Core/Chat: Validate UTF8 in chat messages

(cherry picked from commit e5d63bc5b0)

src/server/game/Handlers/ChatHandler.cpp

@@ -41,6 +41,7 @@
 #include "Util.h"
 #include "World.h"
 #include "WorldPacket.h"
+#include <utf8.h>
 #include <algorithm>
 
 inline bool isNasty(uint8 c)
@@ -72,6 +73,14 @@ inline bool ValidateMessage(Player const* player, std::string& msg)
         }
     }
 
+    // validate utf8
+    if (!utf8::is_valid(msg.begin(), msg.end()))
+    {
+        TC_LOG_ERROR("network", "Player %s (%s) sent a message containing an invalid UTF8 sequence - blocked", player->GetName().c_str(),
+            player->GetGUID().ToString().c_str());
+        return;
+    }
+
     // collapse multiple spaces into one
     if (sWorld->getBoolConfig(CONFIG_CHAT_FAKE_MESSAGE_PREVENTING))
     {