XSS (Cross-Site Scripting) is a type of cyber attack where malicious code (usually JavaScript) is injected into vulnerable websites and executed in users’ browsers. XSS attacks can be used to steal user sessions, inject malicious content, or create fake web pages.
Types of XSS
Stored XSS (Persistent XSS)
- Malicious code is permanently stored on a database or server.
- When a user visits the affected site, the code executes automatically.
- Example: A user injects malicious JavaScript into a comment box, which then runs for all visitors.
Reflected XSS
- The malicious code is not stored on the server but is reflected through URL parameters or input fields.
- The attack occurs when a user clicks on a specially crafted link prepared by the attacker.
DOM-Based XSS
- The malicious code executes directly in the user’s browser without reaching the server.
- Occurs when JavaScript processes user input without proper validation.
Risks of XSS Attacks
- Session Hijacking – Attackers can steal authentication cookies and impersonate users.
- Phishing Attacks – Fake login pages can be created to steal credentials.
- Malware Distribution – Malicious scripts can inject harmful software into users’ devices.
- Website Defacement – Attackers can modify the website’s appearance and content.
Methods to Prevent XSS Attacks
Input Validation & Sanitization
- Validate and sanitize all user inputs.
- Filter out potentially dangerous characters from HTML, JavaScript, or SQL inputs.
Output Encoding
- Avoid displaying raw user input in HTML.
- Convert special characters into encoded formats to prevent execution.
Using HTTP-Only and Secure Cookies
- Prevent JavaScript access to session cookies.
- Use the HTTP-Only flag to restrict browser access to cookies.
Content Security Policy (CSP) Implementation
- Restrict browsers from executing scripts from unauthorized sources.
Using Secure JavaScript Libraries
- Modern frameworks like React, Angular, and Vue have built-in mechanisms to prevent XSS attacks.
Tools for XSS Prevention
- OWASP ZAP – Scans for XSS vulnerabilities and other security risks.
- Burp Suite – Used for security testing and penetration testing.
- ESAPI (OWASP Enterprise Security API) – Provides secure input validation and XSS protection.
Conclusion
XSS attacks are a significant security risk in web applications and can compromise user safety.
✔ Always validate and sanitize user inputs.
✔ Implement secure coding practices to protect HTML, JavaScript, and cookies.
✔ Regularly perform security testing on your website.
A strong XSS prevention strategy ensures both users and systems remain safe from potential threats.
