The WpEvently plugin for WordPress is vulnerable to Stored Cross-Site Scripting via multiple parameters in all versions up to, and including, 4.4.2 due to insufficient input sanitization and 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.
https://wordpress.org/plugins/mage-eventpress/#developers
https://plugins.trac.wordpress.org/changeset/3307484
https://github.com/magepeopleteam/mage-eventpress/commit/c6f8d3233087881d3eb7ed3ebe9a6ebc7795f144