This efun is not privileged, therefore it should be redefined by a nomask simul_efun which then either completely disables the efun or at least performs some security checks. It is easy to undermine a mudlibs security using this efun.
The efun is available only in 3.2.1, a possible simulation for 3.2 could be
void set_this_player(object ob) { /* Insert your privilege checks here */ if (living(ob)) funcall(bind_lambda(#'enable_commands, ob)); }
(suggested by Mark Lewis (Nostradamus@Zebedee))