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Web message manipulation

In this section, we'll explain what web-message manipulation vulnerabilities are and suggest ways to reduce your exposure to them.

What is DOM-based web message manipulation?

Web message vulnerabilities arise when a script sends attacker-controllable data as a web message to another document within the browser. An attacker may be able to use the web message data as a source by constructing a web page that, if visited by a user, will cause the user's browser to send a web message containing data that is under the attacker's control. For more information about the using web messages as a source, please refer to the Controlling the web-message source page.

Which sinks can lead to DOM-based web-message manipulation vulnerabilities?

The postMessage() method for sending web messages can lead to vulnerabilities if the event listener for receiving messages handles the incoming data in an unsafe way.

How to prevent DOM-based web message manipulation

In addition to the general measures described on the DOM-based vulnerabilities page, you should avoid sending web messages that contain data that originated from any untrusted source. When sending cross-origin messages, you should always explicitly specify the target window. Most importantly, make sure to implement robust measures to verify the origin of any incoming messages.