HTML5 Security Cheat-Sheet Essentials

HTML5 introduced many powerful features for developers - but with great power comes great responsibility 🕷️. To keep your web apps safe from modern threats, you need to apply smart security practices. Let’s explore the most important ones 👇

Content Security Policy (CSP) 🧱​

CSP helps block Cross-Site Scripting (XSS) attacks by controlling which resources (scripts, images, styles) can be loaded on your page.

Example:

<meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'self' https://apis.google.com;">

This ensures only trusted scripts can run on your site.

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Cross-Origin Resource Sharing (CORS) 🌐​

CORS defines which external domains can access your resources. Without it, attackers could trick your browser into sending unauthorized requests.

Tip: Always specify trusted origins only - never use Access-Control-Allow-Origin: * for sensitive APIs.

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Secure Input Handling ✍️​

Validate and sanitize all user input before processing it. This prevents SQL injection, XSS, and form-based attacks.

Best practice:

• Use HTML5 input types (e.g., email, number).
• Escape special characters server-side.

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Same-Origin Policy (SOP) 🚫​

SOP prevents malicious scripts from interacting with content from other sites. It’s the cornerstone of browser security - don’t disable it unless absolutely necessary.

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Web Storage & Cookies 🍪​

Sensitive data should never be stored in plain text.

• Use encryption for localStorage/sessionStorage.
• Mark cookies as HttpOnly and Secure to protect them from theft via JavaScript or HTTP sniffing.

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HTTPS Everywhere 🔒​

Always use HTTPS to encrypt communication between the client and the server. This stops man-in-the-middle attacks and keeps data private.

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Subresource Integrity (SRI) ✅​

SRI checks that external files (like scripts or styles from CDNs) haven’t been tampered with.

Example:

<script src="https://cdn.example.com/script.js"
  integrity="sha384-xyz123"
  crossorigin="anonymous"></script>

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Final Tip 🌍​

Following these principles will make your HTML5-based web applications much safer from common attacks. For a deeper dive into browser security and real-world examples, visit 👉 html5sec.org
Stay safe, code smart, and never trust unchecked input 💻🔥