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Cisco ASA 5500 Series Adaptive Security Appliance Clientless VPN ActiveX Control Remote Code Execution Vulnerability

Advisory ID: cisco-sa-20120314-asaclient

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120314-asaclient

Revision 1.0

For Public Release 2012 March 14 16:00  UTC (GMT)


Summary

The Cisco Clientless VPN solution as deployed by Cisco ASA 5500 Series Adaptive Security Appliances (Cisco ASA) uses an ActiveX control on client systems to perform port forwarding operations. Microsoft Windows-based systems that are running Internet Explorer or another browser that supports Microsoft ActiveX technology may be affected if the system has ever connected to a device that is running the Cisco Clientless VPN solution. A remote, unauthenticated attacker who could convince a user to connect to a malicious web page could exploit this issue to execute arbitrary code on the affected machine with the privileges of the web browser.

The affected ActiveX control is distributed to endpoint systems by Cisco ASA.  However, the impact of successful exploitation of this vulnerability is to the endpoint system only and does not compromise Cisco ASA devices.

Cisco has released free software updates that address this vulnerability.

Workarounds that mitigate this vulnerability are available.

This advisory is available at the following link:
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120314-asaclient

Affected Products

Cisco Clientless VPN is a feature available on Cisco ASA 5500 Series Adaptive Security Appliances.

Vulnerable Products

Cisco ASA 5500 Series Adaptive Security Appliances that are running one of the following versions contain the affected ActiveX component:

Affected Version
Affected Release
 Cisco Adaptive Security Appliance Software 7.x
7.1
7.2
 Cisco Adaptive Security Appliance Software 8.x
8.0
8.1
8.2
8.3
8.4
8.6

Note: Cisco ASA Software version 7.0 and 7.1 have reached end of software maintenance.  Customers who are using Cisco ASA Software version 7.0 or 7.1 should contact their Cisco support team for assistance in upgrading to a supported version of Cisco ASA Software.

Note: The affected implementation of the Cisco Clientless VPN solution was introduced with the release of Cisco ASA Software version 7.1.  This issue does not affect devices running Cisco PIX Software.

Administrators may determine whether the Cisco Clientless VPN solution is enabled on their devices by issuing the show running-config webvpn command.  The following example shows the response when the Cisco Clientless VPN solution is enabled:
ciscoasa# show running-config webvpn
webvpn
 enable outside
End user systems running Microsoft Windows may be affected if they have used the Cisco Clientless VPN feature on an affected device from a browser that supports ActiveX technology.  Devices that contain the cscopf.ocx ActiveX control registered with a class ID (CLSID) of {B8E73359-3422-4384-8D27-4EA1B4C01232} are affected.  The affected controls are marked both Safe for Scripting (SFS) and Safe for Initialization (SFI), which may present additional attack vectors when a system has registered and cached the affected control.

Products Confirmed Not Vulnerable

  • Cisco Firewall Service Modules are not affected by this vulnerability
  • Cisco Adaptive Security Appliance Services Modules are not affected by this vulnerability
  • Cisco IOS Software-based devices that use the Cisco Clientless VPN solution (WebVPN) are not affected by this vulnerability

No other Cisco products are currently known to be affected by this vulnerability.

Details

Cisco Adaptive Security Appliances (ASA) contain a feature known as the Cisco Clientless VPN solution.  The Cisco Clientless VPN feature allows users to use a web browser to create an SSL VPN tunnel from an endpoint device to a Cisco ASA device.  When connected, the ASA pushes several ActiveX and Java applications to the endpoint device to allow a number of features to operate.

When a browser that supports Microsoft ActiveX technology is used to create the Clientless VPN tunnel, the Cisco Port Forwarder ActiveX control may be sent to the endpoint system on which the browser is running.  This control contains an exploitable buffer overflow vulnerability that could allow an unauthenticated, remote attacker who can convince a user to visit a malicious website to execute attacker-controlled arbitrary code on the endpoint device.  The attacker-supplied code would be executed with the privileges of the user who invoked the browser used to visit the attacker-controlled website.  If the user has administrative privileges, a complete compromise may occur.

Upgrading a Cisco ASA device to a version of software that contains the fixed control will not remediate the issue on endpoint systems that have downloaded the affected control.  Affected endpoint systems will need to disable the control via one of the methods suggested in the "Workarounds" section of this document.  Endpoint systems may also connect to a Cisco ASA device that is running a version of software that contains the fixed control via the Cisco Clientless VPN solution to update the control to an unaffected version.

When loaded on an endpoint system, the affected control has a binary name of cscopf.ocx and is registered on a system with a CLSID of {B8E73359-3422-4384-8D27-4EA1B4C01232}.  Fixed versions of the cscopf.ocx control are registered with CLSID {C861B75F-EE32-4aa4-B610-281AF26A8D1C}.

Microsoft has set the global kill bit for the affected control at the request of Cisco.  The Microsoft update that included this kill-bit is detailed in Microsoft Knowledge Base article 2695962, and was released May 8th, 2012.  The Microsoft Security Advisory may be found at the following link: Microsoft Security Advisory (2695962) Update Rollup for ActiveX Kill Bits

Once this update has been applied, either via Auto-Update or manually, the affected control will stop operating on affected endpoints that have applied the update.

This advisory addresses the vulnerability in the Cisco Port Forwarder ActiveX control provided by Cisco ASA when the Cisco Clientless VPN feature is used.  This issue is documented in Cisco bug ID CSCtr00165 (registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2012-0358.

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



CSCtr00165, Cisco Clientless VPN Port Forwarder ActiveX Control Remote Code Execution Vulnerability

Calculate the environmental score of CSCtr00165

CVSS Base Score - 9.3

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Medium

None

Complete

Complete

Complete

CVSS Temporal Score - 7.7

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

Impact

Successful exploitation of the vulnerability may allow a remote, unauthenticated attacker to execute arbitrary code on the affected end-user system with the privileges of the user who invoked the web browser.  If the user has administrative privileges, code execution may result in a complete compromise of the affected system.

Software Versions and Fixes

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.

Affected Version
 First Fixed Release
 Recommended Release
Cisco ASA 7.0
Not Vulnerable
Migrate to 7.2 or later
Cisco ASA 7.1
Vulnerable
Vulnerable; Migrate to 7.2 or later
Cisco ASA 7.2
 7.2(5.6) 7.2(5.7)
Cisco ASA 8.0
8.0(5.26) Migrate to 8.2(5.26) or later
Cisco ASA 8.1
 8.1(2.53) Migrate to 8.2(5.26) or later
Cisco ASA 8.2
 8.2(5.18) 8.2(5.26)
Cisco ASA 8.3
 8.3(2.28) Migrate to 8.4(3.8) or later
Cisco ASA 8.4
8.4(2.16)
8.4(3.8)
Cisco ASA 8.5
Not Vulnerable
8.5(1.7)
Cisco ASA 8.6
8.6(1.1)
8.6(1.1)

Note: Cisco ASA Software version 7.0 and 7.1 have reached end of software maintenance. Customers who are using Cisco ASA Software version 7.0 or 7.1 should contact their Cisco support team for assistance in upgrading to a supported version of Cisco ASA Software.

Note: The recommended releases contain the fixes for all vulnerabilities for all the advisories published in the publication. Cisco recommends upgrading to a release that is equal to or later than these recommended releases.

Note:
Upgrading a Cisco ASA device to a version of software that contains the fixed version of the Cisco Port Forwarder ActiveX control does not remove the vulnerability on affected endpoint systems.  Affected endpoint systems will need to download the fixed version by connecting to a Cisco ASA device that is running fixed software via the Cisco Clientless Web solution or disable the affected control via one of the methods mentioned in the "Workarounds" section of this document.

Workarounds

End users or administrators may mitigate Internet Explorer as an attack vector by setting the kill bit for the affected ActiveX control.  This can be achieved by modifying the registry either directly on the affected machine or via an Active Directory Group Policy. 

Warning: Incorrectly modifying the system registry of a Microsoft Windows-based device may cause serious problems.  Neither Cisco nor Microsoft can guarantee that you can resolve problems that may result from improper registry modification from either applying the registry changes via a .reg file or by using the Registry Editor incorrectly.  Modify the registry of your system at your own risk.

To set the kill bit for the CLSID with a value of {B8E73359-3422-4384-8D27-4EA1B4C01232}, paste the following text in a text editor such as Notepad.  Save the file using the .reg filename extension.

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{B8E73359-3422-4384-8D27-4EA1B4C01232}]
"Compatibility Flags"=dword:04000400

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\ActiveX Compatibility\{B8E73359-3422-4384-8D27-4EA1B4C01232}]
"Compatibility Flags"=dword:04000400

End users can apply this .reg file to individual systems by double-clicking the file.  Administrators can also apply the registry change across domains by using Group Policy.  You can find more information about using Group Policy in the following Microsoft TechNet article: Group Policy Collection

When the registry change has been applied, Microsoft Internet Explorer must be restarted for the changes to take effect.  Once the kill bit has been set, the affected control will no longer be accessible by the Cisco Clientless VPN system or a malicious web page when accessed by Internet Explorer.  This change may impact some clientless installations that use the Cisco Port Forwarder ActiveX control. One common component that may stop operating is the ActiveX RDP plug-in.

Mitigations that can be deployed on Cisco devices in a network are available in the Cisco Applied Intelligence companion document for this advisory: http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20120314-asaclient

Note:  When the updated ActiveX Control or the Microsoft Kill Bit update is applied to an endpoint device, the kill bit value in the registry will be changed to 0x00000400 from 0x04000400 if the above workaround has been applied.  This change still effectively blocks the execution of the affected ActiveX control.  The above registry change also sets the binary behaviors kill bit as well as the ActiveX kill bit.  The binary behaviors kill bit is supported on Windows Server 2003 and above, and potentially provides additional protections.  Platforms that do not support the binary behaviors kill bit will ignore this setting and only utilize the ActiveX portion of the bit-mask.

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, or as set forth at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact psirt@cisco.com or security-alert@cisco.com for software upgrades.

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 Center on Cisco.com at http://www.cisco.com.

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 reported to Cisco by Will Dormann of the CERT/CC.

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 Intelligence Operations at the following link:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120314-asaclient

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 1.1 2012-May-15 Added information about the Microsoft Global Kill Bit update release on May 8th, 2012
Revision 1.0 2012-Mar-14 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.