alert tls $EXTERNAL_NET any -> $HOME_NET any (
msg:"ET INFO CIRA Canadian Shield DNS Over HTTPS Certificate Inbound";
flow:established,to_client;
tls.cert_subject;
content:"canadianshield.cira.ca"; fast_pattern;
pcre:"/CN=(?:[^\r\n]+?\.)?canadianshield\.cira\.ca(?!\.)/";
threshold:type both, count 1, seconds 600, track by_src;
reference:url,github.com/curl/curl/wiki/DNS-over-HTTPS;
classtype:misc-activity;
sid:2039450; rev:1;
metadata:attack_target Client_Endpoint, created_at 2022_10_18, deployment Perimeter, confidence High, signature_severity Informational, tag DoH, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_10_18;
)