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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 1.0

For Public Release 2006 January 26 1700 UTC (GMT)

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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

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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 HTTP (Hypertext
Transfer Protocol) packet to the concentrators which may cause the
device to reload and drop user connections.

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

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 running software 4.7.0 through
4.7.2.A are affected by this vulnerability. This includes version
4.7REL. Software versions prior to 4.7.x are not vulnerable.

This series includes models 3005, 3015, 3020, 3030, 3060, and the
3080.

Products Confirmed Not Vulnerable
±-------------------------------

The following products are confirmed not vulnerable:

• Cisco VPN 3002 Hardware Client
• Cisco IPSec VPN Services Module (VPNSM)
• 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 this
vulnerability.

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.

Impact

Successful exploitation of this vulnerability may result in a reload
of the affected device and 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 software version 4.7.2.B and later is not
vulnerable.

Cisco VPN 3000 series users can upgrade to version 4.7.2.B or later
software to resolve this vulnerability. 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 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.

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 proxys
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 see:

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 a 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-center/sw-usingswc.shtml

Do not contact either "[email protected]" or "[email protected]"
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: [email protected]

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.

This issue was discussed at the Schmoocon security conference on
January 12th, 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.

• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]

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 | 26-January-2006 | public |
| | | release. |
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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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