# UNDF: UNDF-2026-000000161
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -29057,12 +29057,22 @@ setup_new_fields(THD *thd, List<Item> &fields,
                  List<Item> &all_fields, ORDER *new_field)
 {
   Item	  **item;
   uint counter;
   enum_resolution_type not_used;
   DBUG_ENTER("setup_new_fields");

   thd->column_usage= MARK_COLUMNS_READ;       // Not really needed, but...
+  // CWE-407 fix (mariadb-0002): build name->item* map once before the loop.
+  // find_item_in_list is O(S) per call; with N new fields this is O(N*S).
+  // An upfront index reduces the loop body to O(1) for name-matched items.
+  std::unordered_map<std::string, Item **> field_index;
+  {
+    List_iterator<Item> idx_it(fields);
+    Item *idx_item;
+    uint idx_pos = 0;
+    while ((idx_item = idx_it++)) {
+      if (idx_item->item_name.is_set())
+        field_index[std::string(idx_item->item_name.ptr())] =
+            fields.elem(idx_pos);
+      ++idx_pos;
+    }
+  }
   for (; new_field ; new_field= new_field->next)
   {
-    if ((item= find_item_in_list(*new_field->item, fields, &counter,
-                                IGNORE_ERRORS, &not_used)))
+    // Fast path: O(1) name lookup via pre-built index
+    std::string lookup_name;
+    if ((*new_field->item)->item_name.is_set())
+      lookup_name = (*new_field->item)->item_name.ptr();
+    auto fast = (!lookup_name.empty()) ? field_index.find(lookup_name)
+                                       : field_index.end();
+    if (fast != field_index.end()) {
+      item = fast->second;
+    } else if ((item= find_item_in_list(*new_field->item, fields, &counter,
+                                        IGNORE_ERRORS, &not_used))) {
+      // fallback to linear scan for alias/table-qualified names
+    } else {
+      item = nullptr;
+    }
+    if (item)
       new_field->item=item;			/* Change to shared Item */
     else
     {