Cisco Security Advisory: Vulnerabilities in the Internet Key Exchange Xauth Implementation

Wed Apr 6 15:54:26 UTC 2005

Cisco Internetwork Operating System (IOS) Software release trains 12.2T, 12.3
and 12.3T may contain vulnerabilities in processing certain Internet Key
Exchange (IKE) Xauth messages when configured to be an Easy VPN Server.

Successful exploitation of these vulnerabilities may permit an unauthorized
user to complete authentication and potentially access network resources.

This advisory will be posted to 
http://www.cisco.com/warp/public/707/cisco-sa-20050406-xauth.shtml

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

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

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

This issue affects all Cisco devices running any unfixed version of Cisco IOS
that supports, and is configured for, Cisco Easy VPN Server Xauth version 6
authentication.

A Cisco device running Easy VPN Server and configured for Xauth authentication
will have the following line in the configuration:

      crypto map <mapname> client authentication list <listname>

The Easy VPN Server XAUTH feature may also be enabled underneath an ISAKMP
profile via a configuration similar to:

      crypto isakmp profile <profilename> 
        match identity group <groupname>
        client authentication list <listname>
        isakmp authentication list <listname>
        client configuration address respond
        qos-group 2

To determine the software running on a Cisco product, log in to the device and
issue the 'show version' command to display the system banner. Cisco IOS
Software will identify itself as "Internetwork Operating System Software" or
simply "IOS." On the next line of output, the image name will be displayed
between parentheses, followed by "Version" and the IOS release name. Other
Cisco devices will not have the show version command or will give different
output.

The following example identifies a Cisco product running IOS release 12.3(6)
with an installed image name of C3640-I-M:

   Cisco Internetwork Operating System Software
   IOS (tm) 3600 Software (C3640-I-M), Version 12.3(6), RELEASE SOFTWARE (fc3)

The next example shows a product running IOS release 12.3(11)T3 with an image
name of C3845-ADVIPSERVICESK9-M:

   Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.3(11)T3, RELEASE SOFTWARE (fc4)
   Technical Support: http://www.cisco.com/techsupport
   Copyright (c) 1986-2005 by Cisco Systems, Inc.

Additional information about Cisco IOS release naming can be found at 
http://www.cisco.com/warp/public/620/1.html.

Cisco Easy VPN Server is an IOS-only feature. Devices that do not run IOS are
not vulnerable.

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

Details
=======

IPSec is a framework of open standards that provides data confidentiality, data
integrity, and data authentication between participating peers. IPSec provides
these security services at the IP layer allowing for data to be transmitted
across a public network without fear of observation, modification, or spoofing,
thus enabling applications such as Virtual Private Networks (VPNs). IPSec uses
the Internet Key Exchange (IKE) protocol to provide authentication of the IPSec
peers, negotiate IPSec security associations (SA), and establish IPSec keys.

Extended Authentication (XAUTH) is an extension to IKE defined in an expired
Internet Engineering Task Force (IETF) Internet Draft,
draft-ietf-ipsec-isakmp-xauth-06.txt, which allows for organizations to utilize
existing legacy authentication methods in order to manage remote access.

Successful VPN establishment consists of two levels of SA's known as phases.
Phase 1 authentication establishes session keys. Using the Xauth feature, the
client waits for a "username/password" challenge after the IKE Phase 1 SA has
been established. When the end user responds to the challenge, the response is
forwarded to the IPsec peers for an additional level of authentication.

The Cisco IOS Easy VPN Server feature introduced in IOS 12.2(8)T allows an IOS
device to act as a VPN concentrator, providing authentication and encrypted
access to network resources.

To determine if Cisco's Easy VPN Server XAUTH feature is enabled, check the
device's configuration for the following line:

      crypto map <mapname> client authentication list <listname>

The Easy VPN Server XAUTH feature may also be enabled underneath an ISAKMP
profile via a configuration similar to:

      crypto isakmp profile <profilename> 
        match identity group <groupname>
        client authentication list <listname>
        isakmp authentication list <listname>
        client configuration address respond
        qos-group 2

Certain packets sent to the IOS Easy VPN Server listening on User Datgram
Protocol (UDP) port 500 may permit an unauthorized user to complete Xauth
authentication and thereby gain access to network resources.

In order for the attack to succeed, an attacker must know the shared group key
to complete the IKE Phase 1 negotiation before the Xauth negotiation takes
place.

This malformed packet vulnerability is documented as Cisco Bug ID CSCin82407. 

A second vulnerability exists in a feature introduced in IOS 12.3(8)T where an
ISAKMP profile can be assigned to a remote access peer based on the certificate
the peer uses during IKE negotiation. If the ISAKMP profile mandates XAUTH (AAA
authentication and authorization lists are configured in the profile), then the
peer must perform XAUTH authentication after Phase 1 negotiation.

A vulnerability exists where the ISAKMP profile is assigned but the attributes
that are configured in the ISAKMP profile are not processed. This can result in
a situtation where both the VPN client and VPN server are expecting to hear
something from the other end of the connection. Normally this deadlock will be
broken by idle timers tearing down the SA, but it is possible for a malicious
client to propose Phase 2 negotiation during this time which may allow for the
IPSec SA to be fully established.

This issue only affects ISAKMP profiles matched by certificate maps.
Configurations with certificate maps configured will contain the commands:

      crypto isakmp profile <profilename> 
        match certificate <mapname> 

This vulnerability is documented as Cisco Bug ID CSCeg00277. 

Impact
======

Successful exploitation may result in the affected device allowing an
unauthorized user to complete authentication and access network resources.

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

Each row of the Cisco IOS software table (below) describes a release train and
the platforms or products for which it is intended. If a given release train is
vulnerable, then the earliest possible releases that contain the fix (the
"First Fixed Release") and the anticipated date of availability for each are
listed in the "Rebuild" and "Maintenance" columns. A device running a release
in the given train that is earlier than the release in a specific column (less
than the First Fixed Release) is known to be vulnerable. The release should be
upgraded at least to the indicated release or a later version (greater than or
equal to the First Fixed Release label).

For further information on the terms "Rebuild" and "Maintenance" please consult
the following URL:

http://www.cisco.com/warp/public/620/1.html

When considering software upgrades, please also 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.

+-------------------------------------------------------------+
|    Major Release    |   Availability of Repaired Releases   |
|---------------------+---------------------------------------|
| Affected 12.2-Based | Rebuild            | Maintenance      |
| Release             |                    |                  |
|---------------------+---------------------------------------|
| 12.2B               | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
|                     | 12.2(15)BC1f       |                  |
| 12.2BC              |--------------------+------------------|
|                     | 12.2(15)BC2e       |                  |
|---------------------+---------------------------------------|
| 12.2BX              | Vulnerable, contact TAC               |
|---------------------+---------------------------------------|
| 12.2BY              | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
| 12.2BZ              | Vulnerable, contact TAC               |
|---------------------+---------------------------------------|
| 12.2CX              | Migrate to 12.3(9a)BC                 |
|---------------------+---------------------------------------|
| 12.2CY              | Migrate to 12.2(15)BC1f or 12.2(15)   |
|                     | BC2e                                  |
|---------------------+---------------------------------------|
| 12.2CZ              | 12.2(15)CZ1        |                  |
|---------------------+--------------------+------------------|
| 12.2JK              | 12.2(15)JK2        |                  |
|---------------------+--------------------+------------------|
| 12.2SU              | 12.2(14)SU2        |                  |
|---------------------+---------------------------------------|
| 12.2SX              | Migrate to 12.2(17d)SXB5              |
|---------------------+---------------------------------------|
| 12.2SXA             | Migrate to 12.2(17d)SXB5              |
|---------------------+---------------------------------------|
| 12.2SXB             | 12.2(17d)SXB5                         |
|---------------------+---------------------------------------|
| 12.2SXD             | 12.2(18)SXD1       |                  |
|---------------------+---------------------------------------|
| 12.2SY              | Migrate to 12.2(17d)SXB5              |
|---------------------+---------------------------------------|
| 12.2T               | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2XJ              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2XK              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2XL              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2XM              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2XW              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2XZ              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YA              | 12.2(4)YA8         |                  |
|---------------------+---------------------------------------|
| 12.2YB              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YD              | Migrate to 12.3(8)T5 or later         |
|---------------------+---------------------------------------|
| 12.2YF              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YG              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YH              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YJ              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YL              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2YM              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2YN              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2YP              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YQ              | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
| 12.2YR              | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
| 12.2YT              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2YU              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2YV              | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
| 12.2YW              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2YX              | Migrate to 12.2(14)SU2 or later       |
|---------------------+---------------------------------------|
| 12.2YY              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2ZB              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2ZC              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2ZD              | Migrate to 12.3(14)T                  |
|---------------------+---------------------------------------|
| 12.2ZE              | Migrate to 12.3 or later              |
|---------------------+---------------------------------------|
| 12.2ZF              | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
| 12.2ZG              | Migrate to 12.3(4)T8 or later         |
|---------------------+---------------------------------------|
| 12.2ZH              | 12.2(13)ZH5        |                  |
|---------------------+---------------------------------------|
| 12.2ZJ              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2ZK              | Contact TAC                           |
|---------------------+---------------------------------------|
| 12.2ZL              | 12.2(15)ZL2        |                  |
|                     | available TBD      |                  |
|---------------------+---------------------------------------|
| 12.2ZN              | Migrate to 12.3T or later             |
|---------------------+---------------------------------------|
| 12.2ZP              | Contact TAC                           |
|---------------------+---------------------------------------|
| Affected 12.3-Based | Rebuild            | Maintenance      |
| Release             |                    |                  |
|---------------------+--------------------+------------------|
|                     | 12.3(6e)           |                  |
|                     |--------------------+------------------|
|                     | 12.3(9c)           |                  |
| 12.3                |--------------------+------------------|
|                     | 12.3(10a)          |                  |
|                     |--------------------+------------------|
|                     |                    | 12.3(12)         |
|---------------------+--------------------+------------------|
| 12.3B               | 12.3(5a)B3         |                  |
|---------------------+--------------------+------------------|
| 12.3BC              | 12.3(9a)BC         |                  |
|---------------------+---------------------------------------|
| 12.3BW              | Migrate to 12.3(7)T6 or later         |
|---------------------+---------------------------------------|
|                     | 12.3(2)T9          |                  |
|                     |--------------------+------------------|
|                     | 12.3(4)T8          |                  |
|                     |--------------------+------------------|
|                     | 12.3(7)T7          |                  |
| 12.3T               |--------------------+------------------|
|                     | 12.3(8)T5          |                  |
|                     |--------------------+------------------|
|                     | 12.3(11)T2         |                  |
|                     |--------------------+------------------|
|                     |                    | 12.3(14)T        |
|---------------------+--------------------+------------------|
| 12.3XA              | 12.3(2)XA3         |                  |
|                     | available TBD      |                  |
|---------------------+---------------------------------------|
| 12.3XB              | Migrate to 12.3(8)T5 or later         |
|---------------------+---------------------------------------|
| 12.3XC              | 12.3(2)XC3         |                  |
|                     | available TBD      |                  |
|---------------------+--------------------+------------------|
| 12.3XD              | 12.3(4)XD4         |                  |
|---------------------+--------------------+------------------|
| 12.3XE              | 12.3(2)XE1         |                  |
|---------------------+---------------------------------------|
| 12.3XF              | Migrate to 12.3(11)T2 or later        |
|---------------------+---------------------------------------|
| 12.3XG              | 12.3(4)XG2         |                  |
|---------------------+---------------------------------------|
| 12.3XH              | Migrate to 12.3(11)T2 or later        |
|---------------------+---------------------------------------|
| 12.3XI              | Contact TAC                           |
|---------------------+---------------------------------------|
| 12.3XJ              | Contact TAC                           |
|---------------------+---------------------------------------|
| 12.3XK              | Migrate to 12.3(11)T2 or later        |
|---------------------+---------------------------------------|
| 12.3XL              |                    | 12.3(11)XL       |
|---------------------+---------------------------------------|
| 12.3XM              | Migrate to 12.3(14)T or later         |
|---------------------+---------------------------------------|
| 12.3XN              | Migrate to 12.3(14)T or later         |
|---------------------+---------------------------------------|
| 12.3XQ              | 12.3(4)XQ1         |                  |
|---------------------+--------------------+------------------|
| 12.3XR              | 12.3(7)XR3         |                  |
|---------------------+--------------------+------------------|
| 12.3XS              | 12.3(7)XS2         |                  |
|---------------------+---------------------------------------|
| 12.3XT              | Contact TAC                           |
|---------------------+---------------------------------------|
| 12.3XU              | 12.3(8)XU3         |                  |
|---------------------+---------------------------------------|
| 12.3XW              | Contact TAC                           |
|---------------------+---------------------------------------|
| 12.3XX              | 12.3(8)XX1         |                  |
|---------------------+---------------------------------------|
| 12.3XY              | Migrate to 12.3(14)T                  |
|---------------------+---------------------------------------|
| 12.3YA              | 12.3(8)YA1         |                  |
|---------------------+--------------------+------------------|
| 12.3YC              | 12.3(8)YC1         |                  |
|---------------------+--------------------+------------------|
| 12.3YD              |                    | 12.3(8)YD        |
|---------------------+--------------------+------------------|
| 12.3YF              |                    | 12.3(11)YF       |
|---------------------+--------------------+------------------|
| 12.3YG              |                    | 12.3(8)YG1       |
|---------------------+--------------------+------------------|
| 12.3YH              |                    | 12.3(8)YH        |
|---------------------+--------------------+------------------|
| 12.3YI              |                    | 12.3(8)YI        |
|                     |                    | available TBD    |
|---------------------+--------------------+------------------|
| 12.3YJ              |                    | 12.3(11)YJ       |
|---------------------+--------------------+------------------|
| 12.3YK              |                    | 12.3(11)YK       |
+-------------------------------------------------------------+

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 at 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 at cisco.com" or "security-alert at 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
===========

The effectiveness of any workaround is dependent on specific deployment
scenarios 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.

Using Strong Group Passwords
+---------------------------

Because the preshared group password (also referred to as the group key) must
be known by an attacker, the use of a best practice to deploy strong preshared
group keys may mitigate a brute-force attack against this group key.

The preshared key can be changed by using the following configuration commands:

          Router(config)#crypto isakmp client configuration group <group-name>
          Router(config)#key <key>

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

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

Both vulnerabilities were reported by Cisco customers

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://www.cisco.com/warp/public/707/cisco-sa-20050406-xauth.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-teams at first.org (includes CERT/CC)
  * bugtraq at securityfocus.com
  * 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 1.0   | 2005-April-6   | Initial 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.
- -------------------------------------------------------------------------------

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