Font upload security restrictions
WordPress released the 4.7.1 version on January 11, 2017. This update included multiple security fixes. Because of these implementations, multiple file types have been blocked from uploading to your site.
Among these are favicon file types and font file types. If you see the following error message when trying to upload a file, this is most probably caused by these new restrictions:
The easiest way to fix this is to use the Disable Real MIME Check plugin. Once installed and activated, you should be able to upload all files that were allowed before 4.7.1.
It has been reported that this issue will be fixed in the 4.7.3 WordPress version, however it still happens sometimes. Thus, if you face the described issue, use this plugin as a workaround for disabling the introduced restrictions.