API Fundamentals Course
API Fundamentals
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Intermediate

XSS

Definition

Cross-Site Scripting. A vulnerability where an attacker injects malicious client-side scripts into web pages viewed by other users.

Explain Like I'm New

If an API allows a user to type their name, and they type `<script>stealCookie()</script>`, and the API saves it. When other users visit the site, the browser sees the `<script>` tag, thinks it's part of the website code, and executes it, stealing their passwords.

Real World Example

A hacker puts a malicious script in a YouTube comment. The API returns the comment to 1,000 users. Their browsers execute the script, which secretly commands their accounts to 'Like' the hacker's video.

Common Use Cases

  • •Input sanitization
  • •Frontend security

Interactive Example

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Interview Questions

basic

  • Does the XSS exploit execute on the Backend Server or the Frontend Browser?

intermediate

  • How do modern frontend frameworks like React protect against XSS by default?

Flash Cards

Question

Where does it execute?

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Answer

The Frontend Browser. The backend just stores the malicious string; the browser is what actually executes it.

Question

How does React protect?

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Answer

React automatically escapes (sanitizes) any variables placed inside curly braces `{}`. It converts `<script>` into plain, harmless text strings before rendering them to the DOM.