Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery <= 4.4.1 - Authenticated (Custom+) Remote Code Execution via XML-RPC 'meta_data' Mass Assignment and Path Traversal

The Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 4.4.1 via the render_image function. This is due to unrestricted mass assignment of caller-supplied meta_data keys onto the image model combined with missing realpath containment in path construction and a bypassable signature check on the public image delivery route. This makes it possible for authenticated attackers, with custom-level access and above, to execute code on the server. Exploitation requires the authenticated attacker to own at least one NextGEN gallery — a condition that can be satisfied by any Subscriber who was ever granted the 'NextGEN Manage gallery' capability, and that access is retained indefinitely due to the stored gallery-author equality fallback in _can_manage_gallery() even after the capability is revoked.