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Cisco Security Advisory

Cisco Secure Access Control System TACACS+ Authentication Bypass Vulnerability

Advisory ID: cisco-sa-20121107-acs

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20121107-acs

Revision 1.0

For Public Release 2012 November 7 16:00  UTC (GMT)

Related Resources:

View related Alert

Summary

Cisco Secure Access Control System (ACS) contains a vulnerability that could allow an unauthenticated, remote attacker to bypass TACACS+ based authentication service offered by the affected product. The vulnerability is due to improper validation of the user-supplied password when TACACS+ is the authentication protocol and Cisco Secure ACS is configured with a Lightweight Directory Access Protocol (LDAP) external identity store.

An attacker may exploit this vulnerability by sending a special sequence of characters when prompted for the user password. The attacker would need to know a valid username stored in the LDAP external identity store to exploit this vulnerability, and the exploitation is limited to impersonate only that user. An exploit could allow the attacker to successfully authenticate to any system using TACACS+ in combination with an affected Cisco Secure ACS.

Cisco has released free software updates that address this vulnerability. There are no workarounds for this vulnerability. This advisory is available at the following link:
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20121107-acs

Affected Products

Vulnerable Products

The following Cisco Secure ACS versions are affected by this vulnerability:

Cisco Secure ACS Version Affected
5.0 Yes
5.1
Yes
5.2
Yes
5.3
Yes
5.4
No

The previous list applies to both the hardware appliance and the software-only versions of the product.

The following methods can be used to determine which version of the Cisco Secure ACS is installed:

  • From the Cisco Secure ACS command-line interface (CLI), issue the show version command, as shown in the following example:
    acs51a/admin# show version
    
    Cisco Application Deployment Engine OS Release: 1.2
    ADE-OS Build Version: 1.2.0.152
    ADE-OS System Architecture: i386
    
    Copyright (c) 2005-2009 by Cisco Systems, Inc.
    All rights reserved.
    Hostname: acs51a
    
    
    Version information of installed applications
    ---------------------------------------------
    
     
    Cisco ACS VERSION INFORMATION
    -----------------------------
    Version : 5.1.0.44.6
    Internal Build ID : B.2347
    Patches : 
    5-1-0-44-3
    5-1-0-44-6
    
    acs51a/admin#
  • On the main login page of the Cisco Secure ACS web-based interface, the version information is displayed on the left side of the screen.
  • From the Cisco Secure ACS web-based interface, log in and click the About link at the top right corner of the screen.

Cisco Secure ACS version 5.1 will identify itself as version 5.1.0.44, Cisco Secure ACS version 5.2 will identify itself as version 5.2.0.26 and Cisco Secure ACS version 5.3 will identify itself as version 5.3.0.40. The presence of an additional digit after the version number indicates the highest patch level installed. For example, a version number of 5.1.0.44.3 indicates Cisco Secure ACS version 5.1 with up to patch 3 installed. The absence of any additional digit after the version string indicates a Cisco Secure ACS version with no patches installed. The example above shows a Cisco Secure ACS running version 5.1 Patch 6.

Products Confirmed Not Vulnerable

The following Cisco Secure ACS products are not affected by this vulnerability:
  • Cisco Secure Access Control Server for Windows
  • Cisco Secure Access Control Server Express
  • Cisco Secure Access Control Server View
  • Cisco Secure Access Control Server Solution Engine
No other Cisco products are currently known to be affected by this vulnerability.

Details

Cisco Secure Access Control System (ACS) operates as a centralized RADIUS and TACACS+ server, combining user authentication, user and administrator device access control, and policy control into a centralized identity networking solution.

Cisco Secure ACS provides authentication, authorization, and accounting (AAA) services to network devices and other clients by using the Cisco Secure ACS network resource repositories and identity stores. The identity stores can be internal or external. An internal identity store has user credentials information stored in an internal database. In an external identity store, Cisco Secure ACS will retrieve information from an external database.

Cisco Secure Access Control System (ACS) contains a vulnerability that could allow an unauthenticated, remote attacker to bypass the TACACS+ based authentication service offered by the affected product.

The vulnerability is due to improper validation of the user-supplied password when TACACS+ is as authentication protocol and Cisco Secure ACS is configured with a Lightweight Directory Access Protocol (LDAP) external identity store.
An attacker could exploit this vulnerability by sending a special sequence of characters when prompted for the user password. The attacker would need to know a valid username stored in the LDAP external identity store in order to exploit this vulnerability, and the exploitation is limited to impersonate only that user. An exploit could allow the attacker to successfully authenticate to any system using TACACS+ in combination with an affected Cisco Secure ACS.

Note: Only a Cisco Secure ACS that is configured for TACACS+ authentication and uses LDAP as the external identity store is vulnerable.
A Cisco Secure ACS used for authentication service in combination with other supported protocols, such as RADIUS, or TACACS+ used in combination with an internal identity store or other external stores (for example, RADIUS Identity Server, Active Directory, and RSA SecurID Token Server), is not vulnerable.

Successful exploitation of this vulnerability could allow the attacker to bypass the authentication of any system that uses TACACS+ and relies on the authentication service provided by an affected Cisco Secure ACS. However, the attacker will not be able to gain unauthorized access to the management interface of the Cisco Secure ACS.


This vulnerability is documented in Cisco bug ID CSCuc65634 (registered customers only) and has been assigned the CVE identifier CVE-2012-5424.

Vulnerability Scoring Details

Cisco has scored the vulnerability in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this security advisory is in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps organizations determine the urgency and priority of a response.

Cisco has provided a base and temporal score. Customers can also compute environmental scores that help determine the impact of the vulnerability in their own networks.

Cisco has provided additional information regarding CVSS at the following link:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

Cisco has also provided a CVSS calculator to compute the environmental impact for individual networks at the following link:

http://intellishield.cisco.com/security/alertmanager/cvss



Cisco Secure ACS TACACS+ Authentication Bypass Vulnerability - CSCuc65634

Calculate the environmental score of CSCuc65634

CVSS Base Score - 5.0

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

Partial

None

None

CVSS Temporal Score - 4.1

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed


Impact

Successful exploitation of this vulnerability could allow a remote attacker impersonate a user and bypass the authentication to any system that uses TACACS+ and relies on the authentication service provided by an affected Cisco Secure ACS.

Software Versions and Fixes

The following table provides software upgrade information to mitigate the vulnerability described in this security advisory:

Cisco Secure ACS Version
Fixed Release
5.0 Migrate to 5.2 Patch 11
5.1
Migrate to 5.2 Patch 11
5.2
5.2 Patch 11
5.3
5.3 Patch 7

When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.


Workarounds

There is no workaround for this vulnerability. If possible, disable anonymous binding on the LDAP external identity store or use Active Directory external identity store to help prevent exploitation of this vulnerability.

Obtaining Fixed Software

Cisco has released free software updates that address the vulnerability described in this advisory. Prior to deploying software, customers are advised to consult their maintenance providers or check the software for feature set compatibility and known issues that are specific to their environments.

Customers may only install and expect support for feature sets they have purchased. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, upgrades should be obtained through the Software Navigator on Cisco.com at http://www.cisco.com/cisco/software/navigator.html.

Customers Using Third-Party Support Organizations

Customers with Cisco products that are provided or maintained through prior or existing agreements with third-party support organizations, such as Cisco Partners, authorized resellers, or service providers, should contact that organization for assistance with the appropriate course of action.

The effectiveness of any workaround or fix depends on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Because of the variety of affected products and releases, customers should consult their service providers or support organizations to ensure that any applied workaround or fix is the most appropriate in the intended network before it is deployed.

Customers Without Service Contracts

Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC):

  • +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

Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade. Customers without service contracts should request free upgrades through the TAC.

Refer to Cisco Worldwide Contacts at http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, instructions, and e-mail addresses for support in various languages.

Exploitation and Public Announcements

The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

This vulnerability was discovered during the resolution of a support case.

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 is posted on Cisco Security at the following link:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20121107-acs

Additionally, a text version of this advisory is clear signed with the Cisco PSIRT PGP key and circulated among the following e-mail addresses:

  • cust-security-announce@cisco.com
  • first-bulletins@lists.first.org
  • bugtraq@securityfocus.com
  • vulnwatch@vulnwatch.org
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • full-disclosure@lists.grok.org.uk

Future updates of this advisory, if any, will reside on Cisco.com but may not be announced on mailing lists. Users can monitor this advisory's URL for any updates.


Revision History

Revision 1.0 2012-November-07 Initial public release.

Cisco Security Procedures

Complete information about reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco is available on Cisco.com at http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html. This web page includes instructions for press inquiries regarding Cisco Security Advisories. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt.


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