alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Activity (GET)"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/image/"; startswith; pcre:"/^[a-z]{256}\.gif$/R"; http.header; content:"Accept|3a 20|text/html,application/xhtml+xml,application/xml|3b|q=0.9,*/*l|3b|q=0.8|0d 0a|"; fast_pattern; reference:url,twitter.com/TheDFIRReport/status/1463175512000368640; reference:md5,36be5b491426de64f9ac85c50f85808c; classtype:trojan-activity; sid:2034540; rev:1; metadata:attack_target Client_Endpoint, created_at 2021_11_23, deployment Perimeter, deployment SSLDecrypt, malware_family Cobalt_Strike, confidence Medium, signature_severity Major, updated_at 2021_11_23, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1001, mitre_technique_name Data_Obfuscation;)