Multiple vulnerabilities for Drupal Core have been discovered. Drupal have released versions 8.3.4 and 7.56 which contain fixes for these security vulnerabilities.
We recommend that you update Drupal as soon as possible.
PECL YAML parser unsafe object handling – Critical – Drupal 8 – CVE-2017-6920
PECL YAML parser does not handle PHP objects safely during certain operations within Drupal core. This could lead to remote code execution.
File REST resource does not properly validate – Less Critical – Drupal 8 – CVE-2017-6921
The file REST resource does not properly validate some fields when manipulating files. A site is only affected by this if the site has the RESTful Web Services (rest) module enabled, the file REST resource is enabled and allows PATCH requests, and an attacker can get or register a user account on the site with permissions to upload files and to modify the file resource.
Files uploaded by anonymous users into a private file system can be accessed by other anonymous users – Moderately Critical – Drupal 7 and Drupal 8 – CVE-2017-6922
Private files that have been uploaded by an anonymous user but not permanently attached to content on the site should only be visible to the anonymous user that uploaded them, rather than all anonymous users. Drupal core did not previously provide this protection, allowing an access bypass vulnerability to occur. This issue is mitigated by the fact that in order to be affected, the site must allow anonymous users to upload files into a private file system.
There have also been reports that this vulnerability is being exploited for spam purposes, similar to the scenario discussed in PSA-2016-003 for the public file system.