Unsafe Client MIME Type Handling Can Enable Arbitrary File Upload in plank/laravel-mediable

plank/laravel-mediable through version 6.4.0 can allow upload of a dangerous file type when an application using the package accepts or prefers a client-supplied MIME type during file upload handling. In that configuration, a remote attacker can submit a file containing executable PHP code while declaring a benign image MIME type, resulting in arbitrary file upload.