basic hostname validation

Spigot-Server-Patches/0703-Validate-bungee-forwarded-hostname.patch

@@ -0,0 +1,54 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Shane Freeder <theboyetronic@gmail.com>
+Date: Sun, 18 Apr 2021 21:27:01 +0100
+Subject: [PATCH] Validate bungee forwarded hostname
+
+Seriously, fix your firewalls. -.-
+
+diff --git a/src/main/java/net/minecraft/server/network/HandshakeListener.java b/src/main/java/net/minecraft/server/network/HandshakeListener.java
+index b97d289afdff81d9959e238639f4e3e186f8e9c8..e13ed3a17866ce3ef0b2ac1dbcb17fb726c89fa8 100644
+--- a/src/main/java/net/minecraft/server/network/HandshakeListener.java
++++ b/src/main/java/net/minecraft/server/network/HandshakeListener.java
+@@ -1,5 +1,8 @@
+ package net.minecraft.server.network;
+ 
++import com.google.common.net.InetAddresses;
++import com.google.common.net.InternetDomainName;
++
+ import net.minecraft.SharedConstants;
+ import net.minecraft.network.EnumProtocol;
+ import net.minecraft.network.NetworkManager;
+@@ -26,6 +29,7 @@ public class HandshakeListener implements PacketHandshakingInListener {
+     private static final IChatBaseComponent a = new ChatComponentText("Ignoring status request");
+     private final MinecraftServer b;
+     private final NetworkManager c; final NetworkManager getNetworkManager() { return this.c; } // Paper - OBFHELPER
++    private static final boolean BYPASS_HOSTCHECK = Boolean.getBoolean("Paper.bypassHostCheck"); // Paper
+ 
+     public HandshakeListener(MinecraftServer minecraftserver, NetworkManager networkmanager) {
+         this.b = minecraftserver;
+@@ -114,6 +118,14 @@ public class HandshakeListener implements PacketHandshakingInListener {
+                 //if (org.spigotmc.SpigotConfig.bungee) { // Paper - comment out, we check above!
+                         String[] split = packethandshakinginsetprotocol.hostname.split("\00");
+                         if ( split.length == 3 || split.length == 4 ) {
++                            // Paper start
++                            if (!BYPASS_HOSTCHECK && !validate(split[0])) {
++                                final ChatMessage message = new ChatMessage("Invalid hostname");
++                                this.c.sendPacket(new PacketLoginOutDisconnect(message));
++                                this.c.close(message);
++                                return;
++                            }
++                            // Paper end
+                             packethandshakinginsetprotocol.hostname = split[0];
+                             c.socketAddress = new java.net.InetSocketAddress(split[1], ((java.net.InetSocketAddress) c.getSocketAddress()).getPort());
+                             c.spoofedUUID = com.mojang.util.UUIDTypeAdapter.fromString( split[2] );
+@@ -158,4 +170,10 @@ public class HandshakeListener implements PacketHandshakingInListener {
+     public NetworkManager a() {
+         return this.c;
+     }
++
++    // Paper start - https://stackoverflow.com/questions/9954140/check-if-a-string-is-a-hostname-or-an-ip-address-in-java
++    public static boolean validate(final String hostname) {
++        //noinspection UnstableApiUsage
++        return InetAddresses.isUriInetAddress(hostname);
++    }
+ }