alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Beacon Activity (GET)"; flow:established,to_server; content:"|0d 0a|Cookie|3a 20|SSID="; fast_pattern; pcre:"/^SSID=(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/C"; http.method; content:"GET"; http.uri; content:".css"; endswith; http.header_names; content:"User-Agent|0d 0a|Connection|0d 0a|Cache-Control|0d 0a 0d 0a|"; content:!"Referer"; reference:md5,9e97ace1f585b0914f99fde7014ed8c5; classtype:trojan-activity; sid:2032335; rev:3; metadata:attack_target Client_Endpoint, created_at 2021_03_25, deployment Perimeter, performance_impact Significant, confidence Medium, signature_severity Major, tag c2, updated_at 2024_04_04, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)