设置HTTP响应头 保护自己的Web

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

Security is as essential as content and SEO of your website, and thousands of website get hacked due to misconfiguration or lack of protection.

If you are a website owner or security engineer and looking to protect your websitefrom Clickjacking, code injection, MIME types, XSS, etc. attacks then this guide will help you.

In this article, I will talk about various HTTP Header to implement in multiple web servers, network edge & CDN provider for better website protection.

Notes:

• You are advised to take a backup of configuration file prior making changes
• Some of the headers may not be supported on all the 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

• Post-implementation, you can use secure headers online tool to verify the results.

If you are using SUCURI Cloud WAF, then you don’t have to worry about adding these manually on your web server as most of them are automatically enabled.

HTTP Headers List

• X-XSS-Protection
• HTTP Strict Transport Security
• X-Frame-Options
• X-Content-Type-Options
• HTTP Public Key Pinning
• Content Security Policy
• X-Permitted-Cross-Domain-Policies
• Referrer Policy
• Expect-CT
• Feature-Policy

X-XSS-Protection

X-XSS-Protection header can prevent some level of XSS (cross-site-scripting) attacks, and this is compatible with IE 8+, Chrome, Opera, Safari & Android.

Google, Facebook, Github use this header, and most of the penetration testing consultancy will ask you to implement this.

There are four possible ways you can configure this header.

Parameter Value	Meaning
0	XSS filter disabled
1	XSS filter enabled and sanitized the page if attack detected
1;mode=block	XSS filter enabled and prevented rendering the page if attack detected
1;report=http://example.com/report_URI	XSS filter enabled and reported the violation if attack detected

Let’s implement 1;mode=block in the following web servers.

Apache HTTP Server

Add the following entry in httpd.conf of your Apache webserver

Header set X-XSS-Protection "1; mode=block"

Restart the apache to verify

Nginx

Add the following in nginx.conf under http block

add_header X-XSS-Protection "1; mode=block";

Nginx restart is needed to get this reflected on your web page response header.

MaxCDN

If you are using MaxCDN, then adding header is easy and on-the-fly.

Go to Edge Rules >> click “New Rule” and select “Add X-XSS-Protection Header” from the drop-down.

Microsoft IIS

• Open IIS Manager
• Select the Site you need to enable the header for
• Go to “HTTP Response Headers.”
• Click “Add” under actions
• Enter name, value and click Ok

• Restart IIS to see the results

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	Configuration is valid for 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

Cloud Flare

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

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

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.

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 limitation 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 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.

Microsoft IIS

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

Restart the site to see the results.

X-Content-Type-Options

Prevent MIME types security risk by adding this header to your web page’s HTTP response. Having this header instruct browser to consider files 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.

WordPress

If you are using WordPress, then you may consider using Security Headers plugin to implement this header.

Microsoft IIS

Open IIS and go to HTTP Response Headers

Click on Add and enter the Name and Value

Click OK and restart the IIS to verify the results.

HTTP Public Key Pinning

Minimize the man-in-the-middle (MITM) attacks risk by pinning certificate. This is possible with HPKP (HTTP Public Key Pinning) header.

You can pin the root certificate public key or immediate certificate. At the time of writing, HPKP currently works in Firefox and Chrome and support SHA-256 hash algorithm.

There are four possible parameter configurations.

Parameter Value	Meaning
report-uri=”url”	Report to the specified URL if pin validation fails. This is optional.
pin-sha256=”sha256key”	Specify the pins here
max-age=	Browser to remember the time in seconds that site is accessible only using one of the pinned keys.
IncludeSubDomains	This is applicable on a subdomain as well.

Let’s see HPKP header example from facebook.com

public-key-pins-report-only:max-age=500; pin-sha256="WoiWRyIOVNa9ihaBciRSC7XHjliYS9VwUGOIud4PB18="; pin-sha256="r/mIkG3eEpVdm+u/ko/cwxzOMo1bk4TyHIlByibiA5E="; pin-sha256="q4PO2G2cbkZhZ82+JgmRUyGMoAeozA+BSXVXQWB8XWQ="; report-uri=http://reports.fb.com/hpkp/

If this is something you need to implement on your website, then head to implementation guide written by Scott Helme.

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.

1. Content-Security-Policy – Level 2/1.0
2. X-Content-Security-Policy – Deprecated
3. X-Webkit-CSP – Deprecated

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

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

X-Permitted-Cross-Domain-Policies

Using Adobe products like PDF, Flash, etc.? You can implement this header to instruct the browser how to handle the requests over a cross-domain. By implementing this header, you restrict loading your site’s assets from other domain 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.

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.

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 requirement 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.

Nginx

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

add_header Referrer-Policy same-origin;

Once configured, you should have the results below.

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 Expect-CT header.

Value	Description
max-age	In seconds, for how long 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.

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"';

Output would be.

Feature-Policy

Control browser’s feature such as geolocation, fullscreen, speaker, USB, autoplay, speaker, vibrate, microphone, payment, vr, etc. to enable or disable within a web application.

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.

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

How about adding multiple features in a single line?

That’s possible too!

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

Restart Apache HTTP to see the result.

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

Nginx

Let’s take another example – disable vibrate feature.

add_header Feature-Policy "vibrate none;";

Or, disable geolocation, camera, and speaker.

add_header Feature-Policy "geolocation none; camera none; speaker none;";

Here is the output after restarting Nginx.

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

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.