alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET HUNTING Connectivity Check With Go User-Agent"; flow:established,to_server; urilen:9; http.method; content:"GET"; http.uri; content:"/ncsi.txt"; fast_pattern; http.host; content:"www.msftncsi.com"; bsize:16; http.user_agent; content:"Go-http-client/"; startswith; http.header_names; content:!"Referer|0d 0a|"; classtype:bad-unknown; sid:2044794; rev:1; metadata:attack_target Client_Endpoint, created_at 2023_03_28, deployment Perimeter, confidence Medium, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2023_03_28; target:src_ip;)