Violating Window’s file naming rules

Going to share an interesting behavior with the “CreateFileW” functions I found this week. Its quite simple, but results in an undeletable file with some other interesting traits.

This is done by creating a file name that Windows does not accept and fails to do operations on once created. As we know, Windows does not allow certain characters in path names, the ones we all know are:


So the “CreateFileW” API call will fail if you even try to create a file with the above characters, however there are other file-naming rules not so black and white which Windows abides by. One of these is that Windows does not allow trailing space in a file name. This can be seen using CreateFileA (which is what is called when you right click and create a file in Windows). CreateFileA will properly remove trailing space characters before making the file. This filtering however does not occur in the CreateFileW API call using \\?\ to prepend the path.  By naming a file with the below syntax, Windows will create a Unicode filename with a trailing space. The \\?\ prefix sends the path straight to the file system with no preprosessing, typically used when trying to get around the MAX_PATH limitation of 255 characters.


When trying to delete the file:


Try rename the file to remove the trailing space – no luck:


Checking the properties of the file:



Even trying CMD prompt with the filename, I was unable to delete the file.
This whole thing led to some other very interesting behavior with directories, that perhaps Ill share a later time.

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