ExploitPreventer is a mod that fixes known or at the moment for most people unknown exploits.
Here is a blog post about a fingerprinting exploit and you can do local requests in the internal lan from the player but you can only get a hash back but it is still bad: https://alaggydev.github.io/posts/cytooxien/
This mod also fixes the sign translation key issue that a server can't get the resolved translation key anymore.
We are a Minecraft Research Group and try to make Minecraft better and fix exploits that are actively used. If we find more stuff we will patch it in this mod.
The link to the Mod is in the blog post at the bottom. I can't send more links because the message will be then deleted.
How we uncovered a device fingerprinting exploit on cytooxien.net and more