alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Beacon Observed"; flow:established,to_server; http.method; content:"GET"; http.start; content:"HTTP/1.1|0d 0a|Accept|3a 20|*/*|0d 0a|Cookie|3a 20|"; fast_pattern; pcre:"/^[a-zA-Z0-9/+]{171}=/R"; http.header_names; content:!"Referer"; reference:md5,d3f53580f7ce72caf9be799106ad89ca; classtype:targeted-activity; sid:2033713; rev:4; metadata:attack_target Client_Endpoint, created_at 2015_09_09, deployment Perimeter, confidence Medium, signature_severity Major, tag c2, updated_at 2020_08_24, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)