CROSS-SITE-SCRIPTING

SECURITY

Cross-Site-Scripting Explained

Cross-Site-Scripting (XSS) is a type of security vulnerability that occurs when an attacker injects malicious scripts into web pages viewed by other users.

The goal of XSS attacks is typically to steal information, manipulate the appearance of a website, or perform actions on behalf of the victim without their consent. To prevent XSS attacks, web developers should employ proper input validation and output encoding techniques. Input validation ensures that user input meets certain criteria before being processed, and output encoding involves encoding user-generated content so that it is treated as data rather than executable code. Additionally, using secure coding practices, such as Content Security Policy (CSP), can help mitigate the risks associated with XSS vulnerabilities.

Three main types of XSS attacks

Stored XSS (Persistent XSS): In this type of attack, the malicious script is permanently stored on the target server, and every time a user accesses the affected page, the script is served to them. This could happen, for example, when user inputs are not properly sanitized, and the malicious code is saved in a database.
Reflected XSS (Non-persistent XSS): In a reflected XSS attack, the injected script is embedded in a URL or another input and is only temporarily served to the victim when they click on a manipulated link. The malicious script is not stored on the target server but is reflected off a web application.
DOM-based XSS: This type of XSS occurs when the manipulation of the Document Object Model (DOM) in a web page is exploited. The attack is typically client-side, and the malicious script is executed in the victim’s browser.

How does cross-site-scripting work

Cross-Site Scripting (XSS) works by exploiting vulnerabilities in web applications that allow attackers to inject malicious scripts into web pages that are viewed by other users. The process generally involves the following steps:

1. Injection of Malicious Code

Attackers identify input fields or areas within a web application where user input is not properly validated or sanitized. This could include fields such as search boxes, comment sections, or user profile forms. The attacker then injects malicious code (usually JavaScript) into these input fields. The injected code becomes part of the content that the web application serves to users.

2. Storing or Reflecting the Malicious Code

In the case of Stored XSS, the injected code is permanently stored on the target server. This code is then served to all users who access the affected page, executing in their browsers. In the case of Reflected XSS, the injected code is included in a URL or another input and is reflected off the web server to the victim’s browser. The victim typically needs to click on a manipulated link for the attack to be successful.

3. Execution in the Victim’s Browser

When a user accesses a page containing the injected malicious code, their browser unknowingly executes the code. This code has access to the same privileges as the user who is viewing the page, potentially allowing the attacker to steal sensitive information, manipulate the appearance of the page, or perform actions on behalf of the victim.

4. Exploitation of User Session and Data

Once the malicious script is executed in the victim’s browser, it can perform various actions. Common objectives include stealing session cookies, which could allow the attacker to impersonate the victim, capturing sensitive information entered on the page (such as login credentials), or performing unauthorized actions on behalf of the user.