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How to add X-Content-Type-Options on Nginx

Last updated · Reviewed by a CISSP-certified security practitioner

To add X-Content-Type-Options on Nginx, set the header in nginx.conf (server block) with the value nosniff. Stops browsers from guessing (sniffing) file types. Run nginx -t, then systemctl reload nginx. Then confirm it with curl -I or a free FixSecurityHeaders scan.

What does X-Content-Type-Options do?

Setting nosniff makes the browser trust the Content-Type you send instead of guessing, so an uploaded text file can't be executed as script.

Risk if missing: MIME sniffing can turn user uploads or JSON responses into executable scripts or styles.

What is the Nginx configuration?

Add this to nginx.conf (server block):

nginx.conf (server block)
# Inside your server { } block
add_header X-Content-Type-Options "nosniff" always;

How do I add it step by step?

  1. Open nginx.conf (server block).
  2. Paste the X-Content-Type-Options configuration shown below.
  3. Run nginx -t, then systemctl reload nginx.
  4. Run curl -I https://yourdomain.com and look for the x-content-type-options line.
  5. Scan your site on FixSecurityHeaders to confirm the grade improved.

How do I verify it worked?

terminal
curl -sI https://yourdomain.com | grep -i "x-content-type-options"
# expected:
# x-content-type-options: nosniff

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What are the common mistakes?

  • Make sure your server sends correct Content-Type headers, or some assets will stop loading.
  • Always add the always flag so headers are sent on error responses too.
  • add_header in a location block replaces all add_header directives inherited from server — repeat them or use an include file.

Quick reference

HeaderX-Content-Type-Options
Recommended valuenosniff
StackNginx
Wherenginx.conf (server block)
ComplianceOWASP ASVS V14.4.4, SOC 2 CC6.8

FAQ

What value should I use for X-Content-Type-Options?

A safe default is nosniff. Make sure your server sends correct Content-Type headers, or some assets will stop loading.

Why isn't X-Content-Type-Options showing up on Nginx?

Always add the always flag so headers are sent on error responses too. Also clear any CDN or page cache, and check you edited the config that actually serves your domain.

Does X-Content-Type-Options affect SEO or performance?

No measurable performance cost — it's a few bytes per response. It doesn't affect rankings directly, but a misconfigured policy can break page resources, so test before enforcing.

Which compliance frameworks reference X-Content-Type-Options?

OWASP ASVS V14.4.4, SOC 2 CC6.8.

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