alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE APT Cheshire Cat CnC Beacon"; flow:established,to_server; http.method; content:"POST"; http.user_agent; bsize:50; content:"Mozilla/4.0 (compatible|3b 20|MSIE 5.0|3b 20|Windows NT 4.0)"; fast_pattern; http.header_names; to_lowercase; content:!"|0d 0a|referer|0d 0a|"; reference:url,kernelmode.info/forum/viewtopic.php?f=16&t=3981; classtype:targeted-activity; sid:2021719; rev:5; metadata:attack_target Client_Endpoint, created_at 2015_08_26, deployment Perimeter, signature_severity Major, tag c2, updated_at 2024_04_29, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)