Drupal Security Team reports:
A visit to install.php can cause cached data to become corrupted.
This could cause a site to be impaired until caches are rebuilt.
Drupal 8 core's file_save_upload() function does not strip the
leading and trailing dot ('.') from filenames, like Drupal 7 did.
Users with the ability to upload files with any extension in
conjunction with contributed modules may be able to use this to
upload system files such as .htaccess in order to bypass protections
afforded by Drupal's default .htaccess file. After this fix,
file_save_upload() now trims leading and trailing dots from filenames.
The Media Library module has a security vulnerability whereby it
doesn't sufficiently restrict access to media items in certain
configurations.
The Drupal project uses the third-party library Archive_Tar, which
has released a security-related feature that impacts some Drupal
configurations. Multiple vulnerabilities are possible if Drupal is
configured to allow .tar, .tar.gz, .bz2 or .tlz file uploads and
processes them. The latest versions of Drupal update Archive_Tar to
1.4.9 to mitigate the file processing vulnerabilities.