The glibc vulnerability, CVE-2015-0235, known as “GHOST”, has been patched on CoreOS. If automatic updates are enabled (default configuration), your server should already be patched.
If automatic updates are disabled, you can force an update by running
Currently, the auto-update mechanism only applies to the base CoreOS, not inside your containers. If your container was built from an older ubuntu base, for example, you’ll need to update the container and get the patch from ubuntu.
If you have any questions or concerns, please join us in IRC freenode/#coreos.