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This document gives you a working example of how to use Secondary File filters.
MSI File Example
If you want to elevate .msi files that are in a network share, you cannot use a commandline filter because the following syntax does not work:
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If you tried to use a command line filter, then you would have to specify each .msi file explicitly and then create several individual elevation policies–an policies–-an extremely tedious task. Or you could create a commandline like \\SERVER\Share\, but this would elevate anything in the share folder. To target and elevate only .msi files efficiently, the solution is to use the Secondary File Filter.
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For an example of a Secondary File filter for use with msiexec and a file share containing msi files to be elvated, go to MSI Files not elevated by Network Share Elevation PolicyElevate MSI files on the network share and see the alternative solution.