Follwowing vulnerabilities have been addressed in Drupal 8.3.7:

* Views - Access Bypass - Moderately Critical - Drupal 8 - CVE-2017-6923:

 When creating a view, you can optionally use Ajax to update the displayed data via filter parameters. The views subsystem/module did not restrict access to the Ajax endpoint to only views configured to use Ajax. This is mitigated if you have access restrictions on the view.

It is best practice to always include some form of access restrictions on all views, even if you are using another module to display them.

* REST API can bypass comment approval - Access Bypass - Moderately Critical - Drupal 8 - CVE-2017-6924:

 When using the REST API, users without the correct permission can post comments via REST that are approved even if the user does not have permission to post approved comments.

This issue only affects sites that have the RESTful Web Services (rest) module enabled, the comment entity REST resource enabled, and where an attacker can access a user account on the site with permissions to post comments, or where anonymous users can post comments.

* Entity access bypass for entities that do not have UUIDs or have protected revisions - Access Bypass - Critical - Drupal 8 - CVE-2017-6925:

There is a vulnerability in the entity access system that could allow unwanted access to view, create, update, or delete entities. This only affects entities that do not use or do not have UUIDs, and entities that have different access restrictions on different revisions of the same entity.

Reference:

https://www.drupal.org/SA-CORE-2017-004