AVG Safeguard and Secure Search ActiveX controls provides insecure methods

Overview

The AVG Secure Search toolbar, also known as AVG Safeguard includes an ActiveX control that provides a number of unsafe methods, which may allow a remote, unauthenticated attacker to execute arbitrary code with the privileges of the user.

Description

AVG Secure Search is a toolbar add-on for web browsers that “… provides an additional security layer while searching and surfing to protect you from infected websites.” One of the components provided by AVG Secure Search is an ActiveX control called ScriptHelperApi, which is provided by ScriptHelper.exe. This ActiveX control is marked as Safe for Scripting in Internet Explorer, which means that the author has determined that the control cannot be repurposed by an attacker. Because this control does not internally enforce any restrictions on which sites may invoke its methods, such as by using the SiteLock template, this means that any website can invoke the methods exposed by the ScriptHelper ActiveX control. The installer for AVG Secure Search also sets the ElevationPolicy registry value for the control, which means that the control is excluded from the Internet Explorer Protected Mode sandbox. The installer for AVG Secure Search also sets the Preapproved registry value, which bypasses the Internet Explorer ActiveX Opt-In feature that was introduced with IE 7.

The AVG Safeguard and Secure Search ScriptHelper ActiveX control versions up to and including version 18.1.6 contain a number of unsafe methods that can be used in Internet Explorer. Other browsers do not appear to be affected.

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Impact

By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message or attachment), an attacker may be able to download and execute arbitrary code with the privileges of the logged-on user.

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Solution

Apply an update

This issue is addressed in AVG Secure Search toolbar version 18.1.7.598 and AVG Safeguard 18.1.7.644. While these versions are still marked as Safe for Scripting, this version of the control has restrictions in place that prevent its use by web pages hosted by domains other than .avg.com or .avg.nation.com. Please also consider the following workaround:

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Disable the AVG ScriptHelper ActiveX control in Internet Explorer

The vulnerable AVG ScriptHelper ActiveX control can be disabled in Internet Explorer by setting the kill bit for the following CLSID:

{F25AF245-4A81-40DC-92F9-E9021F207706}More information about how to set the kill bit is available in Microsoft Support Document 240797. Alternatively, the following text can be saved as a .REG file and imported to set the kill bit for this control:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\``{F25AF245-4A81-40DC-92F9-E9021F207706}``]
"Compatibility Flags"=dword:00000400
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\ActiveX Compatibility\``{F25AF245-4A81-40DC-92F9-E9021F207706}``]
"Compatibility Flags"=dword:00000400

Vendor Information

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AVG Anti-virus Software Affected

Notified: May 19, 2014 Updated: May 27, 2014

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

CVSS Metrics

Group	Score	Vector
Base	9.3	AV:N/AC:M/Au:N/C:C/I:C/A:C
Temporal	8	E:POC/RL:W/RC:C
Environmental	6.0	CDP:ND/TD:M/CR:ND/IR:ND/AR:ND

References

• <http://www.avg.com/us-en/secure-search&gt;
• <http://msdn.microsoft.com/en-us/library/aa751977(v=vs.85).aspx&gt;
• <http://msdn.microsoft.com/en-us/library/aa752035(v=vs.85).aspx#ax_repurposing&gt;
• <http://msdn.microsoft.com/en-us/library/aa752035(v=vs.85).aspx#ax_judging&gt;
• <http://msdn.microsoft.com/en-us/library/bb250462(v=vs.85).aspx&gt;
• <http://windows.microsoft.com/en-us/windows-vista/what-does-internet-explorer-protected-mode-do&gt;
• <http://blogs.msdn.com/b/ieinternals/archive/2011/04/02/activex-control-restrictions-in-ie.aspx&gt;
• <http://msdn.microsoft.com/en-us/library/bb250471(v=vs.85).aspx&gt;

Acknowledgements

This vulnerability was reported by Will Dormann of the CERT/CC.

This document was written by Will Dormann.

Other Information

CVE IDs:	CVE-2014-2956
Date Public:	2014-07-07 Date First Published: