The Event Organiser plugin for WordPress is vulnerable to Stored Cross-Site Scripting in all versions up to, and including, 3.12.9. This is due to the 'eo_events' shortcode accepting attacker-controlled 'no_events' content and rendering it in event list templates without output escaping. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.