Microsoft Security Bulletin MS07-050 - Critical Vulnerability in Vector Markup Language Could Allow Remote Code Execution (938127)

Microsoft Security Bulletin MS07-050 - Critical
Vulnerability in Vector Markup Language Could Allow Remote Code Execution (938127)
Published: August 14, 2007

Version: 1.0
General Information
Executive Summary

This security update resolves a privately reported vulnerability in the Vector Markup Language (VML) implementation in Windows. The vulnerability could allow remote code execution if a user viewed a specially crafted Web page using Internet Explorer. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

The security update is rated critical for supported releases of Internet Explorer 5.01, Internet Explorer 6, and Internet Explorer 7. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by strengthening the validation of requests to render VML within Internet Explorer. For more information about the vulnerability, see the Frequently Asked Questions (FAQ) subsection under the next section, Vulnerability Information.

Recommendation. Microsoft recommends that customers apply the update immediately.

Known Issues. Microsoft Knowledge Base Article 938127 documents the currently known issues that customers may experience when they install this security update. The article also documents recommended solutions for these issues.
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Affected and Non-Affected Software

The software listed here has been tested to determine which versions or editions are affected. Other versions or editions are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, visit Microsoft Support Lifecycle.

Affected Software
Operating System Component Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by This Update
Internet Explorer 5.01 and Internet Explorer 6 Service Pack 1

Microsoft Windows 2000 Service Pack 4

Microsoft Internet Explorer 5.01 Service Pack 4

Remote Code Execution

Critical

MS07-004

Microsoft Windows 2000 Service Pack 4

Microsoft Internet Explorer 6 Service Pack 1

Remote Code Execution

Critical

MS07-004
Internet Explorer 6

Windows XP Service Pack 2

Microsoft Internet Explorer 6

Remote Code Execution

Critical

MS07-004

Windows XP Professional x64 Edition and Windows XP Professional x64 Edition Service Pack 2

Microsoft Internet Explorer 6

Remote Code Execution

Critical

MS07-004

Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2

Microsoft Internet Explorer 6

Remote Code Execution

Critical

MS07-004

Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition Service Pack 2

Microsoft Internet Explorer 6

Remote Code Execution

Critical

MS07-004

Windows Server 2003 with SP1 for Itanium-based Systems and Windows Server 2003 with SP2 for Itanium-based Systems

Microsoft Internet Explorer 6

Remote Code Execution

Critical

MS07-004
Internet Explorer 7

Windows XP Service Pack 2

Windows Internet Explorer 7

Remote Code Execution

Critical

MS07-004

Windows XP Professional x64 Edition and Windows XP Professional x64 Edition Service Pack 2

Windows Internet Explorer 7

Remote Code Execution

Critical

MS07-004

Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2

Windows Internet Explorer 7

Remote Code Execution

Critical

MS07-004

Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition Service Pack 2

Windows Internet Explorer 7

Remote Code Execution

Critical

MS07-004

Windows Server 2003 with SP1 for Itanium-based Systems and Windows Server 2003 with SP2 for Itanium-based Systems

Windows Internet Explorer 7

Remote Code Execution

Critical

MS07-004

Windows Vista

Windows Internet Explorer 7

Remote Code Execution

Critical

None

Windows Vista x64 Edition

Windows Internet Explorer 7

Remote Code Execution

Critical

None
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Frequently Asked Questions (FAQ) Related to This Security Update

What are the known issues that customers may experience when they install this security update?
Microsoft Knowledge Base Article 938127 documents the currently known issues that customers may experience when they install this security update. The article also documents recommended solutions for these issues.

I am using an older release of the software discussed in this security bulletin. What should I do?
The affected software listed in this bulletin have been tested to determine which releases are affected. Other releases are past their support life cycle. To determine the support life cycle for your software release, visit Microsoft Support Lifecycle.

It should be a priority for customers who have older releases of the software to migrate to supported releases to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit the following Microsoft Support Lifecycle. For more information about the extended security update support period for these software releases, visit the Microsoft Product Support Services Web site.

Customers who require custom support for older software must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, visit the Microsoft Worldwide Information Web site, select the country, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Windows Operating System Product Support Lifecycle FAQ.

If I install this security update before upgrading to Internet Explorer 7, will I still need to apply this update after upgrading to Internet Explorer 7?
Yes. Customers who have installed the current VML security update on systems with Internet Explorer 6 and later install Internet Explorer 7, will be offered this update for Internet Explorer 7. The vgx.dll version installed with Windows Internet Explorer 7 is a major-version higher than vgx.dll included in Windows 2000, Windows XP, or Windows Server 2003. When Internet Explorer 7 is installed, it will replace vgx.dll updated by Internet Explorer 6 provided by in this security update.
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Vulnerability Information

Severity Ratings and Vulnerability Identifiers
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software VML Buffer Overrun Vulnerability - CVE-2007-1749
Internet Explorer 5.01 and Internet Explorer 6 Service Pack 1

Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service Pack 4

Critical

Remote Code Execution

Internet Explorer 6 Service Pack 1 when installed on Microsoft Windows 2000 Service Pack 4

Critical

Remote Code Execution
Internet Explorer 6

Internet Explorer 6 for Windows XP Service Pack 2

Critical

Remote Code Execution

Internet Explorer 6 for Windows XP Professional x64 Edition and Windows XP Professional x64 Edition Service Pack 2

Critical

Remote Code Execution

Internet Explorer 6 for Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2

Critical

Remote Code Execution

Internet Explorer 6 for Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition Service Pack 2

Critical

Remote Code Execution

Internet Explorer 6 for Windows Server 2003 with SP1 for Itanium-based Systems and Windows Server 2003 with SP2 for Itanium-based Systems

Critical

Remote Code Execution
Internet Explorer 7

Internet Explorer 7 for Windows XP Service Pack 2

Critical

Remote Code Execution

Internet Explorer 7 for Windows XP Professional x64 Edition and Windows XP Professional x64 Edition Service Pack 2

Critical

Remote Code Execution

Internet Explorer 7 for Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2

Critical

Remote Code Execution

Internet Explorer 7 for Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition Service Pack 2

Critical

Remote Code Execution

Internet Explorer 7 for Windows Server 2003 with SP1 for Itanium-based Systems and Windows Server 2003 with SP2 for Itanium-based Systems

Critical

Remote Code Execution

Internet Explorer 7 in Windows Vista

Critical

Remote Code Execution

Internet Explorer 7 in Windows Vista x64 Edition

Critical

Remote Code Execution
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VML Buffer Overrun Vulnerability - CVE-2007-1749

A remote code execution vulnerability exists in the Vector Markup Language (VML) implementation in Microsoft Windows. An attacker could exploit the vulnerability by constructing a specially crafted Web page or HTML e-mail. When a user views the Web page or the message, the vulnerability could allow remote code execution.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2007-1749.

Mitigating Factors for VML Buffer Overrun Vulnerability - CVE-2007-1749

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:
•

In a Web-based attack scenario, an attacker could host a Web site that contains a Web page that is used to exploit this vulnerability. In addition, compromised Web sites and Web sites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these Web sites. Instead, an attacker would have to persuade users to visit the Web site, typically by getting them to click a link in an e-mail message or Instant Messenger message that takes users to the attacker's Web site.
•

An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
•

In an e-mail based attack of this exploit, customers who read e-mail in plain text are at less risk from this vulnerability. Instead, users would have to either click on a link that would take them to a malicious Web site or open an attachment to be at risk from this vulnerability.
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Workarounds for VML Buffer Overrun Vulnerability - CVE-2007-1749

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:
•

Unregister VGX.DLL

Click Start, click Run, type "%SystemRoot%\System32\regsvr32.exe" -u "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.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.

This security update does not automatically re-register vgx.dll so any applications that render VML will no longer do so until vgx.dll has been re-registered. To re-register vgx.dll follow, these steps:

Click Start, click Run, type "%SystemRoot%\System32\regsvr32.exe" "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll", and then click OK.

A dialog box appears to confirm that the registration process has succeeded. Click OK to close the dialog box.
•

Set Internet and Local intranet security zone settings to “High” to prompt before running ActiveX Controls and Active Scripting in these zones

You can help protect against this vulnerability by changing your settings for the Internet security zone to prompt before running ActiveX controls. You can do this by setting your browser security to High.

To raise the browsing security level in Microsoft Internet Explorer, follow these steps:

On the Internet Explorer Tools menu, click Internet Options.

In the Internet Options dialog box, click the Security tab, and then click the Internet icon.

Under Security level for this zone, move the slider to High. This sets the security level for all Web sites you visit to High.

Note If no slider is visible, click Default Level, and then move the slider to High.

Note Setting the level to High may cause some Web sites to work incorrectly. If you have difficulty using a Web site after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly even with the security setting set to High.

Impact of workaround: There are side effects to prompting before running ActiveX Controls and Active Scripting. Many Web sites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use ActiveX Controls to provide menus, ordering forms, or even account statements. Prompting before running ActiveX Controls or Active Scripting is a global setting that affects all Internet and intranet sites. You will be prompted frequently when you enable this workaround. For each prompt, if you feel you trust the site that you are visiting, click Yes to run ActiveX Controls or Active Scripting. If you do not want to be prompted for all these sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone”.

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 Web sites 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.

To do this, follow these steps:

In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.

In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.

If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box.

In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.

Repeat these steps for each site that you want to add to the zone.

Click OK two times to accept the changes and return to Internet Explorer.

Note Add any sites that you trust not to take malicious action on your computer. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update.
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FAQ for VML Buffer Overrun Vulnerability - CVE-2007-1749

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could take complete control of an affected system remotely. An attacker could then install programs or view, change, or delete data.

What causes the vulnerability?
In the VML implementation in Microsoft Windows, routines in the vector graphics link library, vgx.dll, do not perform sufficient validation of requests to render VML within Internet Explorer.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability?
An attacker could host a specially crafted Web site that is designed to exploit this vulnerability through Internet Explorer and then persuade a user to view the Web site. This can also include compromised Web sites and Web sites that accept or host user-provided content or advertisements. These Web sites could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these Web sites. Instead, an attacker would have to persuade users to visit the Web site, typically by getting them to click a link in an e-mail message or in an Instant Messenger request that takes users to the attacker's Web site. It could also be possible to display specially crafted Web content by using banner advertisements or by using other methods to deliver Web content to affected systems.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user is logged on and reading e-mail messages or is visiting Web sites for any malicious action to occur. Therefore, any systems where e-mail messages are read or where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability. Systems that are not typically used to visit Web sites, such as most server systems, are at a reduced risk.

What does the update do?
The update changes the way that routines in the vector graphics link library, vgx.dll, validate requests to render VML within Internet Explorer.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.

Other Information
Acknowledgments

Microsoft thanks the following for working with us to help protect customers:
•

eEye Digital Security for reporting the VML Buffer Overrun Vulnerability - CVE-2007-1749.
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Support
•

Customers in the U.S. and Canada can receive technical support from Microsoft Product Support Services at 1-866-PCSAFETY. There is no charge for support calls that are associated with security updates.
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International customers can receive support from their local Microsoft subsidiaries. There is no charge for support that is associated with security updates. For more information about how to contact Microsoft for support issues, visit the International Support Web site.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions
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V1.0 (August 14, 2007): Bulletin published.