Cross-Site Scripting (XSS) is a type of security vulnerability in web applications where an attacker injects malicious scripts (usually written in JavaScript) into web pages that are viewed by other users. These scripts then execute in the context of the victim’s browser, potentially allowing the attacker to steal information, manipulate web page content, or perform other malicious actions.
XSS vulnerabilities occur when a web application does not properly validate or sanitize user-generated input before it is displayed on a web page. There are three main types of XSS attacks:
- Stored XSS: In this type of attack, the malicious script is permanently stored on the target web server. When other users view the affected web page, the script is served from the server and executed in their browsers.
- Reflected XSS: Here, the malicious script is embedded in a URL or input field, and it is reflected off the web server to the victim’s browser when they click a link or submit a form. This type of attack often involves tricking the victim into clicking a malicious link.
- DOM-based XSS: This type of XSS attack occurs in the Document Object Model (DOM) of a web page, where the script manipulates the page’s structure or behavior directly within the user’s browser, often without interacting with the web server.
The consequences of XSS attacks can be severe, as they can lead to:
- Theft of user data, such as login credentials or personal information.
- Session hijacking, allowing the attacker to impersonate the victim.
- Defacement of websites and unauthorized content modification.
- Spreading of malware or malicious downloads to users.
- Phishing attacks, tricking users into revealing sensitive information.
To prevent XSS vulnerabilities, web developers should implement security measures such as input validation, output encoding, and the use of security headers like Content Security Policy (CSP). Regular security testing, including code reviews and vulnerability scanning, is crucial to identify and address XSS vulnerabilities in web applications. Users should also be cautious when clicking on links or interacting with websites, especially if they appear suspicious or request sensitive information.