alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE APT28 SEDNIT Variant CnC Beacon 3"; flow:established,to_server; http.method; content:"POST"; http.uri; content:".htm/?"; fast_pattern; pcre:"/\.htm\/\?[A-Za-z0-9]+=(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/"; http.header_names; to_lowercase; content:!"|0d 0a|content-type|0d 0a|"; content:!"|0d 0a|accept"; content:!"|0d 0a|referer|0d 0a|"; reference:md5,c2988e3e4f70d5901b234ff1c1363dcc; classtype:targeted-activity; sid:2023914; rev:6; metadata:attack_target Client_Endpoint, created_at 2016_06_09, deployment Perimeter, signature_severity Major, tag c2, updated_at 2024_04_28, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)