Website security is more important than ever, with cyber threats like Cross-Site Scripting (XSS), clickjacking, and data injection becoming common. A great way to protect your website is by using Content Security Policy (CSP).
CSP acts like a security guard for your website, controlling what content can be loaded and executed. In this blog, we’ll break it down in simple words so you can understand, implement, and benefit from it.
CSP is a security feature that helps prevent malicious code from running on your website. It works by setting rules that tell the browser which resources (scripts, images, styles, etc.) are allowed and which are blocked.
Why is CSP Important?
- Prevents XSS Attacks – Stops hackers from injecting harmful scripts.
- Protects User Data – Keeps sensitive information secure.
- Reduces Clickjacking Risks – Blocks unauthorized iframes.
- Boosts Website Security – Adds an extra layer of protection.
How to Add CSP to Your Website
You can add CSP in two ways:
1. Using HTTP Headers (Recommended)
If you have access to your server, add this header to your response:
Content-Security-Policy: default-src 'self'; script-src 'self' https://apis.example.comThis means:
- By default, content can only load from the same domain (
'self'). - JavaScript is only allowed from the same domain and
https://apis.example.com.
2. Using an HTML Meta Tag
If you can’t modify server headers, add this inside the <head> of your HTML:
<meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'self' https://apis.example.com;">CSP Directives
Directives control what kind of content can be loaded and from where. Let’s break them down:
1. default-src
Acts as a fallback for all other resource types if a more specific rule isn’t defined.
default-src 'self'This means only content from the same origin is allowed.
2. script-src
Controls JavaScript sources.
script-src 'self' https://apis.example.com3. style-src
Controls stylesheets and inline styles.
style-src 'self' 'unsafe-inline'4. img-src
Controls the sources of images.
img-src 'self' https://cdn.example.com5. font-src
Controls font loading.
font-src 'self' https://fonts.example.com6. connect-src
Controls AJAX, WebSockets, and API requests.
connect-src 'self' https://api.example.com7. frame-ancestors
Controls if the page can be embedded into iframes.
frame-ancestors 'none'8. object-src
Controls plugins like Flash (deprecated), or <object>, <embed>, <applet>.
object-src 'none'9. report-uri (or report-to)
Allows reporting CSP violations to a specified endpoint.
report-uri/csp-violation-reportSources in CSP
You specify trusted sources using these keywords:
'self'— Allows loading from the same origin.'none'— Blocks everything.'unsafe-inline'— Allows inline JavaScript or CSS (not recommended for security reasons).'unsafe-eval'— Allows the use ofeval()in JavaScript (also risky).https://example.com— Allows content only from this specific domain.*— Allows any source (dangerous — avoid).
Example CSP Rule
This policy:
- Allows scripts from the same site and
apis.example.com. - Allows styles but also allows inline styles (
'unsafe-inline'). - Blocks iframes (
frame-ancestors 'none'). - Reports violations to
/csp-report.
Best Practices
-
Avoid
'unsafe-inline'and'unsafe-eval'unless absolutely necessary. -
Use Nonces and Hashes for inline scripts and styles:
Then apply the nonce in the script tag:
Content-Security-Policy: script-src 'nonce-abc123'<script nonce="abc123">console.log('Hello, CSP!');</script> -
Use a Report-Only Mode for testing:
Content-Security-Policy-Report-Only: default-src 'self'; script-src 'self'; report-uri /csp-violation-report - Restrict Third-Party Resources — Only allow necessary domains.
Testing and Troubleshooting CSP
- Browser DevTools: Open your browser’s developer tools (F12 or right-click → Inspect), go to the Console, and check for CSP errors.
- CSP Validator: Use tools like CSP Evaluator by Google to test your policy.
-
Report Violations:
Implement a violation reporting endpoint to monitor issues:
report-uri /csp-violation-report -
Common Errors:
- Blocked inline scripts: Add
nonceor avoid inline scripts. - Third-party scripts blocked: Explicitly add the domain in
script-src.
- Blocked inline scripts: Add
Benefits of CSP
- Prevents unauthorized script execution.
- Protects sensitive user data.
- Mitigates attacks like XSS and clickjacking.
- Improves overall website security.
Conclusion
Implementing Content Security Policy (CSP) is an essential step in securing your website against modern cyber threats. By defining what content can and cannot be loaded, you prevent hackers from injecting malicious scripts and improve overall site security.
Secure your website today with CSP! Need help setting it up? Let us know in the comments!
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