Moxa products can disable the Telnet service to mitigate this risk. Please refer to the Console Settings section in the user manual for more details. Firmware version 1.5 or higher will disable Telnet by default on the NPort IA5150A/IA5250A Series. Firmware version 2.0 or higher will disable Telnet by default on the NPort IA5450A Series.

Link to Moxa’s advisory: https://www.moxa.com/en/support/product-support/security-advisory/nport-ia5000a-serial-device-servers-vulnerabilities

Set up a border firewall (or a similar network traffic control solution) passing traffic into the device’s network segment to allow traffic to port 23/TCP from authorized parties only.

Disable Telnet service on NPort device if it is possible in your environments

Firewall. Configure the firewall to restrict access to the industrial network in such a way that only essential communications from authorized sources are allowed. This will help reduce the attack surface. Make sure that the firewall restrictions do not affect core business workflows.

VPN. Use virtual private networks (VPN) to secure remote access to the industrial network. A VPN encrypts network traffic between VPN clients and the VPN server, as well as providing secure authorized access to local resources on the company’s internal network. Traffic encryption protects against traffic eavesdropping attacks, including man-in-the-middle (MitM) and other types of traffic analysis attacks.

Network monitoring. Implement a network intrusion detection solution (NIDS). A comprehensive IDS solution is capable of detecting unusual network connections and abnormal traffic sent to the device, providing timely information about various suspicious activities and sufficiently reducing the attacker’s chances of successful exploitation.

Network segmentation. Compartmentalize your network: implement network segmentation and strict access control for each segment to provide more comprehensive and effective protection against a wide range of threats. Proper network segmentation prevents attackers from reaching critical assets in the event of a network breach