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Credit:
The information has been provided by Microsoft Product Security.
The original article can be found at: http://www.microsoft.com/technet/security/bulletin/ms06-071.mspx
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Affected Components:
* Microsoft XML Core Services 4.0 when installed on Windows (all versions) Download the update (KB927978)
* Microsoft XML Core Services 6.0 when installed on Windows (all versions) Download the update (KB927977)
Non-Affected Software:
* Microsoft XML Core Services 3.0
* Microsoft XML Core Services 5.0
Mitigating Factors for Microsoft XML Core Services Vulnerability - CVE-2006-5745:
* Microsoft XML Core Services 4.0 and Microsoft XML Core Services 6.0 are not included in any versions of Windows.
* In a Web-based attack scenario, an attacker would have to host a Web site that contains a Web page that is used to exploit this vulnerability. An attacker would have no way to force users to visit the page. 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 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.
* The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability by preventing Active Scripting from being used when reading HTML e-mail messages. However, if a user clicks a link in an e-mail message, they could still be vulnerable to this issue through the Web-based attack scenario.
By default, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally, Outlook 2000 opens HTML e-mail messages in the Restricted sites zone if the Outlook E-mail Security Update has been installed. Outlook Express 5.5 Service Pack 2 opens HTML e-mail messages in the Restricted sites zone if Microsoft Security Bulletin MS04-018 has been installed.
* By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that have not been added to Internet Explorer Trusted sites zone. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.
Workarounds for Microsoft XML Core Services Vulnerability - CVE-2006-5745:
Microsoft has tested the following workarounds. Although these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.
* Prevent the XMLHTTP 4.0 and XMLHTTP 6.0 ActiveX Controls from running in Internet Explorer.
You can disable attempts to instantiate these ActiveX controls in Internet Explorer by setting the kill bit for the controls 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:
1. To set the kill bit for a CLSID with a value of {88d969c5-f192-11d4-a65f-0040963251e5} (XMLHTTP 4.0 contained within Microsoft XML Core Services 4.0) and {88d96a0a-f192-11d4-a65f-0040963251e5} (XMLHTTP 6.0 contained within Microsoft XML Core Services 6.0) paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{88d969c5-f192-11d4-a65f-0040963251e5}] "Compatibility Flags"=dword:00000400
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{88d96a0a-f192-11d4-a65f-0040963251e5}] "Compatibility Flags"=dword:00000400
2. 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: Web sites that use the XMLHTTP 4.0 or XMLHTTP 6.0 ActiveX controls may no longer display or function correctly.
This security update does not automatically rollback the kill bit for these ActiveX controls. To rollback the kill bit follow these steps:
1. To rollback the kill bit paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension:
Windows Registry Editor Version 5.00
[-HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{88d969c5-f192-11d4-a65f-0040963251e5}]
[-HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{88d96a0a-f192-11d4-a65f-0040963251e5}]
2. 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.
* Deny Access to the affected CLSID's for Microsoft XML Core Services 4.0 ({88D969C5-F192-11D4-A65F-0040963251E5}) and Microsoft XML Core Services 6.0 ({88D96A0A-F192-11D4-A65F-0040963251E5}) in the registry
To modify access to the affected CLSIDs for Windows 2000, follow these steps:
1. Click Start, click Run, type "regedt32" (without the quotation marks), and then click OK.
2. Expand HKEY_CLASSES_ROOT, and expand CLSID.
3. For Microsoft XML Core Services 4.0 click: {88D969C5-F192-11D4-A65F-0040963251E5}
For Microsoft XML Core Services 6.0 click: {88D96A0A-F192-11D4-A65F-0040963251E5}
4. Click Security, and then click Permissions.
Note Make a note of the permissions that are listed in this dialog box so that you can restore them to their original values at a later time.
5. Click to clear the Allow Inheritable Permissions form the parent to propagate to this object check box. You are prompted to click Copy, Remove, or Cancel. Click Remove, and then click OK.
6. A message will display stating that no one will be able to access this registry key. Click Yes when prompted to do so.
To modify access to the affected CLSIDs for Windows XP Service Pack 2 and later operating systems, follow these steps:
1. Click Start, click Run, type "regedt32" (without the quotation marks), and then click OK.
2. Expand HKEY_CLASSES_ROOT, and expand CLSID.
3. For Microsoft XML Core Services 4.0 click: {88D969C5-F192-11D4-A65F-0040963251E5}
For Microsoft XML Core Services 6.0 click: {88D96A0A-F192-11D4-A65F-0040963251E5}
4. Click Edit, and then click Permissions.
Note Make a note of the permissions that are listed in this dialog box so that you can restore them to their original values at a later time.
5. Click Advanced.
6. Click to clear the Inherit from parent the permission entries that apply to child objects. Include these with entries explicitly defined here check box. You are prompted to click Copy, Remove, or Cancel. Click Remove, and then check OK.
7. A message will display stating that no one will be able to access this registry key. Click Yes when prompted to do so and then click OK to close the Permissions for {88D969C5-F192-11D4-A65F-0040963251E5} or Permissions for {88D96A0A-F192-11D4-A65F-0040963251E5} (depending on which CLSID was chosen) dialog box.
Impact of Workaround: Web sites that use the XMLHTTP 4.0 or XMLHTTP 6.0 ActiveX controls may no longer display or function correctly.
* Configure Internet Explorer to prompt before running Active Scripting or disable Active Scripting in the Internet and Local intranet security zone.
You can help protect against 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, follow these steps:
1. In Internet Explorer, click Internet Options on the Tools menu.
2. Click the Security tab.
3. Click Internet, and then click Custom Level.
4. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
5. Click Local intranet, and then click Custom Level.
6. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
7. Click OK two times to return to Internet Explorer.
Note Disabling Active Scripting in the Internet and Local intranet security zones 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.
Note After you set Internet Explorer to require a prompt before it runs ActiveX controls and/or 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 (without the quotation marks). These are the sites that will host the update, and it requires an ActiveX control to install the update.
Impact of Workaround: There are side effects to prompting before running Active Scripting. Many Web sites that are on the Internet or on an intranet use Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use Active Scripting to provide menus, ordering forms, or even account statements. Prompting before running 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 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 .
* Configure Internet Explorer to prompt before running ActiveX Controls or disable ActiveX Controls in the Internet and Local intranet security zone.
You can help protect against this vulnerability by changing your Internet Explorer settings to prompt before running ActiveX controls. To do this, follow these steps:
1. In Internet Explorer, click Internet Options on the Tools menu.
2. Click the Security tab.
3. Click Internet, and then click Custom Level.
4. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt or Disable, and then click OK.
5. Click Local intranet, and then click Custom Level.
6. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt or Disable, and then click OK.
7. Click OK two times to return to Internet Explorer.
Note After you set Internet Explorer to require a prompt before it runs ActiveX controls and/or 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 (without the quotation marks). These are the sites that will host the update, and it requires an ActiveX control to install the update.
Impact of Workaround: There are side effects to prompting before running ActiveX controls. Many Web sites that are on the Internet or on an intranet use ActiveX 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 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. 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 .
* Set Internet and Local intranet security zone settings to High to prompt before running ActiveX controls and active scripting in the Internet zone and in the Local intranet zone.
You can help protect against this vulnerability by changing your settings for the Internet security zone to prompt before running ActiveX controls and active scripting. You can do this by setting your browser security to High.
To raise the browsing security level in Microsoft Internet Explorer:
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 high security setting.
Alternatively, you can change you settings to prompt before running ActiveX controls only by following these steps:
1. In Internet Explorer, click Internet Options on the Tools menu.
2. Click the Security tab.
3. Click Internet, and then click Custom Level.
4. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt.
5. In the Scripting section, under Active Scripting, click Prompt, and then click OK.
6. Click Local intranet, and then click Custom Level.
7. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt.
8. In the Scripting section, under Active Scripting, click Prompt.
9. Click OK two times to return to Internet Explorer.
Impact of Workaround: There are side effects to prompting before running ActiveX controls. Many Web sites that are on the Internet or on an intranet use ActiveX 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 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. If you do not want to be prompted for all these sites, use the "Restrict Web sites to only your trusted Web sites" workaround.
FAQ for Microsoft XML Core Services Vulnerability - CVE-2006-5745:
What is the scope of the vulnerability?
This is a vulnerability that could allow remote code execution. An attacker could exploit the vulnerability by constructing a specially crafted Web page that could potentially lead to remote code execution if a user visited that page or clicked a link in a specially crafted e-mail message. If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. 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.
What causes the vulnerability?
The XMLHTTP ActiveX control included in Microsoft XML Core Services could, if passed unexpected data, cause Internet Explorer to fail in a way that could allow code execution.
What is Microsoft XML Core Services (MSXML)?
Microsoft XML Core Services (MSXML) provides standards-conformant implementations of: XML 1.0 (DOM & SAX2 APIs), XML Schema (XSD) 1.0, XPath 1.0, and XSLT 1.0. It allows developers to build XML-based applications in Jscript, Visual Basic Scripting Edition (VBScript), Visual Basic 6.0 and native C++ that provide interoperability with other applications that adhere to the XML 1.0 standard. See the MSDN Web site for more information regarding MSXML.
What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of the affected system.
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 Web sites that accept user-provided content or advertisements, Web sites that host user-provided content or advertisements, and compromised Web sites. 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. Systems that are not typically used to visit Web sites, such as most server systems, are at a reduced risk.
I am running Internet Explorer on Windows Server 2003. Does this mitigate these vulnerabilities?
Yes. By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that have not been added to Internet Explorer Trusted sites zone.
What is the Internet Explorer Enhanced Security Configuration?
Internet Explorer Enhanced Security Configuration is a group of preconfigured Internet Explorer settings that reduce the likelihood of a user or of an administrator downloading and running specially crafted Web content on a server. Internet Explorer Enhanced Security Configuration reduces this risk by modifying many security-related settings. This includes the settings on the Security tab and the Advanced tab in the Internet Options dialog box. Some of the important modifications include the following:
* Security level for the Internet zone is set to High. This setting disables scripts, ActiveX controls, Microsoft Java Virtual Machine (MSJVM), and file downloads.
* Automatic detection of intranet sites is disabled. This setting assigns all intranet Web sites and all Universal Naming Convention (UNC) paths that are not explicitly listed in the Local intranet zone to the Internet zone.
* Install On Demand and non-Microsoft browser extensions are disabled. This setting prevents Web pages from automatically installing components and prevents non-Microsoft extensions from running.
* Multimedia content is disabled. This setting prevents music, animations, and video clips from running.
For more information regarding Internet Explorer Enhanced Security Configuration, see the guide, Managing Internet Explorer Enhanced Security Configuration, at the following Web site.
What does the update do?
The update removes the vulnerability by modifying the way that the XMLHTTP ActiveX control performs parameter validation.
When this security bulletin was issued, had this vulnerability been publicly disclosed?
Yes. This vulnerability has been publicly disclosed. It has been assigned Common Vulnerability and Exposure number CVE-2006-5745.
When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
Yes. When the security bulletin was released, Microsoft had received information that this vulnerability was being exploited.
Does applying this security update help protect customers from the code that has been published publicly that attempts to exploit this vulnerability?
Yes. This security update addresses the vulnerability that is currently being exploited. The vulnerability that has been addressed has been assigned the Common Vulnerability and Exposure number CVE-2006-5745.
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