alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET INFO Cloudflare DNS Over HTTPS Certificate Inbound"; flow:established,to_client; threshold:type limit, track by_src, count 1, seconds 300; tls.cert_subject; content:"C=US, ST=California, L=San Francisco, O=Cloudflare, Inc., CN=cloudflare-dns.com"; endswith; fast_pattern; reference:url,developers.cloudflare.com/1.1.1.1/dns-over-https/request-structure/; classtype:misc-activity; sid:2027671; rev:5; metadata:created_at 2019_07_03, confidence Medium, signature_severity Informational, tag DoH, updated_at 2020_09_17;)