alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET INFO Charter DNS Over HTTPS Certificate Inbound"; flow:established,to_client; tls.cert_subject; content:".spectrum.com"; fast_pattern; pcre:"/CN=(?:[^\r\n]+?\.)?doh\x2d\d{2}\.spectrum\.com(?!\.)/"; threshold:type both, count 1, seconds 600, track by_src; reference:url,github.com/curl/curl/wiki/DNS-over-HTTPS; classtype:misc-activity; sid:2039449; rev:1; metadata:created_at 2022_10_18, confidence High, signature_severity Informational, tag DoH, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_10_18;)