[NT] Vulnerability in Remote Installation Service Could Allow Remote Code Execution (MS06-077)

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Vulnerability in Remote Installation Service Could Allow Remote Code
Execution (MS06-077)
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SUMMARY

The Remote Installation Service enables a TFTP service on the server which
by default could allow an anonymous user to potentially overwrite existing
operating system files or upload a specially crafted file. This could
allow an attacker to compromise operating system installs offered by the
RIS server.

DETAILS

Affected Software:
* Microsoft Windows 2000 Service Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=0ed62db9-4534-4f27-a49e-020c7a7d69e0> Download the update

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

Mitigating Factors:
* The attacker must be able to TFTP to the Remote Installation Server to
place a specially crafted file or program.
* The Remote Install Service is not installed by default on Windows 2000
Service Pack 4.
* For customers who require the affected component, 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.

Workarounds:
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.

* Configure the TFTP service as read only.

You can configure the TFTP service as read only by setting a value in the
registry.

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 regedit.exe.

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

To prevent the RIS server from accepting unauthorized access, add the
following to the registry using Regedit.exe.

1. Click Start, and click Run, type regedit (without the quotation
marks), and the click OK.
2. In Registry Editor, create the following registry key:
3. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TFTPD\Parameters
4. Add the DWORD Value: Masters. Set the value to 0. This value disables
writable TFTPD access.
5. You must restart the TFTP service for this change to take effect
6. TP service:
7. Click Start, click Run, type Run type cmd (without the quotation
marks), and then click OK.
8. In the cmd Window type Net stop TFTPD (without the quotation marks)
and press Enter.

* Block port 69 (UDP) at the firewall.
This port is used to initiate a connection with the affected component.
Blocking UDP port 69 at the firewall will help protect 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.

* Stop the TFTP service if it is not needed
1. Click Start, click Run, type cmd (without the quotation marks), and
then click OK.
2. In the cmd Window type "Net stop TFTPD" (without the quotation marks)
and press Enter.

Impact of Workaround: If you disable the TFTP service, users will not be
able to upload, view or write to the contents of TFTP directories.

* To help protect from network-based attempts to exploit this
vulnerability, enable advanced TCP/IP filtering on systems that support
this feature.

You can enable advanced TCP/IP filtering to block all unsolicited inbound
traffic. For more information about how to configure TCP/IP filtering, see
Microsoft Knowledge Base <http://support.microsoft.com/kb/309798> Article
309798.


To help protect from network-based attempts to exploit this vulnerability,
block the affected ports by using IPSec on the affected systems.

Use Internet Protocol security (IPSec) to help protect network
communications. Detailed information about IPSec and about how to apply
filters is available in <http://support.microsoft.com/kb/313190>
Microsoft Knowledge Base Article 313190 and
<http://support.microsoft.com/kb/813878> Microsoft Knowledge Base Article
813878.

CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-5584>
CVE-2006-5584

FAQ:
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.

What causes the vulnerability?
The vulnerability is caused by allowing anonymous access to the file
structure of a hosted operating system build through the RIS TFTP service.

What is RIS?
Remote Installation Services (RIS) is a Pre-boot Execution Environment
(PXE)-based deployment technology that allows Windows setup to initiate
over a network.

Who could exploit the vulnerability?
Any anonymous user who could deliver a specially crafted executable or
file to the affected RIS system could try to exploit this vulnerability at
a later time on systems that are built using the tampered operating system
build.

What systems are primarily at risk from the vulnerability?
All Windows 2000 Server Service Pack 4 systems that have RIS installed are
primarily at risk from this vulnerability.

Could the vulnerability be exploited over the Internet?
Yes. An attacker could try to exploit this vulnerability over the
Internet, but they must first have network permissions to gain access to
the RIS service. Firewall best practices and standard default firewall
configurations can help protect against attacks that originate from the
Internet.

What does the update do?
The update removes the vulnerability by not allowing anonymous TFTP users
the ability to write to the RIS hosted operating system build s file
structure. The update adds the registry key identified in the Workarounds
section of the bulletin.

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 original article can be found at:
<http://www.microsoft.com/technet/security/Bulletin/MS06-077.mspx>
http://www.microsoft.com/technet/security/Bulletin/MS06-077.mspx



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