alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE FormBook CnC Checkin (GET) M5"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/?"; offset:3; pcre:"/^[A-Za-z0-9_\-]{1,15}=(?:[A-Za-z0-9_\-]{1,25}|(?:[A-Za-z0-9\+\/]{4})*(?:[A-Za-z0-9\+\/]{2}==|[A-Za-z0-9\+\/]{3}=|[A-Za-z0-9\+\/]{4}))&[A-Za-z0-9_\-]{1,15}=(?:[A-Za-z0-9_\-]{1,25}|(?:[A-Za-z0-9\+\/]{4})*(?:[A-Za-z0-9\+\/]{2}==|[A-Za-z0-9\+\/]{3}=|[A-Za-z0-9\+\/]{4}))(?:&sql=\d*)?$/R"; http.connection; content:"close"; bsize:5; http.header_names; content:!"Referer"; content:"|0d 0a|Host|0d 0a|Connection|0d 0a|User-Agent|0d 0a 0d 0a|"; fast_pattern; reference:md5,04777e7ab425b2d82227945f81d2c1f8; classtype:command-and-control; sid:2050745; rev:2; metadata:attack_target Client_Endpoint, created_at 2024_02_07, deployment Perimeter, malware_family Formbook, performance_impact Moderate, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_02_07; target:src_ip;)