ZEND_API uint zend_get_executed_lineno(void) /* {{{ */
{
	zend_execute_data *ex = EG(current_execute_data);

	while (ex && (!ex->func || !ZEND_USER_CODE(ex->func->type))) {
		ex = ex->prev_execute_data;
	}
	if (ex) {
		if (EG(exception) && ex->opline->opcode == ZEND_HANDLE_EXCEPTION &&
		    ex->opline->lineno == 0 && EG(opline_before_exception)) {
			return EG(opline_before_exception)->lineno;
		}
		return ex->opline->lineno;
	} else {
		return 0;
	}
}
/* }}} */

The product uses a function that accepts a format string as an argument, but the format string originates from an external source.