Cisco Security Advisory
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CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the phone book feature of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) could allow an authenticated, remote attacker to cause the CPU to increase to 100% utilization, causing a denial of service (DoS) condition on an affected system.
The vulnerability is due to improper handling of the XML input. An attacker could exploit this vulnerability by sending a Session Initiation Protocol (SIP) message with a crafted XML payload to an affected device. A successful exploit could allow the attacker to exhaust CPU resources, resulting in a DoS condition. Manual intervention may be required to recover the device.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. Mitigation options that address this vulnerability are available.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190417-es-tvcs-dos
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Vulnerable Products
This vulnerability affects Cisco Expressway Series and Cisco TelePresence Video Communication Server releases prior to X12.5.1.
Administrators can log in to the web-based GUI of Cisco Expressway Series or Cisco TelePresence VCS and view the current version in the lower-right corner in the Version field. Alternatively, administrators can view the Software version field by navigating to Status > System > Information.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
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There are no workarounds that address this vulnerability; however, there are mitigation options.
Option 1
Disable SIP if not required: Disabling SIP will completely close the attack vector for this vulnerability. However, it may not be suitable for all customers because it is a required feature in many environments.
To disable SIP from the web admin UI, navigate to Configuration > Protocols > SIP, and under the Configuration section, set SIP mode to Off and click Save.
Option 2
Disable Provisioning services if not required: Disabling Provisioning services will completely close the attack vector for this vulnerability. However, it may not be suitable for all customers because it is a required feature in many environments.
To disable Provisioning services from the web admin UI, the steps depend on the software version in use:
- For releases X8.11 and later, navigate to System > Administration settings, and under the Services section, set Provisioning services to Off and click Save.
- For releases prior to X8.11, disable the Phone Book server by removing all Provisioning (P) or Starter Pack (S) option keys.
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Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.htmlAdditionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, 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.
Customers Without Service Contracts
Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC:
https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.htmlCustomers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.
Fixed Releases
This vulnerability is fixed in Cisco Expressway Series and Cisco TelePresence Video Communication Server Releases X12.5.1 and later.
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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.
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This vulnerability was found during internal security testing.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.1 Added mitigation steps for older releases. Workarounds Final 2019-May-03 1.0 Initial public release. — Final 2019-April-17
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