Cisco ATA 187 Analog Telephone Adaptor firmware versions 9.2.1.0 and 9.2.3.1 contain a vulnerability that could allow an unauthenticated, remote attacker to access the operating system of the affected device. Cisco has released software updates that address this vulnerability. Workarounds that mitigate this vulnerability are available. This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20130206-ata187
It is possible to terminate the listening Telnet process on the device by accessing the device remotely, listing the processes, and then terminating the Telnet process. This prevents further remote access to the device until the device is reloaded.
Additional mitigations that can be deployed on Cisco devices within the network are available in the companion document "Identifying and Mitigating Exploitation of the Cisco ATA 187 Analog Telephone Adaptor Remote Access Vulnerability," which is available at the following