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Cisco Security Advisory

Cisco Unified Communications Manager Session Initiation Protocol Denial of Service Vulnerability

Advisory ID: cisco-sa-20120926-cucm

Revision 1.0

For Public Release 2012 September 26 16:00  UTC (GMT)

Related Resources:

View related Security AdvisoryView related Applied Mitigation BulletinView related BlogView related Event ResponseView related Alert


Cisco Unified Communications Manager contains a vulnerability in its Session Initiation Protocol (SIP) implementation that could allow an unauthenticated, remote attacker to cause a critical service to fail, which could interrupt voice services. Affected devices must be configured to process SIP messages for this vulnerability to be exploitable.

Cisco has released software updates that address this vulnerability. A workaround exists for customers who do not require SIP in their environment.

This advisory is available at

Note: The September 26, 2012, Cisco IOS Software Security Advisory bundled publication includes nine Cisco Security Advisories. Eight of the advisories address vulnerabilities in Cisco IOS Software, and one advisory addresses a vulnerability in Cisco Unified Communications Manager. Each Cisco IOS Software Security Advisory lists the Cisco IOS Software releases that correct the vulnerability or vulnerabilities detailed in the advisory as well as the Cisco IOS Software releases that correct all Cisco IOS Software vulnerabilities in the September 2012 bundled publication. 

Individual publication links are in "Cisco Event Response: Semi-Annual Cisco IOS Software Security Advisory Bundled Publication" at the following link:

Cisco IOS Software and Cisco IOS XE Software are affected by the vulnerability described in this advisory. A separate Cisco Security Advisory has been published to disclose the vulnerability that affects Cisco IOS Software and Cisco IOS XE Software at the following location:

Affected Products

Vulnerable Products

The following Cisco Unified Communications Manager software releases are affected:
  • Cisco Unified Communications Manager 6.x
  • Cisco Unified Communications Manager 7.x
  • Cisco Unified Communications Manager 8.x

Note: Cisco Unified Communications Manager version 6.1 reached the End of Software Maintenance on September 3, 2011. Customers using Cisco Unified Communications Manager 6.x versions should contact their Cisco support team for assistance in upgrading to a supported version of Cisco Unified Communications Manager.

Note: Cisco IOS Software and Cisco IOS XE Software are affected by the vulnerability described in this advisory. A separate Cisco Security Advisory has been published to disclose the vulnerability that affects Cisco IOS Software and Cisco IOS XE Software at the following location:

Products Confirmed Not Vulnerable

No other Cisco products are currently known to be affected by this vulnerability.


Cisco Unified Communications Manager 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, VoIP gateways, and multimedia applications.

Session Initiation Protocol (SIP) is a popular signaling protocol that is used to manage voice and video calls across IP networks such as the Internet. The protocol is responsible for handling all aspects of call setup and termination. Voice and video are the most popular types of sessions that SIP handles, but the protocol has the flexibility to accommodate other applications that require call setup and termination. SIP call signaling can use UDP (port 5060), TCP (port 5060), or Transport Layer Security (TLS; TCP port 5061) as the underlying transport protocol.

A vulnerability exists in the SIP implementation in Cisco Unified Communications Manager that could allow a remote attacker to cause a critical service to fail, which could interrupt voice services. This vulnerability is triggered when an affected device processes a crafted SIP message that contains a valid Session Description Protocol (SDP) message. Only traffic destined to the device can trigger the vulnerability; transit SIP traffic is not an exploit vector.

Note: In cases where SIP is running over TCP transport, a TCP three-way handshake is necessary to exploit this vulnerability.

This vulnerability is documented in Cisco bug IDs CSCtw66721 (registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2012-3949.

Note: This vulnerability also affects Cisco IOS Software and Cisco IOS XE Software. The corresponding Cisco bug IDs are CSCtw84664 and CSCtj33003. Refer to the separate Cisco Security Advisory for Cisco IOS Software for additional details.

Vulnerability Scoring Details

Cisco has scored the vulnerability in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this security advisory is in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps organizations determine the urgency and priority of a response.

Cisco has provided a base and temporal score. Customers can also compute environmental scores that help determine the impact of the vulnerability in their own networks.

Cisco has provided additional information regarding CVSS at the following link:

Cisco has also provided a CVSS calculator to compute the environmental impact for individual networks at the following link:

CSCtw66721 -- Crafted SDP message may cause crash or interoperability issue

Calculate the environmental score of CSCtw66721

CVSS Base Score - 7.8

Access Vector

Access Complexity


Confidentiality Impact

Integrity Impact

Availability Impact







CVSS Temporal Score - 6.4


Remediation Level

Report Confidence





Successful exploitation of the vulnerability could allow a remote attacker to cause a critical service to fail, which interrupt voice services. Cisco Unified Communications Manager will restart the affected processes, but repeated attacks may result in a sustained denial of service (DoS) condition.

Software Versions and Fixes

When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses archive at and review subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

  Cisco Unified Communication Manager Version First Fixed Release
 Recommended Release
7.x 7.1(5b)su5 7.1(5b)su5
8.x 8.5(1)su4
8.6(4) (BE3K-only release)
8.6(4) (BE3K-only release)
9.x  Not affected
Not affected


A workaround exists for customers who do not require SIP in their environment. Cisco Unified Communication Manager versions 6.1(4), 7.1(2), and 8.0(1) introduced the ability to disable SIP processing. SIP processing is enabled by default. Use the following instructions to disable SIP processing:

  • Step 1: Log in to the Cisco Unified CM Administration web interface.
  • Step 2: Navigate to System > Service Parameters and choose the appropriate Cisco Unified Communications Manager server and the Cisco CallManager service.
  • Step 3: Change the SIP Interoperability Enabled parameter to False and then click Save.

    Note: For a SIP processing change to take effect, the Cisco CallManager Service must be restarted. For information on how to restart the service, see the "Restarting the Cisco CallManager Service" section of the "Cisco Unified Communications Manager Administration Guide" at
Additional mitigations that can be deployed on Cisco devices in the network are available in the companion document "Identifying and Mitigating Exploitation of the Cisco Unified Communications Manager and Cisco IOS Software Session Initiation Protocol Denial of Service Vulnerability" at the following location:

Obtaining Fixed Software

Cisco has released software updates that address the vulnerability described in this advisory. Prior to deploying software, customers are advised to consult their maintenance providers or check the software for feature set compatibility and known issues that are specific to their environments.

Customers may only install and expect support for feature sets they have purchased. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license at

Customers with Service Contracts

Customers with contracts should obtain software through their regular update channels. For most customers, software patches and bug fixes should be obtained through the Software Navigator on at

Customers Using Third-Party Support Organizations

Customers with Cisco products that 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 organization for assistance with the appropriate course of action.

The effectiveness of any workaround or fix depends on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Because of the variety of affected products and releases, customers should consult their service providers or support organizations to ensure that any applied workaround or fix is the most appropriate in the intended network before it is deployed.

Customers Without Service Contracts

Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through Cisco Authorized partners, resellers, and distributors (authorized 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):

  • +1 800 553 2447 (toll free from within North America)
  • +1 408 526 7209 (toll call from anywhere in the world)
  • e-mail:

Customers should have the product serial number available and be prepared to provide the URL of this advisory 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.

Refer to Cisco Worldwide Contacts at for additional TAC contact information, including localized telephone numbers, instructions, and e-mail addresses for support in various languages.

Exploitation and Public Announcements

The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

This vulnerability was found during troubleshooting of TAC service requests.

Status of This Notice: Final


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 Security at the following link:

Additionally, a text version of this advisory is clear signed with the Cisco PSIRT PGP key and circulated among the following e-mail addresses:


Future updates of this advisory, if any, will reside on but may not be announced on mailing lists. Users can monitor this advisory's URL for any updates.

Revision History

Revision 1.0 2012-September-26 Initial public release.

Cisco Security Procedures

Complete information about reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco is available on at This web page includes instructions for press inquiries regarding Cisco Security Advisories. All Cisco Security Advisories are available at
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