alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE FormBook CnC Checkin (POST) M2"; flow:established,to_server; http.method; content:"POST"; http.uri; content:!"."; content:!"?"; content:!"&"; http.request_body; content:"="; within:15; content:"|00 00 00 00 00 00|"; fast_pattern; isdataat:!1,relative; pcre:"/=[a-z0-9\(_~\-\.\x00]{300,}\x00$/i"; http.accept_enc; content:"gzip, deflate"; depth:13; endswith; http.connection; content:"close"; depth:5; endswith; http.content_len; byte_test:0,>,300,0,string,dec; http.header_names; content:"|0d 0a|Host|0d 0a|Connection|0d 0a|Content-Length|0d 0a|"; depth:36; reference:md5,6f5d2b42f4a74886ac3284fa9a414a87; classtype:command-and-control; sid:2031413; rev:2; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2020_12_16, deployment Perimeter, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_12_16;)