alert http $HTTP_SERVERS any -> $EXTERNAL_NET any (msg:"ET WEB_SERVER Possible Darkleech C2"; flow:established,to_server; http.uri; content:"/blog/?"; depth:7; fast_pattern; content:"&utm_source="; distance:0; pcre:"/^\/blog\/\?[a-z]{3,20}+\&utm_source=\d+\x3a\d+\x3a\d+$/"; http.host; pcre:"/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/"; http.header_names; content:!"Referer|0d 0a|"; reference:url,blog.sucuri.net/2015/12/evolution-of-pseudo-darkleech.html; classtype:command-and-control; sid:2022260; rev:4; metadata:created_at 2015_12_14, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_11_03;)