The following security advisory is sent to the securiteam mailing list, and can
be found at the SecuriTeam web site: http://www.securiteam.com
- - promotion
The SecuriTeam alerts list - Free, Accurate, Independent.
Get your security news from a reliable source.
http://www.securiteam.com/mailinglist.html
- - - - - - - - -
Vulnerability in Microsoft XML Core Services Allows Remote Code Execution
(MS06-071)
------------------------------------------------------------------------
SUMMARY
A vulnerability exists in the XMLHTTP ActiveX control within Microsoft XML
Core Services that could allow for remote code execution. An attacker
could exploit the vulnerability by constructing a specially crafted Web
page that could potentially allow remote code execution if a user visited
that page or clicked a link in an e-mail message. An attacker who
successfully exploited this vulnerability could take complete control of
an affected system. However, user interaction is required to exploit this
vulnerability.
DETAILS
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:
<http://technet2.microsoft.com/WindowsServer/en/library/6d7cb788-b31d-4d17-9f1e-b5ddaa6deecd1033.mspx?mfr=true>
Group Policy collection
<http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/TechRef/47ba1311-6cca-414f-98c9-2d7f99fca8a3.mspx>
What is Group Policy Object Editor?
<http://technet2.microsoft.com/WindowsServer/en/library/e926577a-5619-4912-b5d9-e73d4bdc94911033.mspx?mfr=true>
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:
<http://technet2.microsoft.com/WindowsServer/en/library/6d7cb788-b31d-4d17-9f1e-b5ddaa6deecd1033.mspx?mfr=true>
Group Policy collection
<http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/TechRef/47ba1311-6cca-414f-98c9-2d7f99fca8a3.mspx>
What is Group Policy Object Editor?
<http://technet2.microsoft.com/WindowsServer/en/library/e926577a-5619-4912-b5d9-e73d4bdc94911033.mspx?mfr=true>
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.
ADDITIONAL INFORMATION
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>
http://www.microsoft.com/technet/security/bulletin/ms06-071.mspx
========================================
This bulletin is sent to members of the SecuriTeam mailing list.
To unsubscribe from the list, send mail with an empty subject line and body to:
list-unsubscribe@securiteam.com
In order to subscribe to the mailing list, simply forward this email to:
list-subscribe@securiteam.com
====================
====================
DISCLAIMER:
The information in this bulletin is provided "AS IS" without warranty of any
kind.
In no event shall we be liable for any damages whatsoever including direct,
indirect, incidental, consequential, loss of business profits or special
damages.
