alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE TripleNine RAT Checkin"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/999"; fast_pattern; bsize:4; http.header; content:".0|0d 0a|Host"; http.header_names; content:!"Referer|0d 0a|"; classtype:command-and-control; sid:2017021; rev:7; metadata:created_at 2013_06_15, signature_severity Major, updated_at 2020_09_18;)