This security advisory fixes multiple vulnerabilities in both Drupal 7 and
Drupal 8. See below for a list.
Comment reply form allows access to restricted content - Critical - Drupal 8 -
CVE-2017-6926

Users with permission to post comments are able to view content and comments
they do not have access to, and are also able to add comments to this content.

This vulnerability is mitigated by the fact that the comment system must be
enabled and the attacker must have permission to post comments.
JavaScript cross-site scripting prevention is incomplete - Critical - Drupal 7
and Drupal 8 - CVE-2017-6927

Drupal has a Drupal.checkPlain() JavaScript function which is used to escape
potentially dangerous text before outputting it to HTML (as JavaScript output
is not auto-escaped by either Drupal 7 or Drupal 8). This function does not
correctly handle all methods of injecting malicious HTML, leading to a
cross-site scripting vulnerability under certain circumstances.

The PHP functions which Drupal provides for HTML escaping are not affected.
Private file access bypass - Moderately Critical - Drupal 7 - CVE-2017-6928

When using Drupal's private file system, Drupal will check to make sure a user
has access to a file before allowing the user to view or download it. This
check fails under certain conditions in which one module is trying to grant
access to the file and another is trying to deny it, leading to an access
bypass vulnerability.

This vulnerability is mitigated by the fact that it only occurs for unusual
site configurations.
jQuery vulnerability with untrusted domains - Moderately Critical - Drupal 7 -
CVE-2017-6929

A jQuery cross site scripting vulnerability is present when making Ajax
requests to untrusted domains. This vulnerability is mitigated by the fact that
it requires contributed or custom modules in order to exploit.

For Drupal 8, this vulnerability was already fixed in Drupal 8.4.0 in the
Drupal core upgrade to jQuery 3. For Drupal 7, it is fixed in the current
release (Drupal 7.57) for jQuery 1.4.4 (the version that ships with Drupal 7
core) as well as for other newer versions of jQuery that might be used on the
site, for example using the jQuery Update module.
Language fallback can be incorrect on multilingual sites with node access
restrictions - Moderately Critical - Drupal 8 - CVE-2017-6930

When using node access controls with a multilingual site, Drupal marks the
untranslated version of a node as the default fallback for access queries. This
fallback is used for languages that do not yet have a translated version of the
created node. This can result in an access bypass vulnerability.

This issue is mitigated by the fact that it only applies to sites that a) use
the Content Translation module; and b) use a node access module such as Domain
Access which implement hook_node_access_records().

Note that the update will mark the node access tables as needing a rebuild,
which will take a long time on sites with a large number of nodes.
Settings Tray access bypass - Moderately Critical - Drupal 8 - CVE-2017-6931

The Settings Tray module has a vulnerability that allows users to update
certain data that they do not have the permissions for.

If you have implemented a Settings Tray form in contrib or a custom module, the
correct access checks should be added. This release fixes the only two
implementations in core, but does not harden against other such bypasses.

This vulnerability can be mitigated by disabling the Settings Tray module.
External link injection on 404 pages when linking to the current page - Less
Critical - Drupal 7 - CVE-2017-6932

Drupal core has an external link injection vulnerability when the language
switcher block is used. A similar vulnerability exists in various custom and
contributed modules. This vulnerability could allow an attacker to trick users
into unwillingly navigating to an external site.
Solution: 

Install the latest version:

    If you are using Drupal 8 , upgrade to Drupal 8.4.5
    If you are using Drupal 7 , upgrade to Drupal 7.57

References:
https://www.drupal.org/sa-core-2018-001