Minecraft exploits and how to fix them

Preface

This guide will assume you are running Purpur. Some settings required for this guide to work are not available in Paper or Spigot. Similar exploits might exist in vanilla, fabric or forge servers, and you will have to find mods that fix them on those loaders.

Exploits

Armor stand lag machines

Armor stands can be used to create lag machines. This is done by placing huge amounts of armor stands and forcing them to move via water, pistons or other means. This can be fixed by disabling armor stand tick and collision lookups. This will cause armor stands to not being able to be pushed or pulled (even by gravity).

paper-world-defaults.yml

entities:
  armor-stands:
    do-collision-entity-lookups: false
    tick: false

Collision lag machines

This exploit is similar to the armor stand one, but instead of armor stands, it uses entities that can be pushed by other entities. This can be fixed by setting a smaller limit on how many entities can collide with a singular entity. You can set the max-entity-collisions to 2 to still have relatively natural behavior, or set it to 0 to completely disable collisions.

paper-world-defaults.yml

collisions:
  max-entity-collisions: 2

Command spam

While even spigot will protect you from this exploit, there's a slight oversight that will enable a single command to be usable to perform this one. To fix this, simply remove /skill command from the spam exclusions list in spigot.yml.

spigot.yml

commands:
  spam-exclusions: []

Treasure search

When new treasure map is generated, usually via cartographer villager or opening a chest with treasure map in it, the server searches for the treasure that map should lead to. This search is done in a way that in most cases causes a lot of chunks loading and possibly generating them. This search can halt the server for long enough that watchdog process kills it. It can also be triggered by feeding dolphins fish.

Option 1

To fix this one you basically have to disable treasure maps and dolphins searching for treasure. This is the recommended and 100% effective solution.

paper-world-defaults.yml

environment:
  treasure-maps:
    enabled: false

purpur.yml

world-settings:
  default:
    mobs:
      dolphin:
        disable-treasure-searching: true

Option 2

Alternatively, you can keep the maps enabled, but set up vanilla worldborder and make sure your world is pregenerated within the border. Then you can just make sure that already discovered treasures are valid as the search result. This will prevent the treasure search from loading chunks that are not generated.

paper-world-defaults.yml

  treasure-maps:
    find-already-discovered:
      loot-tables: true
      villager-trade: true