XSS Lab

Overview

Demonstrates how unsanitized output of user input can lead to cross‐site scripting attacks.

Vulnerable Code

// vuln_xss.php
if (isset($_GET['input'])) {
    echo "User input: " . $_GET['input'];
}
      

Exploit Demo

Example URL: ?input=<script>alert('XSS')</script>

Secure Code

// sec_xss.php
echo htmlspecialchars($_GET['input'], ENT_QUOTES, 'UTF-8');
      

Remediation & Lessons

• Always escape user‐supplied data before outputting to HTML.
• htmlspecialchars() with ENT_QUOTES covers both single and double quotes.
• Consider a CSP header to further mitigate XSS risks.