The EventPrime – Events Calendar, Bookings and Tickets plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'new_event_type_background_color' parameter in all versions up to, and including, 4.3.4.2 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with custom-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This requires the plugin's Guest Submissions setting (allow_submission_by_anonymous_user) to be enabled, which allows unauthenticated attackers to submit event types via the frontend form; when that setting is disabled, exploitation requires at minimum a subscriber-level authenticated account.