alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Beacon Activity (GET)"; flow:established,to_server; http.method; content:"GET"; http.uri; content:".css"; endswith; http.cookie; content:"SSID="; fast_pattern; startswith; pcre:"/^SSID=(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/"; http.header_names; to_lowercase; content:"user-agent|0d 0a|connection|0d 0a|cache-control|0d 0a 0d 0a|"; content:!"|0d 0a|referer|0d 0a|"; reference:md5,9e97ace1f585b0914f99fde7014ed8c5; classtype:trojan-activity; sid:2032335; rev:4; 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_05_05, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)