Here we are covering on how toprevent changing root password from single user mode?
open file “/etc/rc1.d/S99single” in your favourite editor and search for line.
exec init -t1 s
Just add the following line above it. save it an exit.
exec sbin/sulogin
Now before entering single user mode you will need to provide root password to proceed. Check again trying to enter single user mode after these changing above said file.