[MC-137370] Multiple entities can spawn with the same UUID as the player while the player is dead

The bug

As long as the player is dead, multiple entities can spawn with their UUID.

Reproduction

This will require you to obtain your own UUIDLeast/UUIDMost pair. You can use the following commands in the chat to get these values:

/data get entity @s UUIDLeast
/data get entity @s UUIDMost

First, place the following command, replacing the UUIDLeast/UUIDMost with your own, in a repeating command block and turn it on. Note in the command block output as well as the game output log that the entity couldn't be summoned due to the player already having the specified UUID.

summon creeper ~ ~1 ~ {UUIDLeast:-9192300185346116154L,UUIDMost:-5068141680530666168L}

Now type the following in the chat:

/kill @s

After your player's death animation, a multitude of creepers will start spawning until you click "respawn". These creepers all have the same UUID as each other, being the same as the player. Under normal circumstances, an entity cannot be created if it would share the same UUID as another entity.

Linked issues

relates to 2

MC-231016 Can summon entities with the same UUID by pausing the game Resolved

MC-136160 The server doesn't send information about entity death to dead players Resolved

Attachments

crash-2021-07-21_08.11.24-server.txt

deobf_crash-2021-07-21_08.11.24-server.txt

latest.log

New World.zip

Comments 6

ampolive 2021-07-21T00:15:36Z

Can confirm in 1.17.1. Beware: reproducing this may end up in losing your world.

This was very unfortunate to reproduce, as I ended up losing my test world. It kicks me out for invalid player data. Note that UUIDLeast and UUIDMost are deprecated and no longer work. Just type

/data get entity @s UUID

, copy your UUID and paste in a repeating command block. After that, it works as described. Upon respawning, the entity will be invisible and you will be softlocked out of the game.

ampolive 2021-07-21T00:28:18Z

Attached a brand new test world for my second reproduction of the issue.

ampolive 2021-07-21T11:12:42Z

Just tested and this did happen in 1.15.2 and 1.16.5 as well, but it produced a proper crash report. No crash report is produced as of 1.17.1. The server does crash instantly, it is just not reported and the game doesn't stop.

ampolive 2021-07-21T21:51:42Z

Also note: it doesn't spawn multiple entities on 1.15.2+, just a singular duplicated entity.

ampolive 2021-10-10T02:06:55Z

Can confirm in 21w40a.

clamlol 2022-04-27T21:14:48Z

Affects 22w17a. Tested while returning from the End after watching credits for a bit, that case should probably be mentioned in the title.

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