Cross-Site Scripting (XSS) is a common security vulnerability that occurs when malicious scripts are injected into trusted websites. This type of attack allows attackers to execute arbitrary scripts in a victim's browser, potentially stealing sensitive data, manipulating web page content, or performing actions on behalf of the victim without their consent.

Types of XSS Attacks:
1. Stored XSS: Malicious scripts are permanently stored on a target server, such as in a database or comment section. When users access the affected page, the script is executed in their browser.
2. Reflected XSS: Malicious scripts are included in the URL or form inputs and reflected back by the server, executing in the user’s browser.
3. DOM-Based XSS: Occurs when client-side scripts process untrusted data, leading to script execution without server interaction.

How It Works:
- An attacker identifies an input field or URL parameter that does not properly sanitize or validate user inputs.
- The attacker injects malicious JavaScript code into the vulnerable input.
- When the victim interacts with the page, the browser executes the attacker’s script.

Potential Impacts:
1. Data Theft: Stealing cookies, session tokens, or other sensitive data.
2. Account Compromise: Hijacking user accounts by exploiting authentication cookies.
3. Defacement: Altering the appearance or content of a web page.
4. Phishing Attacks: Redirecting users to malicious websites.

Prevention Strategies:
1. Input Validation: Ensure that all user inputs are sanitized and validated.
2. Output Encoding: Encode special characters to prevent them from being interpreted as executable code.
3. CSP Implementation: Use a Content Security Policy to restrict the sources of executable scripts.
4. Avoid Dangerous APIs: Limit the use of eval() and similar functions in JavaScript.

Real-World Example:
A poorly secured comment section might allow an attacker to inject a script that steals the session tokens of all users who view the comment.

XSS remains a significant threat to web security, but by adopting robust coding practices and security measures, developers can mitigate the risks effectively.