Catch Themes Demo Import < 3.4 - Missing Authorization to Authenticated (Subscriber+) Single Plugin Installation via 'activate_plugin' Parameter

Description

The Catch Themes Demo Import plugin for WordPress is vulnerable to Missing Authorization in versions up to, and including, 3.3. This is due to the catch_themes_demo_import_activate_plugin() function, hooked on admin_init when the activate_plugin GET parameter is present, calling Plugin_Upgrader::install() to download and install a plugin from WordPress.org before performing the current_user_can('activate_plugins') capability check. This makes it possible for authenticated attackers, with subscriber-level access and above, to install the hardcoded 'essential-content-types' plugin from the WordPress.