alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Beacon Activity"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/userid="; startswith; fast_pattern; pcre:"/^[A-Z]{256}$/R"; http.header; content:"Content-Transfer-Encoding|3a 20|base64|0d 0a|"; http.header_names; content:!"Referer"; reference:md5,435f83b1ab70c68e34bd523bae4217e0; reference:url,twitter.com/bryceabdo/status/1372895643102969861; classtype:trojan-activity; sid:2032274; rev:1; metadata:attack_target Client_Endpoint, created_at 2021_03_22, deployment Perimeter, deployment SSLDecrypt, confidence Medium, signature_severity Major, tag c2, updated_at 2021_03_22, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)