Security experts at Cisco revealed the existence of a default SSH key in many security appliances, an attacker can exploit it to control the devices. The abuse of the SSH key could represent a serious problem for enterprises and organizations that are exposed to cyber attacks. The default key was used for maintenance purposed. The vulnerability was discovered by Cisco experts during internal security testing. The only way to fix the security issue it to apply the patches released by Cisco, the only way is applying the patches to Cisco.”]
Source: https://securityaffairs.co/wordpress/38103/hacking/cisco-default-ssh-key.html