Why does Google prepend `while(1);` to its JSON responses?

Why Google's JSON Responses Begin with while(1);

Question: Why does Google prepend while(1); to its JSON responses?

Answer:

Google's practice of prepending while(1); to JSON responses is a security measure aimed at preventing JSON hijacking.

JSON hijacking occurs when an external website embeds a JSON-retrieving URL within a script tag on its page. Exploiting the same-origin policy, the external site can retrieve JSON data from the target website (e.g., Google) using the user's cookies.

The malicious script can intercept the JSON content, modify its properties, or extract sensitive information. By overriding global array constructor or accessor methods, the external site could gain control over the data manipulation process.

The addition of while(1); or &&&BLAH&&& to the beginning of the JSON string disrupts this process. When the JSON response is loaded via an AJAX request, it is parsed and processed before being displayed. However, when the JSON string is executed within a script tag, it encounters an infinite loop or syntax error, preventing malicious code from accessing the data.

This measure helps protect users from cross-site scripting attacks and ensures that Google's JSON responses remain secure and uncompromised by unauthorized sources.

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