ZK Developer's Reference/Security Tips/Block Request for Inaccessible Widgets

Non-existed Component is Safer than Invisible One

Users can easily access inaccessible elements (such as disabled or invisible ones) by a browser developer tool. For example, a hostile user can make an invisible button visible and then click it to trigger unexpected actions. Thus, it is recommended not to create an element if it is not supposed to be accessible. For example, the first statement is safer than the second one in the following example:

<button unless="${accessible}"/>
<button visible="${accessible}"/>

Block with InaccessibleWidgetBlockService

Since 5.0.0

• Available for ZK:
• 

ZK Enterprise Edition provides a built-in implementation called InaccessibleWidgetBlockService. To apply it to the whole application, just specify the following in WEB-INF/zk.xml as follows.

<listener>
	<listener-class>org.zkoss.zkmax.au.InaccessibleWidgetBlockService$DesktopInit</listener-class>
</listener>

Then, each time a desktop is created, an instance of InaccessibleWidgetBlockService is added to the desktop to block the requests from the inaccessible widgets.

Default Blocking Rules

• Block all events from disabled and invisible components
• Block onChange, onChanging, onSelect of a read-only component
• Not block onOpen

Specify Events to Block

In many cases, you just want to block particular events, not all events. For example, you want to receive onOpen when a menupopup is going to show up. Then, you can specify a library property called IWBS.events to control the behavior of InaccessibleWidgetBlockService. For example,

<library-property>
	<name>org.zkoss.zkmax.au.IWBS.events</name>
	<value>onClick,onChange,onSelect</value>
</library-property>

Supported Components

All invisible components are blocked. Some components are blocked when they are disabled/read-only, as follows:

Component
Button
A
Listbox
Menuitem
Navitem
Textbox
Tree
Intbox
Spinner
Doublebox
Decimalbox
Longbox
Doublespinner
Timepicker
Timebox
Checkbox
Datebox
Combobox
Chosenbox
Selectbox

Implement Your Own Blocking Rules

If you want to block a request for inaccessible widgets for the whole application or for a particular desktop, you can implement the org.zkoss.zk.au.AuService interface to filter out unwanted requests. The implementation of AuService is straightforward. For example, the following example blocks only button and onClick:

public class MyBlockService implements org.zkoss.zk.au.AuService {
	public boolean service(AuRequest request, boolean everError) {
		final Component comp = request.getComponent();
		return (comp instanceof Button) && "onClick".equals(request.getCommand());
			//true means block
	}
}

Version History

Version	Date	Content
8.0.3	2016/09/21	Add "supported components" table