Nagios Core before 4.3.3 creates a nagios.lock PID file after dropping privileges to a non-root account, which might allow local users to kill arbitrary processes by leveraging access to this non-root account for nagios.lock modification before a root script executes a "kill `cat /pathname/nagios.lock`" command.
https://security.gentoo.org/glsa/201710-20
https://github.com/NagiosEnterprises/nagioscore/issues/404
https://github.com/NagiosEnterprises/nagioscore/commit/3baffa78bafebbbdf9f448890ba5a952ea2d73cb
https://github.com/NagiosEnterprises/nagioscore/commit/1b197346d490df2e2d3b1dcce5ac6134ad0c8752
https://github.com/NagiosEnterprises/nagioscore/blob/master/Changelog