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Step by Step Instructions on How to Configure IIS to Allow Downloading of EXE and DAT Files

VMware’s ThinApp 4.0 product has added a new feature to the previous versions of ThinStall called AppSync. Among other things, AppSync allows for administrators to build ThinApp packages that periodically check in to a web site to see if there is an update.

Using VMware’s ThinApp 4.0 AppSync feature with a Microsoft Web Server can require additional configuration to the web server as, by default, IIS 6.0 does not allow access to any file with an unknown extension.


How do you set IIS 6.0 to allow download of files such as EXE’s or DAT’s. By default, Microsoft’s IIS 6.0 will not serve out any unknown extensions. This includes EXE and DAT. Therefore, when a user requests such file, whether it be via ThinApp or directly, IIS will reply back with a 404 status code. A look in the IIS log file will show the sub-status code of 3 meaning the complete status code is 404.3. This means that the MIME restrictions prevented the request.


Basic instruction needed for configuring IIS to allow downloading of EXE and DAT files.

  1. Open IIS Manager.
  2. Browse to the IIS Site or subfolder where the ThinApp EXE and DAT files sit.
  3. Right click on that site or subfolder and select PROPERTIES.
  4. Select the HTTP HEADERS tab.
  5. Click on the MIME TYPES button.
  6. In the extension box, type ".exe".
  7. In the MIME TYPE box, type "application/octet-stream".
  8. Click OK.
  9. Repeat steps 1 โ€“ 8 to add the ".dat" extension.
  10. Click OK on all windows to close them and apply settings.
  11. TEST


NOTE 1:  The solution is the exact same as in IIS 5.0 and IIS 5.1, but since those IIS versions were not locked down by default, there was never any need to apply these configurations (since it works "As Is").

NOTE 2: Instead of adding two MIME types, you can also just add one wildcard MIME Type with the extension of ".*". This, however, is not as secure as just adding the extensions you need.

NOTE 3: If the IIS site points to a folder path outside of the INETPUB folder, you may need to ensure the appropriate INTERNET GUEST ACCOUNT has READ access to the folder and files within it.

This entry was posted in AppSync, Tips on by .
Dean Flaming

About Dean Flaming

Dean is currently an EUC Architect and member of the VMware End User Computing Enablement and Lighthouse Support teams, working to develop communications and IP around VMware End User Computing products and solutions as well as support many various Lighthouse accounts with their own EUC practices. Prior to this, from 2008 through 2012 Dean was one of VMware's End User Computing Specialists. Throughout his time at VMware, Dean has also written and published various articles, videos, and podcasts regarding VMware's EUC Solutions.

4 thoughts on “Step by Step Instructions on How to Configure IIS to Allow Downloading of EXE and DAT Files

  1. Kris

    Hi Dean,
    Do you know if there’s any similar gotcha’s with Apache?
    Also, I take it that in general, it doesn’t matter which web server you use, as far as AppSync is considered it’s just a URL.

  2. Dean Flaming

    I’ve not heard of any issues with Apache web servers.
    As far as AppSync goes, you are correct – it does not care what type of Web Server. ๐Ÿ™‚

  3. wayne hogue

    What about updates id app.exe and then app.1 as a newer version.

  4. Dean Flaming

    Side by side updating or “.#” extensions (app.1 or app.exe.2, etc.) are not a part of AppSync and a separate ability to update the ThinApp package. See this video for a simple example of side-by-side http://download3.vmware.com/community/videos/Thinapp/ThinAppSidebySideUpdating.mp4 and see this video for an example of AppSync. http://communities.vmware.com/static/community/videos/northstarbeta2/AppSync/AppSync.htm

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