[NT] Vulnerability in Microsoft XML Core Services Could Allow Remote Code Execution (MS07-042)



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Vulnerability in Microsoft XML Core Services Could Allow Remote Code
Execution (MS07-042)
------------------------------------------------------------------------


SUMMARY

A remote code execution vulnerability exists in Microsoft XML Core
Services that could allow an attacker who successfully exploited this
vulnerability to make changes to the system with the permissions of the
logged-on user. If a user is logged on with administrative user rights, an
attacker could take complete control of the 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.

DETAILS

Affected Software:
* Windows 2000 Service Pack 4
* Windows XP Service Pack 2
* Windows XP Professional x64 Edition
* Windows XP Professional x64 Edition Service Pack 2
* Windows Server 2003 Service Pack 1
* Windows Server 2003 Service Pack 2
* Windows Server 2003 x64 Edition
* Windows Server 2003 x64 Edition Service Pack 2
* Windows Server 2003 with SP1 for Itanium-based Systems
* Windows Server 2003 with SP2 for Itanium-based Systems
* Windows Vista
* Windows Vista x64 Edition
* Microsoft Office 2003 Service Pack 2
* 2007 Microsoft Office System
* Microsoft Office SharePoint Server
* Microsoft Office Groove Server 2007

CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-2223>
CVE-2007-2223

Mitigating Factors for Microsoft XML Core Services Vulnerability:
* 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, Web sites that accept or host user-provided content, or
compromised Web sites and advertisement servers could contain specially
crafted content that could exploit this vulnerability. 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.

* By default, all supported versions of Microsoft Outlook and Microsoft
Outlook Express open HTML e-mail messages in the Restricted sites zone.
The Restricted sites zone helps reduce the number of successful attacks
that exploit this vulnerability by preventing Active Scripting and ActiveX
controls from being used when reading HTML e-mail. However, if a user
clicks on a link within an e-mail, they could still be vulnerable to this
issue through the Web-based attack scenario.

* 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 subsection of this vulnerability
section for more information about Internet Explorer Enhanced Security
Configuration.

Workarounds for Microsoft XML Core Services Vulnerability:
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:

* Configure Internet Explorer to prompt before running Active Scripting
or to 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.

Impact of Workaround: 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..

* 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
system. 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.

* 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. 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 .

FAQ for Microsoft XML Core Services Vulnerability:
What is the scope of the vulnerability?
If successfully exploited, this remote code execution vulnerability could
allow the attacker to run arbitrary code as the logged on user.

What causes the vulnerability?
Specially crafted script requests may cause memory corruption when using
Microsoft XML Core Services.

What is Microsoft XML Core Services (MSXML)?
Microsoft XML Core Services (MSXML) allows customers who use JScript,
Visual Basic Scripting Edition (VBScript), and Microsoft Visual Studio 6.0
todevelop XML-based applications 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 make
changes to the system with the permissions of the logged-on user. If a
user is logged on with administrative user rights, an attacker could take
complete control of the 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.

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 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
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 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.

I am running Internet Explorer on Windows Server 2003. Does this mitigate
this vulnerability?
Yes. By default, Internet Explorer for Windows Server 2003 runs in a
restricted mode that is known as Enhanced Security Configuration. Enhanced
Security Configuration is a group of preconfigured settings in Internet
Explorer that can reduce the likelihood of a user or administrator
downloading and running malicious Web content on a server. This is a
mitigating factor for Web sites that you have not added to the Internet
Explorer Trusted sites zone. See also Managing Internet Explorer Enhanced
Security Configuration.

What does the update do?
The update removes the vulnerability by validating the memory request
within Microsoft XML Core Services.

When this security bulletin was issued, had this vulnerability been
publicly disclosed?
No. Microsoft received information about this vulnerability through
responsible disclosure. Microsoft had not received any information to
indicate that this vulnerability had been publicly disclosed when this
security bulletin was originally issued.

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.


ADDITIONAL INFORMATION

The information has been provided by Microsoft Security Bulletin MS07-042.
The original article can be found at:
<http://www.microsoft.com/technet/security/Bulletin/MS07-042.mspx>
http://www.microsoft.com/technet/security/Bulletin/MS07-042.mspx



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