Products & Services

Contents

Summary
Affected Products
Details
Vulnerability Scoring Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of this Notice: Final
Distribution
Revision History
Cisco Security Procedures

Vulnerable Products

Products Confirmed Not Vulnerable

The Cisco AnyConnect Secure Mobility Client is the Cisco next-generation VPN client, which provides remote users with secure IPsec (IKEv2) or SSL Virtual Private Network (VPN) connections to Cisco 5500 Series Adaptive Security Appliances (ASA) and devices that are running Cisco IOS Software.

The Cisco AnyConnect Secure Mobility Client is affected by the following vulnerabilities:

Arbitrary Program Execution Vulnerability

The Cisco AnyConnect Secure Mobility Client can be deployed to remote users from the VPN headend, or it can be installed before the endpoint connects to the VPN headend, a process known as pre-deployment. When the Cisco AnyConnect Secure Mobility Client is pre-deployed, the client software is installed and run like any other application.

When the Cisco AnyConnect Secure Mobility Client is deployed from the VPN headend, an SSL connection is initiated to the VPN headend using a web browser. After the user logs in, the browser displays a portal window and when the user clicks the "Start AnyConnect" link, the process of downloading the Cisco AnyConnect Secure Mobility Client begins. This action causes the browser to first download a "helper" application that aids in downloading and executing the actual Cisco AnyConnect Secure Mobility Client. The helper application is a Java applet on the Linux and MacOS X platforms, and either a Java applet on the Windows platform or an ActiveX control if the browser is capable of utilizing ActiveX controls. The downloaded helper application is executed in the context of the originating site in the user's web browser. The helper application then downloads the Cisco AnyConnect Secure Mobility Client from the VPN headend and executes it.

The helper application fails to properly validate the authenticity of the downloaded Cisco AnyConnect Secure Mobility Client executable when the client is deployed from the VPN headend. An attacker could create a malicious web page that looks like the normal VPN web login page and entice a user, through social engineering or exploitation of other vulnerabilities, to visit it. This would allow the attacker to supply an arbitrary executable that the helper application would download and execute on the machine of the affected user. This arbitrary executable would be executed with the same operating system privileges under which the web browser was run.

Fixed versions of the Cisco AnyConnect Secure Mobility Client use code signing to validate the authenticity of components downloaded from the VPN headend.

This vulnerability is documented in Cisco Bug ID CSCsy00904 (registered customers only) for Cisco AnyConnect Secure Mobility Client on the Microsoft Windows platform, and in Cisco Bug ID CSCsy05934 (registered customers only) for Cisco AnyConnect Secure Mobility Client on the Linux and Apple MacOS X platforms. Common Vulnerabilities and Exposures (CVE) IDs CVE-2011-2039 (for CSCsy00904) and CVE-2011-2040 (for CSCsy05934) have been assigned for these vulnerabilities.

Additional Considerations for the Arbitrary Program Execution Vulnerability

Note that while new versions of the ActiveX control and Java applet that are shipped with the Cisco AnyConnect Secure Mobility Client make use of code signing to validate the authenticity of components downloaded from the VPN headend, there is still the issue of old versions that do not validate downloaded components. An attacker may engineer a web page to supply an affected version of the ActiveX control or Java applet and still accomplish arbitrary program execution because of the lack of authenticity validation.

Mitigating the risk of old versions of the ActiveX control can be accomplished in the following ways:

• Load fixed Cisco AnyConnect Secure Mobility Client versions on the VPN headend and establish a VPN connection (via web browser or standalone client). This action will cause the new version of the Cisco AnyConnect Secure Mobility Client, including a new version of the ActiveX control to install. When this occurs, an old version of the ActiveX control will not be instantiated if one is presented for download.
• Pre-deploy a fixed version of Cisco AnyConnect Secure Mobility Client through enterprise software upgrade infrastructure. This action accomplishes the same result as the previous recommendation -- it deploys new, fixed versions of the ActiveX control so that old, vulnerable versions of the control are not instantiated if one is presented for download.
• If deploying the client from the VPN headend is not needed, then the kill bit for the Cisco AnyConnect Secure Mobility Client ActiveX control can be set locally. This action prevents the ActiveX control from being instantiated under any scenario. Instructions for setting the kill bit are beyond the scope of this document; refer to the Microsoft Support article "How to stop an ActiveX control from running in Internet Explorer" at http://support.microsoft.com/kb/240797 and the Microsoft Security Vulnerability Research & Defense's "Kill-Bit FAQ" blog posts referenced in the Microsoft Support article for more information.
  The CLSID (Class Identifier) for the ActiveX control used by the Cisco AnyConnect Secure Mobility Client is 55963676-2F5E-4BAF-AC28-CF26AA587566, and the ProgID (Program Identifier) is "Cisco.AnyConnect.VPNWeb.1". Note that this CLSID did not change with new versions of the ActiveX control that implement code signing validation.

Mitigating the risk of old versions of the Java applet can be accomplished by blacklisting old, vulnerable versions using the Jar blacklist feature introduced with Java SE 6 Update 14. For information on the Jar blacklist feature refer to the Java SE 6 Update 14 release notes, available at http://www.oracle.com/technetwork/java/javase/6u14-137039.html.

The jar files to be blacklisted are identified by the following SHA-1 message digests:

# 2.3.0254, 2.3.1003, 2.3.2016, 2.4.0202, 2.4.1012,
# 2.5.0217, 2.5.1025, 2.5.2001, 2.5.2006, 2.5.2010,
# 2.5.2011, 2.5.2014, 2.5.2017, 2.5.2018, 2.5.2019
SHA1-Digest-Manifest : x17xGEFzBRXY2pLtXiIbp8J7U9M=

# 2.2.0133, 2.2.0136, 2.2.0140
SHA1-Digest-Manifest : ya6YNTzMCFYUO4lwhmz9OWhhIz8=

# 2.0.0343, 2.1.0148
SHA1-Digest-Manifest : YwuPyF/KMcxcQhgxilzNybFM2+8=

Local Privilege Escalation Vulnerability

Unprivileged users can elevate their privileges to those of the LocalSystem account by enabling the Start Before Logon (SBL) feature and interacting with the Cisco AnyConnect Secure Mobility Client graphical user interface in the Windows logon screen.

To prevent this issue, fixed versions of the Cisco AnyConnect Secure Mobility Client limit the amount of interaction that is possible in the client's graphical user interface when it is displayed on the Windows logon screen.

This vulnerability affects only the Cisco AnyConnect Secure Mobility Client for Windows because the SBL feature is not supported by the Linux and MacOS X clients.

This vulnerability is documented in Cisco Bug ID CSCta40556 (registered customers only) and has been assigned CVE ID CVE-2011-2041.

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

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss .

Arbitrary Program Execution Vulnerability

Exploitation of this vulnerability may allow an attacker to execute arbitrary programs on the computer of a Cisco AnyConnect Secure Mobility Client user with the privileges of the user who is establishing the VPN connection.

Local Privilege Escalation Vulnerability

Successful exploitation of this vulnerability may allow users with physical access to a computer that is running the Cisco AnyConnect Secure Mobility Client to elevate their privileges and gain full control of the system.

When considering software upgrades, also consult http://www.cisco.com/go/psirt 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) or your contracted maintenance provider for assistance.

Recommended Releases

The following table lists all recommended releases. These recommended releases contain the fixes for all vulnerabilities in this advisory. Cisco recommends upgrading to a release that is equal to or later than these recommended releases.

Software Download

The Cisco AnyConnect Secure Mobility Client can be downloaded from the Software Center on Cisco.com by visiting http://www.cisco.com/cisco/software/navigator.html and navigating to Products > Security > Virtual Private Networks (VPN) > Cisco VPN Clients > Cisco AnyConnect Secure Mobility Client.

There are no workarounds for the vulnerabilities that are described in this advisory.

Customers with Service Contracts

Customers using Third Party Support Organizations

Customers without Service Contracts

The Cisco PSIRT is not aware of malicious use of the vulnerabilities described in this advisory. Public exploit code has been released in the form of a Metasploit Framework module that is designed to exploit the Arbitrary Program Execution Vulnerability.

The Arbitrary Program Execution Vulnerability was discovered by Elazar Broad and reported to Cisco by iDefense. Cisco would like to thank iDefense for reporting this vulnerability and for working with us towards a coordinated disclosure of the vulnerability.

The Local Privilege Escalation Vulnerability was reported to Cisco by a customer.

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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's worldwide website at:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110601-ac

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
• 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.

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.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.