[c-nsp] Cisco Security Advisory: Cisco Global Site Selector Appliances DNS Vulnerability

Wed Jan 7 11:00:00 EST 2009

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Cisco Security Advisory: Cisco Global Site Selector Appliances DNS
Vulnerability

Advisory ID: cisco-sa-20090107-gss

http://www.cisco.com/warp/public/707/cisco-sa-20090107-gss.shtml

Revision 1.0

For Public Release 2009 January 07 1600 UTC (GMT)

- ---------------------------------------------------------------------

Summary
=======

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 
http://www.cisco.com/warp/public/707/cisco-sa-20090107-gss.shtml

Affected Products
=================

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:

  * Cisco GSS 4480 Global Site Selector
  * Cisco GSS 4490 Global Site Selector
  * Cisco GSS 4491 Global Site Selector
  * Cisco GSS 4492R Global Site Selector

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):

    gss.cisco.com#show version

    Global Site Selector (GSS)
    Model Number: GSS-4491-k9
    Copyright (c) 1999-2007 by Cisco Systems, Inc.

    Version 2.0(1)

    Uptime: 19 Hours 18 Minutes and 14 seconds

    gss.cisco.com#

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
    GSS.cisco.com#

Products Confirmed Not Vulnerable
+--------------------------------

The following products have been confirmed not vulnerable:

  * Cisco Global Site Selector using interaction with Cisco Network
    Registrar
  * Cisco Application Control Engine Module
  * Cisco Network Registrar
  * Cisco Content Services Switch (CSS)

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

Details
=======

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[27261] 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

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

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

http://intellishield.cisco.com/security/alertmanager/cvss

CSCsj70093: GSS DNS service may crash when processing specific DNS
            requests. 

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

Impact
======

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

Workarounds
===========

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 terminal
    GSS(config)#$sserver.returnError 0
    GSS(config)#property set ServerConfig.dnsserver.returnError 0
    GSS(config)#exit
    GSS#write memory

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 psirt at cisco.com or security-alert at cisco.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.

  * +1 800 553 2447 (toll free from within North America)
  * +1 408 526 7209 (toll call from anywhere in the world)
  * e-mail: tac at cisco.com

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
============================

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KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF
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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.

Distribution
============

This advisory is posted on Cisco's worldwide website at :

http://www.cisco.com/warp/public/707/cisco-sa-20090107-gss.shtml

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.

  * cust-security-announce at cisco.com
  * first-bulletins at lists.first.org
  * bugtraq at securityfocus.com
  * vulnwatch at vulnwatch.org
  * cisco at spot.colorado.edu
  * cisco-nsp at puck.nether.net
  * full-disclosure at lists.grok.org.uk
  * comp.dcom.sys.cisco at newsgate.cisco.com

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 History
================

+---------------------------------------+
| Revision |                 | Initial  |
| 1.0      | 2009-January-07 | 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/go/psirt
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