Many Cisco security appliances contain default, authorized SSH keys that can allow an attacker to connect to an appliance and take almost any action he chooses. The default key apparently was inserted into the software for support reasons. The vulnerability is due to the presence of a default authorized SSH key that is shared across all the installations of WSAv, ESAv, and SMAv. An exploit could allow the attacker to access the system with the privileges of the root user. Researchers say the Cisco bug isn t unique, and that it is illustrative of a larger industry issue.
Source: https://threatpost.com/default-ssh-key-found-in-many-cisco-security-appliances/113480/