Cross-Site Scripting (XSS) is a type of security vulnerability commonly found in web applications. It occurs when attackers inject malicious scripts (usually JavaScript) into webpages that other users view. These malicious scripts run in the context of the user’s browser and can be used to steal sensitive information, impersonate users, or manipulate web content.
There are three main types of XSS:
1. Stored XSS – Malicious scripts are stored on the server (e.g., in a database) and then displayed to users, often through comment sections, forums, or profile pages. When other users view these pages, the script executes in their browsers.
2. Reflected XSS – The malicious script is included in a URL or form submission. When a user clicks the link or submits a form, the script executes, affecting only that user session.
3. DOM-based XSS – This type occurs entirely on the client side. It happens when JavaScript code on the page modifies the DOM (Document Object Model) without properly validating user input.
How XSS Attacks Work
An attacker exploits an XSS vulnerability by embedding a malicious script within an application. This script can then perform actions like:
• Stealing cookies or session tokens to impersonate the user.
• Redirecting the user to a malicious site.
• Logging keystrokes or stealing form data entered by the user.
Preventing XSS
To protect against XSS, developers can:
• Sanitize user input by escaping special characters (e.g., <, >, &).
• Use secure frameworks that handle output encoding automatically.
• Implement Content Security Policies (CSP) to limit the sources from which scripts can load.
Understanding and addressing XSS vulnerabilities is essential for secure web development, as these attacks can lead to significant data breaches and privacy issues.