From 31800bcebc22a075fe47ff43986a05ad27956a41 Mon Sep 17 00:00:00 2001
From: AlexProgrammerDE <40795980+AlexProgrammerDE@users.noreply.github.com>
Date: Fri, 23 Aug 2024 18:32:49 +0200
Subject: [PATCH] Fix forcelogin auth exploit

---
 .../listener/data/PluginMessageListener.java  | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/velocity/src/main/java/io/github/_4drian3d/authmevelocity/velocity/listener/data/PluginMessageListener.java b/velocity/src/main/java/io/github/_4drian3d/authmevelocity/velocity/listener/data/PluginMessageListener.java
index 53c3d21..e27ece5 100644
--- a/velocity/src/main/java/io/github/_4drian3d/authmevelocity/velocity/listener/data/PluginMessageListener.java
+++ b/velocity/src/main/java/io/github/_4drian3d/authmevelocity/velocity/listener/data/PluginMessageListener.java
@@ -58,15 +58,20 @@ public final class PluginMessageListener implements Listener<PluginMessageEvent>
     public EventTask executeAsync(final PluginMessageEvent event) {
         return EventTask.async(() -> {
             plugin.logDebug(() -> "PluginMessageEvent | Start");
-            if (notAllowedEvent(event)) {
-                plugin.logDebug(() -> "PluginMessageEvent | Not allowed");
+            if (notHandledEvent(event)) {
+                plugin.logDebug(() -> "PluginMessageEvent | Not handled");
                 return;
             }
 
-            final ServerConnection connection = (ServerConnection) event.getSource();
-
+            // Set the result to handled, the message is dropped at the proxy
             event.setResult(PluginMessageEvent.ForwardResult.handled());
 
+            // Make sure the message is S -> P, NOT P -> S
+            if (!(event.getSource() instanceof ServerConnection connection)) {
+                plugin.logDebug("PluginMessageEvent | Not ServerConnection");
+                return;
+            }
+
             final ByteArrayDataInput input = event.dataAsDataStream();
             final String message = input.readUTF();
             final MessageType type = TYPES.valueOrThrow(message.toUpperCase(Locale.ROOT));
@@ -114,15 +119,11 @@ public final class PluginMessageListener implements Listener<PluginMessageEvent>
         });
     }
 
-    private boolean notAllowedEvent(PluginMessageEvent event) {
+    private boolean notHandledEvent(PluginMessageEvent event) {
         if (!event.getResult().isAllowed()) {
             plugin.logDebug("PluginMessageEvent | Result not allowed");
             return true;
         }
-        if (!(event.getSource() instanceof ServerConnection)) {
-            plugin.logDebug("PluginMessageEvent | Not ServerConnection");
-            return true;
-        }
         final var identifier = event.getIdentifier();
         if (!(identifier.equals(AuthMeVelocityPlugin.MODERN_CHANNEL)
                 || identifier.equals(AuthMeVelocityPlugin.LEGACY_CHANNEL))) {