As shipped, in.rexecd is disabled in /etc/inetd.conf. If you enable it, rexec will still not work because /etc/pam.d/rexec tries to authenticate using securetty PAM authentication (as it should), but in.rexecd does not set the PAM_TTY item. I believe this bug exists in RedHat 5.2 as well. The fix is to add a call to: (void) pam_set_item (pamh, PAM_TTY, "tty"); just before calling pam_authenticate.
Should be fixed in rsh-0.10-23.