ET PHISHING Lets Encrypt Free SSL Cert Observed with IDN/Punycode Domain - Possible Phishing

Query · suricata

flow:established,from_server;
tls.cert_subject;
content:"xn--";
tls.cert_issuer;
content:"O=Let's Encrypt";
Raw source ET PHISHING Lets Encrypt Free SSL Cert Observed with IDN/Punycode Domain - Possible Phishing · Suricata
Esc
Published by Emerging Threats Open ↗, licensed under BSD 3-Clause ↗. Line breaks added for readability; the rule is otherwise unchanged. 
alert tls $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET PHISHING Lets Encrypt Free SSL Cert Observed with IDN/Punycode Domain - Possible Phishing";
    flow:established,from_server;
    tls.cert_subject;
    content:"xn--";
    tls.cert_issuer;
    content:"O=Let's Encrypt";
    reference:url,isc.sans.edu/forums/diary/Tool+to+Detect+Active+Phishing+Attacks+Using+Unicode+LookAlike+Domains/22310/;
    reference:url,letsencrypt.org/about/;
    classtype:policy-violation;
    sid:2024227; rev:4;
    metadata:affected_product Web_Browsers, attack_target Client_Endpoint, created_at 2017_04_19, deployment Perimeter, confidence Medium, signature_severity Critical, tag Phishing, updated_at 2020_08_20, mitre_tactic_id TA0001, mitre_tactic_name Initial_Access, mitre_technique_id T1566, mitre_technique_name Phishing;
)

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