alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Golang/Sandcat Plugin Activity (POST)"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/beacon"; bsize:7; http.user_agent; content:"Go-http-client/"; startswith; http.accept_enc; content:"gzip"; bsize:4; http.request_body; content:"eyJ"; startswith; fast_pattern; pcre:"/^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/"; http.header_names; content:!"Referer"; reference:url,github.com/mitre/sandcat; classtype:trojan-activity; sid:2043217; rev:1; metadata:attack_target Client_Endpoint, created_at 2023_01_05, deployment Perimeter, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2023_01_05;)