What the tool-"dupe" exploit is and how to patch it

How does this actually work?? Reparenting tools from the client doesnt replicate at all, so Im wondering what is going on here?

With this exploit it does. I don’t really understand how- but I witnessed it firsthand in a controlled environment (blank baseplate, tool with no scripts)

after having encountered it in my game just now, i can vouch that this definitely exists and is an ongoing issue, it seems to not be possible outside of using starter gear though… really bizarre that something like this is exploitable in such a way, seems like a massive oversight by roblox (one of many more)

How have I never noticed this? Is this affecting larger games?