[NT] Vulnerability in Windows Media File Format Allows Code Execution (MS07-068)

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Vulnerability in Windows Media File Format Allows Code Execution
(MS07-068)
------------------------------------------------------------------------

SUMMARY

This critical security update resolves a privately reported vulnerability
in Windows Media File Format.

This vulnerability could allow remote code execution if a user viewed a
specially crafted file in Windows Media Format Runtime. 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:
* Windows Media Format Runtime 7.1
* Microsoft Windows 2000 Service Pack 4

* Windows Media Format Runtime 9
* Windows 2000 Service Pack 4
* Windows XP Service Pack 2

* Windows Media Format Runtime 9.5
* 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 Windows Server 2003 Service
Pack 2
* Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition
Service Pack 2

* Windows Media Format Runtime 9.5 x64 Edition
* Windows XP Professional x64 Edition and Windows XP Professional x64
Edition Service Pack 2
* Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition
Service Pack 2

* Windows Media Format Runtime 11
* Windows XP Service Pack 2
* Windows XP Professional x64 Edition and Windows XP Professional x64
Edition Service Pack 2
* Windows Vista
* Windows Vista x64 Edition

* Windows Media Services 9.1
* Windows Server 2003 Service Pack 1 and Windows Server 2003 Service
Pack 2
* Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition
Service Pack 2

Non-Affected Software:
* Windows Media Player 6.4 when installed on Microsoft Windows 2000
* Windows Media Player 6.4 when installed on Windows XP
* Windows Media Player 6.4 when installed on Windows Server 2003
* Windows Media Services 4.1 when installed on Microsoft Windows 2000
* Microsoft Windows 2003 For Itanium-Based Systems and Windows Server
2003 with SP1 for Itanium-based Systems

Windows Media Format Remote Code Execution Vulnerability Parsing ASF -
CVE-2007-0064:
A remote code execution vulnerability exists in Windows Media Format
Runtime due to the way it handles Advanced Systems Format (ASF) files. In
client applications, such as Windows Media Player, an attacker could
exploit the vulnerability by constructing specially crafted Windows Media
Format Runtime content that could potentially allow remote code execution
if a user visits a specially crafted Web site or opens an e-mail message
with specially crafted content. In server applications, such as Windows
Media Services, an attacker could exploit the vulnerability by
constructing specially crafted Windows Media Format Runtime content that
could potentially allow remote code execution if the server processes the
specially crafted content. In client and server applications, an attacker
who successfully exploited this vulnerability could take complete control
of an affected system.

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-2007-0064>
CVE-2007-0064.

Mitigating Factors for Windows Media Format Remote Code Execution
Vulnerability Parsing ASF - CVE-2007-0064:
Mitigation refers to a setting, common configuration, or general
best-practice, existing in a default state, which could reduce the
severity of exploitation of a vulnerability. The following mitigating
factors may be helpful in your situation:

* Mitigating Factors for Client Application:

* 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 convince 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 affected
than users who operate with administrative user rights.

* Windows Media Player 6.4 when installed on Windows 2000, Windows XP, or
Windows Server 2003 is not affected.

* Mitigating Factors for Server Application:

* An attacker who successfully exploited this vulnerability could gain
the same privileges as the network service account.

* Windows Media Services 9.1, which includes wmsserver.dll, is an
optional operating system component on all supported 32-bit editions of
Windows Server 2003, and x64-based editions of Windows Server 2003.

Workarounds for Windows Media Format Remote Code Execution Vulnerability
Parsing ASF - CVE-2007-0064:
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:

The core workaround for these vulnerabilities is to deny access to the
vulnerable DLLs on each affected operating system.

* For client applications deny access to WMASF.DLL

From an administrative command prompt in Windows XP and Windows Server
2003 run the following command:
Echo y| cacls exe %WINDIR%\SYSTEM32\WMASF.DLL /E /P everyone:N

From an elevated command prompt in Windows Vista run the following
commands:
Takeown.exe /f %WINDIR%\SYSTEM32\WMASF.DLL
Icacls.exe %WINDIR%\SYSTEM32\WMASF.DLL /save %TEMP%\WMASF_ACL.TXT
Icacls.exe %WINDIR%\SYSTEM32\WMASF.DLL /deny everyone:(F)

Impact of Workaround: Users will be unable to play Advanced Systems Format
(ASF) files.

* For server applications, Microsoft has not identified any workarounds
for this vulnerability.

FAQ for Windows Media Format Remote Code Execution Vulnerability Parsing
ASF - CVE-2007-0064:
What is the scope of the vulnerability?
A remote code execution vulnerability exists in Windows Media Format
Runtime due to the way it handles Advanced Systems Format (ASF) files. In
client applications, such as Windows Media Player, an attacker could
exploit the vulnerability by constructing specially crafted Windows Media
Format Runtime content that could potentially allow remote code execution
if a user visits a specially crafted Web site or opens an e-mail message
with specially crafted content. In server applications, such as Windows
Media Services, an attacker could exploit the vulnerability by
constructing specially crafted Windows Media Format Runtime content that
could potentially allow remote code execution if the server processes the
specially crafted content. In client and server applications, an attacker
who successfully exploited this vulnerability could take complete control
of an affected system.

What causes the vulnerability?
Incorrect parsing of Advanced Systems Format (ASF) files within the
Windows Media Format Runtime.

What is Windows Media Format Runtime?
The Microsoft Windows Media Format Runtime provides information and tools
for applications that use Windows Media content. For more information, see
the product documentation.

What is Windows Media Services 9.1?
The Windows Media Services 9.1, which includes wmsserver.dll, is an
optional operating system component on all supported 32-bit editions of
Windows Server 2003, and x64-based editions of Windows Server 2003. This
server application runs as a low privileged networking service account for
processing media files. For more information, see the product
documentation.

What is Advanced Systems Format (ASF)?
ASF (Advanced Systems Format) is a file format that stores audio and video
information and is specially designed to run over networks like the
Internet. It is a compressed format that contains streaming audio, video,
slide shows, and synchronized events. ASF enables content to be delivered
to you as a continuous flow of data. ASF files may have the file
extensions ASF, WMV, or WMA.

What might an attacker use the vulnerability to do?
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
are less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability?
In a client Web-based attack scenario, an attacker could host a Web site
designed to exploit this vulnerability through Windows Media Player. In no
case, however, would an attacker have a way to force users to visit these
Web sites. Instead, an attacker would have to convince 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. In server applications an attacker could exploit the vulnerability
by constructing specially crafted Windows Media Format Runtime content
that could potentially allow remote code execution if the server processes
the specially crafted content.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user is logged on and opens the
specially crafted ASF file in any Windows Media Format Runtime-based
application for any malicious action to occur. Therefore, any systems
where Windows Media Format Runtime or Windows Media Server 9.1 s 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 modifying the way that Windows
Media Format Runtime parses Advanced Systems Format (ASF) files.

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 information has been provided by Microsoft Security Bulletin MS07-068.
The original article can be found at:
<http://www.microsoft.com/technet/security/bulletin/ms07-068.mspx>

http://www.microsoft.com/technet/security/bulletin/ms07-068.mspx

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