Remote code execution
A 3rd party development library including with Drupal 8 development dependencies is vulnerable to remote code execution. This is mitigated by the default .htaccess protection against PHP execution, and the fact that Composer development dependencies aren't normal installed. You might be vulnerable to this if you are running a version of Drupal. To be sure you aren’t vulnerable, you can remove the /vendor/phpunit directory from the site root of your production deployments.
Information Exposure
The Views module in Drupal and the Views module might allow remote authenticated users to bypass intended access restrictions and obtain sensitive Statistics information via unspecified vectors.
Saving user accounts can sometimes grant the user all roles
The User module in Drupal allows remote authenticated users to gain privileges via vectors involving contributed or custom code that triggers a rebuild of the user profile form.
Improper Access Control
PHP does not attempt to address RFC section namespace conflicts and therefore does not protect applications from the presence of untrusted client data in the `HTTP_PROXY` environment variable, which might allow remote attackers to redirect an application's outbound HTTP traffic to an arbitrary proxy server via a crafted Proxy header in an HTTP request, as demonstrated by (1) an application that makes a getenv('HTTP_PROXY') call or (2) a CGI configuration of PHP, aka an `httpoxy` issue.