Do you know most of the security vulnerabilities can be fixed by implementing necessary headers in the response header?

Security is as essential as the content and SEO of your website, and thousands of websites get hacked due to misconfiguration or lack of protection. If you are a website owner or security engineer and looking to protect your website from Clickjacking, code injection, MIME types, XSS, etc. attacks then this guide will help you.

In this article, I will talk about various HTTP Headers (recommended by OWASP) to implement in multiple web servers, network edge & CDN providers for better website protection.

Notes:

  • You are advised to take a backup of the configuration file prior to making changes
  • Some of the headers may not be supported on all browsers, so check out the compatibility before the implementation.
  • Mod_headers must be enabled in Apache to implement these headers. Ensure the following line uncommented in httpd.conf file.
LoadModule headers_module modules/mod_headers.so

Using WordPress?: you may want to try using the HTTP Headers plugin, which takes care of these headers and a lot more.

Let’s get it started…👨‍💻

HTTP Strict Transport Security

HSTS (HTTP Strict Transport Security) header to ensure all communication from a browser is sent over HTTPS (HTTP Secure). This prevents HTTPS click-through prompts and redirects HTTP requests to HTTPS.

Before implementing this header, you must ensure all your website page is accessible over HTTPS else they will be blocked.

HSTS header is supported on all the major latest version of a browser like IE, Firefox, Opera, Safari, and Chrome. There are three parameters configuration.

Parameter Value Meaning
max-age Duration (in seconds) to tell a browser that requests are available only over HTTPS.
includeSubDomains The configuration is valid for the subdomain as well.
preload Use if you would like your domain to be included in the HSTS preload list

So let’s take an example of having HSTS configured for one year, including preload for domain and sub-domain.

Apache HTTP Server

You can implement HSTS in Apache by adding the following entry in httpd.conf file

Header set Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"

Restart apache to see the results

Nginx

To configure HSTS in Nginx, add the next entry in nginx.conf under server (SSL) directive

add_header Strict-Transport-Security 'max-age=31536000; includeSubDomains; preload';

As usual, you will need to restart Nginx to verify

Cloudflare

If you are using Cloudflare, then you can enable HSTS in just a few clicks.

  • Log in to Cloudflare and select the site
  • Go to the “Crypto” tab and click “Enable HSTS.”

cloudflare-hsts-config

Select the settings the one you need, and changes will be applied on the fly.

Microsoft IIS

Launch the IIS Manager and add the header by going to “HTTP Response Headers” for the respective site.

iis-hsts

Restart the site

X-Frame-Options

Use the X-Frame-Options header to prevent Clickjacking vulnerability on your website. By implementing this header, you instruct the browser not to embed your web page in frame/iframe. This has some limitations in browser support, so you got to check before implementing it.

You can configure the following three parameters.

Parameter Value Meaning
SAMEORIGIN Frame/iframe of content is only allowed from the same site origin.
DENY Prevent any domain to embed your content using frame/iframe.
ALLOW-FROM Allow framing the content only on a particular URI.

Let’s take a look at how to implement “DENY” so no domain embeds the web page.

Apache

Add the following line in httpd.conf and restart the webserver to verify the results.

Header always append X-Frame-Options DENY

Nginx

Add the following in nginx.conf under server directive/block.

add_header X-Frame-Options “DENY”;

Restart to verify the results

F5 LTM

Create an iRule with the following and associated with the respective virtual server.

when HTTP_RESPONSE {

HTTP::header insert "X-FRAME-OPTIONS" "DENY"

}

You don’t need to restart anything, changes are reflected in the air.

WordPress

You can get this header implemented through WordPress too. Add the following in a wp-config.php file

header('X-Frame-Options: DENY);

If you are not comfortable editing the file, then you can use a plugin as explained here or mentioned above.

Microsoft IIS

Add the header by going to “HTTP Response Headers” for the respective site.

iis-x-frame-options

Restart the site to see the results.

X-Content-Type-Options

Prevent MIME types of security risk by adding this header to your web page’s HTTP response. Having this header instructs browser to consider file types as defined and disallow content sniffing. There is only one parameter you got to add “nosniff”.

Let’s see how to advertise this header.

Apache

You can do this by adding the below line in httpd.conf file

Header set X-Content-Type-Options nosniff

Don’t forget to restart the Apache webserver to get the configuration active.

Nginx

Add the following line in nginx.conf file under server block.

add_header X-Content-Type-Options nosniff;

As usual, you got to restart the Nginx to check the results.

Microsoft IIS

Open IIS and go to HTTP Response Headers

Click on Add and enter the Name and Value

iis-mime-types

Click OK and restart the IIS to verify the results.

Content Security Policy

Prevent XSS, clickjacking, code injection attacks by implementing the Content Security Policy (CSP) header in your web page HTTP response. CSP instruct browser to load allowed content to load on the website.

All browsers don’t support CSP, so you got to verify before implementing it. There are three ways you can achieve CSP headers.

  • Content-Security-Policy – Level 2/1.0
  • X-Content-Security-Policy – Deprecated
  • X-Webkit-CSP – Deprecated

If you are still using the deprecated one, then you may consider upgrading to the latest one.

There are multiple parameters possible to implement CSP, and you can refer to OWASP for an idea. However, let’s go through the two most used parameters.

Parameter Value Meaning
default-src Load everything from a defined source
script-src Load only scripts from a defined source

The following example of loading everything from the same origin in various web servers.

Apache

Get the following added in httpd.conf file and restart the webserver to get effective.

Header set Content-Security-Policy "default-src 'self';"

Nginx

Add the following in the server block in nginx.conf file

add_header Content-Security-Policy "default-src 'self';";

Microsoft IIS

Go to HTTP Response Headers for your respective site in IIS Manager and add the following

iis-csp

Check out this to implement frame-ancestors using CSP. This is an advanced version of X-Frame-Options.

X-Permitted-Cross-Domain-Policies

Using Adobe products like PDF, Flash, etc.?

You can implement this header to instruct the browser on how to handle the requests over a cross-domain. By implementing this header, you restrict loading your site’s assets from other domains to avoid resource abuse.

There are a few options available.

Value Description
none no policy is allowed
master-only allow only the master policy
all everything is allowed
by-content-only Allow only a certain type of content. Example – XML
by-ftp-only applicable only for an FTP server

Apache

If you don’t want to allow any policy.

Header set X-Permitted-Cross-Domain-Policies "none"

You should see the header like the following.

permitted-cross-domain

Nginx

And, let’s say you need to implement master-only then add the following in nginx.conf under server block.

add_header X-Permitted-Cross-Domain-Policies master-only;

And the result.

nginx-permitted-cross

Referrer-Policy

Looking to control the referrer-policy of your site? There are certain privacy and security benefits. However, not all the options are supported by all the browsers, so review your requirements before the implementation.

Referrer-Policy supports the following syntax.

Value Description
no-referrer Referrer information will not be sent with the request.
no-referrer-when-downgrade The default setting where referrer is sent to the same protocol as HTTP to HTTP, HTTPS to HTTPS.
unsafe-url full URL will be sent with the request.
same-origin Referrer will be sent only for same origin site.
strict-origin send only when a protocol is HTTPS
strict-origin-when-cross-origin the full URL will be sent over a strict protocol like HTTPS
origin send the origin URL in all the requests
origin-when-cross-origin send FULL URL on the same origin. However, send only origin URL in other cases.

Apache

You can add the following if you want to set no-referrer.

Header set Referrer-Policy "no-referrer"

And after the restart, you should have in the response headers.

referrer-policy-apache

Nginx

Let’s say you need to implement the same origin, so you got to add the following.

add_header Referrer-Policy same-origin;

Once configured, you should have the results below.

referrer-nginx-same-origin

Expect-CT

A new header still in experimental status is to instruct the browser to validate the connection with web servers for certificate transparency (CT). This project by Google aims to fix some of the flaws in the SSL/TLS certificate system.

The following three variables are available for the Expect-CT header.

Value Description
max-age In seconds, for how long the browser should cache the policy.
enforce An optional directive to enforce the policy.
report-uri Browser to send a report to the specified URL when valid certificate transparency not received.

Apache

Let’s assume you want to enforce this policy, report, and cache for 12 hours then you got to add the following.

Header set Expect-CT 'enforce, max-age=43200, report-uri="https://somedomain.com/report"'

And, here is the result.

expect-ct-apache-http

Nginx

What if you want to report and cache for 1 hour?

add_header Expect-CT 'max-age=60, report-uri="https://mydomain.com/report"';

The output would be.

expect-ct-nginx

Permissions-Policy

Earlier known as Feature-Policy, it is renamed as Permissions-Policy with enhanced features. You can check out this to understand the big changes between Feature-Policy to Permissions-Policy.

With Permissions Policy, you can control browser features such as geolocation, fullscreen, speaker, USB, autoplay, speaker, microphone, payment, battery status, etc. to enable or disable within a web application. By implementing this policy, you let your server instruct a client (browser) to obey the web application functionality.

Apache

Let’s say you need to disable the fullscreen feature and to do so, you can add the following in httpd.conf or apache2.conf file depending on the flavor of the Apache HTTP server you use.

Header always set Permissions-Policy "fullscreen 'none' "

How about adding multiple features in a single line?

That’s possible too!

Header always set Permissions-Policy "fullscreen 'none'; microphone 'none'"

Restart Apache HTTP to see the result.

HTTP/1.1 200 OK
Date: Thu, 29 Apr 2021 06:40:43 GMT
Server: Apache/2.4.37 (centos)
Permissions-Policy: fullscreen 'none'; microphone 'none'
Last-Modified: Thu, 29 Apr 2021 06:40:41 GMT
ETag: "3-5c116c620a6f1"
Accept-Ranges: bytes
Content-Length: 3
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

The above code will instruct the browser to disable fullscreen and microphone.

You may also disable the feature entirely by keeping the allowlist empty.

For example, you can add the following to disable the geolocation feature.

Header always set Permissions-Policy "geolocation=()"

This would output on the browser like below.

HTTP/1.1 200 OK
Date: Thu, 29 Apr 2021 06:44:19 GMT
Server: Apache/2.4.37 (centos)
Permissions-Policy: geolocation=()
Last-Modified: Thu, 29 Apr 2021 06:40:41 GMT
ETag: "3-5c116c620a6f1"
Accept-Ranges: bytes
Content-Length: 3
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

Nginx

Let’s take another example – disable vibrate feature.

add_header Permissions-Policy "vibrate 'none';";

Or, disable geolocation, camera, and speaker.

add_header Permissions-Policy "geolocation 'none'; camera 'none'; speaker 'none';";

Here is the output after restarting Nginx.

HTTP/1.1 200 OK
Server: nginx/1.14.1
Date: Thu, 29 Apr 2021 06:48:35 GMT
Content-Type: text/html
Content-Length: 4057
Last-Modified: Mon, 07 Oct 2019 21:16:24 GMT
Connection: keep-alive
ETag: "5d9bab28-fd9"
Permissions-Policy: geolocation 'none'; camera 'none'; speaker 'none';
Accept-Ranges: bytes

All the Nginx configuration goes under http block in nginx.conf or any custom file you use.

Clear Site Data

As you may guess by the name, implementing a Clear-Site-Data header is a great way to tell a client to clear browsing data such as cache, storage, cookies, or everything. This gives you more control over how you want to store the website’s data in the browser.

Apache

Let’s say you want to clear the origin cache, you can add below.

Header always set Clear-Site-Data "cache"

Which will output HTTP response as below.

HTTP/1.1 200 OK
Date: Thu, 29 Apr 2021 07:52:14 GMT
Server: Apache/2.4.37 (centos)
Clear-Site-Data: cache
Last-Modified: Thu, 29 Apr 2021 06:40:41 GMT
ETag: "3-5c116c620a6f1"
Accept-Ranges: bytes
Content-Length: 3
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

or, to clear everything.

Header always set Clear-Site-Data "*"

Nginx

Let’s set Nginx to clear cookies.

add_header Clear-Site-Data "cookies";

And, you will see the output below.

HTTP/1.1 200 OK
Server: nginx/1.14.1
Date: Thu, 29 Apr 2021 07:55:58 GMT
Content-Type: text/html
Content-Length: 4057
Last-Modified: Mon, 07 Oct 2019 21:16:24 GMT
Connection: keep-alive
ETag: "5d9bab28-fd9"
Clear-Site-Data: cookies
Accept-Ranges: bytes

Conclusion

Securing a website is challenging, and I hope by implementing the above headers, you add a layer of security. If you are running a business site, then you may also consider using cloud-WAF like SUCURI to protect your online business. The good thing about SUCURI is it offers both security and performance.

If you go for SUCURI WAF, you will find additional headers section under the Firewall >> Security tab.

sucuri-secure-headers