JustTalDevelops

Exploiting the Blob Cache in Minecraft: Bedrock Edition

...and why it matters.

Preface

You might have seen my HiveCorruptor plugin on Poggit. To be clear, I don't have a vendetta against The Hive or anything like that, the plugin was more so a comedic demonstration of how the blob cache can be exploited to crash clients. The next thing you're probably thinking is "how the hell does this work?" - and this is what this article will go over.

Introduction

Kazzuk

package org.example;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.util.concurrent.Promise;
import org.cloudburstmc.netty.channel.raknet.RakPong;
import org.cloudburstmc.protocol.bedrock.BedrockPong;

import java.util.concurrent.ScheduledFuture;

Alemiz112

public class PaletteHashTest {

    private static final int FNV1_32_INIT = 0x811c9dc5;
    private static final int FNV1_PRIME_32 = 0x01000193;

    public static void main(String[] args) throws Exception {
        NbtMap blockState = NbtMap.builder()
                .putString("name", "minecraft:bamboo_hanging_sign")
                .putCompound("states", NbtMap.builder()
                        .putInt("facing_direction", 3)

camullen

Installing KDE on WSL2

Inspiration: https://www.most-useful.com/kde-plasma-on-wsl.html

Setup

1. Update WSL
   • In windows command prompt run: wsl --update
2. Add systemd to ubuntu

• In ubuntu prompt run: sudo nano /etc/wsl.conf

valorad

Ubuntu:

sudo apt install xrdp 
sudo adduser xrdp ssl-cert 
sudo systemctl restart xrdp

Fedora:

Tomcc

Client Blob Cache

What's the Client Blob Cache

The Client Blob Cache is a new Bedrock optimization - it allows blocks and biomes to be cached on Clients to avoid resending identical chunks over and over. Chunks and biomes make up the vast majority of network traffic in a lot of common cases (eg. login, teleport or dimension switches) but at the same time, they rarely change. Allowing the Client to reuse chunks it has seen in the past can save a ton of traffic and latency!

The Client Cache is a Content Addressed Storage (a bit like git) that stores Blobs and retrieves them based on their full hashes (BlobIds). This means that the cache doesn't actually know about Chunks - in the future, we might start using it for more types of data, like skins or data driven entities.

A nice thing we get from the CAS approach is that the cache is persistent: returning players will be able to reuse content that was sent them in previous sessions or even previous sessions in different servers as long as tha

roooodcastro

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Stroke;
import java.util.ArrayList;