diff --git a/custom_components/shopping_list_manager/websocket/handlers.py b/custom_components/shopping_list_manager/websocket/handlers.py
index 57a696f..f00c527 100644
--- a/custom_components/shopping_list_manager/websocket/handlers.py
+++ b/custom_components/shopping_list_manager/websocket/handlers.py
@@ -48,6 +48,62 @@ from .. import get_storage
 _LOGGER = logging.getLogger(__name__)
 
 
+# =============================================================================
+# ACCESS-CHECK HELPERS
+# =============================================================================
+
+def _user_can_access_list(lst, user) -> bool:
+    """Return True if the user may read or write to this list.
+
+    Global lists (owner_id=None) are accessible to everyone.
+    Private lists are accessible to their owner, anyone in allowed_users, and admins.
+    """
+    if lst.owner_id is None:
+        return True
+    if user is None:
+        return False
+    if user.is_admin or user.id == lst.owner_id:
+        return True
+    return user.id in (lst.allowed_users or [])
+
+
+def _check_list_access(storage, connection, msg, list_id, require_owner=False):
+    """Verify the connected user may access list_id.
+
+    Sends the appropriate WebSocket error if access is denied.
+    Returns the ShoppingList object on success, or None if an error was sent.
+
+    Args:
+        require_owner: When True, only the list owner (or an admin) is allowed.
+                       Use for destructive/administrative operations.
+    """
+    lst = storage.get_list(list_id)
+    if lst is None:
+        connection.send_error(msg["id"], "not_found", "List not found")
+        return None
+
+    user = connection.user
+    if require_owner:
+        if lst.owner_id is not None and not (user and (user.is_admin or user.id == lst.owner_id)):
+            connection.send_error(msg["id"], "forbidden", "Only the list owner can perform this action")
+            return None
+    else:
+        if not _user_can_access_list(lst, user):
+            connection.send_error(msg["id"], "forbidden", "You do not have access to this list")
+            return None
+
+    return lst
+
+
+def _find_item_list_id(storage, item_id):
+    """Return the list_id that contains item_id, or None if not found."""
+    for list_id, items in storage._items.items():
+        for item in items:
+            if item.id == item_id:
+                return list_id
+    return None
+
+
 # =============================================================================
 # LIST HANDLERS
 # =============================================================================
@@ -62,16 +118,28 @@ async def websocket_subscribe(
     msg: dict,
 ) -> None:
     """Subscribe to shopping list manager events via WebSocket."""
-    
+    storage = get_storage(hass)
+
     @callback
     def forward_event(event):
-        """Forward HA bus event to WebSocket connection."""
+        """Forward HA bus event to WebSocket connection.
+
+        Events that reference a list_id are only forwarded if the connected
+        user has access to that list, preventing cross-user data leakage.
+        """
+        data = event.data
+        list_id = data.get("list_id")
+        if list_id:
+            lst = storage.get_list(list_id)
+            if lst and not _user_can_access_list(lst, connection.user):
+                return  # skip — user cannot see this list
+
         connection.send_message(
             websocket_api.event_message(
                 msg["id"],
                 {
                     "event_type": event.event_type,
-                    "data": event.data,
+                    "data": data,
                 }
             )
         )
@@ -248,7 +316,10 @@ async def websocket_update_list(
     """Handle update list command."""
     storage = get_storage(hass)
     list_id = msg["list_id"]
-    
+
+    if _check_list_access(storage, connection, msg, list_id, require_owner=True) is None:
+        return
+
     # Build update kwargs
     update_data = {}
     if "name" in msg:
@@ -334,7 +405,10 @@ async def websocket_set_active_list(
     """Handle set active list command."""
     storage = get_storage(hass)
     list_id = msg["list_id"]
-    
+
+    if _check_list_access(storage, connection, msg, list_id) is None:
+        return
+
     success = await storage.set_active_list(list_id)
     
     if not success:
@@ -369,7 +443,10 @@ def websocket_get_items(
     """Handle get items command."""
     storage = get_storage(hass)
     list_id = msg["list_id"]
-    
+
+    if _check_list_access(storage, connection, msg, list_id) is None:
+        return
+
     items = storage.get_items(list_id)
     
     connection.send_result(
@@ -404,7 +481,10 @@ async def websocket_add_item(
     """Handle add item command."""
     storage = get_storage(hass)
     list_id = msg["list_id"]
-    
+
+    if _check_list_access(storage, connection, msg, list_id) is None:
+        return
+
     # Build item data
     item_data = {
         "name": msg["name"],
@@ -463,7 +543,14 @@ async def websocket_update_item(
     """Handle update item command."""
     storage = get_storage(hass)
     item_id = msg["item_id"]
-    
+
+    list_id = _find_item_list_id(storage, item_id)
+    if list_id is None:
+        connection.send_error(msg["id"], "not_found", "Item not found")
+        return
+    if _check_list_access(storage, connection, msg, list_id) is None:
+        return
+
     # Build update data
     update_data = {}
     update_fields = ["name", "quantity", "unit", "note", "price", "category_id", "image_url"]
@@ -548,7 +635,14 @@ async def websocket_delete_item(
     """Handle delete item command."""
     storage = get_storage(hass)
     item_id = msg["item_id"]
-    
+
+    list_id = _find_item_list_id(storage, item_id)
+    if list_id is None:
+        connection.send_error(msg["id"], "not_found", "Item not found")
+        return
+    if _check_list_access(storage, connection, msg, list_id) is None:
+        return
+
     success = await storage.delete_item(item_id)
     
     if not success:
@@ -931,10 +1025,12 @@ def websocket_get_integration_settings(
     )
 
 
+_VALID_COUNTRIES = ["NZ", "AU", "US", "GB", "CA"]
+
 @websocket_api.websocket_command(
     {
         vol.Required("type"): "shopping_list_manager/set_country",
-        vol.Required("country"): str,
+        vol.Required("country"): vol.In(_VALID_COUNTRIES),
     }
 )
 @websocket_api.async_response