Allowed file types#

Not every kind of file should be stored in a CMS's asset management system. For example, allowing users to upload JavaScript files could lead to a risk of Cross-Site Scripting (XSS) attacks.

Out of the box, your Silverstripe CMS project will limit what type of files can be uploaded into the assets management section. There's two type of restriction in place based on:

• the extensions of the files
• the MIME type of the files.

File extensions validation#

The silverstripe/assets module ships with a whitelist of allowed file extensions. Any file with an extensions not in this whitelist will not be allowed to be stored in Silverstripe's assets management system.

The whitelist is controlled by the SilverStripe\Assets\File::$allowed_extensions variable.

You can whitelist additional file extensions by adding them in your YAML configuration.

SilverStripe\Assets\File:
  allowed_extensions:
    - 7zip
    - xzip

Any file not included in this config, or in the default list of extensions, will be blocked from any requests to the assets directory. Invalid files will be blocked regardless of whether they exist or not, and will not invoke any PHP processes.

You can also remove pre-existing entries from the whitelist by setting them to false.

SilverStripe\Assets\File:
  allowed_extensions:
    zip: false

MIME type validation#

Another type of validation that can be applied to files uploaded in Silverstripe CMS is MIME type validation. When MIME type validation is enabled, Silverstripe will analyse the content of files at upload time to determine their MIME type and will reject files with invalid type.

MIME type validation also uses a whitelist of allowed MIME types.

Enabling MIME type validation#

You need to install the silverstripe/mimevalidator module in your project to enable MIME type validation. If your project has silverstripe/recipe-core as a dependency, the silverstripe/mimevalidator module will already be installed and enabled.

Look at the app/_config/mimevalidator.yml file to view the default configuration.

You can explicitly require the module by running this command

composer require silverstripe/mimevalidator

Enable globally#

In your app/_config/config.yml file:

SilverStripe\Core\Injector\Injector:
  SilverStripe\Assets\Upload_Validator:
    class: SilverStripe\MimeValidator\MimeUploadValidator

Enable on an individual upload field#

$field = UploadField::create();
$field->setValidator(MimeUploadValidator::create());

Adding MIME types#

By default MIME types are checked against HTTP.MimeTypes config set in framework. This can be limiting as this only allows for one MIME type per extension. To allow for multiple MIME types per extension, you can add these in your YAML config as below:

SilverStripe\MimeValidator\MimeUploadValidator:
  MimeTypes:
    ics:
      - 'text/plain'
      - 'text/calendar'

Adding new image types#

Silverstripe CMS support JPEG, GIF, PNG and WebP image formats out of the box. Silverstripe CMS can be configured to support other less common image formats (e.g: AVIF). For this to work, your version of PHP and of the intervention/image library must support these alternative image formats.

For example, this snippet can be added to the configuration of older Silverstripe CMS projects to allow them to work with AVIF images.

---
Name: myproject-assetsfiletypes
After: '#assetsfiletypes'
---
SilverStripe\Assets\File:
  file_types:
    avif: 'AVIF Image'
  allowed_extensions:
    - avif
  app_categories:
    image:
      - avif
    image/supported:
      - avif
  class_for_file_extension:
    avif: SilverStripe\Assets\Image

SilverStripe\Assets\Storage\DBFile:
  supported_images:
    - image/avif

---
Name: myproject-mimevalidator
After: '#mimevalidator'
Only:
  moduleexists: silverstripe/mimevalidator
---
SilverStripe\MimeValidator\MimeUploadValidator:
  MimeTypes:
    avif:
      - image/avif