If user which executes

"maxctrl -c"

It is only be possible, if maxctrl.cnf have permission on user level.

otherwise error is thrown

Error: /tmp/maxctrl.cnf exists, but can be accessed by group and world. Remove all rights from everyone else but owner

This is hard limited in the code:

// As the file may contain a password, we are picky about the bits.

  if ((stats.mode & 31) != 0) {

    throw Error(

      "Error: " +

        filename +

        " exists, but can be accessed by group and world." +

        " Remove all rights from everyone else but owner"

    );

  }

With expanding to maxscale group , it is secure enough and every user , which added to maxsacale group can access to maxctrl.cnf with "maxctrl -c"

Error: /tmp/maxctrl.cnf exists, but can be accessed by group and world. Remove all rights from everyone else but owner