Drupal 9.3.12 Released
Drupal 9.3 implemented a generic entity access API for entity revisions. However, this API was not completely integrated with existing permissions, resulting in some possible access bypass for users who have access to use revisions of content generally, but who do not have access to individual items of node and media content.
This vulnerability only affects sites using Drupal's revision system.
The solution is to install the latest version, if you are using Drupal 9.3, update to Drupal 9.3.12.
All releases prior to Drupal 9.3 (including Drupal 7) are not affected.