alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE ELF/Muhstik - IRC CnC Checkin"; flow:established,to_server; dsize:<250; content:"NICK|20|"; startswith; content:"|0a|USER|20|muhstik"; distance:0; content:"|20 3a|muhstik-"; distance:0; fast_pattern; pcre:"/^\d+\x0a$/R"; reference:url,unit42.paloaltonetworks.com/muhstik-botnet-attacks-tomato-routers-to-harvest-new-iot-devices/; classtype:command-and-control; sid:2029319; rev:1; metadata:affected_product Linux, attack_target Networking_Equipment, created_at 2020_01_23, deployment Perimeter, malware_family Muhstik, performance_impact Low, confidence High, signature_severity Major, tag IRC, updated_at 2020_01_23;)