MulerTech CSP Bundle

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Symfony bundle for Content Security Policy (CSP) header management with named nonce support.

Installation

composer require mulertech/csp-bundle

Configuration

The bundle ships with secure defaults for all directives. You only need to override what differs from the defaults.

Minimal config/packages/mulertech_csp.yaml:

mulertech_csp:
    directives:
        script-src:
            - "'self'"
            - "nonce(main)"
        style-src:
            - "'self'"
            - "'unsafe-inline'"

Full reference

Here is the complete list of available options with their default values:

mulertech_csp:
    enabled: true                    # true by default
    report_only: false               # false by default
    always_add: []                   # Origins added to ALL directives
    report:
        url: ~                       # External URL for report-uri/report-to
        route: ~                     # Symfony route name (alternative to url)
        route_params: []             # Route parameters
        chance: 100                  # 0-100, % of requests with reporting
    directives:                      # Only override what you need
        default-src:
            - "'self'"
        script-src:
            - "'self'"
            - "nonce(main)"
        style-src:
            - "'self'"
            - "'unsafe-inline'"
        img-src:
            - "'self'"
            - "data:"
        font-src:
            - "'self'"
        connect-src:
            - "'self'"
        media-src:
            - "'self'"
        object-src:
            - "'none'"
        frame-src:
            - "'none'"
        frame-ancestors:
            - "'none'"
        base-uri:
            - "'self'"
        form-action:
            - "'self'"
        upgrade-insecure-requests: true

Default directives

Directive	Default
default-src	'self'
script-src	'self' + nonce(main)
style-src	'self' 'unsafe-inline'
img-src	'self' data:
font-src	'self'
connect-src	'self'
media-src	'self'
object-src	'none'
frame-src	'none'
frame-ancestors	'none'
base-uri	'self'
form-action	'self'
upgrade-insecure-requests	true

Named nonces

Use nonce(handle) syntax in directives to create named nonces:

mulertech_csp:
    directives:
        script-src:
            - "'self'"
            - "nonce(main)"           # For your main scripts
            - "nonce(analytics)"      # For analytics scripts

Each named nonce generates a unique 256-bit (32 bytes) cryptographically secure value.

always_add

Add origins to all directives automatically (except those set to 'none'):

mulertech_csp:
    always_add:
        - "https://cdn.example.com"
    directives:
        default-src:
            - "'self'"
        object-src:
            - "'none'"               # always_add is NOT merged here

Violation reporting

Report CSP violations to an external endpoint:

mulertech_csp:
    report:
        url: "https://report.example.com/csp"
        chance: 50                    # Only 50% of requests

Or use a Symfony route:

mulertech_csp:
    report:
        route: "app_csp_report"
        route_params: {}

Report-only mode

Test your CSP policy without enforcing it:

mulertech_csp:
    report_only: true

This sets the Content-Security-Policy-Report-Only header instead of Content-Security-Policy.

Usage

In Twig templates

Use the csp_nonce('handle') function with a named handle:

<script nonce="{{ csp_nonce('main') }}">
    // Your inline JavaScript
</script>

<script nonce="{{ csp_nonce('analytics') }}">
    // Analytics script
</script>

Dynamic CSP customization

Listen to the BuildCspHeaderEvent to customize CSP per-request:

use MulerTech\CspBundle\Event\BuildCspHeaderEvent;
use Symfony\Component\EventDispatcher\Attribute\AsEventListener;

#[AsEventListener(event: BuildCspHeaderEvent::NAME)]
class CspListener
{
    public function __invoke(BuildCspHeaderEvent $event): void
    {
        if ($event->getRequest()->getPathInfo() === '/admin') {
            $event->setHeaderValue("default-src 'self'; script-src 'self'");
        }
    }
}

Inject the nonce generator

use MulerTech\CspBundle\CspNonceGenerator;

class MyService
{
    public function __construct(
        private readonly CspNonceGenerator $nonceGenerator,
    ) {}

    public function getMainNonce(): string
    {
        return $this->nonceGenerator->getNonce('main');
    }
}

Upgrading from v1.x

Breaking changes

1. Directives format: Changed from scalar strings to arrays of sources

# v1.x
mulertech_csp:
    directives:
        script-src: "'self' 'nonce-{nonce}'"

# v2.0
mulertech_csp:
    directives:
        script-src:
            - "'self'"
            - "nonce(main)"

2. Twig function: csp_nonce() now requires a handle argument

{# v1.x #}
<script nonce="{{ csp_nonce() }}">

{# v2.0 #}
<script nonce="{{ csp_nonce('main') }}">

3. Nonce placeholder: {nonce} replaced by nonce(handle) syntax

Requirements

• PHP >= 8.2
• Symfony 6.4 or 7.x
• Twig (optional, for the csp_nonce() function)
• symfony/routing (optional, for route-based reporting)

License

MIT