Blind Cross-Site Scripting (XSS) is a more covert form of the Stored XSS attack. In a traditional Stored XSS attack, the attacker's malicious script is stored on the web server and then executed in the browser of any user who accesses the affected page. The attacker can typically see the impact of their attack directly, either by observing changes on the website or receiving data sent by the script.

In contrast, with Blind XSS:

  1. Invisibility of Payload Execution: The key characteristic of Blind XSS is that the attacker does not have a direct way to observe the execution of their payload. This happens because the payload might be stored in a location that is not immediately visible or accessible to the attacker, such as in a database entry only displayed in certain administrative or less-accessed pages.

  2. Entry Points: The entry points for Blind XSS are similar to those of Stored XSS. This includes any point where user input is taken and stored, such as:

    • Comment sections

    • Feedback forms

    • User profiles

    • Support ticket systems

    • Any form input that might be viewed later by another user, especially administrative users

  3. Use of Callbacks: Due to the covert nature of Blind XSS, it's crucial to include a callback mechanism in the payload. This allows the attacker to be notified when and if their payload is executed. The callback typically involves:

    • Embedding a URL (usually pointing to a server controlled by the attacker) in the script.

    • When the malicious script executes, it sends a request to the specified URL.

    • The attacker monitors this server for incoming requests, which act as a confirmation that the payload executed.

    • Information about where, when, and in what context the payload executed can also be transmitted to the attacker via parameters in the request.

  4. Challenges and Considerations: Blind XSS is more challenging to execute and requires patience. Since the attacker does not know when or if their payload will be triggered, they must wait and monitor their callback endpoint. Additionally, Blind XSS can be more dangerous as the payload might be executed by users with higher privileges, like administrators, thus potentially granting more significant access or more sensitive data.

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