This bug is about as serious as they come for enterprises. An attacker who is able to discover the default SSH key would have virtually free reign on vulnerable boxes, which, given Cisco’s market share and presence in the enterprise worldwide, is likely a high number. 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 attacker could exploit this vulnerability by obtaining the SSH private key and using it to connect to any WSAv, ESAv, or SMAv. An exploit could allow the attacker to access the system with the privileges of the root user," Cisco said.