Cross-Site Scripting (XSS) Challenges
OWASP A03:2021 - Injection (XSS)
Cross-Site Scripting (XSS) flaws occur when an application includes untrusted data in a web page without proper validation or escaping, allowing attackers to execute scripts in victim's browsers.
Cross-Site Scripting (XSS) flaws occur when an application includes untrusted data in a web page without proper validation or escaping, allowing attackers to execute scripts in victim's browsers.
Beginner
Reflected XSS
Exploit a search feature that reflects user input without sanitization. Learn how URL parameters can be used to inject malicious scripts.
- Points: 100
- Estimated Time: 15 minutes
- Skills: HTML injection, JavaScript execution
Easy
Stored XSS
Inject a persistent script into a comment system that executes for all visitors. Understand the dangers of stored/persistent XSS attacks.
- Points: 150
- Estimated Time: 20 minutes
- Skills: Persistent payloads, session hijacking
Medium
DOM-based XSS
Exploit client-side JavaScript that unsafely processes user input. Learn about DOM manipulation vulnerabilities and dangerous sinks.
- Points: 200
- Estimated Time: 25 minutes
- Skills: DOM manipulation, JavaScript sinks
Learning Resources
Types of XSS
- Reflected XSS: Malicious script is reflected off the web server in error messages, search results, or other responses that include input from a request.
- Stored XSS: Malicious script is permanently stored on the target servers (in a database, message forum, comment field, etc.).
- DOM-based XSS: The vulnerability exists in client-side code rather than server-side code, occurring entirely in the browser.
Impact of XSS
- Session hijacking via cookie theft
- Account takeover
- Defacement of websites
- Keylogging and credential theft
- Phishing attacks
- Malware distribution
Prevention Techniques
- Output Encoding: Encode data when rendering in HTML, JavaScript, CSS, or URLs
- Content Security Policy (CSP): Restrict sources of executable scripts
- Input Validation: Validate and sanitize all user input
- HTTPOnly Cookies: Prevent JavaScript access to session cookies
- Use Modern Frameworks: React, Angular, Blazor automatically escape output