If you are using velocity and have the plugin enabled on your server then you are unaffected by this also if you are not using a proxy at all you are also uneffected.

Also, if you are still using the versions for 1.12 or below, this won't affect you at all.

Massive thanks to roote.rs for making me aware of this as well as helping me test a fix for this.

If you use a proxy and rely on the bungee: and warp: tags working in tandem then just go into the config.yml and set
EnableProxySupport to true

For a full writeup of the issue see
https://roote.rs/posts/advancedportals/

We had done a fix years ago, though the past fix was only helping velocity configurations with the plugin on the proxy or if you were not using a proxy at all.

To ensure that users are not able to download older vulnerable versions I will be archiving all of the versions on the modrinth and bukkit websites.

To be clear these vulnerabilities have been tested on both bungee and velocity configurations,.