Microsoft Bob

Just a short, simple blog for Bob to share some tips and tricks.

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Month List

Life after FPSE (Part 6)

In this latest installment on my series about configuring your server for hosting without the FrontPage Server Extensions (FPSE), I'd like to discuss a couple of WebDAV best practices that I like to use.

Blocking FPSE-related Folders with Request Filtering

In my How to Migrate FPSE Sites to WebDAV walkthough, I discuss the following FPSE-related folders:

Folder Notes
_fpclass Should contain publicly-available FrontPage code - but should be secured.
_private The FrontPage Server Extensions often keep sensitive data files in this folder, so it should be secured to prevent browsing.
_vti_bin This is the virtual directory for the FrontPage Server Extensions executables. This path is configured to allow executables to function, and since we are migrating sites to WebDAV it should be secured to prevent browsing.
_vti_cnf The FrontPage Server Extensions keep sensitive metadata files in this folder, so it should be deleted or secured to prevent browsing.
_vti_log The FrontPage Server Extensions keep author logs in this folder, so it should be deleted or secured to prevent browsing.
_vti_pvt This folder holds several files that contain various metadata for your website, and should be secured.
_vti_txt This folder contains the text indices and catalogs for the older FrontPage WAIS search. Since later versions of FrontPage only used Index Server, it is safe to delete this folder, but at the very least it should be secured to prevent browsing.
fpdb FrontPage keeps databases in this folder, so it should be secured to prevent browsing.

One of the actions that I usually take on my servers is to lock down all of these folders for my entire server using Request Filtering. To do so, open a command prompt and enter the following commands:

cd %WinDir%\System32\inetsrv

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_vti_cnf']" /commit:apphost

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_fpclass']" /commit:apphost

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_private']" /commit:apphost

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_vti_log']" /commit:apphost

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_vti_pvt']" /commit:apphost

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_vti_txt']" /commit:apphost

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='fpdb']" /commit:apphost

Note: You should only enter the following commands if you are sure that you will not be using FPSE anywhere on your server!

cd %WinDir%\System32\inetsrv

appcmd.exe set config -section:system.webServer/security/requestFiltering /+"hiddenSegments.[segment='_vti_bin']" /commit:apphost

These settings will prevent any of the FPSE-related paths from being viewed over HTTP from a web browser; web clients will receive an HTTP Error 404.8 - Not Found message when they attempt to access those paths. But that being said - when you enable WebDAV for a website by using the Internet Information Services (IIS) Manager, it will configure the Request Filtering settings that enable WebDAV clients to access those paths through WebDAV requests, even though access from a web browser is still blocked. (All of this is made possible through the built-in integration between WebDAV and Request Filtering. ;-]) Enabling access to these folders over WebDAV is necessary if you are opening your website over a WebDAV-mapped drive while you are using authoring clients that do not have native WebDAV support, such as FrontPage or Visual Studio.

Two Sites are Better Than One

In part 4 of this blog series I discussed why I like to set up two websites when using WebDAV; as a quick review, here is the general idea for that environment:

  • The first website (e.g. www.example.com) is used for normal HTTP web browsing
  • The second website (e.g. authoring.example.com) is used for for WebDAV authoring

There is a list of several reasons in that blog post why using two sites that point to the same content can be beneficial, and I won't bother quoting that list in this blog post - you can view that information by looking at that post.

But that being said, one of the items that I mentioned in that list was using separate application pools for each website. For example:

  • The first application pool (e.g. www.example.com) is configured to use delegated configuration
  • The second application pool (e.g. authoring.example.com) is configured to ignore delegated configuration

This configuration helps alleviate problems from uploading invalid Web.config files that might otherwise prevent HTTP access to your website. By way of explanation, the WebDAV module attempts to validate Web.config files when they are uploaded over WebDAV - this is done to try and prevent crashing your HTTP functionality for a website and being unable to fix it. Here's what I mean by that: IIS 7 allows configuration settings to be delegated to Web.config files, but if there is a mistake in a Web.config file, IIS 7 will return an HTTP Error 500.19 - Internal Server Error message for all HTTP requests. Since WebDAV is HTTP-based, that means that you won't be able to fix the problem over WebDAV. (If the WebDAV module didn't perform any validation, that means that your website would become unusable and unrepairable if you had uploaded the bad Web.config file over WebDAV.) To help alleviate this, the WebDAV module performs a simple validation check to prevent uploading invalid Web.config files. But if you save an invalid Web.config file through some other means, like the local file system or over FTP, then you will have no way to repair the situation through WebDAV.

This leads us back to the idea that you can implement when you are using two websites - you can configure the application pool for the WebDAV-enabled website to ignore delegated configuration settings; so it doesn't matter if you have an invalid Web.config file - you will always be able to fix the problem over WebDAV. To configure an application pool to ignore delegated configuration settings, open a command prompt and enter the following commands:

cd %WinDir%\System32\inetsrv

appcmd.exe set config -section:system.applicationHost/applicationPools /[name='authoring.example.com'].enableConfigurationOverride:"False" /commit:apphost

Note: you need to update the highlighted section of that example with the name of your website, such as "Default Web Site," etc.

When you have two websites configured in this example and you have an invalid Web.config file that is causing the HTTP 500 error for the www.example.com website, you can still connect to authoring.example.com via WebDAV and fix the problem.

More Information

For additional information on the concepts that were discussing in this blog, see the following topics:

  • Life after FPSE (Part 4) - This blog post discusses a couple of WebDAV-related topics, and includes my list of additional reasons why configuring two websites when you are using WebDAV can be advantageous.
  • Adding Application Pools - This topic contains the detailed information about the enableConfigurationOverride setting for an application pool.
  • Using the WebDAV Redirector - This walkthrough discusses mapping drives to WebDAV-enabled websites.

I hope this helps. ;-]

Note: This blog was originally posted at http://blogs.msdn.com/robert_mcmurray/
Posted: Jan 31 2011, 12:06 by Bob | Comments (0)
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IIS 6.0 WebDAV and Compound Document Format Files

We recently ran into a situation where a customer thought that they were seeing file corruption when they were transferring files from a Windows 7 client to their IIS 6.0 server using WebDAV. More specifically, the file sizes were increasing for several specific file types, and for obvious reasons the checksums for these files would not match for verification. Needless to say this situation caused a great deal of alarm on the WebDAV team when we heard about it - file corruption issues are simply unacceptable.

To alleviate any fears, I should tell you right up front that no corruption was actually taking place, and the increase in file size was easily explained once we discovered what was really going on. All of that being said, I thought that a detailed explanation of the scenario would make a great blog entry in case anyone else runs into the situation.

The Customer Scenario

First of all, the customer was copying installation files using a batch file over WebDAV; more specifically the batch file was copying a collection of MSI and MST files. After the batch file copied the files to the destination server it would call the command-line comp utility to compare the files. Each MSI and MST file that was copied would increase by a small number of bytes so the comparison would fail. The customer computed checksums for the files to troubleshoot the issue and found that the checksums for the files on the source and destination did not match. Armed with this knowledge the customer contacted Microsoft for support, and eventually I got involved and I explained what the situation was.

The Architecture Explanation

Windows has a type of file format called a Compound Document, and many Windows applications make use of this file format. For example, several Microsoft Office file formats prior to Office 2007 used a compound document format to store information.

A compound document file is somewhat analogous to a file-based database, or in some situations like a mini file system that is hosted inside another file system. In the case of an MST or MSI file these are both true: MST and MSI files store information it various database-style tables with rows and columns, and they also store files for installation.

With that in mind, here's a behind-the-scenes view of WebDAV in IIS 6.0:

The WebDAV protocol extension allows you to store information in "properties", and copying files over the WebDAV redirector stores several properties about a file when it sends the file to the server. If you were to examine a protocol trace for the WebDAV traffic between a Windows 7 client and an IIS server, you will see the PUT command for the document followed by several PROPPATCH commands for the properties.

IIS needs a way to store the properties for a file in a way where they will remain associated with the file in question, so the big question is - where do you store properties?

In IIS 7 we have a simple property provider that stores the properties in a file named "properties.dav," but for IIS 5.0 and IIS 6.0 WebDAV code we chose to write the properties in the compound document file format because there are lots of APIs for doing so. Here's the way that it works in IIS 5 and IIS 6.0:

  • If the file is already in the compound document file format, IIS simply adds the WebDAV properties to the existing file. This data will not be used by the application that created the file - it will only be used by WebDAV. This is exactly what the customer was seeing - the file size was increasing because the WebDAV properties were being added to the compound document.
  • For other files, WebDAV stores a compound document in an NTFS alternate data stream that is attached to the file. You will never see this additional data from any directory listing, and the file size doesn't change because it's in an alternate data stream.

So believe it or not, no harm is done by modifying a compound document file to store the WebDAV properties. Each application that wants to pull information from a compound document file simply asks for the data that it wants, so adding additional data to a compound document file in this scenario was essentially expected behavior. I know that this may seem counter-intuitive, but it's actually by design. ;-]

The Resolution

Once I was able to explain what was actually taking place, the customer was able to verify that their MST and MSI files still worked exactly as expected. Once again, no harm was done by adding the WebDAV properties to the compound document files.

You needn't take my word for this, you can easily verify this yourself. Here's a simple test: Word 2003 documents (*.DOC not *.DOCX) are in the compound document file format. So if you were to create a Word 2003 document and then copy that document to an IIS 6.0 server over WebDAV, you'll notice that the file size increases by several bytes. That being said, if you open the document in Word, you will see no corruption - the file contains the same data that you had originally entered.

I hope this helps. ;-]

Posted: Apr 21 2010, 20:11 by Bob | Comments (0)
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WebDAV Module for Windows Server 2008 GoLive Beta is released

Earlier today the IIS product team released the GoLive beta version of the new WebDAV extension module for IIS 7. (This version is currently available for Windows Server 2008 only.)

Listed below are the links for the download pages for each of the individual installation packages:

We've loaded this version with many great new features such as:

  • Integration with IIS 7.0: The new WebDAV extension module is fully integrated with the new IIS 7.0 administration interface and configuration store.
  • Per-site Configuration: WebDAV can be enabled at the site-level on IIS 7.0, which differed from IIS 6.0 where WebDAV was enabled at the server-level through a Web Service Extension.
  • Per-URL Security: WebDAV-specific security is implemented through WebDAV authoring rules that are configured on a per-URL basis.

Here are a couple of screenshots of the new WebDAV UI in action:

WebDAV UI WebDAV Authoring Rules

Additional documentation about installing and using this version of WebDAV can be found at the following URL:

Installing and Configuring WebDAV on IIS 7.0:
http://go.microsoft.com/fwlink/?LinkId=105146

While this release is a beta version and not technically supported, feedback about this release and requests for information can be posted to the following web forum:

IIS7 - Publishing:
http://forums.iis.net/1045.aspx

I would be remiss if I did not mention that special thanks go to:

  • Keith – for building it
  • Eok, Sriram, Ciprian – for testing it
  • Gurpreet, Brian, Reagan – for making it look pretty
  • Vijay, Will, Taylor – for helping keep everything on track ;-]

Thanks!

Note: This blog was originally posted at http://blogs.msdn.com/robert_mcmurray/
Posted: Dec 22 2007, 11:55 by Bob | Comments (0)
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