Chunk Save State Dupe bug fixed (1.12.2+)

:fire: [IMPORTANT UPDATE] :fire:
Many of you are aware of a dupe exploit spreading like wildfire revolving around chunk saving. This is an extremely complicated bug, but we have a solution for it. This bug has existed since Minecraft 1.3, but as we do not support anything older than 1.12.2, you must use at least 1.12.2 to get the fix.

1.13.2 in build 524+ https://papermc.io/downloads#Paper-1.13
1.12.2 in build 1597+ https://papermc.io/downloads#Paper-1.12

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Please do a quick test on a backup/local copy of your world to be sure of no uncaught bugs, but we are fairly sure the fix is stable, and solves the problem.

:fire: Switching to a non Paper jar while having oversized chunks is strongly discouraged. While the chunks will save with a format that Spigot and Vanilla can read, large chests/entities will be missing until you return to Paper.

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Log messages will print anytime this exploit has been encountered and tell you exactly where. You should visit those chunks, identify what player(s) are trying to exploit them, clear out the chests, and enact the ban hammer or what ever punishment you deem necessary. These chunks will be super slow to save and load and will cause lag spikes, so be on the look out for it!

Then as players realize the exploit no longer works, hopefully they will stop trying it. If you want to prevent players from even filling up the chunks, you can utilize the Paper book limits config, and further blockage you will need to look into plugins to help control it even more.

Please report any “Exceptions” or concerns of data loss to us on Discord.

And please spread the word for anyone using Spigot to switch to Paper to get this fix!

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Would you be able to add any technical information on why players were able to Dupe the items and maybe how it was fixed (in future posts)? It would be really interesting for people like server owners and just in general for developers to get an insight on how things work :slight_smile:

Information is in the patch file header located here: https://github.com/PaperMC/Paper/blob/c3c889523fb08d918fe94f1ebecc06345f2f4b74/Spigot-Server-Patches/0414-Allow-Saving-of-Oversized-Chunks.patch#L6