Pwncat : Fancy Reverse And Bind Shell Handler

Pwncat is a post-exploitation platform for Linux targets. It started out as a wrapper around basic bind and reverse shells and has grown from there. It streamlines common red team operations while staging code from your attacker machine, not the target.

pwncat used to only support Linux, but there has been a lot of work recently to support multiple platforms. Currently, there is alpha support for Windows targets. Please see the latest documentation for details on how to use pwncat with a Windows target.

pwncat intercepts the raw communication with a remote shell and allows the user to perform automated actions on the remote host including enumeration, implant installation and even privilege escalation.

After receiving a connection, pwncat will setup some common configurations for working with remote shells.

• Disable history in the remote shell
• Normalize shell prompt
• Locate useful binaries (using which)
• Attempt to spawn a pseudo-terminal (pty) for a full interactive session

pwncat knows how to spawn pty’s with a few different methods and will cross-reference the methods with the executables previously enumerated. After spawning a pty, it will setup the controlling terminal in raw mode, so you can interact in a similar fashion to ssh.

pwncat will also synchronize the remote pty settings (such as rows, columns, TERM environment variable) with your local settings to ensure the shell behaves correctly with interactive applications such as vim or nano.

John Hammond and I presented pwncat at GRIMMCon. Our presentation, which can be found on YouTube here. This video demonstrates an early version of the API and interface. Please refer to the documentation for up to date usage and API documentation!

pwncat documentation is being built out on Read the Docs. Head there for the latest usage and development documentation!

pwncat requires Python 3.9+ on Linux

Windows Support

pwncat now supports connections from Windows targets starting at v0.4.0a1. The Windows platform utilizes a .Net-based C2 library which is loaded automatically. Windows targets should connect with either a cmd.exe or powershell.exe shell, and pwncat will take care of the rest.

The libraries implementing the C2 are implemented at pwncat-windows-c2. The DLLs for the C2 will be automatically downloaded from the targeted release for you. If you do not have internet connectivity on your target machine, you can tell pwncat to pre-stage the DLLs using the --download-plugins argument. If you are running a release version of pwncat, you can also download a tarball of all built-in plugins from the releases page.

The plugins are stored by default in ~/.local/share/pwncat, however this is configurable with the plugin_path configuration. If you download the packaged set of plugins from the releases page, you should extract it to the path pointed to by plugin_path.

Aside from the main C2 DLLs, other plugins may also be available. Currently, the only provided default plugins are the C2 and an implementation of BadPotato. pwncat can reflectively load .Net binaries to be used a plugins for the C2. For more information on Windows C2 plugins, please see the documentation.

Version Details

Currently, there are two versions of pwncat available. The last stable version is v0.3.1. There is a tagged commit for that version. It does not support multiple platforms or multi-session interaction. The documentation for that version is still available on Read the Docs as the stable version.

The current master branch is v0.4.3. This version has overhauled a lot of the framework to support multiple platforms and multi-session environments. Documentation for this version is available in the latest version on Read the Docs.

v0.3.1 will not be updated further

Modules

Recently, the architecture of the pwncat framework was redesigned to incorporate a generic “module” structure. All functionality is now implemented as modules. This includes enumeration, persistence and privilege escalation. Interacting with modules is similar to most other post-exploitation platforms. You can utilize the familiar run, search and info commands and enter module contexts with the use command. Refer to the documentation for more information.

Install

pwncat only depends on a working Python development environment running on Linux. In order to install some of the packages required with pip, you will likely need your distribution’s “Python Development” package. On Debian based systems, this is python-dev. For Arch, the development files are shipped with the main Python repository. For Enterprise Linux, the package is named python-devel.

pwncat is configured as a standard python package with distutils. You can install pwncat directly from GitHub with:

pip install git+https://github.com/calebstewart/pwncat.git

Or, you can install after cloning the repository with:

python setup.py install

It is recommended to install pwncat from a virtual environment.

python3 -m venv pwncat-env
source pwncat-env/bin/activate
python setup.py install

If you would like to develop custom privilege escalation or persistence modules, we recommend you use the develop target vice the install target for setup.py. This allows changes to the local repository to immediately be observed with your installed package.

The setup script will install three binaries. They are all identical, but provide convenience aliases for pwncat. The three binaries are: pwncat, pc and pcat

BlackArch Packaging

Installation on BlackArch is as simple as:

pacman -Syu pwncat-caleb

Connecting To A Victim

The command line parameters for pwncat attempt to be flexible and accept a variety of common connection syntax. Specifically, it will try to accept common netcat and ssh like syntax. The following are all valid:

#Connect to a bind shell
pwncat connect://10.10.10.10:4444
pwncat 10.10.10.10:4444
pwncat 10.10.10.10 4444
#Listen for reverse shell
pwncat bind://0.0.0.0:4444
pwncat 0.0.0.0:4444
pwncat :4444
pwncat -lp 4444
#Connect via ssh
pwncat ssh://user:password@10.10.10.10
pwncat user@10.10.10.10
pwncat user:password@10.10.10.10
pwncat -i id_rsa user@10.10.10.10
#SSH w/ non-standard port
pwncat -p 2222 user@10.10.10.10
pwncat user@10.10.10.10:2222
#Reconnect utilizing installed persistence
#If reconnection fails and no protocol is specified,
#SSH is used as a fallback.
pwncat reconnect://user@10.10.10.10
pwncat reconnect://user@c228fc49e515628a0c13bdc4759a12bf
pwncat user@10.10.10.10
pwncat c228fc49e515628a0c13bdc4759a12bf
pwncat 10.10.10.10

By default, pwncat assumes the target platform is Linux. In order to connect to a Windows reverse or bind shell, you must pass the --platform/-m argument:

pwncat -m windows 10.10.10.10 4444
pwncat -m windows -lp 4444

For more information on the syntax and argument handling, see the help information with pwncat --help or visit the documentation.

Docker Image

The recommended installation method is a Python virtual environment. This provides the easiest day-to-day usage of pwncat. However, there has been interest in using pwncat from a docker image, so I have provided a Dockerfile which provides a working pwncat installation. To build the image use:

docker build -t pwncat .

This will build the pwncat docker image with the tag “pwncat”. The working directory within the container is /work. The entry point for the container is the pwncat binary. It can be used like so:

#Connect to a bind shell at 10.0.0.1:4444
docker run -v “/some/directory”:/work -t pwncat 10.0.0.1 4444

In this example, only the files in /some/directory are exposed to the container. Obviously, for upload/download, the container will only be able to see the files exposed through any mounted directories.

Features And Functionality

pwncat provides two main features. At it’s core, it’s goal is to automatically setup a remote PseudoTerminal (pty) which allows interaction with the remote host much like a full SSH session. When operating in a pty, you can use common features of your remote shell such as history, line editing, and graphical terminal applications.

The other half of pwncat is a framework which utilizes your remote shell to perform automated enumeration, persistence and privilege escalation tasks. The local pwncat prompt provides a number of useful features for standard penetration tests including:

• File upload and download
• Automated privilege escalation enumeration
• Automated privilege escalation execution
• Automated persistence installation/removal
• Automated tracking of modified/created files
  • pwncat also offers the ability to revert these remote “tampers” automatically

The underlying framework for interacting with the remote host aims to abstract away the underlying shell and connection method as much as possible, allowing commands and plugins to interact seamlessly with the remote host.

You can learn more about interacting with pwncat and about the underlying framework in the documentation. If you have an idea for a new privilege escalation method or persistence method, please take a look at the API documentation specifically. Pull requests are welcome!

Planned Features

pwncat would like to be come a red team swiss army knife. Hopefully soon, more features will be added.

• More privilege escalation methods (sudo -u#-1 CVE, LXD containers, etc.)
• Persistence methods (bind shell, cronjobs, SSH access, PAM abuse, etc.)
• Aggression methods (spam randomness to terminals, flush firewall, etc.)
• Meme methods (terminal-parrot, cowsay, wall, etc.)
• Network methods (port forward, internet access through host, etc.)

Known Issues

Because pwncat is trying to abstractly interact with any shell with minimal remote system dependencies, there are some edge cases we have found. Where we find them, we do everything we can to account for them and hide them from the user. However, some have slipped through the cracks and been observed in the wild. When this happens, pwncat will do whatever it can to preserve your terminal, but you may be greeted with some peculiar output or command failures.

BSD Support

While BSD is a Unix-based kernel, in practice it’s userland tools are noticeably different from their Linux counterparts. Due to this, many of the automated features of pwncat will not work or outright fail when running against a BSD based target. I have tried to catch all errors or edge cases, however there are likely some hiccups which haven’t been fully tested against BSD. In any case, the stabilized shell should function within a BSD environment, but I don’t provide any guarantees.

If I find some time later down the road, I may try to stabilize pwncat on BSD, but for now my focus is on Linux-based distributions. If you’d like to contribute to making pwncat behave better on BSD, you are more then welcome to reach out or just fork the repo. As always, pull requests are welcome!