Cisco Security Advisory: RADIUS Authentication Bypass

29 Jun 2005

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 IDs:

  * CSCee45312 -- Radius authentication bypass when configured with a none
    fallback method

This advisory will be posted at http://www.cisco.com/warp/public/707/cisco-sa-20050629-aaa.shtml.

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

  * 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.

Impact
======

Successful exploitation of the vulnerability may result in bypassing the RADIUS
authentication.

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

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/warp/public/620/1.html

+---------------------------------------------+
|    Major    |   Availability of Repaired    |
|   Release   |           Releases            |
|-------------+-------------------------------|
| Affected    |               |               |
| 12.2-Based  | Rebuild       | Maintenance   |
| Release     |               |               |
|-------------+-------------------------------|
| 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 |
|-------------+-------------------------------|
|             | 12.2(25)EWA2, |               |
| 12.2EWA     | 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                |
|-------------+-------------------------------|
|             | 12.2(25)SEB2  |               |
|             |---------------+---------------|
| 12.2SE      |               | 12.2(25)SEC,  |
|             |               | available     |
|             |               | 21-July-05    |
|-------------+---------------+---------------|
| 12.2SXD     | 12.2(18)SXD5  |               |
|-------------+---------------+---------------|
|             | 12.2(18)SXE2, |               |
| 12.2SXE     | available     |               |
|             | 18-July-05    |               |
|-------------+-------------------------------|
| 12.2T       | Vulnerable; contact TAC       |
|-------------+-------------------------------|
| 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                 |
|-------------+-------------------------------|
| 12.2XT      | 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  | Rebuild       | Maintenance   |
| Release     |               |               |
|-------------+---------------+---------------|
| 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                     |
|-------------+-------------------------------|
|             | 12.3(7)T11,   |               |
| 12.3T       | 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  | Rebuild       | Maintenance   |
| Release     |               |               |
|-------------+---------------+---------------|
| 12.4        |               | 12.4(1)       |
+---------------------------------------------+

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@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@cisco.com" or "security-alert@cisco.com"
for software upgrades.

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 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 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.

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

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

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-20050629-aaa.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@cisco.com
  * first-teams@first.org (includes CERT/CC)
  * bugtraq@securityfocus.com
  * vulnwatch@vulnwatch.org
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * full-disclosure@lists.grok.org.uk
  * comp.dcom.sys.cisco@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  | 2005-Jun-29 | Initial public    |
| 1.0       |             | 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.h...
. 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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Cisco Security Advisory: RADIUS Authentication Bypass

Cisco Systems Product Security Incident Response Team