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Developing for FakeNet-NG

This guide is divided into two parts:

  • Programming
  • Source Code and Release Management

Programming

For background on FakeNet-NG internals and architecture, see:

Developing Listeners

All listeners must implement just two methods: start() and stop(). Below is a sample listener template:

import logging

import sys

import threading
import socket

class MyListener():

    def __init__(self, config, name = 'MyListener', logging_level = logging.INFO):
        self.logger = logging.getLogger(name)
        self.logger.setLevel(logging_level)

        self.config = config
        self.name = name

        self.logger.info('Starting...')

        self.logger.debug('Initialized with config:')
        for key, value in config.iteritems():
            self.logger.debug('  %10s: %s', key, value)

    def start(self):

        # Start listener
        # ...

    def stop(self):

        # Stop listener
        # ...

The main listener class MyListener() will be provided with a parsed configuration dictionary containing information such as port to listen on, protocol, etc. The main listener class will also receive the current listener instance name and the logging info set by the user.

The only requirement for listener implementation is that you use threading so that when FakeNet-NG calls the start() method, the listener will not block but spawn a new thread that handles incoming connections.

Another requirement is to ensure that the listener can reliably shutdown when the stop() method is called. For example, make use of connection timeouts to ensure that the listener does not block on some connection for too long.

Listeners that implement the function taste(self, data, dport) will be considered when packets are directed by the Proxy. The function must return a score which indicates the likelihood that the Listener handles the protocol that is contained in the packet.

The logging convention used by FakeNet-NG's listeners is to use the self.logger object for the output. That way the logging is uniform across the application. For example to display an error or warning you would use the following:

self.logger.error("This is an error")
self.logger.warning("This is a warning")

Finally, after you finish developing the listener, copy it to the listeners\ directory and append you module name to __all__ varialbe in the listeners\__init__:

__all__ = ['RawListener', 'HTTPListener', 'DNSListener', 'SMTPListener', 'MyListener']

At this point you can let the application use the newly created listener by adding it to the configuration file:

[MyAwesomeListener]
Enabled:     True
Port:        1337
Protocol:    TCP
Listener:    MyListener

Developing Diverters

FakeNet-NG uses the open source WinDivert library in order to perform the traffic redirection on Windows Vista+ operating systems. The implementation of the Windows Diverter is located in fakenet\diverters\windows.py.

FakeNet-NG uses the open source python-netfilterqueue Cython module to perform traffic redirection on Linux. The Linux Diverter implementation is located in fakenet\diverters\linux.py.

Much Windows-specific functionality is implemented in fakenet\diverters\winutil.py using ctypes to call many of the Windows API functions directly. Likewise, much Linux-specific functionality is implemented in fakenet\diverters\linutil.py.

For detailed information on Diverter internals specific to Linux, see internals.md.

Source Code and Release Management

The token <ver> indicates the dot-decimal representation of the FakeNet-NG version number, with no spaces or other punctuation. For example purposes, version 1.4.3 is used in many cases to exemplify where and how FakeNet-NG version numbers are to be incorporated in artifacts such as directory names.

Branching, Pull Requests, and Merging

Mandiant only:

  • Create branches directly under the mandiant/ GitHub repository, not under a private fork.
  • Create a new local branch:
git clone https://github.com/mandiant/flare-fakenet-ng.git
git checkout -b <your_branch_name>
  • Make necessary changes, commit and push your local branch to remote:
git push origin <your_branch_name>
  • Create a pull request

All contributors:

  • Pull request comment should bear bulleted list for inclusion in change log.
  • New features must be accompanied by updated configuration files under test/ to ensure that test/test.py always works.
  • New features or fixes should feature a test in test/test.py unless it is intractable to do so.
  • After review, but before merging, at reviewer discretion, either developer or reviewer must update the FakeNet-NG version as described below.

FakeNet-NG Versioning

As of this writing, the minor version should be incremented any time there is a merge that includes changes to a code or data file. Exceptions are:

  • Modifications to documentation
  • Whitespace changes
  • Adding, removing, or modifying comments

Expressly included are changes that only modify banners, FakeNet logging output, etc.

Here is where to update the version:

File How to update
CHANGELOG.txt Increment version, paste pull request comments
fakenet/fakenet.py Update version in banner string
setup.py Update version parameter to setup()

Various listeners report FakeNet/1.3 as their version. As of this writing, this is disregarded; only the banner, changelog, and setuptools versions are updated. A future change should be issued to induce listeners to pull their version number from a central location or not to report a version number at all.

Building a Stand-Alone Executable (Release Binary) for Windows

The release binary for Windows should be a 32-bit binary, allowing it to be loaded on both 32-bit systems and 64-bit systems (as a WOW64 process). Ensure that you install and are using a 32-bit version of Python and its associated utilities (i.e. pip). Use an administrative command prompt where applicable for installing Python modules for all users.

Pre-requisites:

Before installing pyinstaller, you may wish to take the following steps to prevent the error ImportError: No module named PyInstaller:

python -m pip install --upgrade pip
pip install certifi

Install FakeNet-NG to acquire most modules:

python setup.py install

Obtain PyDivert 2.0.9, the only version known to work with FakeNet-NG releases prepared with PyInstaller:

pip install pydivert==2.0.9

Install pyinstaller:

pip install pyinstaller

Finally, generate the executable file with PyInstaller:

pyinstaller fakenet.spec

The stand-alone executable fakenet.exe will be available in the dist/ directory.

Building a Release Distribution for Windows

The stand-alone executable depends on several files to be able to execute. To provide a full release distribution, create a release directory named fakenet<ver> (e.g. fakenet1.4.3) and copy the following directory and file structure:

fakenet1.4.3\
    +-- LICENSE.txt
    +-- CHANGELOG.txt
    +-- fakenet.exe
    +-- README.md
    |
    +-- docs\
    |   +-- contributors.md
    |   +-- CustomResponse.md
    |
    +-- configs\
    |   +-- default.ini
    |   +-- CustomProviderExample.py
    |   +-- sample_custom_response.ini
    |   +-- sample_raw_response.txt
    |   +-- sample_raw_tcp_response.txt
    |
    +-- defaultFiles\
    |   +-- FakeNet.gif
    |   +-- FakeNet.html
    |   +-- FakeNet.ico
    |   +-- FakeNet.jpg
    |   +-- FakeNetMini.exe
    |   +-- FakeNet.pdf
    |   +-- FakeNet.png
    |   +-- FakeNet.txt
    |   +-- ncsi.txt
    |
    +-- listeners\
        +-- ssl_utils
    		+-- __init__.pyc
    		+-- privkey.pem
    		+-- server.pem
    		+-- ssl_detector.py

Mandiant only:

  • Create a zip file of the release distribution named fakenet<ver>.zip, where <ver> is the dot-decimal version number. For example: fakenet1.4.3.zip.
  • The top-level directory in the zip file should be fakenet<ver> e.g. fakenet1.4.3.
  • Test the distribution before adding it to the appropriate release tag.

Tagging a Release (Mandiant only)

  1. Visit https://github.com/mandiant/flare-fakenet-ng/releases
  2. Click Draft a new release
  3. Tag version: v<ver>, e.g. v1.4.3
  4. Release title: FakeNet-NG <ver>, e.g. FakeNet-NG 1.4.3
  5. Description: copy the changes from CHANGELOG.txt through to the previous version
  6. Binaries: Attach the release distribution zip file described above