The vulnerability arises because the application's selectList method (Curd.php) accepts the 'selectFields' parameter from the user and passes it to the ORM's field() method (BaseQuery.php). The field() method directly incorporates this input into SQL queries without sanitization. The GitHub issue explicitly traces this flow, demonstrating that unsanitized input reaches the SQL construction phase. While the ORM's field() method is designed to handle trusted input, the application's failure to validate or escape the user-controlled 'selectFields' parameter before passing it to this method makes both the application-layer method (selectList) and the ORM method (field) part of the vulnerable code path.