Cross-site scripting

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Cross-site scripting


Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications that enables malicious attackers to inject client-side script into web pages viewed by other users. Because HTML documents have a flat, serial structure that mixes control statements, formatting, and the actual content, any non-validated user-supplied data included in the resulting page without proper HTML encoding may lead to markup injection.

All Input Components Block XSS

To prevent a XSS attack, ZK components encode any value that might be input by a user, such as the value of label and textbox, by escaping & and other unsafe characters. For example, the following statement is totally safe no matter what the value of any_value might be:

<textbox value="${any_value}"/>

However, there are still some notes worth to pay attention to.

Some Attributes are Not-Encoded on Purpose

The content Attribute of Html and Comboitem

The content property of the html and combitem components (Html.setContent(String) and Comboitem.setContent(String)) are designed to allow applications to generate HTML content directly. In other words, it is not encoded. Thus, it is better not to carry the value input by an user, unless it is encoded property. For example, if the value of any_content is, in the following example, generated directly and vulnerable to XSS attack if it is the value provided by an user and without proper encoding.


Some methods of Clients

As the name says this utility allows more direct 'client' side access. Thus the methods don't encode the strings passed into them to allow formatting of the messages at client side, e.g.:

Clients.showNotification("Successfully processed: <br/>" + myTextbox.getValue());

When displaying user input using methods such as Clients.showBusy(String) or Clients.showNotification(String) ... and especially when dynamically concatenated JS code is executed using Clients.evalJavaScript(String) user input should be escaped carefully.

Sanitize User Input

Apache Commons Lang's StringEscapeUtils can sanitize a user input.

Client-side Actions

The client-side action is not encoded and the options is interpreted as a JSON object. Thus, you could encode it by yourself, if you allow the end user to specify it (which is generally not suggested at all).

Version History

Last Update : 2018/12/17

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