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Cisco Security Advisory: Cisco Global Site Selector Appliances DNS Vulnerability
Advisory ID: cisco-sa-20090107-gss
For Public Release 2009 January 07 1600 UTC (GMT)
The Cisco Application Control Engine Global Site Selector (GSS) contains a vulnerability when processing specific Domain Name System (DNS) requests that may lead to a crash of the DNS service on the GSS. Cisco has released free software updates that address this vulnerability.
A workaround that mitigates this vulnerability is available.
This advisory is posted at
All versions of GSS system software prior to 3.0(1) are affected by this vulnerability. If the GSS is configured with the optional Cisco Network Registrar (CNR) software, the device is not vulnerable.
Vulnerable Products +------------------
The following GSS products are affected by this vulnerability:
In order to determine the software that runs on a GSS device, users should log in to the device and issue the show version command to display the system software banner. The version is indicated on the line starting with Version. The following example shows a GSS that runs system software 2.0(1):
Global Site Selector (GSS)
Model Number: GSS-4491-k9
Copyright (c) 1999-2007 by Cisco Systems, Inc.
Uptime: 19 Hours 18 Minutes and 14 seconds
In order to determine if CNR is enabled on the GSS device, users should log in to the device and issue the show running-config | grep cnr command to display the system CNR configuration. If CNR is enabled, cnr enable will be displayed in the output. If CNR is disabled, no cnr enable will be displayed. The following example shows a GSS that does not have CNR enabled:
GSS.cisco.com#show running-config | grep cnr
no cnr enable
Products Confirmed Not Vulnerable +--------------------------------
The following products have been confirmed not vulnerable:
No other Cisco products are currently known to be affected by this vulnerability.
The Cisco GSS platform allows customers to leverage global content deployment across multiple distributed and mirrored data locations, optimizing site selection, improving Domain Name System (DNS) responsiveness, and ensuring data center availability.
The GSS is inserted into the traditional DNS hierarchy and is closely integrated with the Cisco CSS, Cisco Content Switching Module (CSM), or third-party server load balancers (SLBs) to monitor the health and load of the SLBs in customers data centers. The GSS uses this information and user-specified routing algorithms to select the best-suited and least-loaded data center in real time.
A vulnerability exists in the GSS when processing a specific sequence of DNS requests. An exploit of the vulnerability may result in a crash of the DNS service on the GSS.
When the DNS server crashes, an error message will appear in the logs similar to the following example:
Dec 18 04:47:21 gss NMR-6-LAUNCHSVR_EXIT dnsserver' has exited [ExitUnknown(139)]"
This vulnerability is documented in Cisco Bug ID: CSCsj70093
This vulnerability has been assigned the Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-3819.
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 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
CSCsj70093: GSS DNS service may crash when processing specific DNS
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 may result in a crash of the GSS DNS service. Repeated exploitation may result in a sustained denial of service (DoS) attack.
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. +---------------------------------------+ | GSS | First Fixed | Recommended | | Major | Release | Release | | Version | | | |---------+---------------+-------------| | | Vulnerable; | | | 1.x(y) | Migrate to | 3.0(2) | | | 3.0(1) or | | | | later | | |---------+---------------+-------------| | | Vulnerable; | | | 2.x(y) | Migrate to | 3.0(2) | | | 3.0(1) or | | | | later | | |---------+---------------+-------------| | 3.x(y) | Not | | | | Vulnerable | | +---------------------------------------+
GSS fixed system software is available for download from http://www.cisco.com/cgi-bin/tablebuild.pl/gss-3des?psrtdcat20e2
A workaround for this vulnerability includes setting the property "ServerConfig.dnsserver.returnError" to disabled (or zero). The following example shows how to set the property to disabled. It is enabled by default:
GSS(config)#property set ServerConfig.dnsserver.returnError 0
Note: Negative responses (NXDOMAIN and NODATA) will not be sent out by the GSS with this setting disabled. Also, by using the DNS server statistics (show statistics dns global), it will not be possible to differentiate between the NXDOMAIN or NODATA mismatches because both of these will increment the DNSQueriesUnmatched counter.
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 http://www.cisco.com/en/US/products/prod_warranties_item09186a008088e31f.html or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml
Do not contact firstname.lastname@example.org or email@example.com for software upgrades.
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 is deployed.
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.
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 aware of active exploitations where malicious use of the vulnerability described in this advisory has occurred.
This vulnerability was discovered by investigating customer TAC service requests.
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 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.
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/go/psirt
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