IIS Hidden Static Files Return HTTP 404 or Access Denied Errors

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This article was previously published under Q216803

We strongly recommend that all users upgrade to Microsoft Internet Information Services (IIS) version 7.0 running on Microsoft Windows Server 2008. IIS 7.0 significantly increases Web infrastructure security. For more information about IIS security-related topics, visit the following Microsoft Web site:

http://www.microsoft.com/technet/security/prodtech/IIS.mspx (http://www.microsoft.com/technet/security/prodtech/IIS.mspx)

For more information about IIS 7.0, visit the following Microsoft Web site:

http://www.iis.net/default.aspx?tabid=1 (http://www.iis.net/default.aspx?tabid=1)

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SYMPTOMS

Static files that have the hidden attribute set may return an HTTP 404 or an Access Denied error when browsed, while dynamic files can still be browsed.

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CAUSE

This behavior is by design.

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RESOLUTION

Configuring access control for all Web files should always be implemented through NTFS permissions.

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MORE INFORMATION

Dynamic files such as Active Server Pages (ASP) or Server-Side Includes (SSI) are implemented through script-mapped ISAPI extensions, in this case the Asp.dll and Ssiinc.dll files respectively. These extensions preprocess the executable code in the files being requested and can therefore read hidden files and return the expected HTML output to a client. Direct Web browsing of hidden static files results in a "File not Found" or an "Access Denied" error message.

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