The plugin accepts all zip files and automatically extracts the zip file without validating the extracted file type. Allowing high privilege users such as admin to upload an arbitrary file like PHP, leading to RCE
As an admin upload a php file containing the palyload zipped along with a valid XML file via the New Import Upload page of the plugin:
https://example.com//wp-admin/admin.php?page=pmxi-admin-import
When the upload finishes you'll be able to find the random directory it was sent to by checking the links on the source code of the Managed Imports page:
http://example.com/wp-admin/admin.php?page=pmxi-admin-manage
The file will be located at something like:
https://example.com/wp-content/uploads/wpallimport/uploads/f8ac124b335362e2faed2da06d2123d5/folder/filename.php