In Drupal 8.7.4, when the experimental Workspaces module is enabled, an access bypass condition is created.
This can be mitigated by disabling the Workspaces module. It does not affect any release other than Drupal 8.7.4.
Drupal 8.7.3 and earlier, Drupal 8.6.x and earlier, and Drupal 7.x are not affected.
If the site is running Drupal 8.7.4, upgrade to Drupal 8.7.5.
Note, manual step needed. For sites with the Workspaces module enabled,
update.php needs to run to ensure a required cache clear. If there is a reverse proxy cache or content delivery network (e.g. Varnish, CloudFlare) it is also advisable to clear these as well.