alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Suspected REDCURL CnC Activity M2"; flow:established,to_server; http.method; content:"HEAD"; http.uri; content:".jpg"; endswith; http.user_agent; content:"curl/"; startswith; fast_pattern; http.header_names; content:"|0d 0a|Host|0d 0a|User-Agent|0d 0a|Accept|0d 0a 0d 0a|"; bsize:30; content:!"Referer"; reference:url,www.group-ib.com/resources/threat-research/red-curl.html; reference:md5,12ec7e6876dc86f158f448ebfba9e0eb; classtype:command-and-control; sid:2030689; rev:2; metadata:attack_target Client_Endpoint, created_at 2020_08_17, deployment Perimeter, deployment SSLDecrypt, performance_impact Moderate, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_08_17;)