Course 1 - BurpSuite Bug Bounty Web Hacking from Scratch | Episode 10: XSS: Overview, Security Level Testing, and Real-World Attacks

In this lesson, you’ll learn about:Definition of Cross-Site Scripting (XSS):A client-side web vulnerability where an application executes user-supplied JavaScript instead of treating it as text. It typically occurs in user input areas such as search fields, comment boxes, or feedback forms.Main Types of XSS:Reflected XSS (Non-persistent):The malicious input is not stored in the database.It only affects users who execute the injected script (e.g., by clicking a crafted link).Commonly found in search or URL parameters.Stored XSS (Persistent):The injected payload is saved in the application database (e.g., in comments).The script runs automatically for every visitor who loads the infected page.This type has a higher impact and broader reach.DOM-based XSS:The vulnerability exists in the Document Object Model (DOM) layer.The HTML response may appear unchanged, but JavaScript execution happens client-side.Potential Consequences:Theft of cookies and session tokens.Hijacking user accounts or sessions.Launching Cross-Site Request Forgery (CSRF) attacks.Delivering malicious redirects or keyloggers.Practical Demonstrations:Reflected XSS (OWASP Mutillidae Example):Using Burp Suite to intercept and inject a simple payload:If the response returns the payload unmodified, the application is vulnerable.DVWA Demonstrations Across Security Levels:Low Level: The script runs immediately without filters.Medium Level: Filtering is attempted (e.g., removing the word “script”). Bypassed using mixed-case payloads like:High Level: Stronger filtering, but DOM-based XSS succeeds using:Real-World Exploitation Example:Attackers send phishing emails containing legitimate-looking links that include malicious JavaScript in the query string.When clicked, the script executes on the target site, allowing theft of credentials or session data.This is often referred to as first-order XSS, primarily exploiting GET requests.Prevention Techniques:Validate and sanitize all user input (both client and server-side).Implement output encoding for HTML, JavaScript, and URL contexts.Use modern Content Security Policy (CSP) headers.Avoid using innerHTML for dynamic content updates.Educate users to verify links before clicking, especially in unsolicited emails.You can listen and download our episodes for free on more than 10 different platforms:https://linktr.ee/cybercode_academy