emerging Threats Open ↗, licensed under BSD 3-Clause ↗. Line breaks added for readability; the rule is otherwise unchanged. 
alert tcp $SMTP_SERVERS 25 -> $EXTERNAL_NET any (
    msg:"GPL SMTP AUTH LOGON brute force attempt";
    flow:from_server,established;
    content:"Authentication unsuccessful"; offset:54; nocase;
    threshold:type threshold, track by_dst, count 5, seconds 60;
    classtype:suspicious-login;
    sid:2102275; rev:3;
    metadata:created_at 2010_09_23, signature_severity Unknown, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;
)

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