alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Ursnif Variant CnC Beacon"; flow:established,to_server; urilen:>125; http.method; content:"GET"; http.uri; content:"/images/"; fast_pattern; content:".gif"; distance:100; pcre:"/\/images(?:\/[a-zA-Z0-9_]+)+\.gif$/"; http.header_names; content:!"|0d 0a|Accept"; content:!"|0d 0a|Referer|0d 0a|"; http.header; pcre:"/^User-Agent\x3a\x20(?:Mozilla\/|Shockwave)/mi"; http.user_agent; content:!"ms-office"; reference:md5,f48f626cf746a2c3c73182c752c481b6; reference:md5,8ab21ac9199d3ced2230924b90f49f0d; classtype:command-and-control; sid:2021813; rev:10; metadata:attack_target Client_Endpoint, created_at 2015_09_23, deployment Perimeter, performance_impact Significant, signature_severity Major, tag c2, updated_at 2024_04_29, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)