src/de/steamwar/bungeecore/commands/TeamCommand.java

@@ -35,7 +35,7 @@ import net.md_5.bungee.api.chat.TextComponent;
 import net.md_5.bungee.api.config.ServerInfo;
 import net.md_5.bungee.api.connection.ProxiedPlayer;
 
-import java.net.InetSocketAddress;
+import java.net.*;
 import java.time.Instant;
 import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
@@ -600,6 +600,15 @@ public class TeamCommand extends BasicCommand {
             return;
         }
         String server = args[1];
+        try {
+            if (isLocalhost(InetAddress.getByName(server))) {
+                Message.send("TEAM_SERVER_ADDRESS_INVALID", player);
+                return;
+            }
+        } catch (UnknownHostException e) {
+            Message.send("TEAM_SERVER_ADDRESS_INVALID", player);
+            return;
+        }
         int port = 25565;
         if (args.length == 3) {
             try {
@@ -619,6 +628,19 @@ public class TeamCommand extends BasicCommand {
         Message.send("TEAM_SERVER_SET", player);
     }
 
+    private static boolean isLocalhost(InetAddress addr) {
+        // Check if the address is a valid special local or loop back
+        if (addr.isAnyLocalAddress() || addr.isLoopbackAddress())
+            return true;
+
+        // Check if the address is defined on any interface
+        try {
+            return NetworkInterface.getByInetAddress(addr) != null;
+        } catch (SocketException e) {
+            return false;
+        }
+    }
+
     private void changeColor(ProxiedPlayer player, SteamwarUser user, Team team) {
         if(notLeader(player, user, team))
             return;

src/de/steamwar/messages/BungeeCore.properties

@@ -476,6 +476,7 @@ TEAM_COLOR_TITLE=Choose color
 TEAM_SERVER_USAGE=§8/§7team server §8[§eIP/address§8] §8(§7port§8) §8- §7Sets the address of the team server.
 TEAM_SERVER_SET=§7You changed the team server address§8!
 TEAM_SERVER_PORT_INVALID=§cInvalid port number.
+TEAM_SERVER_ADDRESS_INVALID=§cInvalid address.
 TEAM_NO_ADDRESS=§cNo team server address set.
 TEAM_TP_NO_TEAM=§cUnknown team.
 

src/de/steamwar/messages/BungeeCore_de.properties

@@ -455,6 +455,7 @@ TEAM_COLOR_TITLE=Farbe wählen
 TEAM_SERVER_USAGE=§8/§7team server §8[§eIP/Adresse§8] §8(§7Port§8) §8- §7Setzt Adresse des Teamservers.
 TEAM_SERVER_SET=§7Du hast die Teamserveradresse geändert§8!
 TEAM_SERVER_PORT_INVALID=§cUnmögliche Portnummer.
+TEAM_SERVER_ADDRESS_INVALID=§cInvalide Adresse.
 TEAM_NO_ADDRESS=§cTeamserveradresse nicht gesetzt.
 TEAM_TP_NO_TEAM=§cUnbekanntes Team.