Joinchat 6.3.2 - 6.4.1 - Author+ Stored XSS via Button Block Message Attribute

The Joinchat WordPress plugin before 6.4.2 does not escape the message of its button block before outputting it in an HTML attribute on the front end, which could allow users with the Author role and above to perform Stored Cross-Site Scripting attacks against any visitor of the post, including administrators.