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Cisco Security Advisory: Cisco Unified Communications Manager CAPF Denial of Service Vulnerability`
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Cisco Security Advisory: Cisco Unified Communications Manager CAPF
Denial of Service Vulnerability
Advisory ID: cisco-sa-20090121-cucmcapf
For Public Release 2009 January 21 1600 UTC (GMT)
Cisco Unified Communications Manager, formerly Cisco CallManager,
contains a denial of service (DoS) vulnerability in the Certificate
Authority Proxy Function (CAPF) service. Exploitation of this
vulnerability could cause an interruption in voice services. The CAPF
service is disabled by default.
Cisco has released free software updates that address this
vulnerability. Workarounds available that mitigate this vulnerability
This advisory is posted at:
These products are vulnerable:
* Cisco Unified Communications Manager 5.x versions prior to 5.1(3e)
* Cisco Unified Communications Manager 6.x versions prior to 6.1(3)
Administrators of systems that are running Cisco Unified
Communications Manager versions 5.x and 6.x can determine the
software version by viewing the main page of the Cisco Unified
Communications Manager Administration interface. The software version
can also be determined by running the command show version active by
way of the command line interface (CLI).
Products Confirmed Not Vulnerable
Cisco Unified Communications Manager version 4.x and Cisco Unified
Communications Manager Express are not affected by this
vulnerability. No other Cisco products are currently known to be
affected by this vulnerability.
Note: Cisco Unified Communications Manager 7.0(1) shipped with the
software fix for this vulnerability and is not affected.
The CAPF service of Cisco Unified Communications Manager versions 5.x
and 6.x contain a vulnerability when handling malformed input that
may result in a DoS condition. The CAPF service is disabled by
default; however, if it is enabled, the CAPF service listens by
default on TCP port 3804 and the listening port is configurable by
the user. There is a workaround for this vulnerability. This
vulnerability is fixed in Cisco Unified Communications Manager
versions 5.1(3e) and 6.1(3). This vulnerability is documented in
Cisco Bug ID CSCsq32032 and has been assigned Common Vulnerabilities
and Exposures (CVE) identifier CVE-2009-0057.
Vulnerability Scoring Details
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
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
Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at:
CSCsq32032 - CAPF DoS when client terminates prematurely
CVSS Base Score - 7.8
Access Vector - Network
Access Complexity - Low
Authentication - None
Confidentiality Impact - None
Integrity Impact - None
Availability Impact - Complete
CVSS Temporal Score - 6.4
Exploitability - Functional
Remediation Level - Official-Fix
Report Confidence - Confirmed
Successful exploitation of the vulnerability described in this
advisory may result in the interruption of voice services.
Software Versions and Fixes
When considering software upgrades, also consult
http://www.cisco.com/go/psirt and any subsequent advisories to
determine exposure and a complete upgrade solution.
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 assistance.
Cisco Unified Communications Manager version 5.1(3e) contains the fix
for this vulnerability and can be downloaded here:
Cisco Unified Communications Manager version 6.1(3) contains the fix
for this vulnerability can downloaded here:
To mitigate against this vulnerability, system administrators can
disable the CAPF service if it is not necessary for business
operations. Access to the CAPF service is only required if Cisco
Unified Communications Manager systems and IP phone devices are
configured to use certificates for a secure deployment. If phones are
not configured to use certificates, then the CAPF service can be
disabled. The CAPF service is controlled by the Cisco Certificate
Authority Proxy Function menu selection.
It is possible to mitigate the CAPF vulnerability by implementing
filtering on screening devices if the CAPF service is required. If
the CAPF service is enabled, allow access to TCP port 3804 only from
networks that contain IP phone devices that require the CAPF service.
The CAPF port is user configurable, and if modified, filtering on
screening devices should be based on the TCP port that is used.
For Cisco Unified Communications Manager 5.x and 6.x systems, please
consult the following documentation for details on how to disable
Cisco Unified Communications Manager services:
Additional mitigation techniques that can be deployed on Cisco
devices within the network are available in the Cisco Applied
Mitigation Bulletin companion document for this advisory:
Obtaining Fixed Software
Cisco has released free 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 psirt@xxxxxxxxx or security-alert@xxxxxxxxx for
Customers with Service Contracts
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 http://www.cisco.com.
Customers using Third Party Support Organizations
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
Customers without Service Contracts
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 acquire upgrades 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)
* e-mail: tac@xxxxxxxxx
Customers should have their product serial number available and be
prepared to give the URL of this notice as evidence of entitlement to
a free upgrade. Free upgrades for non-contract customers must be
requested through the TAC.
Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html
for additional TAC contact
information, including localized telephone numbers, and instructions
and e-mail addresses for use in various languages.
Exploitation and Public Announcements
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 VoIPshield.
Status of this Notice: FINAL
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
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.
| Revision | | Initial |
| 1.0 | 2009-January-21 | public |
| | | release |
Cisco Security Procedures
Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's worldwide website at http://www.cisco.com/en/US/products/
products_security_vulnerability_policy.html. This includes
instructions for press inquiries regarding Cisco security notices.
All Cisco security advisories are available at http://www.cisco.com/
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