Upgrade to the most recent version of Drupal 7 or 8 core.

If you are running 7.x, upgrade to Drupal 7.58. (If you are unable to update immediately, you can attempt to apply this patch to fix the vulnerability until such time as you are able to completely update.)

(If you are unable to update immediately, you can attempt to apply this patch to fix the vulnerability until such time as you are able to completely update.) If you are running 8.5.x, upgrade to Drupal 8.5.1. (If you are unable to update immediately, you can attempt to apply this patch to fix the vulnerability until such time as you are able to completely update.)

Drupal 8.3.x and 8.4.x are no longer supported and we don't normally provide security releases for unsupported minor releases. However, given the potential severity of this issue, we are providing 8.3.x and 8.4.x releases that includes the fix for sites which have not yet had a chance to update to 8.5.0.

Your site's update report page will recommend the 8.5.x release even if you are on 8.3.x or 8.4.x. Please take the time to update to a supported version after installing this security update.

If you are running 8.3.x, upgrade to Drupal 8.3.9 or apply this patch.

If you are running 8.4.x, upgrade to Drupal 8.4.6 or apply this patch.

This issue also affects Drupal 8.2.x and earlier, which are no longer supported. If you are running any of these versions of Drupal 8, update to a more recent release and then follow the instructions above.

This issue also affects Drupal 6. Drupal 6 is End of Life. For more information on Drupal 6 support please contact a D6LTS vendor.