Summary

• Remote Authentication Dial In User Service (RADIUS) authentication on a device that is running certain versions of Cisco Internetworking Operating System (IOS) and configured with a fallback method to none can be bypassed.

  Systems that are configured for other authentication methods or that are not configured with a fallback method to none are not affected.

  Only the systems that are running certain versions of Cisco IOS are affected. Not all configurations using RADIUS and none are vulnerable to this issue. Some configurations using RADIUS, none and an additional method are not affected.

  Cisco has made free software available to address this vulnerability. There are workarounds available to mitigate the effects of the vulnerability.

  The vulnerabilities are documented as the following Cisco Bug ID:

  CSCee45312 -- Radius authentication bypass when configured with a none fallback method.
  
  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050629-aaa.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  Systems that are running the following release trains of Cisco IOS are affected if configured with RADIUS authentication and a none fallback method.

  • 12.2T based trains
  • 12.3 based trains
  • 12.3T based trains
  • 12.4 based trains

  A system configured for RADIUS authentication and none fallback method will have a command line in show running-configuration output which is similar to the following .

  aaa authentication login xxxxxx group radius none (This is an affected configuration)

  aaa authentication ppp xxxxxx group radius none (This is an affected configuration)

  A system that is configured for RADIUS authentication with local and none fallback methods is also affected. An example to this configuration may look like similar to the following.

  aaa authentication login xxxxxx group radius local none (This is an affected configuration)

  aaa authentication ppp xxxxxx group radius local none (This is an affected configuration)

  A system is only vulnerable if none method is used as a fallback to RADIUS without any other method in between, or if only local method is used in between. Systems that are configured for RADIUS authentication with a fallback method other than local prior to none method are not affected.

  Refer to the Details section for more information about affected and unaffected configurations.

  Products Confirmed Not Vulnerable

  These products are not vulnerable:

  • Products that are not running Cisco IOS are not affected.
  • Products running Cisco IOS versions 12.1 and earlier (including 12.0S) and 12.2 mainline are not affected.
  • Products that are running Cisco IOS are not affected unless they are configured for RADIUS authentication with a fallback method to none.

  No other Cisco products are currently known to be affected by this vulnerability.

Details

• Authentication, Authorization, and Accounting (AAA) network security services provide the primary framework through which access control is set up on a device.

  AAA authentication services are used to control access to different services on a system. Multiple AAA authentication services can be configured on a system to fall back to a backup authentication method in case the primary authentication method is unavailable.

  AAA authentication can be used for different purposes (controlling access to the routers, authenticating remote subscribers etc.).

  Refer to the following URL for more information on AAA: http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fsecur_c/fsaaa/index.htm

  Remote Authentication Dial In User Service (RADIUS) is defined in RFC2865 and describes a protocol for carrying authentication, authorization, and configuration information.

  There is a vulnerability in AAA RADIUS authentication if none is used as a fallback method. Sending a sufficiently long username will bypass the RADIUS authentication and succeed.

  Following algorithm can be used to determine whether a configuration is vulnerable:

  1. Are you using an affected version of IOS?

  No: You are not vulnerable.

  Yes: Go to step 2.

  2. Is AAA RADIUS Authentication used?

  No: You are not vulnerable.

  Yes: Go to step 3.

  3. Is none used as an alternative to RADIUS?

  No: You are not vulnerable.

  Yes: Go to step 4.

  4. Is there any other method between RADIUS and none?

  No: You are vulnerable.

  Yes: Go to step 5.

  5. Is the other authentication method local?

  No: You are not vulnerable.

  Yes: Go to step 4.

  Based on the algorithm above sample affected and unaffected configurations are given below.

  aaa authentication login xxxxxx group radius none (This is an affected configuration)

  aaa authentication login xxxxxx group radius local none (This is an affected configuration)

  aaa authentication login xxxxxx group radius group tacacs+ none (This is an unaffected configuration)

  aaa authentication login xxxxxx group radius enable none (This is an unaffected configuration)

  aaa authentication login xxxxxx group radius line none (This is an unaffected configuration)

  aaa authentication login xxxxxx group radius local line none (This is an unaffected configuration)

  Removing the none fallback method or putting at least one additional method other than local between RADIUS and none will mitigate this vulnerability.

Workarounds

• The effectiveness of any workaround 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 is the most appropriate for use in the intended network before it is deployed.

  • Removing none as a fallback to RADIUS or putting an additional method other than local between RADIUS and none will mitigate this vulnerability.
    For example, an affected system which has a configuration similar to the following aaa authentication login xxxxxx group radius none can be changed to one of the followingaaa authentication login xxxxxx group radius aaa authentication login xxxxxx group radius enable aaa authentication login xxxxxx group radius enable none aaa authentication login xxxxxx group radius line none as a workaround.
    

    Warning: Removing none as a fallback method may create problems if the RADIUS server becomes unavailable. With a none fallback in place, all authentication requests will succeed when the RADIUS server is unavailable. Removing none fallback method or replacing it with enable or another mechanism may result in authentication failure if RADIUS server becomes unavailable.

Fixed Software

• 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.

  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/web/about/security/intelligence/ios-ref.html

  Major Release	Availability of Repaired Releases
  Affected 12.2-Based Release	Rebuild	Maintenance
  12.2B	Vulnerable; migrate to 12.3(11)T or later
  12.2BC	Vulnerable; migrate to 12.3(13)BC, available TBD
  12.2BW	Vulnerable; migrate to 12.3(10) or later
  12.2BX	Vulnerable; migrate to 12.3(7)XI6, available TBD
  12.2BY	Vulnerable; migrate to 12.3(11)T or later
  12.2BZ	Vulnerable; migrate to 12.3(7)XI6, available TBD
  12.2CX	Vulnerable; migrate to 12.3(13)BC, available TBD
  12.2CY	Vulnerable; migrate to 12.3(13)BC, available TBD
  12.2CZ	Vulnerable; contact TAC
  12.2EW	Vulnerable; migrate to 12.2(25)EWA2, available 7-July-05
  12.2EWA	12.2(25)EWA2, available 7-July-05
  12.2EY	12.2(25)EY2
  12.2EZ	Vulnerable; migrate to 12.2(25)SEC, available 21-July-05
  12.2JA	Vulnerable; migrate to 12.3(7)JA, available on 08-Aug-05
  12.2JK	Vulnerable; contact TAC
  12.2MB	Vulnerable; migrate to 12.2SW
  12.2MC	Vulnerable; migrate to 12.3(11)T or later
  12.2MX	Vulnerable; migrate to 12.3(11)T or later
  12.2SE	12.2(25)SEB2
  		12.2(25)SEC, available 21-July-05
  12.2SXD	12.2(18)SXD5
  12.2SXE	12.2(18)SXE2, available 18-July-05
  12.2T	Vulnerable; migrate to 12.3 train
  12.2XB	Vulnerable; migrate to 12.3(10) or later
  12.2XC	Vulnerable; migrate to 12.3(11)T or later
  12.2XD	Vulnerable; migrate to 12.3(10) or later
  12.2XE	Vulnerable; migrate to 12.3(10) or later
  12.2XF	Vulnerable; migrate to 12.3(13)BC, available TBD
  12.2XG	Vulnerable; migrate to 12.3(10) or later
  12.2XH	Vulnerable; migrate to 12.3(10) or later
  12.2XI	Vulnerable; migrate to 12.3(10) or later
  12.2XJ	Vulnerable; migrate to 12.3(10) or later
  12.2XK	Vulnerable; migrate to 12.3(10) or later
  12.2XL	Vulnerable; migrate to 12.3(10) or later
  12.2XM	Vulnerable; migrate to 12.3(10) or later
  12.2XQ	Vulnerable; migrate to 12.3(10) or later
  12.2XR/12.2(2)XR/12.2(4)XR	Vulnerable; migrate to 12.3(10) or later
  12.2(15)XR	Vulnerable; migrate to 12.3(7)JA, available on 08-Aug-05
  12.2XT	Vulnerable; migrate to 12.3(10) or later
  12.2XW	Vulnerable; migrate to 12.3(10) or later
  12.2YA	Vulnerable; contact TAC
  12.2YB	Vulnerable; migrate to 12.3(10) or later
  12.2YC	Vulnerable; migrate to 12.3(10) or later
  12.2YD	Vulnerable; migrate to 12.3(11)T or later
  12.2YF	Vulnerable; migrate to 12.3(10) or later
  12.2YG	Vulnerable; migrate to 12.3(10) or later
  12.2YH	Vulnerable; migrate to 12.3(10) or later
  12.2YJ	Vulnerable; migrate to 12.3(10) or later
  12.2YL	Vulnerable; migrate to 12.3(11)T or later
  12.2YM	Vulnerable; migrate to 12.3(11)T or later
  12.2YN	Vulnerable; migrate to 12.3(11)T or later
  12.2YP	Vulnerable; migrate to 12.3(10) or later
  12.2YQ	Vulnerable; migrate to 12.3(11)T or later
  12.2YR	Vulnerable; migrate to 12.3(11)T or later
  12.2YT	Vulnerable; migrate to 12.3(10) or later
  12.2YU	Vulnerable; migrate to 12.3(11)T or later
  12.2YV	Vulnerable; migrate to 12.3(11)T or later
  12.2YW	Vulnerable; migrate to 12.3(11)T or later
  12.2YY	Vulnerable; migrate to 12.3(11)T or later
  12.2ZB	Vulnerable; migrate to 12.3(11)T or later
  12.2ZC	Vulnerable; migrate to 12.3(11)T or later
  12.2ZD	Vulnerable; migrate to 12.3(11)T or later
  12.2ZE	Vulnerable; migrate to 12.3(10) or later
  12.2ZF	Vulnerable; migrate to 12.3(11)T or later
  12.2ZG	Vulnerable; migrate to 12.3(11)T or later
  12.2ZH	Vulnerable; contact TAC
  12.2ZJ	Vulnerable; migrate to 12.3(11)T or later
  12.2ZL	Vulnerable; contact TAC
  12.2ZN	Vulnerable; migrate to 12.3(11)T or later
  12.2ZO	Vulnerable; migrate to 12.3(10) or later
  12.2ZP	Vulnerable; migrate to 12.3(11)T or later
  Affected 12.3-Based Release	Rebuild	Maintenance
  12.3		12.3(10)
  12.3B	Vulnerable; migrate to 12.3(11)T or later
  12.3BC		12.3(13)BC, available TBD
  12.3BW	Vulnerable; migrate to 12.3(11)T or later
  12.3JA	12.3(7)JA, available on 08-Aug-05
  12.3T	12.3(7)T11, available TBD	12.3(11)
  	12.3(8)T4
  12.3XA	Vulnerable; migrate to 12.3(11)T or later
  12.3XB	Vulnerable; migrate to 12.3(11)T or later
  12.3XC	Vulnerable; contact TAC
  12.3XD	Vulnerable; migrate to 12.3(11)T or later
  12.3XE	Vulnerable; migrate to 12.3(11)T or later
  12.3XF	Vulnerable; migrate to 12.3(11)T or later
  12.3XG	Vulnerable; migrate to 12.3(11)T or later
  12.3XH	Vulnerable; migrate to 12.3(11)T or later
  12.3XI	12.3(7)XI6, available TBD
  12.3XJ	Vulnerable; migrate to 12.3(11)T or later
  12.3XK	Vulnerable; migrate to 12.3(14)T or later
  12.3XL		12.3(11)XL
  12.3XM	Vulnerable; migrate to 12.3(14)T or later
  12.3XN	Vulnerable; migrate to 12.3(14)T or later
  12.3XQ	Vulnerable; migrate to 12.3(14)T or later
  12.3XR	Vulnerable; contact TAC
  12.3XS	Vulnerable; migrate to 12.3(14)T or later
  12.3XT	Vulnerable; contact TAC
  12.3XU	Vulnerable; contact TAC
  12.3XW	Vulnerable; migrate to 12.3(11)T or later
  12.3XX	Vulnerable; migrate to 12.3(14)T or later
  12.3XY	12.3(8)XY5
  12.3YA	Vulnerable; migrate to 12.3(14)T or later
  12.3YB	Vulnerable; contact TAC
  12.3YD		12.3(8)YD
  12.3YF		12.3(11)YF
  12.3YG		12.3(8)YG
  12.3YH		12.3(8)YH
  12.3YI		12.3(8)YI
  12.3YJ		12.3(11)YJ
  12.3YK		12.3(11)YK
  12.3YL		12.3(11)YL
  12.3YN		12.3(11)YN
  12.3YR		12.3(11)YR
  12.3YS		12.3(11)YS
  12.3YQ		12.3(14)YQ
  Affected 12.4-Based Release	Rebuild	Maintenance
  12.4		12.4(1)

Exploitation and Public Announcements

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

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050629-aaa

Revision History

• Revision 1.1	2005-July-1	Added 12.2XR/12.2(2)XR/12.2(4)XR and 12.2(15)XR to Software Version and Fixes Table. Updated 12.2T row.
  Revision 1.0	2005-Jun-29	Initial public release.

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