Cross-Site Scripting (XSS) is a critical web security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This type of attack exploits the trust a user has in a particular website, enabling unauthorized code execution within the victim's browser.

How XSS Works

XSS vulnerabilities occur when a web application fails to properly validate, filter, or encode user-supplied input before rendering it in the browser. When malicious code—typically JavaScript, but also VBScript or HTML—is injected into a vulnerable page, the browser executes it as if it were legitimate content from the trusted website.

Types of XSS Attacks

• Stored XSS: Malicious script is permanently stored on the target server and executed when users access the affected page.
• Reflected XSS: The injected script is reflected off a web server through error messages, search results, or other responses.
• DOM-based XSS: The vulnerability exists in client-side code rather than server-side code, manipulating the Document Object Model.

Potential Consequences

Successful XSS attacks can result in:

• Theft of session cookies and login credentials
• User session hijacking
• Website defacement
• Redirection to malicious or phishing sites
• Malware installation
• Identity theft and data breaches

Prevention Strategies

Protecting against XSS requires a multi-layered approach:

• Implement strict input validation and sanitization
• Apply proper output encoding for all user-supplied data
• Use Content Security Policy (CSP) headers
• Employ HTTPOnly and Secure flags for cookies
• Utilize modern frameworks with built-in XSS protection