Cisco Nexus and Cisco Multilayer Director Switches MOTD Telnet Login Reset Vulnerability

A vulnerability in the Message of the Day (MOTD) or banner functionality of the NX-OS Software could allow an unauthenticated, remote attacker to cause the login process to reset.   The vulnerability is due to the MOTD display handling when a certain type of terminal session is requested via Telnet. An attacker could exploit this vulnerability by repeatedly issuing a Telnet session to the NX-OS device, causing the login process to reset. An exploit could allow the attacker to cause the login process of the NX-OS device to reset repeatedly. Cisco has confirmed the vulnerability; however, software updates are not available. To exploit this vulnerability, an attacker would need to start a Telnet session with the targeted device. This requirement may decrease the likelihood of a successful exploit depending on how the targeted device is configured. Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.

Administrators are advised to contact the vendor regarding future updates and releases.

Administrators are advised to allow only trusted users to have network access.

Administrators can help protect affected systems from external attacks by using a solid firewall strategy.

Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.

Administrators are advised to monitor affected systems.