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Vector Markup Language (VML) Code Execution (MS07-004)
------------------------------------------------------------------------
SUMMARY
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.
DETAILS
Affected Software:
* Microsoft Windows 2000 Service Pack 4
* Microsoft Windows XP Service Pack 2 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=81FB6A72-AC8A-4B28-905F-A44691D69432>
Download the update
* Microsoft Windows XP Professional x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=D06FD167-4F3E-4A2C-B52C-7426DDAD6828>
Download the update
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service
Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=4FEE481F-DACE-4EAC-9AFE-BC28ADD70CC5>
Download the update
* Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft
Windows Server 2003 with SP1 for Itanium-based Systems -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=C517FB85-128E-43DB-A659-38AF32283716>
Download the update
* Microsoft Windows Server 2003 x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=FF4A1F24-C1E9-4223-965B-14C4793AAF96>
Download the update
Non-Affected Software:
* Windows Vista
Affected Components:
* Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service
Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=B1C7F765-772C-4EEB-9438-BC820CB929E1>
Download the update
* Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service
Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=922A3569-85D1-4584-9B84-4AA7304C69BB>
Download the update
* Internet Explorer 7 on Microsoft Windows XP Service Pack 2 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=55A0A6EC-FEFA-40BB-BB6B-3AAB50275A73>
Download the update
* Internet Explorer 7 on Microsoft Windows XP Professional x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=B5A8B1F2-6AF0-4F03-989C-C8DE2EACE71D>
Download the update
* Internet Explorer 7 on Microsoft Windows Server 2003 and Microsoft
Windows Server 2003 Service Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=08E5CD2E-55C0-4AC9-859F-1B24497B31CE>
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 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=48B4D271-D494-4A5C-ABA8-11B3B4584902>
Download the update
* Internet Explorer 7 on Microsoft Windows Server 2003 x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=F9C3E0DE-DB66-4D83-829F-C93052BDB1FA>
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
<http://msdn.microsoft.com/library/default.asp?url=/workshop/security/szone/overview/esc_changes.asp>
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
<http://www.microsoft.com/downloads/details.aspx?FamilyID=d41b036c-e2e1-4960-99bb-9757f7e9e31b&DisplayLang=en%20http://www.microsoft.com/downloads/details.aspx?FamilyID=d41b036c-e2e1-4960-99bb-9757f7e9e31b&DisplayLang=en>
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.
ADDITIONAL INFORMATION
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>
http://www.microsoft.com/technet/security/bulletin/ms07-004.mspx
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