Payload Type Development

This section describes new Payload Types

Creating a new Apfell agent

You want to create a new agent that fully integrates with Apfell - Apfell builds the code and Docker containers for the agent are controlled by Apfell. What all does that entail? It's not too crazy, just a few pieces are needed:

  • Agent base code that's command agnostic, commands, C2 profile information

    • This allows Apfell to piece everything together at build time

  • An Apfell container for the payload type that's taskable

  • Transforms that'll turn your code into the final product

  • Optionally: A custom C2 profile that this agent supports, see C2 Profile Development for that piece though

Registering the agent in the UI

The first step is to register the agent in the web user interface.

  • Go to "Manage Operations" -> "Payload Management".

  • Click "+ Payload Type"

    • The "name" of the agent will be how you identify the agent, the corresponding docker container, and paths within the system.

    • The "payload file extension" is the file extension of the files that make up the agent. For example, the apfell-jxa agent uses JavaScript files (.js) and the viper agent uses (.py) files. So, here you'd specify things like js, py, c, go, etc (without the leading . ).

    • The "supported os" field isn't necessary, but provides context for the user

    • Leave the two toggles un-checked. This agent is not a wrapper and is being created within apfell.

    • The "Select payload code files to upload" button allows you to upload base agent code for the agent.

      • Arbitrary folder structures are now available when editing commands and payload types, so if you need code within specific folders, wait until the payload type is registered to then go through to add folders and upload files to specific folders. Any code added at this point will be added to the root directory of your agent: i.e. apfell-docker/app/payloads/{name}/payload/{uploading here now}.

    • The rest of the information is explained here and isn't strictly necessary

For information about the actual agent code, see the Agent Code section.

You should now see the new payload type appear in the area at the bottom. Initially the light will be green, but after 30 seconds it'll flash red to indicate that there's no heartbeat happening from the docker container (which doesn't exist yet). So, let's do that next.

Creating a docker container for your new agent

There are docker containers for each payload type that are customized build environments. This allows two payload types that might share the same language to still have different environment variables, build paths, tools installed, etc. There are only two requirements for the containers:

  1. They must have python 3.6 installed and in the environment path

  2. They must have the same directory structure and entry point as the base payload_type container

These two requirements makes sure that the container can connect to Apfell, receive tasking, and execute the python 3.6 based transforms.

This part has to happen outside of the web UI at the moment. The web UI is running in its own docker container, and as such, can't create, start, or stop entire docker containers. So, make sure this part is done via CLI access to where Apfell is installed.

Within Apfell/Payload_Types/ make a new folder that matches the name of your agent. Inside of this folder make a file called Dockerfile. This is where you have a choice to make - either use the default Payload Type docker container as a starting point and make your additions from there, or use a different container base.

Using the default container base

The default container base can be seen at Apfell/Payload_Types/Dockerfile. It's a python:3.6-jessie container that is pretty bare bones except for python 3.6. Start your Dockerfile off with:

From payload_type_base

On the next lines, just add in any extra things you need for your agent to properly build, such as:

RUN pip install python_module_name
RUN shell_command
RUN apt-get install -y tool_name

This happens all in a script for docker, so if a command might make a prompt for something (like apt-get), make sure to auto handle that or your stuff won't get installed properly

If you want to copy a file into the container, place the file in your folder, Apfell/Payload_Types/{payload type name}/file_to_copy and copy it in with the following line:

COPY ["file_to_copy", "/path/of/where/to/put.it"]

The file system within the container is separate from the OS, so make sure to copy in what you need.

Using your own container

There isn't too much that's different if you're going to use your own container, it's just on you to make sure that python3.6 is up and running and the entrypoint is set properly. Here's an example from the Poseidon container that uses xgo to build:

From karalabe/xgo-latest
RUN apt-get update
RUN apt-get install software-properties-common apt-utils -y
RUN add-apt-repository ppa:jonathonf/python-3.6
RUN apt-get update
RUN apt-get install -y build-essential python3.6 python3.6-dev python3-pip python3.6-venv
RUN python3.6 -m pip install aio_pika
RUN alias python3=python3.6
RUN mkdir /Apfell_service 2>/dev/null
RUN mkdir /Apfell 2>/dev/null
RUN mkdir /Apfell/apfell 2>/dev/null
RUN touch /Apfell/apfell/__init__.py 2>/dev/null
RUN touch /Apfell/__init__.py 2>/dev/null
COPY ["/apfell_heartbeat.py", "/Apfell_service/apfell_heartbeat.py"]
COPY ["/apfell_service.py", "/Apfell_service/apfell_service.py"]
COPY ["/payload_service.sh", "/Apfell_service/payload_service.sh"]
RUN chmod +x /Apfell_service/payload_service.sh
WORKDIR /Apfell/
RUN /build.sh &
ENTRYPOINT ["/Apfell_service/payload_service.sh"]

Notice that it installs python3.6, sets it up correctly, installs the required packages (aio_pika) for Apfell, and gets the directory structure all set up like the default container template does. In this case, you also need to copy the apfell_heartbeat.py, apfell_service.py, and payload_service.sh files into your Apfell/Payload_Types/{payload type name}/ directory so that they can be copied in correctly.

Starting your Docker container

To start your new payload type docker container, use the ./start_payload_types.sh script and supply the name of your payload type. For example, to start just the viper payload type container, run:

sudo ./start_payload_types.sh viper

Your container should pull down all the necessary files, run the necessary scripts, and finally start. If it started successfully, you should see it listed in the payload types section when you run sudo ./status_check.sh.

If you go back in the web UI at this point, you should see the red light next to your payload type change to green to indicate that it's now getting heartbeats. If it's not, then something went wrong along the way. You can use the sudo ./display_output.sh payload_type_name to see the output from the container to potentially troubleshoot.

If you want to go interactively within the container to see what's up, use the following command:

sudo docker exec -it {payload type name} /bin/bash

From there, you can start exploring around and seeing why it's not running.

Uploading Files

At this point, you should have your container up and running and the payload type registered within the system. Now, if you want to upload more files relating to your base agent, you can go back to "Manage Operations" -> "Payload Management", click the yellow edit drop down at the bottom of your payload type, click "Edit Info and Files". You'll see the file section look something like:

Payload Type file management

The top section allows you to upload, download, delete files or even create/delete folders that relate to the the payload's code. The bottom portion, "Server Files", relates to uploading, downloading, and deleting files that relate to the docker container that does the processing for your new payload type. If you need to upload a new config, upload new files, etc, you can do that here.

If there is no associated Apfell container for the payload type or it is currently offline, then the bottom portion for "Server Files" will not show up since it is not taskable.

Registering Commands

From the "Manage Operations" -> "Payload Management" page, you can start adding commands to your payload type. You don't technically have to upload code with these commands, but the command has to be registered here other the main tasking UI won't allow you to issue the command to your agent.

Registering commands

At the bottom of the screen for the payload type you just registered, you'll see something like the above screenshot. Click the green "+" to add a command, the yellow edit to edit a command, or the red trash button to delete commands.

The main information about all the pieces is already captured in the Understand Commands section of this documentation. You can upload any files you want when clicking the green "+", but they will all be at the base path of apfell-docker/app/payloads/{payload type name}/commands/{command name}/{uploads go here}. If you want things in a different folder structure, you will need to do that from the edit button after the command has been registered. If you just type code into the visual editor, then that will be saved as commandName.payload_type_extension. So a command of test with a payload type extension of py would result in a test.py file being created.

When you click to edit a command, the display will look like:

Editing a command

Notice that there's nothing in the code editor piece. To edit a specific file, click the blue edit button next to the file you want to edit. This will bring that file's code to the code editing portion:

Editing command code

From here, make any changes you want and click the green save icon. That'll save the code back for that file. To edit another file, just click the blu edit button for that file and the top portion will be replaced.

C2 profile associations

Now that you have the payload type registered, commands registered, and the associated container running, the next step is to associate your payload type with the C2 profiles that it understands. In the "Manage Operations" -> "C2 Profile Management" page, you'll see all of the C2 profiles.

The point here is that the C2 communications piece of an agent isn't tied into the commands or the base agent, it's a separate implementation. The interface should be the same (upload, download, get tasking, etc), but the actual end implementation shouldn't matter to the rest of your agent's code. That C2 comms piece of the code is what you're uploading here.

For each C2 profile that your agent supports, click the yellow dropdown and select "Supported Payloads". You should see your new payload type as an option. Make sure it is selected (in addition to all of the others that were already selected), and you should see a new row appear for you to upload files for your payload type. Upload the C2 comms piece here. To confirm your files uploaded, select the "Download/Delete listener files" from the same yellow dropdown, and you should see a table for your payload type with the files you uploaded.

Creating your agent with transforms

The last piece is to combine it all together into the final payload. This could mean a single script file, a compiled binary, or a series of files - it's up to you. First, decide what you need to happen with all of your files at a high level and decide how you're identifying the final thing you're going to call your payload.

In "Manage Operations" -> "Transform Management" is a big python file. You can edit in the browser or download, edit, and re-upload if you want. The important piece to look at is the TransformOperations class:

class TransformOperation:
def __init__(self, working_dir=""):
self.working_dir = working_dir
self.saved_state = {}

When you run your transforms, they'll happen sequentially and are all functions in this class. So, you can save your own state between transforms by simply writing to self.saved_state dictionary and pull it out in another transform.

Your transform code will run within the payload type Apfell container (could be a docker container, VM, or host machine) with the self.working_dir set to a random newly created folder for each instance of you creating a payload. If you want to see what the final state of all your modified files are before trying to do any special transforms, simply use one transform called outputAsZipFolder. This transform just zips up the self.working_dir directory and returns it.

Output files to zip

In this case, your final payload (regardless of what you call it) would actually be a zip file. This is helpful as you start troubleshooting so you can see how everything is getting stamped together, making sure folder structures are as you expect, etc. You can also write out debugging information or temporary files into your self.working_dir folder and then this will zip those up as well.

Once you're confident that your code looks and is formatted the way you want, you can start doing other transforms instead. These can be as simple or as complex as you want, can execute shell commands, leverage environment variables, call code from other files you loaded into the container, etc.

Every transform has the same general format:

async def outputAsZipFolder(self, prior_output: str, parameter: None) -> bytes:
try:
# this does force .zip to output: ex: payload.location of test-payload becomes test-payload.zip on disk
temp_uuid = str(uuid.uuid4())
shutil.make_archive(temp_uuid, 'zip', self.working_dir)
data = open(temp_uuid + ".zip", 'rb').read()
os.remove(temp_uuid + ".zip")
return data
except Exception as e:
raise Exception(str(e))

Since we're doing python 3.6 and asynchronous calls, the function is always async def followed by the function name. The first parameter is self, so you can access things like self.working_dir. Then there are two important parameters:

  • prior_output is the output of the previous transform. If you're using more than one transform, then the output of one transform is provided (via this parameter) as input to the next transform. You don't have to use this, but it can be helpful.

  • parameter is an optional value provided as input to that step in the transform chain specifically. It will come in as a string, but you can parse and cast it however you need to. This is helpful if you want to take additional context such as a compilation flag that's optional.

The last transform in your series must return the actual contents of the payload as bytes. Whatever is returned in the final transform is what will be saved to the payload's name you specify when creating a payload. If you want to stop somewhere along the process and return an error message or information back to the operator, simply raise an exception with the message you want to show, such as raise Exception("My personal error message here").

Creating an external agent

This is the fastest way to get up and going within Apfell as you create an agent.

  1. In the "Payload Management" page, select to create a new Payload Type

  2. See the Payload Types section on what the pieces mean and fill out the initial sections, being sure to select that Is this payload going to be created externally to Apfell as blue.

    1. You don't need to upload any files since you're going to take care of all of that on your end

  3. Submit it. You should now see a new Payload Type show up on the screen with a Blue light. If it's green or red, give it about 30 seconds and it'll settle on Blue (indicating that it's an external payload type with no container associated with it)

    1. Because there is no container, you will not be able to do Create Transforms, Load Transforms, or Command Transforms for this payload type. For more information on what those mean, check out Create and Load Transforms and Command Transforms.

  4. Now you need to associate commands with your payload type

    1. Click the green plus sign next to the Commands for the payload type to add a command.

    2. Check out Understanding Commands for information about all of the pieces. You don't need to submit any code though since your agent is created externally.

    3. In this section, focus on adding the commands and parameters that your agent will support.

  5. Go to the "C2 Profiles Management" page

    1. Your agent will need to "speak" the language of a C2 profile. You can either hit the RESTful endpoints directly (default c2 profile), or you can modify the mapping between the endpoints your agent hits and the actual endpoints (RESTful Patchthrough profile). For more information on how the RESTful Patchthrough profile works, see the RESTful Patchthrough section.

    2. Select the edit dropdown for the profile your agent will speak, and select "Supported Payloads"

    3. In addition to the payloads highlighted, also select your new one. This is a running list of all the payload types that speak this profile. Since this payload type is externally created, you don't need to upload any code.

  6. Now you need to create a payload in the database. Normally, this process would create the actual agent, but since you're creating it externally, all this will do is register the metadata in the database for when you do create your actual agent

    1. Go to "Create Components" -> "Create Payload"

    2. Select the C2 profile you're going to use for this payload and fill in any necessary parameter values

    3. Select your agent type, provide a name, and a default tag that will be used to populate the description field of any new callback based on this payload

    4. Select the commands that you plan to include in the agent

    5. Hit submit

    6. You'll get back a payload UUID and a new entry in the "Payload Management" page

  7. Use this information in your agent

    1. Check out the Agent Code section for how to hit the different endpoints for the agent, what data is required, and what the responses look like. The main thing you need from Step 6 is the payload UUID that you will need to include in the initial checkin (Initial Checkin).

  8. Run your agent and you should get a new callback in your UI that you can task.

    1. Once you have basic tasking, check out Hooking Features for what kinds of information you can include in your responses to hook into more of the features of Apfell.

Turning a VM into an Apfell container

There are scenarios in which you need an Apfell container for an agent, but you can't (or don't want) to use the normal docker containers that Apfell uses. This could be for reasons like:

  • You have a very custom build environment that you don't want to recreate

  • You have specific kernel versions or operating systems you're wanting to develop with

  • You want interactive access to the container where the compilations/transforms are happening for debugging or greater control

So, to leverage your own custom VM or physical computer into an Apfell recognized container, there are just a few steps.

  1. Install python 3.6 in the VM

  2. pip3 install aio_pika (this is used to communicate via rabbitmq)

  3. Create a folder on the computer or VM (let's call it path /pathA).

  4. Copy the following files into the /pathA folder from the main Apfell install

    1. /Apfell/Payload_Types/apfell_heartbeat.py

    2. /Apfell/Payload_Types/apfell_service.py

    3. /Apfell/Payload_Types/apfell_service.sh

    4. /Apfell/Payload_Types/rabbitmq_config.json

  5. Edit the rabbitmq_config.json with the parameters you need

    1. the host value should be the IP address of the main Apfell install

    2. the name value should be the name of the payload type (this is tied into how the routing is done within rabbitmq)

    3. the container_files_path should be the absolute path to where you're going to host your files within the container. When you look at your 'container's files to upload/download/delete, it'll all be from within this path. This is also where the temporary directories and zip files will be created during payload creation.

  6. Finally, run /Apfell_service/apfell_service.sh and now your VM should be calling back to the main Apfell server's rabbitmq service.

    1. this script just runs the apfell_heartbeat.py file in the background and starts the apfell_service.py file.

  7. If you already had the corresponding payload type registered in the Apfell interface, you should now see the red light turn green. If you haven't done that yet, register a new payload type within the Apfell UI with the name matching the hostname of the VM.

When everything fully registers, the main Apfell server will send down the transforms.py file and save it to a sub-directory in the container_files_path called apfell.

Caveats

There are a few caveats to this process over using the normal process. You're now responsible for making sure that the right python version and dependencies are installed, and you're now responsible for making sure that the user context everything is running from has the proper permissions.