The Brilliance <= 1.2.7, Activello <= 1.4.0, and Newspaper X <= 1.3.1 themes for WordPress are vulnerable to Plugin Activation/Deactivation. This is due to the 'activello_activate_plugin' and 'activello_deactivate_plugin' functions in the 'inc/welcome-screen/class-activello-welcome.php' file missing capability and security checks/nonces. This makes it possible for unauthenticated attackers to activate and deactivate arbitrary plugins installed on a vulnerable site.