CVE-2026-4809: 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. If the uploaded file is stored in a web-accessible and executable location, this may lead to remote code execution. At the time of publication, no patch was available and the vendor had not responded to coordinated disclosure attempts.