External image replace <= 1.0.8 - Authenticated (Contributor+) Arbitrary File Upload

The External image replace plugin for WordPress is vulnerable to arbitrary file uploads due to missing file type validation in the 'external_image_replace_get_posts::replace_post' function in all versions up to, and including, 1.0.8. This makes it possible for authenticated attackers, with contributor-level and above permissions, to upload arbitrary files on the affected site's server which may make remote code execution possible.