The ImageMagick Engine plugin for WordPress is vulnerable to deserialization of untrusted input via the 'cli_path' parameter in versions up to, and including 1.7.5. This makes it possible for unauthenticated users to call files using a PHAR wrapper, granted they can trick a site administrator into performing an action such as clicking on a link, that will deserialize and call arbitrary PHP Objects that can be used to perform a variety of malicious actions granted a POP chain is also present. It also requires that the attacker is successful in uploading a file with the serialized payload.
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.