Content Security Policy

New in version 12.3.

Introduction

Content Security Policy (CSP) is a security standard introduced to prevent cross-site scripting (XSS), clickjacking and other code injection attacks resulting of malicious content being executed in the trusted web page context.

See also

If you are not familiar with Content Security Policy, please read the following resources:

At the TYPO3 Developer Days 2023 Oliver Hader talked about Content Security Policy in general and in TYPO3:

Content Security Policy declarations can be applied to a TYPO3 website in frontend and backend scope with a dedicated API.

To delegate Content Security Policy handling to TYPO3 frontend, the feature flag security.frontend.enforceContentSecurityPolicy needs to be enabled.

Changed in version 13.0.

In TYPO3 backend the Content Security Policy is always enforced.

Configuration

Policy builder approach

The following approach illustrates how a policy is build:

<?php

use TYPO3\CMS\Core\Security\ContentSecurityPolicy\Directive;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\Policy;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\SourceKeyword;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\SourceScheme;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\UriValue;
use TYPO3\CMS\Core\Security\Nonce;

$nonce = Nonce::create();
$policy = (new Policy())
    // Results in `default-src 'self'`
    ->default(SourceKeyword::self)

    // Extends the ancestor directive ('default-src'),
    // thus reuses 'self' and adds additional sources
    // Results in `img-src 'self' data: https://*.typo3.org`
    ->extend(Directive::ImgSrc, SourceScheme::data, new UriValue('https://*.typo3.org'))

    // Extends the ancestor directive ('default-src'),
    // thus reuses 'self' and adds additional sources
    // Results in `script-src 'self' 'nonce-[random]'`
    // ('nonce-proxy' is substituted when compiling the policy)
    ->extend(Directive::ScriptSrc, SourceKeyword::nonceProxy)

    // Sets (overrides) the directive,
    // thus ignores 'self' of the 'default-src' directive
    // Results in `worker-src blob:`
    ->set(Directive::WorkerSrc, SourceScheme::blob);

header('Content-Security-Policy: ' . $policy->compile($nonce));

The result of the compiled and serialized result as HTTP header would look similar to this (the following sections are using the same example, but utilize different techniques for the declarations):

Content-Security-Policy: default-src 'self';
    img-src 'self' data: https://*.typo3.org; script-src 'self' 'nonce-[random]';
    worker-src blob:

Note

The policy builder is the low-level representation and interaction in PHP, any other configuration is using the same verbs to describe the CSP instructions. The \TYPO3\CMS\Core\Security\ContentSecurityPolicy\Policy object is used for compiling the CSP in a middleware. Thus, custom controllers or middlewares could use this approach; the last line

header('Content-Security-Policy: ' . $policy->compile($nonce));

is an example to show the basic principle without having to explain PSR-7/PSR-15 details.

For project integrations the "mutations" (via configuration, YAML, resolutions in the UI or events) shall be used.

Extension-specific

Policies for frontend and backend can be applied automatically by providing a Configuration/ContentSecurityPolicies.php file in an extension, for example:

EXT:my_extension/Configuration/ContentSecurityPolicies.php
<?php

declare(strict_types=1);

use TYPO3\CMS\Core\Security\ContentSecurityPolicy\Directive;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\Mutation;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\MutationCollection;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\MutationMode;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\Scope;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\SourceKeyword;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\SourceScheme;
use TYPO3\CMS\Core\Security\ContentSecurityPolicy\UriValue;
use TYPO3\CMS\Core\Type\Map;

return Map::fromEntries([
    // Provide declarations for the backend
    Scope::backend(),
    // NOTICE: When using `MutationMode::Set` existing declarations will be overridden

    new MutationCollection(
        // Results in `default-src 'self'`
        new Mutation(
            MutationMode::Set,
            Directive::DefaultSrc,
            SourceKeyword::self
        ),

        // Extends the ancestor directive ('default-src'),
        // thus reuses 'self' and adds additional sources
        // Results in `img-src 'self' data: https://*.typo3.org`
        new Mutation(
            MutationMode::Extend,
            Directive::ImgSrc,
            SourceScheme::data,
            new UriValue('https://*.typo3.org')
        ),
        // NOTICE: the following two instructions for `Directive::ImgSrc` are identical to the previous instruction,
        // `MutationMode::Extend` is a shortcut for `MutationMode::InheritOnce` and `MutationMode::Append`
        // new Mutation(MutationMode::InheritOnce, Directive::ImgSrc, SourceScheme::data),
        // new Mutation(MutationMode::Append, Directive::ImgSrc, SourceScheme::data, new UriValue('https://*.typo3.org')),

        // Extends the ancestor directive ('default-src'),
        // thus reuses 'self' and adds additional sources
        // Results in `script-src 'self' 'nonce-[random]'`
        // ('nonce-proxy' is substituted when compiling the policy)
        new Mutation(
            MutationMode::Extend,
            Directive::ScriptSrc,
            SourceKeyword::nonceProxy
        ),

        // Sets (overrides) the directive,
        // thus ignores 'self' of the 'default-src' directive
        // Results in `worker-src blob:`
        new Mutation(
            MutationMode::Set,
            Directive::WorkerSrc,
            SourceScheme::blob
        ),
    ),
]);

Site-specific (frontend)

In frontend, a dedicated sites/<my_site>/csp.yaml can be used to declare policies for a specific site, for example:

config/sites/<my_site>/csp.yaml | typo3conf/sites/<my_site>/csp.yaml
# Inherits default site-unspecific frontend policy mutations (enabled per default)
inheritDefault: true
mutations:
  # Results in `default-src 'self'`
  - mode: set
    directive: 'default-src'
    sources:
      - "'self'"

  # Extends the ancestor directive ('default-src'),
  # thus reuses 'self' and adds additional sources
  # Results in `img-src 'self' data: https://*.typo3.org`
  - mode: extend
    directive: 'img-src'
    sources:
      - 'data:'
      - 'https://*.typo3.org'

  # Extends the ancestor directive ('default-src'),
  # thus reuses 'self' and adds additional sources
  # Results in `script-src 'self' 'nonce-[random]'`
  # ('nonce-proxy' is substituted when compiling the policy)
  - mode: extend
    directive: 'script-src'
    sources:
      - "'nonce-proxy'"

  # Results in `worker-src blob:`
  - mode: set
    directive: 'worker-src'
    sources:
      - 'blob:'

Nonce

The nonce attribute is useful to allowlist specific elements, such as a particular inline script or style elements. It can help you to avoid using the CSP unsafe-inline directive, which would allowlist all inline scripts or styles.

—MDN Web Docs, https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/nonce

It may look like this in your HTML code:

<link
    rel="stylesheet"
    href="/_assets/af46f1853e4e259cbb8ebcb816eb0403/Css/styles.css?1687696548"
    media="all"
    nonce="sqK8LkqFp-aWHc7jkHQ4aT-RlUp5cde9ZW0F0-BlrQbExX-PRMoTkw"
>

<style nonce="sqK8LkqFp-aWHc7jkHQ4aT-RlUp5cde9ZW0F0-BlrQbExX-PRMoTkw">
    /* some inline styles */
</style>

<script
    src="/_assets/27334a649e36d0032b969fa8830590c2/JavaScript/scripts.js?1684880443"
    nonce="sqK8LkqFp-aWHc7jkHQ4aT-RlUp5cde9ZW0F0-BlrQbExX-PRMoTkw"
></script>

<script nonce="sqK8LkqFp-aWHc7jkHQ4aT-RlUp5cde9ZW0F0-BlrQbExX-PRMoTkw">
    /* some inline JavaScript */
</script>

The nonce changes with each request so that (possibly malicious) inline scripts or styles are blocked by the browser.

The nonce is applied automatically, when scripts or styles are defined with the TYPO3 API, like TypoScript (page.includeJS, etc.) or the asset collector.

TYPO3 provides APIs to get the nonce for the current request:

Retrieve with PHP

The nonce can be retrieved via the nonce request attribute:

// use TYPO3\CMS\Core\Domain\ConsumableString

/** @var ConsumableString|null $nonce */
$nonceAttribute = $this->request->getAttribute('nonce');
if ($nonceAttribute instanceof ConsumableString) {
    $nonce = $nonceAttribute->consume();
}

In a Fluid template

The f:security.nonce ViewHelper is available, which provides the nonce in a Fluid template, for example:

<script nonce="{f:security.nonce()}">const inline = 'script';</script>

Reporting of violations

Potential CSP violations are reported back to the TYPO3 system and persisted internally in the database table sys_http_report. A corresponding Admin Tools > Content Security Policy backend module supports users to keep track of recent violations and - if applicable - to select potential resolutions (stored in the database table sys_csp_resolution) which extends the Content Security Policy for the given scope during runtime:

../../_images/BackendModule.png

Backend module "Content Security Policy" which displays the violations

Clicking on a row displays the details of this violation on the right side including suggestions on how to resolve this violation. You have the choice to apply this suggestion, or to mute or delete the specific violation.

Note

If you apply the suggestion, it is stored in the database table sys_csp_resolution. To have all policies in one place, you should consider adding the suggestion to your extension-specific or site-specific CSP definitions manually.

Using a third-party service

As an alternative, the reporting URL can be configured to use a third-party service as well:

// For backend
$GLOBALS['TYPO3_CONF_VARS']['BE']['contentSecurityPolicyReportingUrl']
    = 'https://csp-violation.example.org/';

// For frontend
$GLOBALS['TYPO3_CONF_VARS']['FE']['contentSecurityPolicyReportingUrl']
    = 'https://csp-violation.example.org/';

Violations are then sent to the third-party service instead of the TYPO3 endpoint.

PSR-14 events

The following PSR-14 events are available: