alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Activity (GET)"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/api/3"; bsize:6; fast_pattern; http.header_names; content:"|0d 0a|Accept|0d 0a|Host|0d 0a|Cookie|0d 0a|User-Agent|0d 0a|Connection|0d 0a|Cache-Control|0d 0a 0d 0a|"; bsize:65; reference:md5,c3c7bfb6c4f0e5c7a455ee1066893552; reference:url,blog.talosintelligence.com/2021/11/attackers-use-domain-fronting-technique.html; classtype:trojan-activity; sid:2034528; rev:1; metadata:attack_target Client_Endpoint, created_at 2021_11_22, deployment Perimeter, malware_family Cobalt_Strike, confidence Medium, signature_severity Major, updated_at 2021_11_22, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1001, mitre_technique_name Data_Obfuscation;)