[NT] Vulnerability in Windows Explorer Allows Code Execution (MS06-045)

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Vulnerability in Windows Explorer Allows Code Execution (MS06-045)
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SUMMARY

A remote code execution vulnerability exists in Windows Explorer because
of the way that Windows Explorer handles Drag and Drop events. An attacker
could exploit the vulnerability by constructing a malicious Web page that
could potentially allow an attacker to save a file on the user s system if
a user visited a malicious Web site or viewed a malicious e-mail message.
An attacker who successfully exploited this vulnerability could take
complete control of an affected system. User interaction is required to
exploit this vulnerability

DETAILS

Affected Software:
* Microsoft Windows 2000 Service Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=38cee83e-b17a-4c08-90ce-fb836b9615ad> Download the update
* Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service
Pack 2 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=6ef68858-4c91-47fb-ae34-0be556f10ede> Download the update
* Microsoft Windows XP Professional x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=50935f4e-e383-493e-97c6-599cbb2b87cc> Download the update
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service
Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=759435a3-98f9-4115-b52e-d7fa9d024f16> 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=462131c6-a728-4b3c-94de-85deccc42c3e> Download the update
* Microsoft Windows Server 2003 x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=50eef5c5-861d-4802-85a2-6b0627aafc2a> Download the update

Mitigating Factors for Folder GUID Code Execution Vulnerability -
CVE-2006-3281:
* Firewall best practices and standard default firewall configurations
can help protect networks from attacks that originate outside the
enterprise perimeter. Best practices recommend that systems that are
connected to the Internet have a minimal number of ports exposed.

* 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. After they click the link, they would be prompted to
perform several actions. An attack could only occur after they performed
these actions.

* 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 described previously.

By default, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML
e-mail messages in the Restricted sites zone. Additionally, Outlook 98 and
Outlook 2000 open 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.

* The vulnerability could not be exploited automatically through e-mail.
For an attack to be successful a user must open an attachment or click on
a link that is sent in an e-mail message.

Workarounds for Folder GUID Code Execution Vulnerability - CVE-2006-3281:
Microsoft has tested the following workarounds. While 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.

* Disable the Web Client service
Disabling the Web Client service will help protect the affected system
from attempts to exploit this vulnerability. To disable the Web Client
service, follow these steps:

1. Click Start, and then click Control Panel. Alternatively, point to
Settings, and then click Control Panel.
2. Double-click Administrative Tools.
3. Double-click Services.
4. Double-click WebClient.
5. In the Startup type list, click Disabled.
6. Click Stop, and then click OK.

You can also stop and disable the Web Client service by using the
following command at the command prompt:
sc stop WebClient & sc config WebClient start= disabled

Impact of Workaround: If the Web Client service is disabled, Web
Distributed Authoring and Versioning (WebDAV) requests are not
transmitted. If the Web Client service is disabled, any services that
explicitly depend on the Web Client service will not start, and an error
message will be logged in the System log. Windows Server 2003 users will
not be able to use the "Open as Web Folder" functionality.

* Use the Group Policy settings to disable the WebClient service on all
affected systems that do not require this feature.
Because the Web Client service is a possible attack vector, disable the
service by using the Group Policy settings. You can disable the startup of
this service at either the local, site, domain, or organizational-unit
level by using Group Policy object functionality in Windows 2000 domain
environments or in Windows Server 2003 domain environments.

Note You may also review the Windows Server 2003 Security Guide. This
guide includes information about how to disable services.

For more information about Group Policy, visit the following Microsoft Web
sites:

* Step-by-Step Guide to Understanding the Group Policy Feature Set

* Windows 2000 Group Policy

* Group Policy in Windows Server 2003

Impact of Workaround: If the Web Client service is disabled, Web
Distributed Authoring and Versioning (WebDAV) requests are not
transmitted. If the Web Client service is disabled, any services that
explicitly depend on the Web Client service will not start, and an error
message will be logged in the System log. Windows Server 2003 users will
not be able to use the "Open as Web Folder" functionality.

* Disable the file: protocol handler.

Note Using Registry Editor incorrectly can cause serious problems that may
require you to reinstall your operating system. Microsoft cannot guarantee
that problems resulting from the incorrect use of Registry Editor can be
solved. Use Registry Editor at your own risk. For information about how to
edit the registry, view the "Changing Keys And Values" Help topic in
Registry Editor (Regedit.exe) or view the "Add and Delete Information in
the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

Note We recommend backing up the registry before you edit it.

To disable the file: protocol handler, follow these steps:

1. Close all instances of Internet Explorer
2. Click Start, click Run, type "regedt32 " (without the quotation marks),
and then click OK
3. In Registry Editor, locate the following registry
key:HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
4. Add or edit the DWORD value NoFileUrl
5. Set the value to 1

Impact of Workaround: URLs utilizing the file: handler will not function.

* Block TCP ports 139 and 445 at the firewall:

Although WebDAV uses TCP port 80 for outbound communication, TCP ports 139
and 445 can be used outbound to attempt to connect to a malicious service
and try to exploit this vulnerability. Blocking them at the firewall can
help prevent systems that are behind that firewall from attempts to
exploit this vulnerability. We recommend that you block all unsolicited
inbound communication from the Internet to help prevent attacks that may
use other ports. For more information about ports, visit the following
<http://go.microsoft.com/fwlink/?LinkId=21312> Web site.

FAQ for Folder GUID Code Execution Vulnerability - CVE-2006-3281:
What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who
successfully exploited this vulnerability could remotely 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.

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?
Improper handling by Windows Explorer of Drag and Drop events. User
interaction is required to exploit this vulnerability

What might an attacker use the vulnerability to do?
An attacker who could successfully convince a user to visit attacker's web
site and save a specially crafted file to the affected system could take
complete control of the users system.

What systems are primarily at risk from the vulnerability?
Workstations and terminal servers are primarily at risk. Servers could be
at more risk if users who do not have sufficient administrative
permissions are given the ability to log on to servers and to run
programs. However, best practices strongly discourage allowing this.

What does the update do?
The update removes the vulnerability by preventing specially crafted files
and directories from invoking arbitrary code without specific user
interaction.

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-2006-3281. It also has been
named Microsoft Internet Explorer Information Disclosure and HTA File
Execution Vulnerability by the larger security community.

When this security bulletin was issued, had Microsoft received any reports
that this vulnerability was being exploited?
No. Microsoft had seen examples of proof of concept code published
publicly but had not received any information to indicate that this
vulnerability had been publicly used to attack customers when this
security bulletin was originally issued.

How does this vulnerability relate to the vulnerability that is corrected
by MS06-015?
Both vulnerabilities were in Windows Explorer. However, this update
addresses a new vulnerability that was not addressed as part of MS06-015.
MS06-015 helps protect against the vulnerability that is discussed in that
bulletin, but does not address this new vulnerability. This update does
not replace MS06-015


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/MS06-045.mspx>
http://www.microsoft.com/technet/security/Bulletin/MS06-045.mspx



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