In Oracle Database 11g Release 2 (11.2), the password feature is being deprecated. This does not cause a loss of security because authentication is enforced through local operating system authentication.
Oracle11gR2废弃listener设置密码，认为已经通过了本地操作系统的认证，所以是安全的。
文中ACTIONS部分列出，如果要使用远程管理listener，只能通过SSH登陆到运行listener的本地主机，通过认证，然后本地管理listener，或使用oracle OEM方式进行管理。
6、oracle 11gR2官方对listener的安全说明与管理方式建议
Local listener administration is secure through local operating system authentication,
which restricts listener administration to the user who started the listener or to the
super user. By default, remote listener administration is disabled.
Oracle recommends that you perform listener administration in the default mode, and
access the system remotely using a remote login. When you administer the listener
remotely, use Oracle Enterprise Manager or Secure Shell (SSH) to access the remote
host.
本地listener管理默认为本地系统认证，这样限制了listener的管理者。默认情况下远程listener程序管理被禁用，建议采用OEM或ssh方式登陆目标端主机后进行管理。