The Forex Calculators plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the ajax_settings_callback() function in all versions up to, and including, 1.3.5. This makes it possible for authenticated attackers, with Subscriber-level access and above, to update the plugin's settings.
https://plugins.trac.wordpress.org/browser/fx-calculators/tags/1.3.5/forex-calculators.php#L101