Advisory ID: cisco-sa-20050406-xauth

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050406-xauth

Revision 1.1

For Public Release 2005 April 6 16:00  UTC (GMT)


Contents

Summary
Affected Products
Details
Vulnerability Scoring 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

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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050406-xauth

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

Affected Products

This section provides details on 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.

Products Confirmed Not Vulnerable

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. ( registered ) customers only.

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. ( registered ) customers only.

Vulnerability Scoring Details

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.htmland 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 Release

Rebuild

Maintenance

12.2B

Migrate to 12.3(4)T8 or later

12.2BC

12.2(15)BC1f

 

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 Release

Rebuild

Maintenance

12.3

12.3(6e)

 

12.3(9c)

 

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

12.3T

12.3(2)T9

 

12.3(4)T8

 

12.3(7)T7

 

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

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>
      

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 "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.

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 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 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 will be posted on Cisco's worldwide website at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050406-xauth.

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.

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/web/about/security/psirt/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.