Image Watermark <= 1.7.3 - Missing Authorization to Authenticated (Subscriber+) Watermark Modification

The Image Watermark plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the watermark_action_ajax() function in all versions up to, and including, 1.7.3. This makes it possible for authenticated attackers, with subscriber-level access and above, to apply and remove watermarks from images.