[NT] Vulnerability in Microsoft Agent Allows Code Execution (MS06-068)



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Vulnerability in Microsoft Agent Allows Code Execution (MS06-068)
------------------------------------------------------------------------


SUMMARY

There is a remote code execution vulnerability in the way that Microsoft
Agent handles specially crafted .ACF files. An attacker could exploit the
vulnerability by constructing a specially crafted Web page that could
potentially allow remote code execution if a user viewed the Web page. An
attacker who successfully exploited this vulnerability could take complete
control of an affected system.

DETAILS

Affected Software:
* Microsoft Windows 2000 Service Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=c72ceec8-3e4d-4281-8183-11b724693217> Download the update
* Microsoft Windows XP Service Pack 2 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=c16e1607-f396-4113-89f6-1fe89ec54b6a> Download the update
* Microsoft Windows XP Professional x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=b4002a2a-b03e-4428-a26a-84293270d149> Download the update
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service
Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=8f1a3f85-830b-4662-a4cc-8dff9f59acea> 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=b528f61d-ad54-4bad-b9a0-b650385de216> Download the update
* Microsoft Windows Server 2003 x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=3da7ff4a-2389-4ce4-a6bb-b7e02f646b74> Download the update

Non-Affected Software:
* Windows Vista

Mitigating Factors for Microsoft Agent Memory Corruption Vulnerability -
CVE-2006-3445:
* 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.

* 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.

* The Restricted sites zone helps reduce attacks that could try to
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, 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 Agent Memory Corruption Vulnerability -
CVE-2006-3445:
* Temporarily prevent the Microsoft Agent ActiveX control from running in
Internet Explorer

You can help prevent attempts to instantiate this ActiveX control in
Internet Explorer by setting the kill bit for the control 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 the 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.

To set the kill bit for a CLSID with a value of {CLSID}, 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\{D45FD31B-5C6E-11D1-9EC1-00C04FD7081F}]

"Compatibility Flags"=dword:00000400

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX
Compatibility\{F5BE8BD2-7DE6-11D0-91FE-00C04FD701A5}]

"Compatibility Flags"=dword:00000400

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX
Compatibility\{4BAC124B-78C8-11D1-B9A8-00C04FD97575}]

"Compatibility Flags"=dword:00000400

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX
Compatibility\{D45FD31D-5C6E-11D1-9EC1-00C04FD7081F}]

"Compatibility Flags"=dword:00000400

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX
Compatibility\{D45FD31E-5C6E-11D1-9EC1-00C04FD7081F}]

"Compatibility Flags"=dword:00000400

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://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/TechRef/6d7cb788-b31d-4d17-9f1e-b5ddaa6deecd.mspx> 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://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/TechRef/e926577a-5619-4912-b5d9-e73d4bdc9491.mspx> 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 Microsoft Agent ActiveX
Control may no longer display or function correctly.

* 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.

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 .

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
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.

* 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 .

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
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.

FAQ for Microsoft Agent Memory Corruption Vulnerability - CVE-2006-3445:
What is the scope of the vulnerability?
This is a remote code execution vulnerability. 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.

What causes the vulnerability?
When Microsoft Agent handles specially crafted .ACF files it may corrupt
system memory in such a way that an attacker could execute arbitrary code.

What is Microsoft Agent?
Microsoft Agent is a software technology that enables an enriched form of
user interaction that can make using and learning to use a computer easier
and more natural. For more information, see the Microsoft Agent Web site.

What might an attacker use the vulnerability to do?
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.

Who could exploit the vulnerability?
In a Web-based attack scenario, an attacker would have to host a Web site
that contains a Web page that is used to attempt to exploit this
vulnerability. An attacker would have no way to force users to visit a
specially crafted Web site. Instead, an attacker would have to persuade
them to visit the Web site, typically by getting them to click a link that
takes them to the attacker's site.

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 7. Does this mitigate this vulnerability?
Yes. Customers who are running Internet Explorer 7 with default settings,
are not at risk until the MS Agent ActiveX control has been activated
through the ActiveX opt-in feature in the Internet Zone.

What is the ActiveX Opt-in feature in Internet Explorer 7?
Internet Explorer 7 includes an ActiveX opt-in feature, which means that
nearly all pre-installed ActiveX controls are off by default. Users are
prompted by the Information Bar before they can access a previously
installed ActiveX Control that has not yet been used on the Internet. This
enables a user to permit or deny access on a control-by-control basis. For
more information about this and other new features see the Windows
Internet Explorer 7 features page.

I am running Internet Explorer on Windows Server 2003. Does this mitigate
this vulnerability?
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. See the FAQ section of this security update
for more information about Internet Explorer Enhanced Security
Configuration.

What is 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 administrator downloading and running malicious Web content on a
server. Internet Explorer Enhanced Security Configuration reduces this
threat by modifying numerous security-related settings, including Security
and Advanced tab settings in Internet Options. Some of the key
modifications include:

* Security level for the Internet zone is set to High. This setting
disables scripts, ActiveX components, Microsoft virtual machine (Microsoft
VM) HTML content, 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, please consult the Managing Internet Explorer Enhanced
Security Configuration guide, which can be found at the following Web
site.

What does the update do?
The update removes the vulnerability by modifying the way that Microsoft
Agent validates the length of a message before it passes the message to
the allocated buffer.

When this security bulletin was issued, had this vulnerability been
publicly disclosed?
No. Microsoft 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?
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 Product Security.
The original article can be found at:
<http://www.microsoft.com/technet/security/bulletin/ms06-068.mspx>
http://www.microsoft.com/technet/security/bulletin/ms06-068.mspx



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