Cisco Unified Communications Manager (CUCM), formerly CallManager, contains a heap overflow vulnerability in the Certificate Trust List (CTL) Provider service that could allow a remote, unauthenticated user to cause a denial of service (DoS) condition or execute arbitrary code. There is a workaround for this vulnerability.
Cisco has made free software available to address these vulnerabilities for affected customers.
Cisco Unified Communications Manager (CUCM) is the call processing component of the Cisco IP telephony solution that extends enterprise telephony features and functions to packet telephony network devices, such as IP phones, media processing devices, voice-over-IP (VoIP) gateways, and multimedia applications.
When a CUCM server is deployed in secure mode, a Certificate Trust List (CTL) is used by Cisco Unified IP Phone devices to verify the identity of CUCM servers. The CTL contains public keys and other information to allow the Cisco IP Phone devices to establish a trusted relationship with a CUCM server. The CTL is provisioned using the CTL Provider service on a CUCM server and with the CTL Provider client on an administrator workstation. The CTL Provider service needs to be enabled during the initial configuration of a CUCM server/cluster or when changes are required to the CTL. Please consult the Workarounds section of this advisory for information on how to determine if the CTL Provider service is enabled on a CUCM server.
The CTL Provider service of the CUCM contains a heap overflow vulnerability that could allow a remote, unauthenticated user to cause a DoS condition or execute arbitrary code. The CTL Provider service listens on TCP port 2444 by default, but the port can be modified by the user. This issue is documented in Cisco Bug ID CSCsj22605.
Successful exploitation of this vulnerability may result in a DoS condition or the execution of arbitrary code.
It is possible to workaround the vulnerability by disabling the CTL Provider service when not in use. Access to the CTL Provider service is required for the initial configuration of the CUCM authentication and encryption features, or during configuration updates. For the CUCM 4.x systems, please consult the following documentation for details on how to disable the CUCM services:
Filtering traffic to the affected CUCM systems on screening devices can be used as a mitigation technique for this vulnerability. To mitigate the CTL Producer service overflow, access to TCP port 2444 should be permitted only between the CUCM servers and administrator workstations running the CTL Provider client. There is currently no supported method to configure filtering directly on a CUCM system.
It is possible to change the default ports of the CTL Provider (TCP port 2444) service. If changed, filtering should be based on the port value used. The value of the port can be viewed in CUCM Administration interface by following the System > Service Parameters menu and selecting the CTL Provider service.