Six weeks ago the WordPress team released version 4.7.1 to the world. This update included 8 security fixes (but left one that was introduced in 4.7.0) and fixed 61 bugs. Three weeks ago the released version 4.7.2 to the world, this was a must update as it closed a large security issue that was introduced in 4.7.0.
WordPress version 4.7.1 also introduced a new bug which affected the allowed file types that could be uploaded via the built-in Media uploader. As of 4.7.1, you could no longer upload the following file types without receiving a security error: .docx, .pptx, .xlsx, .mp3, .mp4, .m4v, .csv and more.
The WordPress team has stated that this bug will be fixed in WordPress version 4.7.3, until then you can fix this issue by installing the Disable Real MIME Check plugin. Just remember to remove the plugin once WordPress 4.7.3 is released.
We hope you found this article helpful in fixing this frustrating little bug.