Minecraft Version

1.16.5

Forge Version

36.2.0

Mod Version

modular-routers-1.16.5-7.5.1-69.jar

Describe your problem, including steps to reproduce it

Using insert and Extract, you can duplicate any item in a filter. (See Picture)

Any other comments?

Which mod adds those insert and extract buttons?

Never mind, I figured out it's Quark.

In any case, this is on them, not me. I've looked at their code, and they just copy items out of the slots / item handler, without checking to see if the slots or underlying item handler actually permit item extraction. See https://github.com/VazkiiMods/Quark/blob/master/src/main/java/vazkii/quark/base/handler/InventoryTransferHandler.java#L177-L186 for what I mean.

They should either check Slot#mayPickup() and/or use IItemHandler.extractItem(), not just blindly read the item out of the inventory.

Fine I'll transfer it to Quark then. Thanks for taking a look :)