A third Chrome 67 update has come to the Chrome OS Stable Channel today, bringing further security fixes to the platform as well as a clarification on a security patch. The update is build 67.0.3396.99 or 67.0.3396.101 (Platform version: 10575.58.0) depending on your device. It comes two weeks after the second update was released back on June 13.
If your Chromebook is in the Stable Channel, you can check for the update by typing chrome://help in the browser bar and then clicking the Check for update button next to your current build information. The release of this update happened last yesterday so it could still take a while for everyone to see the update as being available.