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| 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 that could potentially allow remote code execution if a user visited the Web page or viewed the message. An attacker who successfully exploited this vulnerability could take complete control of an affected system. |
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Credit:
The information has been provided by MS07-004.
The original article can be found at:
http://www.microsoft.com/technet/security/bulletin/ms07-004.mspx
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Affected Software:
* Microsoft Windows 2000 Service Pack 4
* Microsoft Windows XP Service Pack 2 - Download the update
* Microsoft Windows XP Professional x64 Edition - Download the update
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1 - Download the update
* Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems - Download the update
* Microsoft Windows Server 2003 x64 Edition - Download the update
Non-Affected Software:
* Windows Vista
Affected Components:
* Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service Pack 4 - Download the update
* Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service Pack 4 - Download the update
* Internet Explorer 7 on Microsoft Windows XP Service Pack 2 - Download the update
* Internet Explorer 7 on Microsoft Windows XP Professional x64 Edition - Download the update
* Internet Explorer 7 on Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1 - Download the update
* Internet Explorer 7 on Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems - Download the update
* Internet Explorer 7 on Microsoft Windows Server 2003 x64 Edition - Download the update
Mitigating Factors for VML Buffer Overrun Vulnerability - CVE-2007-0024:
* 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.
* 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.
* In an e-mail based attack of this exploit, customers who read e-mail using Outlook Express on Windows XP Service Pack 2 and Windows Server 2003 Service Pack 1, are at less risk from this vulnerability because Binary and Script Behaviors is disabled by default in the Restricted sites zone.
* 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.
* By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability in Windows Server 2003 Service Pack 1 because Binary and Script Behaviors is disabled by default in the Internet zone.
* By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability in the e-mail vector for Outlook Express because reading e-mail messages in plain text is the default configuration. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.
Workarounds for VML Buffer Overrun Vulnerability - CVE-2007-0024:
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.
* Unregister VGX.DLL
1.Click Start, click Run, type "%SystemRoot%\System32\regsvr32.exe" -u "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll", and then click OK.
2. 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:
1. Click Start, click Run, type "%SystemRoot%\System32\regsvr32.exe" "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll", and then click OK.
2. 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
Applying this workaround may cause the installation of security updates provided with this security bulletin to fail:
To modify the Access Control List (ACL) on vgx.dll to be more restrictive, follow these steps:
1. Click Start, click Run, type "cmd" (without the quotation marks), and then click OK.
2. 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 Shared\VGX\vgx.dll"
3. Type the following command at a command prompt to deny the everyone group access to this file:
echo y| cacls "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll" /d everyone
4. 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.
Before this security update can be installed, this workaround must be reverted to the previous ACL configuration for vgx.dll. To revert to the previous vgx.dll ACL s follow these steps:
1. Click Start, click Run, type "cmd" (without the quotation marks), and then click OK.
2. To revert to the previous ACL configuration for vgx.dll, type the following command and replace the ACL on vgx.dll with the ACL s it previously had, which were recorded in step 2 of this workaround The command line to do so will vary depending on your environment:
echo y| cacls "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll" /g original ACL s
3. Close Internet Explorer, and reopen it for the changes to take effect.
Note If this workaround is applied, software that redistributes vgx.dll may fail to install. An example of this is Internet Explorer 7 Release Candidate 1 and subsequent versions of Internet Explorer 7. Before this software can be installed, this workaround must be reverted to the previous ACL configuration for vgx.dll.
Note Customers wishing to revert to the default installed ACL configuration for vgx.dll, type the following:
For Windows 2000 Service Pack 4:
echo y| cacls "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll" /P BUILTIN\Users:R "BUILTIN\Power Users:C" BUILTIN\Administrators:F "NT AUTHORITY\SYSTEM:F"
For Windows XP Service Pack 2:
echo y| cacls "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll" /P BUILTIN\Users:R "BUILTIN\Power Users:C" BUILTIN\Administrators:F "NT AUTHORITY\SYSTEM:F"
For Windows 2003 and Windows 2003 Service Pack 1:
echo y| cacls "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll" /P BUILTIN\Users:R "BUILTIN\Power Users:C" BUILTIN\Administrators:F "NT AUTHORITY\SYSTEM:F" NT AUTHORITY\TERMINAL SERVER USER:C
* Configure Internet Explorer 6 for Microsoft Windows XP Service Pack 2 to disable Binary and Script Behaviors in the Internet and Local Intranet security zone
You can help protect against this vulnerability by changing your settings to disable binary and script behaviors 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 ActiveX controls and plug-ins section, under Binary and Script Behaviors, click 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 Binary and Script Behaviors, click Disable, and then click OK.
7. Click OK two times to return to Internet Explorer.
Impact of Workaround: Disabling binary and script behaviors in the Internet and Local intranet security zones may cause some Web sites that rely on VML to not function correctly.
* Read e-mail messages in plain text format if you are using Outlook 2002 or a later version, or Outlook Express 6 SP1 or a later version, to help protect yourself from the HTML e-mail attack vector
Microsoft Outlook 2002 users who have applied Office XP Service Pack 1 or a later version and Microsoft Outlook Express 6 users who have applied Internet Explorer 6 Service Pack 1 or a later version can enable this setting and view e-mail messages that are not digitally signed or e-mail messages that are not encrypted in plain text only.
Digitally signed e-mail messages or encrypted e-mail messages are not affected by the setting and may be read in their original formats. For more information about how to enable this setting in Outlook 2002, see Microsoft Knowledge Base Article 307594.
For information about this setting in Outlook Express 6, see Microsoft Knowledge Base Article 291387.
Impact of Workaround: E-mail messages that are viewed in plain text format will not contain pictures, specialized fonts, animations, or other rich content. Additionally:
* The changes are applied to the preview pane and to open messages.
* Pictures become attachments so that they are not lost.
* Because the message is still in Rich Text or HTML format in the store, the object model (custom code solutions) may behave unexpectedly.
* Block VML Vulnerability Traffic with ISA Server
Customers with Microsoft Internet Security and Acceleration (ISA) Server 2004 or 2006 may also block malicious traffic intended to exploit this vulnerability. For more information about how to enable this setting in ISA Server, see Learn How Your ISA Server Helps Block VML Vulnerability Traffic.
FAQ for VML Buffer Overrun Vulnerability - CVE-2007-0024:
What is the scope of the vulnerability?
This is a remote code execution vulnerability 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 that could potentially allow remote code execution if a user visited the Web page or viewed the message.
If a user were 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 affected than users who operate with administrative user rights.
What causes the vulnerability?
An unchecked buffer in the VML implementation in Microsoft Windows.
What is VML?
Vector Markup Language (VML) is an XML-based exchange, editing, and delivery format for high-quality vector graphics on the Web that meets the needs of both productivity users and graphic design professionals. XML is a simple, flexible, and open text-based language that complements HTML. For more information on the VML, see the product documentation.
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?
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.
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.
Customers who read e-mail in plain text would also be at less risk when using the Outlook or Outlook Express preview panes.
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 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 Windows validates the length of data before storing it in the allocated buffer.
When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft originally 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?
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-2007-0024.
How does this vulnerability relate to the vulnerability that is corrected by MS06-055?
While both vulnerabilities were in VML, this update addresses a new vulnerability that was not addressed as part of MS06-055. MS06-055 helps protect against the vulnerability that is discussed in that bulletin, but does not address this new vulnerability. You must install this update to help protect your system against both vulnerabilities.
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