Legacy REST methods fail to perform sufficient structural validation before appending an authenticated caller's query parameter as a SQL WHERE clause. This issue occurs at the '/service/v4 1/rest.php' endpoint and involves the `get entry list`, `get entries count`, and `query` functions. An account with list permissions on a module can bypass the `user hash` filter to retrieve password hashes and other sensitive database information, potentially allowing the use of administrative credentials to compromise the application.