Advisory ID: cisco-sa-20080116-cucmctl
For Public Release 2008 January 16 16:00 UTC (GMT)
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.
Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-0027 has
been assigned to this vulnerability.
This advisory is posted at
Note: Cisco Unified CallManager Versions 4.2, 4.3, 5.1 and 6.0 have been
renamed as Cisco Unified Communications Manager. CUCM Versions 3.3, 4.0, 4.1
and 5.0 retain the Cisco Unified CallManager name.
These products are vulnerable:
Cisco Unified CallManager 4.0
Cisco Unified CallManager 4.1 Versions prior to 4.1(3)SR5c
Cisco Unified Communications Manager 4.2 Versions prior to
Cisco Unified Communications Manager 4.3 Versions prior to
The version of software running on a CUCM 4.x system can be determined
by navigating to Help > About Cisco Unified CallManager and
selecting the Details button via the CUCM Administration
CUCM Versions 3.3, 5.0, 5.1, 6.0, 6.1 and Cisco CallManager Express are
not affected by this vulnerability. No other Cisco products are currently known
to be affected by this vulnerability.
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
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.
Cisco has provided scores for the vulnerabilities in this advisory
based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in
this Security Advisory is done in accordance with CVSS Version 2.0.
CVSS is a standards-based scoring method that conveys
vulnerability severity and helps determine urgency and priority of response.
Cisco has provided a base and temporal score. Customers can
then compute environmental scores to assist in determining the impact of the
vulnerability in individual networks.
Cisco has provided an FAQ to answer additional questions
regarding CVSS at
Cisco has also provided a CVSS calculator to help compute
the environmental impact for individual networks at
CSCsj22605 - CUCM CTL Provider Heap Overflow
registered customers only)
Calculate the environmental score of
CVSS Base Score - 10
CVSS Temporal Score - 8.3
Successful exploitation of this vulnerability may result in a DoS
condition or the execution of arbitrary code.
When considering software upgrades, also consult
and any subsequent advisories to determine exposure and a complete upgrade
In all cases, customers should exercise caution to be
certain the devices to be upgraded contain sufficient memory and that current
hardware and software configurations will continue to be supported properly by
the new release. If the information is not clear, contact the Cisco Technical
Assistance Center (TAC) or your contracted maintenance provider for
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
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.
Filters blocking access to TCP port 2444 should be deployed at the
network edge as part of a transit access control list (tACL). Further
information about transit access control lists is available in the white paper
"Transit Access Control Lists: Filtering at Your Edge," which is available at
the following link:
Additional mitigations that can be deployed on Cisco devices within the
network are available in the Cisco Applied Mitigation Bulletin companion
document for this advisory:
Cisco has released software updates that address these vulnerabilities. Prior to deploying software, customers should consult their
maintenance provider or check the software for feature set compatibility and
known issues specific to their environment.
Customers may only install and expect support for the
feature sets they have purchased. By installing, downloading, accessing or
otherwise using such software upgrades, customers agree to be bound by the
terms of Cisco's software license terms found at
or as otherwise set forth at Cisco.com Downloads at
Do not contact email@example.com or firstname.lastname@example.org
for software upgrades.
Fixed software for CUCM can be obtained here:
Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades should be
obtained through the Software Center on Cisco's worldwide website at
Customers whose Cisco products are provided or maintained through prior
or existing agreements with third-party support organizations, such as Cisco
Partners, authorized resellers, or service providers should contact that
support organization for guidance and assistance with the appropriate course of
action in regards to this advisory.
The effectiveness of any workaround or fix is dependent on
specific customer situations, such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected products
and releases, customers should consult with their service provider or support
organization to ensure any applied workaround or fix is the most appropriate
for use in the intended network before it is deployed.
Customers who purchase direct from Cisco but do not hold a Cisco
service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain software patches and bug fixes by contacting the Cisco Technical Assistance Center (TAC). TAC
contacts are as follows.
+1 800 553 2447 (toll free from within North America)
+1 408 526 7209 (toll call from anywhere in the world)
Customers should have the product serial number available and be prepared to provide the URL of this notice as evidence of entitlement to a software patch or bug fix. Customers without service contracts should request a software patch or bug fix through the TAC.
for additional TAC contact information, including localized telephone numbers,
and instructions and e-mail addresses for use in various languages.
The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.
This vulnerability was reported to Cisco by TippingPoint. Cisco would
like to thank TippingPoint for reporting this vulnerability and working with us
towards resolution of this problem.
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.
This advisory is posted on Cisco's worldwide website at :
In addition to worldwide web posting, a text version of
this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.
Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check the
above URL for any updates.
Initial public release.