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  NSFOCUS SA2007-01 : Microsoft IE5 CSS Parsing Memory Corruption Vulnerability

From:MICROSOFT <secure_(at)_microsoft.com>
Date:14.08.2007
Subject:Microsoft Security Bulletin MS07-045 - Critical Cumulative Security Update for Internet Explorer (937143)

Microsoft Security Bulletin MS07-045 - Critical
Cumulative Security Update for Internet Explorer (937143)
Published: August 14, 2007

Version: 1.0
General Information
Executive Summary

This critical security update resolves three privately reported vulnerabilities. These vulnerabilities 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 and Internet Explorer 6 Service Pack 1. For Internet Explorer 6 for supported versions and editions of Windows XP Home and Windows XP Professional, the security update is also rated critical, otherwise it is rated moderate for other supported operating systems. For Internet Explorer 7 for supported versions and editions of Windows XP and Windows XP Professional, and Internet Explorer 7 in Windows Vista, the security update is rated Important, otherwise it is rated low. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses two vulnerabilities by setting the kill bit for ActiveX controls, and addresses the third vulnerability by modifying the way that Internet Explorer handles certain strings in CSS files. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. Microsoft recommends that customers apply the update immediately.

Known Issues. Microsoft Knowledge Base Article 937143 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


MS07-033

Microsoft Windows 2000 Service Pack 4


Microsoft Internet Explorer 6 Service Pack 1


Remote Code Execution


Critical


MS07-033
Internet Explorer 6

Windows XP Service Pack 2


Microsoft Internet Explorer 6


Remote Code Execution


Critical


MS07-033

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


Microsoft Internet Explorer 6


Remote Code Execution


Critical


MS07-033

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


Microsoft Internet Explorer 6


Remote Code Execution


Moderate


MS07-033

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


Microsoft Internet Explorer 6


Remote Code Execution


Moderate


MS07-033

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


Moderate


MS07-033
Internet Explorer 7

Windows XP Service Pack 2


Windows Internet Explorer 7


Remote Code Execution


Important


MS07-033

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


Windows Internet Explorer 7


Remote Code Execution


Important


MS07-033

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


Windows Internet Explorer 7


Remote Code Execution


Low


MS07-033

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


Windows Internet Explorer 7


Remote Code Execution


Low


MS07-033

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


Low


MS07-033

Windows Vista


Windows Internet Explorer 7


Remote Code Execution


Important


MS07-033

Windows Vista x64 Edition


Windows Internet Explorer 7


Remote Code Execution


Important


MS07-033
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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 937143 documents the currently known issues that customers may experience when they install this security update. The article also documents recommended solutions for these issues.

Why does this update address several reported security vulnerabilities?
This update addresses several vulnerabilities because the modifications for these issues are located in related files. Instead of having to install several updates that are almost the same, customers need to install this update only.

Does this update contain any security-related changes that are not Internet Explorer specific?
Yes. The changes are listed under the specific vulnerability entries, “ActiveX Object Instantiation Memory Corruption Vulnerability - CVE-2007-2216” and “ActiveX Object Instantiation Memory Corruption Vulnerability - CVE-2007-3041,” in the next section, Vulnerability Information.

Does this update contain any security-related changes to functionality?
Yes. Besides the changes that are listed in the “Vulnerability Details” section of this bulletin, this update includes the following security-related changes:


This update sets a kill bit for the ActiveX control, ouactrl.ocx, that is out of support:


{8936033C-4A50-11D1-98A4-00A0C90F27C6}


This update sets the kill bit for ActiveX controls addressed in previous Microsoft Security Bulletins:


The CAPICOM control addressed in Microsoft Security Bulletin MS07-028: Vulnerability in CAPICOM Could Allow Remote Code Execution (931906):


{FBAB033B-CDD0-4C5E-81AB-AEA575CD1338}


{17E3A1C3-EA8A-4970-AF29-7F54610B1D4C}

This update includes killbits that will prevent the following ActiveX controls from being run in Internet Explorer:


This security update sets a kill bit for the Download Manager ActiveX control, available from Akamai Technologies. Akamai Technologies has released an update that addresses a vulnerability in the affected component. For more information please see, CVE-2007-1892 and CVE-2007-1891. This kill bit is set at the request of the owner of the ActiveX control. The class identifier (CLSID) for this ActiveX control is:


{2AF5BD25-90C5-4EEC-88C5-B44DC2905D8B}


This security update sets a kill bit for an ActiveX control available from Lenovo. Lenovo has released a security bulletin and an update that addresses a vulnerability in the effected component. For more information and download locations, see the security bulletin from Lenovo. This kill bit is being set at the request of the owner of the ActiveX control. The class identifiers (CLSID) for this ActiveX control are:


{76E5AF9D-2B3E-4FEB-A31F-A9E63A27FA29}


{E598AC61-4C6F-4F4D-877F-FAC49CA91FA3}


This security update sets a kill bit for an ActiveX control available from Motive Incorporated. Motive Incorporated has released a security bulletin and an update that addresses a vulnerability in the effected component. For more information and download locations, see the security bulletin from Motive Incorporated. This kill bit is being set at the request of the owner of the ActiveX control. The class identifier (CLSID) for this ActiveX control is:


{D256B2D9-9C58-445A-8C38-C3AAA84EF137}

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.
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Vulnerability Information

Severity Ratings and Vulnerability Identifiers
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software CSS Memory Corruption Vulnerability - CVE-2007-0943 ActiveX Object Vulnerability - CVE-2007-2216 ActiveX Object Memory Corruption Vulnerability - CVE-2007-3041 Aggregate Severity Rating
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


Critical

Remote Code Execution


Critical

Remote Code Execution


Critical

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


None


Critical

Remote Code Execution


Critical

Remote Code Execution


Critical
Internet Explorer 6

Internet Explorer 6 for Windows XP Service Pack 2


None


Critical

Remote Code Execution


Critical

Remote Code Execution


Critical

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


None


Critical

Remote Code Execution


Critical

Remote Code Execution


Critical

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


None


Moderate

Remote Code Execution


Moderate

Remote Code Execution


Moderate

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


None


Moderate

Remote Code Execution


Moderate

Remote Code Execution


Moderate

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


None


Moderate

Remote Code Execution


Moderate

Remote Code Execution


Moderate
Internet Explorer 7

Internet Explorer 7 for Windows XP Service Pack 2


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

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


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

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


None


Low

Remote Code Execution


Low

Remote Code Execution


Low

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


None


Low

Remote Code Execution


Low

Remote Code Execution


Low

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


None


Low

Remote Code Execution


Low

Remote Code Execution


Low

Internet Explorer 7 in Windows Vista


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Internet Explorer 7 in Windows Vista x64 Edition


None


Important

Remote Code Execution


Important

Remote Code Execution


Important
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CSS Memory Corruption Vulnerability - CVE-2007-0943

A remote code execution vulnerability exists in the way Internet Explorer parses certain strings in CSS. An attacker could exploit the vulnerability by constructing a specially crafted Web page. When a user views the Web page, the vulnerability could allow remote code execution. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on user..

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2007-0943.

Mitigating Factors for CSS Memory Corruption Vulnerability - CVE-2007-0943

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.


Internet Explorer 6 and 7 are not affected by this vulnerability.
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Workarounds for CSS Memory Corruption Vulnerability - CVE-2007-0943

We have not identified any workarounds for this vulnerability.
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FAQ for CSS Memory Corruption Vulnerability - CVE-2007-0943

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on user.

What causes the vulnerability?
When Internet Explorer parses certain CSS strings under certain conditions, memory may be corrupted in such a way that an attacker could execute arbitrary code in the context of the logged-on user.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on 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 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 visits a Web site for any malicious action to occur. Therefore, any systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What is CSS?
CSS or Cascading Style Sheets is a formatting method for Web pages using HTML. For more information about CSS, visit the Microsoft TechNet Web site.

What does the update do?
The update prevents memory corruption when Internet Explorer parses CSS text.

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.
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ActiveX Object Vulnerability - CVE-2007-2216

A remote code execution vulnerability exists in the ActiveX control, tblinf32.dll. This control can also be found under the name of vstlbinf.dll. Both of these components were never intended to be supported in Internet Explorer. An attacker could exploit the vulnerability by constructing a specially crafted Web page that could potentially allow remote code execution if a user visited the Web page. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on user.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2007-2216.

Mitigating Factors for ActiveX Object Vulnerability - CVE-2007-2216

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 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 convince users to visit the Web site, typically by getting them to click a link in an e-mail 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.
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Workarounds for ActiveX Object Vulnerability - CVE-2007-2216

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:


Prevent COM objects from running in Internet Explorer

You can disable attempts to instantiate a COM object in Internet Explorer by setting the kill bit for the control in the registry.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

For detailed steps that you can use to prevent a control from running in Internet Explorer, see Microsoft Knowledge Base Article 240797. Follow these steps in this article to create a Compatibility Flags value in the registry to prevent a COM object from being instantiated in Internet Explorer.

Note The Class Identifiers and corresponding files where the COM objects are contained are documented under “What does the update do?” in the “FAQ for ActiveX Object Vulnerability - CVE-2007-2216” subsection. Replace {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} below with the Class Identifiers found in that FAQ subsection.

To set the kill bit for a CLSID with a value of {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}, paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{ XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX }]
"Compatibility Flags"=dword:00000400

You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites:


Group Policy collection


What is Group Policy Object Editor?


Core Group Policy tools and settings

Note You must restart Internet Explorer for your changes to take effect.

Impact of Workaround: There is no impact as long as the object is not intended to be used in Internet Explorer.


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:

1.


On the Internet Explorer Tools menu, click Internet Options.

2.


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

3.


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:

1.


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

2.


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

3.


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.

4.


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

5.


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

6.


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 ActiveX Object Vulnerability - CVE-2007-2216

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on user.

What causes the vulnerability?
The control implemented IObjectsafety incorrectly. For more information about IObjectsafety, visit the Microsoft TechNet Web site

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 convince 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 convince 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 be logged on and visit a Web site for any malicious action to occur. Therefore, any systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What is the ActiveX opt-in feature in Windows Internet Explorer 7?
Windows Internet Explorer 7 includes an ActiveX opt-in feature, which means that nearly all pre-installed ActiveX controls are off by default. Users are prompted by the Information Bar before they can instantiate a previously installed ActiveX control that has not yet been used on the Internet. This enables a user to permit or deny access on a control-by-control basis. For more information about this and other new features, see the Windows Internet Explorer 7 features page.

What does the update do?
This update sets the kill bit for a list of Class Identifiers (CLSIDs).

The Class Identifiers are as follows:
Class Identifier Software

{8B217746-717D-11CE-AB5B-D41203C10000}


Microsoft Visual Basic 6

{8B217752-717D-11CE-AB5B-D41203C10000}


Microsoft Visual Basic 6

{8B21775E-717D-11CE-AB5B-D41203C10000}


Microsoft Visual Basic 6

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.
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ActiveX Object Memory Corruption Vulnerability - CVE-2007-3041

A remote code execution vulnerability exists in the ActiveX object, pdwizard.ocx. An attacker could exploit the vulnerability by constructing a specially crafted Web page. When a user views the Web page, the vulnerability could allow remote code execution. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on user.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2007-3041.

Mitigating Factors for ActiveX Object Memory Corruption Vulnerability - CVE-2007-3041

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 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 convince users to visit the Web site, typically by getting them to click a link in an e-mail 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.
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Workarounds for ActiveX Object Memory Corruption Vulnerability - CVE-2007-3041

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:


Prevent COM objects from running in Internet Explorer

You can disable attempts to instantiate a COM object in Internet Explorer by setting the kill bit for the control in the registry.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

For detailed steps that you can use to prevent a control from running in Internet Explorer, see Microsoft Knowledge Base Article 240797. Follow these steps in this article to create a Compatibility Flags value in the registry to prevent a COM object from being instantiated in Internet Explorer.

Note The Class Identifiers and corresponding files where the COM objects are contained are documented under “What does the update do?” in the “FAQ for ActiveX Object Memory Corruption Vulnerability - CVE-2007-3041” subsection. Replace {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} below with the Class Identifiers found in this section.

To set the kill bit for a CLSID with a value of {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}, paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension.


[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{ XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX }]
"Compatibility Flags"=dword:00000400

You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites:


Group Policy collection


What is Group Policy Object Editor?


Core Group Policy tools and settings

Note You must restart Internet Explorer for your changes to take effect.

Impact of Workaround: There is no impact as long as the object is not intended to be used in Internet Explorer.


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:

1.


On the Internet Explorer Tools menu, click Internet Options.

2.


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

3.


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:

1.


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

2.


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

3.


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.

4.


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

5.


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

6.


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 ActiveX Object Memory Corruption Vulnerability - CVE-2007-3041

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on user.

What causes the vulnerability?
When the ActiveX object is used in Internet Explorer, the objects may corrupt the system state in such a way that an attacker could execute arbitrary code.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could gain the same user rights as the logged on 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 convince 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 convince 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 be logged on and visit a Web site for any malicious action to occur. Therefore, any systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What is the ActiveX opt-in feature in Windows Internet Explorer 7?
Windows Internet Explorer 7 includes an ActiveX opt-in feature, which means that nearly all pre-installed ActiveX controls are off by default. Users are prompted by the Information Bar before they can instantiate a previously installed ActiveX control that has not yet been used on the Internet. This enables a user to permit or deny access on a control-by-control basis. For more information about this and other new features, see the Windows Internet Explorer 7 features page.

What does the update do?
This update sets the kill bit for a list of Class Identifier (CLSIDs).

The Class Identifier is as follows:
Class Identifier Software

{0DDF3B5C-E692-11D1-AB06-00AA00BDD685}


Microsoft Visual Basic 6.0

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:


NSFocus Security Team for reporting the CSS Memory Corruption Vulnerability - CVE-2007-0943.


Brett Moore of Security-Assessment.com for reporting the ActiveX Object Vulnerability - CVE-2007-2216.

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.


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.
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Revisions


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

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