alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Win32/Chopstick Checkin (APT28 Related)"; flow:to_server,established; http.method; content:"POST"; http.uri; content:"/webhp?rel="; fast_pattern; content:"ai="; distance:0; pcre:"/^(?:[A-Za-z0-9_-]{4})*(?:[A-Za-z0-9_-]{2}==|[A-Za-z0-9_-]{3}=|[A-Za-z0-9_-]{4})+/R"; reference:url,www.fireeye.com/resources/pdfs/apt28.pdf; reference:md5,6fc8602c8b3a18765bb6d2307d8a4ae1; classtype:targeted-activity; sid:2019537; rev:4; metadata:created_at 2014_10_28, malware_family Win32_Chopstick, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_05_13;)