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Cisco Security Advisory:Cisco 11500 Content Services Switch SSL Malformed Client Certificate Vulnerability
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Thursday, 19 Oct 2005 11:00:00 -0500

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Cisco Security Advisory: Cisco 11500 Content Services Switch SSL
Malformed Client Certificate Vulnerability
==========================================================================

Document ID: 67919

Revision 1.0

For Public Release 2005 October 19 1600 UTC (GMT)
+-------------------------------------------------------------------------

Contents

    Summary
    Affected Products
    Details
    Impact
    Software Versions and Fixes
    Obtaining Fixed Software
    Workarounds
    Exploitation and Public Announcements
    Status of This Notice: FINAL
    Distribution
    Revision History
    Cisco Security Procedures

+------------------------------------------------------------------------

Summary
=======

Cisco CSS 11500 Series Content Services Switches (CSS) configured with
Secure Socket Layer (SSL) termination services are vulnerable to a
Denial of Service (DoS) attack when processing malformed client
certificates. Cisco has made free software available to address this
vulnerability. There are workarounds available to mitigate the effects
of the vulnerability.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20051019-css.shtml

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

Vulnerable Products
+------------------

Cisco CSS 11500 Series Content Services Switches running the following
versions of the Cisco WebNS operating system:

  * 7.1
  * 7.2
  * 7.3
  * 7.4
  * 7.5

The version of Cisco WebNS running on a CSS can be determined by
running the following command:

    # show version

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

Cisco CSS 11000 Series Content Services Switches

No other Cisco products are currently known to be affected by these
vulnerabilities.

Details
=======

The Cisco CSS 11500 Content Service Switch is load balancing device
designed to provide robust, scalable network services (Layer 4-7) for
data centers. The Cisco CSS 11500 performs an analysis of protocol
headers and directs requests to an appropriate resource based on
configurable policies. With integrated SSL modules, a Cisco CSS 11500
can simplify the management of digital cerfiticates and provide SSL
acceleration services to optimize performance.

A Cisco CSS 11500 may reload due to a memory corruption issue when
presented with a malformed digital client certificate during the
negotiation of a SSL session. This condition is present even if the CSS
did not request a client certificate during SSL session negotiations.
This vulnerability is only present if a CSS is configured to support
SSL termination services. SSL termination services are not configured
by default.

Users can determine if SSL termination services are configured on a CSS
by performing the following steps.

  * View the current running configuration:
   
        # show running-config
   
  * In the Services section of the configuration, users can find
    enabled SSL termination services. An example of an enabled SSL
    termination service called ssl-serv1 will look similar to the
    following. The type command with the option ssl-accel or 
    ssl-accel-backend indicates that the service is associated with a
    SSL module, and the active command signifies that a SSL termination
    service is enabled.
   
        service ssl-serv1
                type ssl-accel
                slot 3
                keepalive type none
                add ssl-proxy-list ssl list1
                active
   
The vulnerability is documented in the following Cisco Bug ID:

  * CSCee64771 ( registered customers only) -- CSS running SSL may
    crash with malformed client certificates

Impact
======

Successful exploitation of the vulnerability may result in the
immediate reload of the device. Repeated exploitation could result in a
sustained DoS attack.

Software Versions and Fixes
===========================

When considering software upgrades, consult 
http://www.cisco.com/en/US/products/
products_security_advisories_listing.html 
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") for assistance.

+----------------------------------------+
|        Train        |  Fixed Releases  |
|---------------------+------------------|
| 7.3                 | 7.30.4.02 and    |
|                     | later            |
|---------------------+------------------|
| 7.4                 | 7.40.2.02 and    |
|                     | later            |
|---------------------+------------------|
| 7.5                 | 7.50.1.03 and    |
|                     | later            |
+----------------------------------------+

Customers running Cisco WebNS 7.10 and 7.20 are encouraged to upgrade
CSS platforms to a fixed version of Cisco WebNS 7.30 or greater. Fixed
software may be obtained by registered users at 
http://www.cisco.com/pcgi-bin/tablebuild.pl/css11500-maint

Obtaining Fixed Software
========================

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 agreement with third-party support organizations such as
Cisco Partners, authorized resellers, or service providers should
contact that support organization for assistance with the upgrade,
which should be free of charge.

Customers without Service Contracts
+----------------------------------

Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their 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 () cisco com

Have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC.

Do not contact either "psirt () cisco com" or "security-alert () cisco com"
for software upgrades.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml
for additional TAC contact information, including special localized
telephone numbers and instructions and e-mail addresses for use in
various languages.

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/public/sw-license-agreement.html,
or as otherwise set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

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

The effectiveness of any workaround 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 is the most
appropriate for use in the intended network before it is deployed.

If upgrading to a fixed version of Cisco WebNS software is not
possible, the following workarounds are available.

  * Disable SSL termination for network services if not needed.
    In service configuration mode, a user can disable a SSL service
    using the following commands. ssl-serv1 is the name of a user
    defined SSL service.
   
        (config)# no service ssl-serv1
        Delete service <ssl>, [y/n]:y
   
    Documentation for configuring SSL services on a CSS running Cisco
    WebNS 7.40 can be found at 
    http://www.cisco.com/en/US/products/hw/contnetw/ps792/
    products_configuration_guide_book09186a008027ab4e.html.
    
    Documentation for configuring SSL services on a CSS running Cisco
    WebNS 7.50 can be found at 
    http://www.cisco.com/en/US/products/hw/contnetw/ps792/
    products_configuration_guide_book09186a0080405453.html.
   
  * Use Access Control Lists (ACL) on a CSS or network device in front
    of a CSS to restrict access to SSL terminated services to trusted
    networks.
    Documentation for configuring an ACL on a CSS running Cisco WebNS
    7.40 can be found at 
    http://www.cisco.com/en/US/products/hw/contnetw/ps792/
    products_configuration_guide_chapter09186a008029b1db.html#wp1133930
    
    Documentation for configuring an ACL on a CSS running Cisco WebNS
    7.50 can be found at 
    http://www.cisco.com/en/US/products/hw/contnetw/ps792/
    products_configuration_guide_chapter09186a008040aeb9.html#wp1133930

Exploitation and Public Announcements
=====================================

The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.

Status of This Notice: FINAL

THIS ADVISORY IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY
KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF
MERCHANTABILITY. YOUR USE OF THE INFORMATION ON THE ADVISORY OR
MATERIALS LINKED FROM THE ADVISORY IS AT YOUR OWN RISK. CISCO RESERVES
THE RIGHT TO CHANGE OR UPDATE THIS NOTICE AT ANY TIME.

A stand-alone copy or paraphrase of the text of this security advisory
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-20051019-css.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 () cisco com
  * first-teams () first org (includes CERT/CC)
  * bugtraq () securityfocus com
  * vulnwatch () vulnwatch org
  * cisco () spot colorado edu
  * cisco-nsp () puck nether net
  * full-disclosure () lists grok org uk
  * comp.dcom.sys.cisco () 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      | 2005-October-19 | 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

+----------------------------------------------------------------------

All contents are Copyright © 1992-2005 Cisco Systems, Inc. All rights
reserved. Important Notices and Privacy Statement.

+----------------------------------------------------------------------

Updated: Oct 19, 2005                                Document ID: 67919

+----------------------------------------------------------------------
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