Cisco Secure Access Control System TACACS+ Authentication Bypass Vulnerability

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 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.

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.

Fixed Software

• 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.

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.

URL

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

Revision History

• Revision 1.0

  2012-November-07

  Initial public release.

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