Cisco Systems has released a security update that closes a backdoor allowing attackers to control software that large organizations use to manage voice over IP (VoIP) calls and messaging over their networks.

The default secure shell (SSH) key made it possible for hackers to gain highly privileged administrative access to the Cisco Unified Communications Domain Manager, the networking company warned in an advisory published Wednesday. From there, intruders could execute arbitrary commands or gain persistent access to the systems. The advisory didn't explicitly say that attackers could monitor discussions or track the times that calls or messages were made and who sent and received them, but it wouldn't be surprising if those capabilities were also possible in an e-mail, a Cisco representative said these capabilities were not possible. In addition to VoiP management, the Cisco Unified Communications Domain Manager also allows users to manage Cisco Jabber, a cloud-based service for instant messaging, voice and video communications, desktop sharing, and conferencing.

"The vulnerability is due to the presence of a default SSH private key, which is stored in an insecure way on the system," Wednesday's advisory stated. "An attacker could exploit this vulnerability by obtaining the SSH private key. For example, the attacker might reverse engineer the binary file of the operating system. This will allow the attacker to connect by using the support account to the system without requiring any form of authentication. An exploit could allow the attacker to gain access to the system with the privileges of the root user."

The backdoor was one of three vulnerabilities recently patched in the Cisco platform. A separate flaw allowed unauthenticated remote attackers to gain administrative control by tricking a valid administrator to click on a booby-trapped Web link. The vulnerability is the result of improper authentication and authorization controls built in to the Administrator interface. A third vulnerability in the Web framework of the platform made it possible for attackers to access and modify some user information and settings, including personal phone directories, speed dials, and call forwarding.

Post updated to add comment from Cisco representative.