# UNDF: UNDF-2026-000000175
--- a/sql/auth/sql_authorization.cc
+++ b/sql/auth/sql_authorization.cc
@@ -4875,16 +4875,26 @@ mysql_show_grants(THD *thd, LEX_USER *lex_user,
   if (have_using_clause) {
     std::vector<Role_id> mandatory_roles;
     get_mandatory_roles(&mandatory_roles);
     List_of_granted_roles granted_roles;
     get_granted_roles(lex_user, &granted_roles);
-    for (auto &role_ref : using_roles) {
-      std::string authid(create_authid_str_from(role_ref));
-      if (find(granted_roles.begin(), granted_roles.end(), authid) ==
-          granted_roles.end()) {
-        if (std::find_if(mandatory_roles.begin(), mandatory_roles.end(),
-                         [&](const Role_id &id) -> bool {
-                           std::string id_str, rid_str;
-                           id.auth_str(&id_str);
-                           Role_id rid(role_ref.first, role_ref.second);
-                           rid.auth_str(&rid_str);
-                           return (Role_id(role_ref.first, role_ref.second) ==
-                                   id);
-                         }) == mandatory_roles.end()) {
+    // CWE-407 fix (mysql-0001): build O(1) lookup sets before the loop so
+    // membership checks are not O(G) and O(M) per using_role element.
+    std::unordered_set<std::string> granted_set;
+    for (const auto &gr : granted_roles) {
+      granted_set.insert(gr.first);  // gr.first is the authid string
+    }
+    std::unordered_set<std::string> mandatory_set;
+    for (const auto &rid : mandatory_roles) {
+      std::string s;
+      rid.auth_str(&s);
+      mandatory_set.insert(s);
+    }
+    for (auto &role_ref : using_roles) {
+      std::string authid(create_authid_str_from(role_ref));
+      if (granted_set.find(authid) == granted_set.end()) {
+        std::string rid_str;
+        Role_id(role_ref.first, role_ref.second).auth_str(&rid_str);
+        if (mandatory_set.find(rid_str) == mandatory_set.end()) {
           my_error(ER_ROLE_NOT_GRANTED, MYF(0), role_ref.first.str,
                    role_ref.second.str, lex_user->user.str, lex_user->host.str);
           return true;
         }
       }
     }
   }