GMS-2022-26: Unhandled exception when decoding form response JSON

Impact

When handling form responses from the client (ModalFormResponsePacket), the Minecraft Windows client may send weird JSON that json_decode() can’t understand. A workaround for this is implemented in InGamePacketHandler::stupid_json_decode().

An InvalidArgumentException is thrown by this function when it fails to fix an error found in the JSON, which is not caught by the caller. This leads to a server crash.

Patches

56fe71d939c38fe14e18a31a673a9331bcc0e4ca

Workarounds

A plugin may handle DataPacketReceiveEvent, capture ModalFormResponsePacket and run the provided JSON through stupid_json_decode.

Note that this requires copying the body of the function to a plugin, since the function is currently private.

For more information

If you have any questions or comments about this advisory:

• Email us at team@pmmp.io