ET HUNTING Observed Lets Encrypt Certificate - Possible COVID-19 Related M2

Query · suricata

flow:established,to_client;
tls.cert_subject;
content:"corona"; nocase; fast_pattern;
tls.cert_issuer;
content:"Lets Encrypt";
Raw source ET HUNTING Observed Lets Encrypt Certificate - Possible COVID-19 Related M2 · 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 HUNTING Observed Lets Encrypt Certificate - Possible COVID-19 Related M2";
    flow:established,to_client;
    tls.cert_subject;
    content:"corona"; nocase; fast_pattern;
    tls.cert_issuer;
    content:"Lets Encrypt";
    classtype:bad-unknown;
    sid:2029704; rev:2;
    metadata:affected_product Web_Browsers, attack_target Client_Endpoint, created_at 2020_03_23, deployment Perimeter, confidence Medium, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_03_23;
)

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