alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET INFO Google DNS Over HTTPS Certificate Inbound"; flow:established,to_client; threshold:type both, track by_src, count 1, seconds 300; tls.cert_subject; content:"CN=dns.google"; endswith; fast_pattern; tls.cert_issuer; content:"C=US, O=Google Trust Services"; reference:url,developers.google.com/speed/public-dns/docs/doh/; reference:md5,206a146a84eb6c2cca82ac245615349a; reference:md5,8064d8e4bfa66d1b6f665faf1ddf46b2; classtype:misc-activity; sid:2049796; rev:5; metadata:affected_product Any, attack_target Client_Endpoint, created_at 2019_08_21, deployment Perimeter, performance_impact Low, confidence High, signature_severity Informational, tag DoH, updated_at 2023_12_20, reviewed_at 2024_04_22, former_sid 2838109; target:src_ip;)