Internet Explorer versions 6-11 vulnerable to remote code execution
Posted by: Jon Ben-Mayor on 04/27/2014 12:24 PM
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A Zero-day vulnerability has been confirmed by Microsoft that involves IE6 through IE11. The vulnerability is a remote code execution vulnerability which exists in the way that Internet Explorer accesses an object in memory that has been deleted or has not been properly allocated.
Microsoft details the vulnerability on security advisory (29639830), stating that the vulnerability may corrupt memory in a way that could allow an attacker to execute arbitrary code in the context of the current user within Internet Explorer. An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website.
On completion of this investigation, Microsoft will take the appropriate action to protect our customers, which may include providing a solution through our monthly security update release process, or an out-of-cycle security update, depending on customer needs.
We are actively working with partners in our Microsoft Active Protections Program (MAPP) to provide information that they can use to provide broader protections to customers. For information about protections released by MAPP partners, see MAPP Partners with Updated Protections.
Microsoft notes that there are several things that can be done to protect your computer against the vulnerability:
Deploy the Enhanced Mitigation Experience Toolkit 4.1
The Enhanced Mitigation Experience Toolkit (EMET) helps mitigate the exploitation of this vulnerability by adding additional protection layers that make the vulnerability harder to exploit.
EMET 4.1 is officially supported by Microsoft. At this time, EMET is only available in the English language.
Set Internet and Local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones
You can help protect against exploitation of this vulnerability by changing your settings for the Internet security zone to block ActiveX controls and Active Scripting. You can do this by setting your browser security to High.
To raise the browsing security level in Internet Explorer, perform the following steps:
-On the Internet Explorer Tools menu, click Internet Options.
-In the Internet Options dialog box, click the Security tab, and then click Internet.
-Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
-Click Local intranet.
-Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
-Click OK to accept the changes and return to Internet Explorer.
Impact of workaround. There are side effects to blocking ActiveX Controls and Active Scripting. Many websites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality.
Add sites that you trust to the Internet Explorer Trusted sites zone
After you set Internet Explorer to require a prompt before it runs ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted websites exactly as you do today, while helping to protect you from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.
Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone
You can help protect against exploitation of this vulnerability by changing your settings to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone. To do this, perform the following steps:
-In Internet Explorer, click Internet Options on the Tools menu.
-Click the Security tab.
-Click Internet, and then click Custom Level.
-Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
-Click Local intranet, and then click Custom Level.
-Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
-Click OK two times to return to Internet Explorer.
Impact of workaround. There are side effects to prompting before running Active Scripting. Many websites that are on the Internet or on an intranet use Active Scripting to provide additional functionality.
Unregister VGX.DLL
-Click Start, click Run, type "%SystemRoot%System32regsvr32.exe" -u "%CommonProgramFiles%Microsoft SharedVGXvgx.dll", and then click OK.
-A dialog box appears to confirm that the un-registration process has succeeded. Click OK to close the dialog box.
Impact of Workaround: Applications that render VML will no longer do so once vgx.dll has been unregistered.
When a security update is available to address this issue, you should re-register vgx.dll after installing the security update. To re-register vgx.dll follow these steps:
Click Start, click Run, type "%SystemRoot%System32regsvr32.exe" "%CommonProgramFiles%Microsoft SharedVGXvgx.dll", and then click OK.
A dialog box appears to confirm that the registration process has succeeded. Click OK to close the dialog box.
Modify the Access Control List on VGX.DLL to be more restrictive
-To modify the Access Control List (ACL) on vgx.dll to be more restrictive, follow these steps:
-Click Start, click Run, type "cmd" (without the quotation marks), and then click OK.
-Type the following command at a command prompt make a note of the current ACL’s that are on the file (including inheritance settings) for future reference to undo this modification:
cacls "%CommonProgramFiles%Microsoft SharedVGXvgx.dll"
-Type the following command at a command prompt to deny the 'everyone' group access to this file:
echo y| cacls "%CommonProgramFiles%Microsoft SharedVGXvgx.dll" /d everyone
-Close Internet Explorer, and reopen it for the changes to take effect.
Impact of Workaround: Applications and Web sites that render VML may no longer display or function correctly.
Protect your PC
We continue to encourage customers to follow our Protect Your Computer guidance of enabling a firewall, getting software updates, and installing antimalware software.
Keep Microsoft Software Updated
Users running Microsoft software should apply the latest Microsoft security updates to help make sure that their computers are as protected as possible. If you are not sure whether your software is up to date, visit Microsoft Update, scan your computer for available updates, and install any high-priority updates that are offered to you. If you have automatic updating enabled and configured to provide updates for Microsoft products, the updates are delivered to you when they are released, but you should verify that they are installed.
Microsoft details the vulnerability on security advisory (29639830), stating that the vulnerability may corrupt memory in a way that could allow an attacker to execute arbitrary code in the context of the current user within Internet Explorer. An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website.On completion of this investigation, Microsoft will take the appropriate action to protect our customers, which may include providing a solution through our monthly security update release process, or an out-of-cycle security update, depending on customer needs.
We are actively working with partners in our Microsoft Active Protections Program (MAPP) to provide information that they can use to provide broader protections to customers. For information about protections released by MAPP partners, see MAPP Partners with Updated Protections.
Microsoft notes that there are several things that can be done to protect your computer against the vulnerability:
Deploy the Enhanced Mitigation Experience Toolkit 4.1
The Enhanced Mitigation Experience Toolkit (EMET) helps mitigate the exploitation of this vulnerability by adding additional protection layers that make the vulnerability harder to exploit.
EMET 4.1 is officially supported by Microsoft. At this time, EMET is only available in the English language.
Set Internet and Local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones
You can help protect against exploitation of this vulnerability by changing your settings for the Internet security zone to block ActiveX controls and Active Scripting. You can do this by setting your browser security to High.
To raise the browsing security level in Internet Explorer, perform the following steps:
-On the Internet Explorer Tools menu, click Internet Options.
-In the Internet Options dialog box, click the Security tab, and then click Internet.
-Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
-Click Local intranet.
-Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
-Click OK to accept the changes and return to Internet Explorer.
Impact of workaround. There are side effects to blocking ActiveX Controls and Active Scripting. Many websites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality.
Add sites that you trust to the Internet Explorer Trusted sites zone
After you set Internet Explorer to require a prompt before it runs ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted websites exactly as you do today, while helping to protect you from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.
Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone
You can help protect against exploitation of this vulnerability by changing your settings to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone. To do this, perform the following steps:
-In Internet Explorer, click Internet Options on the Tools menu.
-Click the Security tab.
-Click Internet, and then click Custom Level.
-Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
-Click Local intranet, and then click Custom Level.
-Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
-Click OK two times to return to Internet Explorer.
Impact of workaround. There are side effects to prompting before running Active Scripting. Many websites that are on the Internet or on an intranet use Active Scripting to provide additional functionality.
Unregister VGX.DLL
-Click Start, click Run, type "%SystemRoot%System32regsvr32.exe" -u "%CommonProgramFiles%Microsoft SharedVGXvgx.dll", and then click OK.
-A dialog box appears to confirm that the un-registration process has succeeded. Click OK to close the dialog box.
Impact of Workaround: Applications that render VML will no longer do so once vgx.dll has been unregistered.
When a security update is available to address this issue, you should re-register vgx.dll after installing the security update. To re-register vgx.dll follow these steps:
Click Start, click Run, type "%SystemRoot%System32regsvr32.exe" "%CommonProgramFiles%Microsoft SharedVGXvgx.dll", and then click OK.
A dialog box appears to confirm that the registration process has succeeded. Click OK to close the dialog box.
Modify the Access Control List on VGX.DLL to be more restrictive
-To modify the Access Control List (ACL) on vgx.dll to be more restrictive, follow these steps:
-Click Start, click Run, type "cmd" (without the quotation marks), and then click OK.
-Type the following command at a command prompt make a note of the current ACL’s that are on the file (including inheritance settings) for future reference to undo this modification:
cacls "%CommonProgramFiles%Microsoft SharedVGXvgx.dll"
-Type the following command at a command prompt to deny the 'everyone' group access to this file:
echo y| cacls "%CommonProgramFiles%Microsoft SharedVGXvgx.dll" /d everyone
-Close Internet Explorer, and reopen it for the changes to take effect.
Impact of Workaround: Applications and Web sites that render VML may no longer display or function correctly.
Protect your PC
We continue to encourage customers to follow our Protect Your Computer guidance of enabling a firewall, getting software updates, and installing antimalware software.
Keep Microsoft Software Updated
Users running Microsoft software should apply the latest Microsoft security updates to help make sure that their computers are as protected as possible. If you are not sure whether your software is up to date, visit Microsoft Update, scan your computer for available updates, and install any high-priority updates that are offered to you. If you have automatic updating enabled and configured to provide updates for Microsoft products, the updates are delivered to you when they are released, but you should verify that they are installed.
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