With the development of web applications, the use of JavaScript has become widespread to increase interaction between users and to provide more dynamic content. However, security vulnerabilities may arise in this dynamic content creation process. In this article, we will focus specifically on a vulnerability called DOM-based Cross-Site Scripting (DomXSS).
What is DomXSS?
DomXSS is a special type of Cross-Site Scripting (XSS). While XSS usually occurs on the server side, DomXSS occurs on the client side, that is, in the browser. This vulnerability can allow a malicious attacker to manipulate the JavaScript code that users run in their browsers.
How DomXSS Occurs?
DomXSS usually occurs when untrusted data such as user logins are processed in the browser. This vulnerability occurs when a web application embeds user input directly into HTML, which is then interpreted by the browser.
Example Scenario:
Let’s say a web application has a page that allows users to edit their profile. There is a text box for users to change their username. However, because the application embeds these usernames directly into the HTML on the page, an attacker could insert malicious JavaScript code into this username field.
For example, the username could be:
“><script>alert(“DomXSS Attack”)</script>“
In this case, the browser inserts the username into the HTML content on the page, while at the same time executing the malicious JavaScript code sent by the attacker. This causes a warning window to open in the browser.
Conclusion:
DomXSS is a serious vulnerability that threatens the security of web applications. It is important for developers to securely process user input, filter output, and carefully check JavaScript code executed on the browser side. In addition, proper use of security features provided by browsers and security tools can also help prevent such vulnerabilities.
Example Code:
<!DOCTYPE html>
<html lang=”en”>
<head>
<meta charset=”UTF-8″>
<meta http-equiv=”X-UA-Compatible” content=”IE=edge”>
<meta name=”viewport” content=”width=device-width, initial-scale=1.0″>
<title>DomXSS Example</title>
</head>
<body>
<h1>Welcome, <span id=”username”></span>!</h1>
<script>
// Assume user input is directly placed into the DOM
var userInput = ‘“><script>alert(“DomXSS Attack”)</script>’;
document.getElementById(‘username’).innerHTML = userInput; // DomXSS vulnerability
</script>
</body>
</html>
This example causes DomXSS because it inserts user input directly into the HTML.
To protect against these vulnerabilities, it is important for developers to adopt secure coding principles and comply with browser security policies.
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