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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 https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050406-xauth
Cisco has made free software available to address this vulnerability for affected customers.
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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.
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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.
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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>
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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
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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
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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