qh_help in Nagios Core version 4.4.1 and earlier is prone to a NULL pointer dereference vulnerability, which allows attacker to cause a local denial-of-service condition by sending a crafted payload to the listening UNIX socket.

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.