ROMMONkit Cisco Router Firmware Modification

This rule detects attempts to modify Cisco router firmware using ROMMONkit. It specifically looks for TCP traffic to the HOME_NET on port 23 (Telnet) containing the case-insensitive strings "rommon" and "tftpdnld". This combination suggests an attempt to interact with the router's ROM Monitor mode for firmware manipulation, often associated with malicious activities like installing backdoors or persistent malware.