This update includes many security related fixes.
Version 4.2.0 fixes:
- CVE-2008-4796
- CVE-2013-4214
Version 4.2.2 fixes:
- CVE-2016-9565
Version 4.2.3 fixes:
- CVE-2016-8641
See https://www.nagios.org/projects/nagios-core/history/4x/ for full
detail changes.