For GOS 4.2 a new patch level is available:
http://www.greenbone.net/en/roadmap-lifecycle/
This release mainly updates the encryption key for the Greenbone Support Package. The old key expires on November 23rd 2018. If not upgraded to at least 4.2.23 means that you can not encrypt support packages from that date. Apart from this the release covers a collection of various bug fixes, most for Web-UI. The scanner detection of UDP services is improved.
In total the patch level covers 10 improvements.