Typical severity: Medium. Likelihood of attack: Low. An adversary adds a space character to the end of a file extension and takes advantage of an application that does not properly neutralize trailing special elements in file names. This extra space, which can be difficult for a user to notice, affects which default application is used to operate on the file and can be leveraged by the adversary to control execution.
File extensions should be checked to see if non-visible characters are being included.