Kirby Content Security Policy Header

Kirby Plugin for easier Content Security Policy (CSP) Headers setup.

Installation

• unzip master.zip as folder site/plugins/kirby3-security-headers or
• git submodule add https://github.com/bnomei/kirby3-security-headers.git site/plugins/kirby3-security-headers or
• composer require bnomei/kirby3-security-headers

Default CSP Headers

The following headers will be applied by default, you do not need to set them explicitly. They provide a good starting point for most websites and ensure a sane level of security.

X-Powered-By:                 "" # unset
X-Frame-Options:              "SAMEORIGIN"
X-XSS-Protection:             "1; mode=block"
X-Content-Type-Options:       "nosniff"
Strict-Transport-Security:    "max-age=31536000; includeSubdomains"
Referrer-Policy:              "no-referrer-when-downgrade"
Permissions-Policy:           "interest-cohort=()" # flock-off
# + various Feature-Policies...

Tip

See \Bnomei\SecurityHeaders::HEADERS_DEFAULT for more details.

Zero Configuration? Almost.

Installing the plugin is enough to protect your website. A route:before-hook takes care of sending the CSP headers automatically. But you will most likely need to customize the CSP headers when using third-party services like

• Content Delivery Networks (CDN),
• analytic scripts like Google-Tag-Manager/Fathom/Matomo/Piwik/Plausible/Umami,
• embedding external media like from Youtube/Vimeo/Instagram/X,
• external newsletter sign-up forms from Brevo/Mailchimp/Mailjet/Mailcoach,
• any other third-party service not hosted on your domain or subdomain or
• when using inline <script> and/or <style>.

Tip

The plugin will automatically disable itself on local setups to not get in your way while developing. To test the CSP headers locally, you can use the 'bnomei.securityheaders.enabled' => true, option to enforce sending the headers.

Customizing CSP Headers & Nonces

You can customize the CSP headers by providing a custom Loader and/or Setter via the Kirby config.

Loader

The Loader is used to initially create the CSP-Builder object with a given set of mostly static data. You can provide a path to a file, return an array or null to create blank CSP-Builder object.

Tip

See \Bnomei\SecurityHeaders::LOADER_DEFAULT for more details.

Warning

Consider using a custom loader ONLY if you find yourself adding a lot of configurations in the Setter. The default loader is already quite extensive and should cover most use-cases.

Setter

The Setter is applied after the Loader. Use it to add dynamic stuff like rules for external services, hashes and nonces.

/site/config/config.php

<?php
return [
    'bnomei.securityheaders.setter' => function ($instance) {
        // https://github.com/paragonie/csp-builder
        // #build-a-content-security-policy-programmatically
        /** @var ParagonIE\CSPBuilder\CSPBuilder $csp */
        $csp = $instance->csp();
        
        // allowing all inline scripts and styles is
        // not recommended, try using nonces instead
        // $csp->setAllowUnsafeEval('script-src', true);
        // $csp->setAllowUnsafeInline('script-src', true);
        // $csp->setAllowUnsafeInline('style-src', true);
        
        // youtube
        $csp->addSource('frame', 'https://www.youtube.com');
        $csp->addSource('frame', 'https://youtube.com');
        $csp->addSource('image', 'https://ggpht.com');
        $csp->addSource('image', 'https://youtube.com');
        $csp->addSource('image', 'https://ytimg.com');
        $csp->addSource('script', 'https://google.com');
        $csp->addSource('script', 'https://youtube.com');

        // vimeo
        $csp->addSource('frame', 'player.vimeo.com');
        $csp->addSource('image', 'i.vimeocdn.com');
        $csp->addSource('script', 'f.vimeocdn.com');
        $csp->addSource('source', 'player.vimeo.com');
        $csp->addSource('style', 'f.vimeocdn.com');
    },
    // other options...
];

Tip

You can define nonces in the Setter-option and later retrieved using $page->nonce(...) or $page->nonceAttr(...). But the plugin also provides a single nonce for frontend use out of the box.

Nonces

For convenience the plugin also provides you with a single frontend nonce to use as attribute in <link>, <style> and <script> elements. You can retrieve the nonce with site()->nonce().

<script nonce="<?= site()->nonce() ?>">
/* ... */
</script>

Note

This plugin automatically registers the nonce that Kirby creates for its panel (in case that ever might be needed).

Disabling the plugin

The CSP headers will be sent before Kirby renders HTML using a route:before hook but the plugin will be automatically disabled if one the following conditions apply:

• Kirby determines it is a local setup or
• The plugins setting bnomei.securityheaders.enabled is set to false.

Warning

By default, CSP headers are never sent for any Kirby Panel, API and Media routes.

Settings

bnomei.securityheaders.	Default	Description
enabled	null/true/false	will set headers
seed	callback	returns a unique seed for frontend nonces on every request
headers	callback	array of sensible default values
loader	callback	returning filepath or array
setter	callback	instance which allows customizing the CSPBuilder

Dependencies

• paragonie/csp-builder

Disclaimer

This plugin is provided "as is" with no guarantee. Use it at your own risk and always test it yourself before using it in a production environment. If you find any issues, please create a new issue.

License

MIT

It is discouraged to use this plugin in any project that promotes racism, sexism, homophobia, animal abuse, violence or any other form of hate speech.