Advisory ID: cisco-sa-20121107-acs
For Public Release 2012 November 7 16:00 UTC (GMT)
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:
The following Cisco Secure ACS versions are affected by this
|Cisco Secure ACS Version
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
acs51a/admin# show version
Cisco Application Deployment Engine OS Release: 1.2
ADE-OS Build Version: 188.8.131.52
ADE-OS System Architecture: i386
Copyright (c) 2005-2009 by Cisco Systems, Inc.
All rights reserved.
Version information of installed applications
Cisco ACS VERSION INFORMATION
Version : 184.108.40.206.6
Internal Build ID : B.2347
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
220.127.116.11, Cisco Secure ACS version 5.2 will identify
itself as version 18.104.22.168 and Cisco Secure ACS version 5.3 will identify
itself as version 22.214.171.124. The presence of an additional
digit after the version number indicates the highest patch level installed. For
example, a version number of 126.96.36.199.3 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.
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.
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
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
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
and has been assigned
the CVE identifier CVE-2012-5424.
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:
Cisco has also provided a CVSS calculator to compute the environmental impact for individual networks at the following link:
Cisco Secure ACS TACACS+ Authentication Bypass Vulnerability - CSCuc65634
Calculate the environmental score of CSCuc65634
CVSS Base Score - 5.0
CVSS Temporal Score - 4.1
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.
The following table provides software upgrade information to mitigate the vulnerability described in this security
|Cisco Secure ACS Version
||Migrate to 5.2 Patch 11
|Migrate to 5.2 Patch 11
|5.2 Patch 11
|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
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.
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 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 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: firstname.lastname@example.org
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.
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.
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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.
This advisory is posted on Cisco Security at the following link:
Additionally, a text version of this advisory is clear signed with the Cisco PSIRT PGP key and circulated among the following e-mail addresses:
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.
||Initial public release.