Public Vulnerability Reports

Cisco AnyConnect VPN Client Arbitrary Program Execution Vulnerability

01.06.11

BACKGROUND

Cisco's AnyConnect VPN solution provides remote access to customers via the Web browser. This is accomplished through the use of an ActiveX control. The control itself is provided by the server upon connecting. Cisco states that AnyConnect VPN supports all Adaptive Security Appliance (ASA) models. For more information, visit the following URL.

http://www.cisco.com/en/US/docs/security/vpn_client/anyconnect/anyconnect23/release/notes/anyconnect23rn.html

DESCRIPTION

Remote exploitation of a design error within Cisco Systems Inc's AnyConnect VPN client allows attackers to execute arbitrary code with the privileges of a user running Internet Explorer.

The vulnerability exists within the ActiveX control with the following identifiers:

 CLSID: 55963676-2F5E-4BAF-AC28-CF26AA587566 ProgId: Cisco.AnyConnect.VPNWeb.1 File: %WINDIR%system32vpnweb.ocx 

This ActiveX control is not marked as safe for initialization or scripting within the registry, but it does implement IObjectSafety. When queried, this control's IObjectSafety interface reports that it is safe for both scripting and initialization.

This ActiveX control is used to install the VPN client. Once it is instantiated, it will attempt to download two files from the site supported in the "url" property. As such, an attacker can craft a page such that the control will download an executable of their choosing.

One of the files will be executed upon the successful completion of the download. This allows an attacker to execute an arbitrary executable on the user's system.

ANALYSIS

Exploitation allows attackers to execute arbitrary code in the context of the currently logged-on user. To exploit this vulnerability, a targeted user must load a malicious Web page created by an attacker. An attacker typically accomplishes this via social engineering or injecting content into compromised, trusted sites.

Additionally, in a default configuration, a targeted user must have this control already installed or must accept several warning prompts at the time that the attack is taking place. This control is not on the white list included with Internet Explorer 7.0. More information can be found at the following URL.

http://msdn.microsoft.com/en-us/library/bb250471.aspx

DETECTION

Cisco AnyConnect VPN client versions prior to 2.3.185 for Windows, 2.5.3041 and 3.0.629 for Linux and Apple Mac OS X are vulnerable.

WORKAROUND

Setting the kill-bit for this control will prevent it from being loaded within Internet Explorer. However, doing so will prevent legitimate use of the control.

VENDOR RESPONSE

Cisco has released an advisory which describes methods of updating the AnyConnect Secure Mobility Client. For more information, consult their advisory at the following URL.

http://www.cisco.com/en/US/products/products_security_advisory09186a0080b80123.shtml

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2011-2039 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

DISCLOSURE TIMELINE

02/24/2009 Initial Vendor Notification
02/25/2009 Initial Vendor Reply
06/01/2011 Coordinated Public Disclosure

CREDIT

This vulnerability was reported to iDefense by Elazar Broad.

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LEGAL NOTICES

Copyright © 2011 Verisign, Inc.

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