composer require silverstripe/mimevalidatorChecks uploaded file content roughly matches a known MIME type for the file extension.
It can be used with FileField or any subclasses like UploadField.
For example, it will fail validation if someone renames a .exe file to .jpg
and attempts to upload the file.
Install with composer by running composer require silverstripe/mimevalidator in the root of your Silverstripe project.
Silverstripe CMS Recipe 4.6 and above include this module via silverstripe/recipe-core.
Therefore, it is unnecessary to directly install this module if your project has been upgraded to,
or was created with CMS Recipe 4.6.0 or later.
Read Allowed file types on the Silverstripe CMS documentation for details on configuring MIME type validation.