Enable Security Headers

Security headers can effectively prevent a variety of hacking attempts. Therefore, you should consider Strict-Transport-Security, Content-Security-Policy, X-Frame-Options, or X-XSS-Protection titles.

Security Assessment

CVSS Vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Vulnerability Information

They are directives to increase the protection and create more defense against vulnerabilities using browsers. For example, they modify the behavior of web browsers to avoid security vulnerabilities by accepting one kind of valid server certificate like TLS.

Types of security headers include:

• HTTP Strict Transport Security (HSTS)
• Content Security Policy (CSP)
• HTTP Public Key Pinning (HPKP)

How security headers can prevent vulnerabilities

Inserting a security header can prevent a variety of hacking attempts. 

You can refer to OWASP Secure Headers Project for the top HTTP response headers that provide security and usability. 

Here are some of the vulnerabilities you can avoid by using a security header:

• Protocol downgrade attacks like Poodle 
• Content Injection attacks like XSS and Clickjacking 
• Reflective XSS attack
• Cross-Site Request Forgery attack
• Cross-Site Scripting attack

Before you apply a security-related HTTP response header for attack prevention, check whether it's compatible with the browsers you're targeting. 

Hot to enable security headers

Use the following guides to set correct security headers for your web application:

• Webserver Configuration (Apache, NGINX)
• HTTP Strict Transport Security (HSTS)
• X-Frame-Options
• X-XXS-Protection
• X-Content-Type-Options
• Same-Site Cookie
• Content-Security-Policy
• Referrer-Policy
• Access-Control-Allow-Origin

Webserver configuration

Use the following configurations to configure your webserver to contain all described headers. Below, you find further descriptions of the single headers.

Apache

On Apache you need to update your configuration to include the correct header directives. Add this to the virtual host configuration in /etc/apache2/sites-enabled/domain.conf or /etc/httpd/sites-enabled/domain.conf:

<VirtualHost *:443>
    Header always set Strict-Transport-Security "max-age=31536000"
    Header always set X-Frame-Options "deny"
    Header always set X-XSS-Protection "1; mode=block"
    Header always set X-Content-Type-Options "nosniff"
    Header always set Content-Security-Policy "default-src 'self'"
    Header always set Referrer-Policy "strict-origin-when-cross-origin"
</VirtualHost>

nginx

On Nginx you need to update your configuration file which is usually located at /etc/nginx/nginx.conf, /etc/nginx/sited-enabled/yoursite.com (Ubuntu / Debian) or /etc/nginx/conf.d/nginx.conf (RHEL / CentOS) to include the correct header with the add_header directives:

server {
    add_header Strict-Transport-Security "max-age=63072000; includeSubdomains;" always;
    add_header X-Frame-Options "deny" always;
    add_header X-XSS-Protection "1; mode=block" always;
    add_header X-Content-Type-Options "nosniff" always;
    add_header Content-Security-Policy "default-src 'self'" always;
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
}

HTTP Strict Transport Security (HSTS)

The HSTS header enforces HTTPS connections. This prevents downgrade attacks to an insecure HTTP connection. See Enable HSTS for the correct settings.

X-Frame-Options

The X-Frame-Options header declares whether this site may be embedded as a frame into other websites. The values are:

Setting this header, e.g., to deny, will protect the website against clickjacking attacks where an attacker overlays your web page's iframe with arbitrary content to bait his victims in clicking on certain links on your website.

X-XXS-Protection

Some web browsers are shipped with a Cross-Site-Scripting (XSS) filter. This filter can detect specific XSS attacks and prevent them. To configure the browser filter behavior, use the X-XSS-Protection header.

Setting this header, e.g., to 1; mode=block will tell the browser that it should not render the web page if it detects an attack.

X-Content-Type-Options

Browsers try to detect the MIME-type of files sent by the webserver. For example, suppose an attacker manages to upload a malicious (executable) file to a webserver, which only sends images. The MIME-type can provide protection, as it tells the browser that it should expect an image and not an executable file. Therefore, the browser must not detect the MIME-type but only use the webserver provided MIME-type. To enforce this behavior, use the X-Content-Type-Options header and set it to nosniff.

Same-Site Cookie

The Same-Site cookie flag tells the browser not to send cookies and cross-site requests. This cookie flag prevents the risk of cross-site information leakage and can also help to mitigate Cross-Site Request Forgery attacks. Possible values are Strict, Lax, or None. If the Same-Site cookie flag is set to None, the Secure flag must be set to prevent sending the cookie in an insecure context.

Content-Security-Policy

The Content-Security-Policy (CSP) header tells the browser from which domain further resources such as scripts, images, or stylesheets may be loaded. This can prevent various Cross-Site-Scripting (XSS) and other Cross-Site-Injection attacks. However, the policy needs to be hand-crafted for the particular usage, as it may easily prohibit analytic scripts, fonts, or other resources that are loaded from a third party.

A specific and restrictive policy can be default-src 'self.' Test your configuration thoroughly, as you may not want to block your analytics script or other third-party resources.

Referrer-Policy

The Referrer-Policy header defines how much information about the referrer is sent when the user clicks on a link. The referrer may leak sensitive information such as user-specific URLs. Therefore the referrer-policy might be set to some more restrictive value. A relatively secure setting is strict-origin-when-cross-origin.

Cache-Control

The Cache-Control header defines how caching in the browser is configured. Depending on the header's value, the browser may cache the website, including any sensitive information. The header should be set to no-store for pages where confidentiality is an issue.

Access-Control-Allow-Origin

The Access-Control-Allow-Origin header defines which applications may consume your API. Consider this article. It should be set to the domain of your frontend, such as:

Access-Control-Allow-Origin: https://example.org

Please consult this blog article if you have multiple applications using your API.