[NT] Vulnerability in Microsoft Agent Allows Code Execution (MS07-051)



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Vulnerability in Microsoft Agent Allows Code Execution (MS07-051)
------------------------------------------------------------------------


SUMMARY

A remote code execution vulnerability exists in Microsoft Agent in the way
that it handles certain specially crafted URLs. The vulnerability could
allow an attacker to remotely execute code on the affected system. 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:
* Microsoft Windows 2000 Service Pack 4

Non-Affected Software:
* Windows XP Service Pack 2
* Windows XP Professional x64 Edition and Windows XP Professional x64
Edition Service Pack 2
* Windows Server 2003 Service Pack 1 and Server 2003 Service Pack 2
* Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition
Service Pack 2
* Windows Server 2003 with SP1 for Itanium-based Systems and Windows
Server 2003 with SP2 for Itanium-based Systems
* Windows Vista
* Windows Vista x64 Edition

Agent Remote Code Execution Vulnerability:
A remote code execution vulnerability exists in Microsoft Agent in the way
that it handles certain specially crafted URLs. The vulnerability could
allow an attacker to remotely execute code on the affected system. 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.

To view this vulnerability as a standard entry in the Common
Vulnerabilities and Exposures list, see
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-3040>
CVE-2007-3040.

Mitigating Factors for Agent Remote Code Execution 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 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 a malicious 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 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 ActiveX controls 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, 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 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.

Workarounds for Agent Remote Code Execution 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:

* Temporarily prevent the 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
{D45FD31B-5C6E-11D1-9EC1-00C04FD7081F}, 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 will no longer work correctly via Internet Explorer.

* Unregister AgentSvr.exe

Enter the following at a command line or in a logon or machine startup
script:
%windir%\msagent\agentsvr.exe /unregserver

Impact of workaround: Microsoft Agent will no longer work.

* 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. To continue receiving security updates from Microsoft, add are
*.windowsupdate.microsoft.com and *.update.microsoft.com. These are the
sites that will host the update, and you must have 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 Agent Remote Code Execution Vulnerability:
What is the scope of the vulnerability?
A remote code execution vulnerability exists in Microsoft Agent in the way
that it handles certain specially crafted URLs. 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?
Supplying a specially crafted URL to the Microsoft Agent ActiveX control
could corrupt system memory so that an attacker could execute arbitrary
code.

What is Microsoft Agent?
Microsoft Agent is a component of the Microsoft Windows operating system
that uses interactive animated characters to guide users and can make
using and learning to use a computer easier. For more information, see the
<http://www.microsoft.com/msagent/> Microsoft Agent Web site.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability 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.

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 convince
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. Any systems where Internet Explorer is
used frequently, such as workstations or terminal servers, are at the most
risk from this vulnerability.

What does the update do?
The update removes the vulnerability by changing the way Microsoft Agent
handles specially crafted URLs.

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/ms07-051.mspx>
http://www.microsoft.com/technet/security/bulletin/ms07-051.mspx



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