The The Events Calendar plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the ‘data-date-*’ parameters in all versions up to, and including, 6.13.2 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://plugins.trac.wordpress.org/changeset/3307301/
https://github.com/uxsolutions/bootstrap-datepicker/blob/master/js/bootstrap-datepicker.js#L131
https://bootstrap-datepicker.readthedocs.io/en/latest/index.html#data-api