alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE FormBook CnC Checkin (GET)"; flow:established,to_server; content:"Connection|3a 20|close|0d 0a 0d 0a 00 00 00 00 00 00|"; fast_pattern; http.method; content:"GET"; http.uri; content:"/?"; pcre:"/^[A-Za-z0-9_\-]{1,15}=(?:[A-Za-z0-9_\-]{1,25}|(?:[A-Za-z0-9\+\/]{4})*(?:[A-Za-z0-9\+\/]{2}==|[A-Za-z0-9\+\/]{3}=|[A-Za-z0-9\+\/]{4}))&[A-Za-z0-9_\-]{1,15}=(?:[A-Za-z0-9_\-]{1,25}|(?:[A-Za-z0-9\+\/]{4})*(?:[A-Za-z0-9\+\/]{2}==|[A-Za-z0-9\+\/]{3}=|[A-Za-z0-9\+\/]{4}))(?:&sql=\d*)?$/R"; http.connection; content:"close"; depth:5; endswith; http.header_names; content:"|0d 0a|Host|0d 0a|Connection|0d 0a 0d 0a|"; depth:22; endswith; reference:md5,a6a114f6bc3e86e142256c5a53675d1a; classtype:command-and-control; sid:2031412; rev:10; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2017_12_19, deployment Perimeter, malware_family Formbook, performance_impact Moderate, confidence Medium, signature_severity Major, updated_at 2023_08_10, reviewed_at 2024_02_13;)