alert tls $EXTERNAL_NET any -> $HOME_NET any (
msg:"ET POLICY SSL/TLS Certificate Observed (Free File Hosting Service (api .anonfiles .com))";
flow:established,to_client;
tls.cert_subject;
content:"CN=api.anonfiles.com"; bsize:20; fast_pattern;
tls.cert_issuer;
content:"C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3"; bsize:52;
reference:md5,74d2206a0f29c6d975cba20028284ca2;
classtype:policy-violation;
sid:2031019; rev:1;
metadata:attack_target Client_Endpoint, created_at 2020_10_14, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, updated_at 2020_10_14;
)