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Cisco Security Advisory: Cisco VPN 3000 Concentrator Vulnerable to Crafted HTTP Attack
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Wed, 26 Apr 2006 12:18:09 -0400

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Cisco Security Advisory: 
Cisco VPN 3000 Concentrator Vulnerable to Crafted HTTP Attack

Advisory ID: cisco-sa-20060126-vpn

http://www.cisco.com/warp/public/707/cisco-sa-20060126-vpn.shtml

Revision 2.0

Last Updated 26 April 2006 1600 UTC (GMT)

For Public Release 2006 January 26 1700 UTC (GMT)


Contents
========

    Summary
    Affected Products
    Details
    Impact
    Software Versions and Fixes
    Workarounds
    Obtaining Fixed Software
    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 crafted packets to a
concentrator which may cause the device to halt and/or drop user
connections. The power must then be reset on the device to recover.

Cisco has made free software available to address this vulnerability
for affected customers. There are workarounds available to mitigate
this vulnerability as well.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20060126-vpn.shtml

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

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

Cisco VPN 3000 series concentrators 3005, 3015, 3020, 3030 and the
3080 are affected by this vulnerability.

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

The following products are confirmed not vulnerable:

  * Cisco VPN 3002 Hardware Client
  * Cisco IPSec VPN Services Module (VPNSM)
  * Cisco WebVPN Service Module (WebVPN)
  * Cisco VPN 5000 Concentrators
  * Cisco PIX Firewalls
  * Cisco Adaptive Security Appliance (ASA)
  * 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 these
vulnerabilities.

Details
+------

Hypertext Transfer Protocol (HTTP) is a set of rules for exchanging
files (text, graphic images, sound, video, and other multimedia
files) on the World Wide Web. HTTP is an application protocol for
which the default TCP port is 80. Due to this vulnerability, a
malicious user may send crafted HTTP packets which may result in a
reload of the affected device and/or user connections being dropped.

The affected products are only vulnerable if they have the HTTP
service enabled. By default, HTTP is enabled on VPN 3000 devices,
however it may be manually disabled. Affected devices are not
vulnerable to transit traffic, only traffic that is destined to them
may exploit this vulnerability.

To check if the HTTP service is enabled, please do the following:

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

This vulnerability is documented in the Cisco Bug Toolkit as Bug ID 
CSCsb77324 and CSCsd26340.

Vulnerable versions of Cisco VPN 3000 do not manage certain TCP
connections aggressively, which may leave the concentrator vulnerable
to a denial of service attack.

  * CSCsb77324 - A malicious user may be able to send a small series
    of crafted HTTP packets to a concentrator which will cause the
    device to halt and drop user connections. The power must then be
    reset on the device to recover.
   
  * CSCsd26340 - The concentrator does not manage TCP connections to
    port 80 aggressively enough, leading to a scenario where memory
    and other resources are consumed with open connections. In
    specific scenarios, the concentrator will stall and drop user
    connections. The device must then be restarted via console access
    or by resetting power on the device. Alternatively, the device
    will recover automatically within about 20 minutes, however
    during this time the device is unavailable except via console
    access.

Impact
======

Successful exploitation of these vulnerabilities may cause the device
to halt and drop user connections.

Software Versions and Fixes

+----------------------------------------------------------------+
| Vulnerability  | Affected Major Release | First Fixed Release  |
|----------------+------------------------+----------------------|
|                | 4.0.X or earlier       | Not Vulnerable       |
|                |------------------------+----------------------|
| HTTP DoS Attack| 4.1.X                  | Not Vulnerable       |
|  (CSCsb77324)  |------------------------+----------------------|
|                | 4.7.2.                 | 4.7.2.B              |
|----------------+------------------------+----------------------|
|                | 4.0.X or earlier       | Not Vulnerable       |
|                |------------------------+----------------------|
|   TCP Attack   | 4.1.X                  | 4.1.7.L              |
|  (CSCsd26340)  |------------------------+----------------------|
|                | 4.7.X                  | 4.7.2.F              |
+----------------------------------------------------------------+

Cisco VPN 3000 series users can upgrade to version 4.1.7.L or 4.7.2.F
or later software to resolve both vulnerabilities.

Cisco VPN 3000 software is available for download at
http://www.cisco.com/cgi-bin/tablebuild.pl/vpn3000-3des

When considering software upgrades, also consult
http://www.cisco.com/go/psirt and any subsequent advisories to
determine exposure and a compelete 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.

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

Disable HTTP
+-----------

Disabling HTTP will effectively mitigate this vulnerability.

With HTTP disabled, the concentrator can be configured to use HTTPS
(HyperText Transfer Protocol Secure) for both concentrator management
and WebVPN connectivity if WebVPN connectivity is configured on the
concentrator.

To implement this workaround, first enable HTTPS, then disable HTTP.

If WebVPN is used, it is important to also disable any HTTP proxies
that may be configured (HTTPS is always enabled for WebVPN if WebVPN
is enabled).

For details on how to enable HTTPS management of the concentrator,
please reference:

http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_configuration_guide_chapter09186a00803ee1e4.html#wp1309312

For details on how to disable HTTP management of the concentrator,
please reference:

http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_configuration_guide_chapter09186a00803ee11f.html#wp999607

For details on how to disable WebVPN HTTP proxies, please reference:

http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_configuration_guide_chapter09186a00803ee1e4.html#wp1400335

Infrastructure ACLs
+------------------

HTTP to the VPN3000 could be blocked as part of an Infrastructure ACL
on screening routers, switches and firewalls controlling all access
to the trusted network. Infrastructure 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 "Protecting Your
Core: Infrastructure Protection Access Control Lists" presents
guidelines and recommended deployment techniques:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801a1a55.shtml

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

Cisco has made free software available to address this vulnerability
for affected customers. 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/public/sw-license-agreement.html, or as otherwise
set forth at Cisco.com Downloads at 
http://www.cisco.com/public/sw-centeri/sw-usingswc.shtml

Do not contact either "psirt () cisco com" or "security-alert () 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 agreement 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 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.

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.

Exploitation and Public Announcements
+------------------------------------

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

These issues were reported to Cisco by Eldon Sprickerhoff from
eSentire and discussed at the ShmooCon security conference on 
January 14th, 2006.

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.

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

This advisory is posted on Cisco's worldwide website at
http://www.cisco.com/warp/public/707/cisco-sa-20060126-vpn.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
  * 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 | 26-April-2006     | Updated to include DDTS CSCsd26340.|
| 2.0      |                   |                                    |
|----------+-------------------+------------------------------------|
|          |                   |   * Corrected impact of successful |
|          |                   |     exploitation of this           |
| Revision | 01-February-2006  |     vulnerability - device halts   |
| 1.1      |                   |   * Fixed typo in name of security |
|          |                   |     conference where this          |
|          |                   |     vulnerability was discussed.   |
|----------+-------------------+------------------------------------|
| Revision | 26-January-2006   | Initial public release.            |
| 1.0      |                   |                                    |
+-------------------------------------------------------------------+

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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