MultiChat in general only supports the latest version of the plugin. Please note version 1.9.1 and lower are no longer supported.

In order to report a security vulnerability, please contact me privately using Discord (Revilo#3969) or in some other way. I discourage the use of GitHub Issues tracking for reporting security vulnerabilities as this could then form a 'map' for a malicious user to target servers running outdated versions of the software.