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ESB-2005.0257 -- Cisco Security Advisory -- Cisco VPN 3000 Concentrator Vulnerable to Crafted SSL Attack

Date: 31 March 2005

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Click here for PGP verifiable version
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===========================================================================
             AUSCERT External Security Bulletin Redistribution

                 ESB-2005.0257 -- Cisco Security Advisory
       Cisco VPN 3000 Concentrator Vulnerable to Crafted SSL Attack
                               31 March 2005

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

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Cisco 3000 Series VPN Concentrators 4.1.7.A and prior
Publisher:         Cisco Systems
Impact:            Denial of Service
Access:            Remote/Unauthenticated

Original Bulletin: 
  http://www.cisco.com/warp/public/707/cisco-sa-20050330-vpn3k.shtml

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=================================================================
Cisco Security Advisory: Cisco VPN 3000 Concentrator Vulnerable to Crafted SSL
attack
=================================================================

Revision 1.0

For Public Release 2005 March 30 1600 UTC (GMT)

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

Please provide your feedback on this document.

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

Contents
========

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

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

Summary
=======

The Cisco VPN 3000 series concentrators are a family of purpose-built, remote
access Virtual Private Network (VPN) platforms for data encryption and
authentication.

A malicious user may be able to send a crafted attack via SSL (Secure Sockets
Layer) to the concentrators which may cause the device to reload, and/or drop
user connections.

Repeated exploitation will create a sustained DoS (denial of service).

Workarounds are available to mitigate this vulnerability.

Cisco has made free software available to address this vulnerability for all
affected customers.

This vulnerability is documented in the Cisco Bug Toolkit as Bug ID CSCeg11424
( registered customers only)

This advisory is available at 
http://www.cisco.com/warp/public/707/cisco-sa-20050330-vpn3k.shtml

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

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

Cisco VPN 3000 series concentrators running software 4.1.7.A and earlier are
affected by this vulnerability.

This series includes models 3005, 3015, 3020, 3030, 3060, 3080 and the Cisco
VPN 3002 Hardware Client.

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

The following products are confirmed not vulnerable:

  * Cisco IPSec VPN Services Module (VPNSM)
  * Cisco VPN 5000 Concentrators
  * Cisco PIX Firewalls
  * Any Cisco device that runs Cisco's Internetwork Operating System (IOS)
  * Any Cisco device that runs Cisco's Catalyst Operating System (CatOS)

No other Cisco products are currently known to contain this vulnerability.

Details
=======

Secure Sockets Layer (SSL) is a protocol used to encrypt the data transferred
over a TCP session. SSL in Cisco products is mainly used by the HyperText
Transfer Protocol Secure (HTTPS) web service for which the default TCP port is
443. Due to this vulnerability, a malicious user may send crafted HTTPS packets
which may result in a reload of the affected device or and/or user connections
being dropped.

The affected products are only vulnerable if they have the HTTPS service
enabled and the access to the service is not limited to trusted hosts or
network management workstations. By default, HTTPS is not enabled on VPN 3000
devices, and must be manually enabled. Affected devices are not vulnerable to
transit traffic, only traffic that is destined to them may exploit this
vulnerability.

To check if the HTTPS service is enabled, one can do the following:

 1. Check the configuration on the device to verify the status of the HTTPS
    service.
 2. Try to connect to the device using a standard web browser that supports SSL
    using a URL similar to https://ip_address_of_device/.

No authentication is required to exploit this vulnerability.

This vulnerability is documented in the Cisco Bug Toolkit as Bug ID CSCeg11424
( registered customers only)

Impact
======

Successful exploitation of this vulnerability may result in a reload of the
affected device or and/or user connections being dropped. Repeated exploitation
of this vulnerability could result in a sustained Denial of Service.

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

Cisco VPN 3000 series users can upgrade to version 4.1.7.B or later software to
resolve this vulnerability.

When considering software upgrades, please also consult
http://www.cisco.com/warp/public/707/advisory.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.

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

Please 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.

Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
for software upgrades.

See 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
===========

Disable HTTPS
+------------

Disabling HTTPS will effectively mitigate this vulnerability, provided the
concentrator is used only for IPSEC, PPTP or L2TP over IPsec VPN connections.
If the concentrator is configured for WebVPN connectivity, disabling HTTPS will
also render WebVPN inoperable.

For details on how to disable HTTPS, please reference
www.cisco.com/en/US/products/hw/vpndevc/ps2284/
products_configuration_guide_chapter09186a00803ee1e4.html#wp1309633.

Transit ACLs
+-----------

SSL to the VPN3000 could be blocked as part of a Transit ACL on screening
routers, switches and firewalls controlling all access to the trusted network.
Transit ACLs are considered a network security best practice and should be
considered as a long-term addition to good network security, as well as a
workaround for this specific vulnerability. The white paper entitled "Transit
Access Control Lists: Filtering at Your Edge" presents guidelines and
recommended deployment techniques for transit ACLs:

http://www.cisco.com/warp/public/707/tacl.html.

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.

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

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

This vulnerability was discovered during internal Cisco security review.

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 will be posted on Cisco's worldwide website at
http://cisco.com/warp/public/707/cisco-sa-20050330-vpn3k.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   | 2005-March-30 | Initial        |
| 1.0        |               | 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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===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
===========================================================================

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