As you may know, Drupal 6 has reached End-of-Life (EOL) which means the Drupal Security Team is no longer doing Security Advisories or working on security patches for Drupal 6 core or contrib modules - but the Drupal 6 LTS vendors are and we're one of them!
Today, there is a Critical security release for Drupal core to fix a Remote Code Execution (RCE) vulnerability. You can learn more in the security advisory:
If you have a Drupal 6 site, we recommend you update immediately! We have already deployed the patch for all of our Drupal 6 Long-Term Support clients. :-)
FYI, there were other Drupal core security advisories made today, but those don't affect Drupal 6.
If you'd like all your Drupal 6 modules to receive security updates and have the fixes deployed the same day they're released, please check out our D6LTS plans.
Note: if you use the myDropWizard module (totally free!), you'll be alerted to these and any future security updates, and will be able to use drush to install them (even though they won't necessarily have a release on Drupal.org).