alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Beacon Activity (GET)"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/btn_bg.html?contact=true"; fast_pattern; bsize:25; http.cookie; content:"HSID="; startswith; pcre:"/^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/R"; http.accept; content:"image/jpeg"; bsize:10; http.header_names; content:!"Referer"; reference:url,twitter.com/Unit42_Intel/status/1437787000690683911; reference:url,github.com/pan-unit42/tweets/blob/master/2021-09-13-IOCs-for-TA551-Trickbot-with-Cobalt-Strike-and-DarkVNC.txt; reference:md5,3963abbca3932a7d1e2b77cef1f6d57e; classtype:trojan-activity; sid:2033948; rev:1; metadata:attack_target Client_Endpoint, created_at 2021_09_14, deployment Perimeter, malware_family Cobalt_Strike, confidence Medium, signature_severity Major, updated_at 2021_09_14, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1001, mitre_technique_name Data_Obfuscation;)