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:

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.

Echo y| cacls exe %WINDIR%\SYSTEM32\WMASF.DLL  /E /P everyone:N
       

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)
       

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.