alert tcp $EXTERNAL_NET [!9000,!9001,!9002,!9003,!9004,!2032,1024:] -> $HOME_NET any (msg:"ET MALWARE NanoCore RAT Keepalive Response 2"; flow:established,to_client; dsize:37; content:"|21 00 00 00|"; depth:4; content:!"|00 00 00 00|"; within:4; content:!"|0d 00|"; within:2; flowbits:isset,ET.NanoCore; threshold:type both, track by_src, count 10, seconds 10; stream_size:client,<,5000; reference:md5,bf994dce3712fb66afa4a2ce5b3ceee4; reference:url,medium.com/@the_abjuri5t/nanocore-rat-hunting-guide-cb185473c1e0; classtype:trojan-activity; sid:2046910; rev:10; metadata:attack_target Client_Endpoint, created_at 2015_03_27, deployment Perimeter, malware_family NanoCore, performance_impact Moderate, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2023_07_26, former_sid 2810291;)