Custom Agents

Havoc’s Service API enables you to create custom agents in any language that can communicate over WebSocket. These agents appear in the Havoc UI alongside Demon agents with full command and control capabilities.

Overview

Custom agents allow you to:

Cross-Platform

Build agents for Linux, macOS, mobile, embedded systems

Any Language

Python, Go, Rust, C#, or any language with WebSocket support

Custom Protocols

Implement specialized communication methods

Unified Management

Manage alongside Demon agents in one interface

Architecture

┌─────────────────┐
│  Havoc Client   │  ◄─── Operator interacts with agent
└────────┬────────┘
         │ WebSocket
         │
┌────────▼────────┐
│   Teamserver    │
│  ┌───────────┐  │
│  │ Service   │  │
│  │ API       │◄─┼──────┐ WebSocket (Service)
│  └───────────┘  │      │
└─────────────────┘      │
                         │
                    ┌────▼──────────┐
                    │  Python       │  ◄─── Your agent connector
                    │  Service      │
                    │  (havoc-py)   │
                    └────┬──────────┘
                         │ Custom Protocol
                         │
                    ┌────▼──────────┐
                    │  Your Agent   │  ◄─── On target system
                    │  Implant      │
                    └───────────────┘

Talon: Reference Implementation

Talon is an official example of a custom agent written in Python. It demonstrates:

Agent registration and lifecycle
Custom command implementation
Binary packing/unpacking
Session management

We’ll reference Talon throughout this guide as a practical example.

Getting Started

Prerequisites

Enable Service API

Add to your Teamserver profile:

profiles/havoc.yaotl

Service {
    Endpoint = "service-endpoint"
    Password = "service-password"
}

Install havoc-py

git clone https://github.com/HavocFramework/havoc-py
cd havoc-py
pip install .

Start Teamserver

sudo ./havoc server --profile ./profiles/havoc.yaotl -v --debug

Creating an Agent Type

Define Agent Class

Extend the AgentType class to define your agent:

agent.py

from havoc.agent import AgentType
from havoc.service import HavocService

class MyCustomAgent(AgentType):
    Name = "MyAgent"                    # Agent name in UI
    Author = "@YourHandle"              # Your attribution
    Version = "0.1"                     # Agent version
    Description = "Custom Linux agent"   # Brief description
    MagicValue = 0xDEADBEEF            # Unique identifier

    # Supported output formats
    Formats = [
        {
            "Name": "Executable",
            "Extension": "elf"
        },
        {
            "Name": "Shellcode",
            "Extension": "bin"
        }
    ]

    # Supported operating systems
    SupportedOS = [
        "Linux",
        "MacOS"
    ]

    # Build configuration options
    BuildingConfig = {
        "Sleep": "5",
        "Jitter": "10",
    }

    Commands = []  # Will populate with commands

    def __init__(self):
        super().__init__()

Register Agent Type

Connect to the Teamserver and register your agent:

main.py

from havoc.service import HavocService
from agent import MyCustomAgent

def main():
    # Create agent instance
    agent = MyCustomAgent()

    # Connect to Teamserver Service API
    havoc_service = HavocService(
        endpoint="ws://0.0.0.0:40056/service-endpoint",
        password="service-password"
    )

    # Register the agent type
    havoc_service.register_agent(agent)

    print(f"[+] Registered agent: {agent.Name}")
    print(f"[*] Agent will appear in Attack -> Payload menu")

if __name__ == "__main__":
    main()

Your agent type now appears in the Havoc UI under Attack → Payload.

Implementing Commands

Command Structure

Extend the Command class to create custom commands:

commands.py

from havoc.agent import Command, CommandParam
from havoc.packer import Packer

# Command IDs (unique per command)
COMMAND_SHELL = 0x100
COMMAND_UPLOAD = 0x101
COMMAND_DOWNLOAD = 0x102

class CommandShell(Command):
    CommandId = COMMAND_SHELL
    Name = "shell"
    Description = "Execute shell commands"
    Help = "Usage: shell <command>"
    NeedAdmin = False
    Mitr = ["T1059"]  # MITRE ATT&CK techniques

    Params = [
        CommandParam(
            name="command",
            is_file_path=False,
            is_optional=False
        )
    ]

    def job_generate(self, arguments: dict) -> bytes:
        """
        Generate the binary command to send to the agent.
        
        Args:
            arguments: Dictionary with command parameters
        
        Returns:
            Packed binary data
        """
        packer = Packer()

        # Pack command ID
        packer.add_int(self.CommandId)

        # Pack command string
        packer.add_data(arguments['command'])

        return packer.buffer

Command Parameters

Define parameters with CommandParam:

from havoc.agent import CommandParam

# Simple string parameter
CommandParam(
    name="message",
    is_file_path=False,
    is_optional=False
)

# File path parameter (will show file picker in UI)
CommandParam(
    name="local_file",
    is_file_path=True,
    is_optional=False
)

# Optional parameter
CommandParam(
    name="timeout",
    is_file_path=False,
    is_optional=True
)

Using Packer

The Packer class helps build binary command payloads:

from havoc.packer import Packer

packer = Packer()

# Add integer (4 bytes, little-endian)
packer.add_int(0x100)

# Add string (null-terminated)
packer.add_data("whoami")

# Add bytes
packer.add_bytes(b"\x00\x01\x02\x03")

# Get buffer
command_bytes = packer.buffer

Registering Commands

Add commands to your agent class:

agent.py

from commands import CommandShell, CommandUpload, CommandDownload

class MyCustomAgent(AgentType):
    # ... other properties ...

    Commands = [
        CommandShell(),
        CommandUpload(),
        CommandDownload()
    ]

Session Management

Agent Check-in

When an agent checks in, register it with the Teamserver:

session.py

import json
from havoc.agent import AgentType

class SessionManager:
    def __init__(self, havoc_service):
        self.havoc = havoc_service

    def register_session(self, agent_data):
        """
        Register a new agent session.
        
        Args:
            agent_data: Dictionary with agent metadata
        """
        message = {
            "Head": {
                "Type": "Agent"
            },
            "Body": {
                "Type": "AgentRegister",
                "AgentHeader": {
                    "Size": str(len(agent_data)),
                    "MagicValue": "deadbeef",
                    "AgentID": agent_data['agent_id']
                },
                "RegisterInfo": {
                    "Hostname": agent_data['hostname'],
                    "Username": agent_data['username'],
                    "DomainName": agent_data['domain'],
                    "InternalIP": agent_data['internal_ip'],
                    "Process Name": agent_data['process_name'],
                    "Process ID": str(agent_data['pid']),
                    "OS Version": agent_data['os_version'],
                    "OS Arch": agent_data['arch'],
                }
            }
        }

        # Send to Teamserver
        self.havoc.websocket.send(json.dumps(message))

Sending Command Output

Send agent output back to the Havoc UI:

def send_output(self, agent_id, output_data):
    """
    Send command output to Teamserver.
    
    Args:
        agent_id: Agent identifier
        output_data: Command output (dict)
    """
    message = {
        "Head": {
            "Type": "Agent"
        },
        "Body": {
            "Type": "AgentOutput",
            "AgentID": agent_id,
            "Callback": {
                "Type": "Output",
                "Message": output_data['output']
            }
        }
    }

    self.havoc.websocket.send(json.dumps(message))

Retrieving Tasks

Poll for commands from the Teamserver:

import base64
import json

def get_tasks(self, agent_info):
    """
    Retrieve pending tasks for an agent.
    
    Args:
        agent_info: Agent metadata dict
    
    Returns:
        Binary task data
    """
    message = {
        "Head": {
            "Type": "Agent"
        },
        "Body": {
            "Type": "AgentTask",
            "Agent": agent_info,
            "Task": "Get"
        }
    }

    self.havoc.websocket.send(json.dumps(message))
    response = json.loads(self.havoc.websocket.recv())

    if "TasksQueue" in response["Body"]:
        tasks_b64 = response["Body"]["TasksQueue"]
        return base64.b64decode(tasks_b64)
    
    return b""

Complete Example: Talon-Inspired Agent

agent.py
commands.py
main.py

from havoc.agent import AgentType
from commands import CommandShell, CommandPwd, CommandCd

class TalonAgent(AgentType):
    Name = "Talon"
    Author = "@HavocFramework"
    Version = "0.1"
    Description = "Python-based Linux/macOS agent"
    MagicValue = 0x5041594C

    Formats = [
        {
            "Name": "Python Script",
            "Extension": "py"
        }
    ]

    SupportedOS = [
        "Linux",
        "MacOS"
    ]

    BuildingConfig = {
        "Sleep": "5",
        "Jitter": "10",
        "Host": "0.0.0.0",
        "Port": "8080"
    }

    Commands = [
        CommandShell(),
        CommandPwd(),
        CommandCd()
    ]

    def generate(self, config: dict) -> str:
        """
        Generate the agent payload.
        
        Args:
            config: Build configuration
        
        Returns:
            Generated payload as string
        """
        # Read template
        with open('templates/agent_template.py', 'r') as f:
            template = f.read()

        # Replace placeholders
        payload = template.replace('{{SLEEP}}', config['Sleep'])
        payload = payload.replace('{{JITTER}}', config['Jitter'])
        payload = payload.replace('{{HOST}}', config['Host'])
        payload = payload.replace('{{PORT}}', config['Port'])

        return payload

from havoc.agent import Command, CommandParam
from havoc.packer import Packer

COMMAND_SHELL = 0x100
COMMAND_PWD = 0x101
COMMAND_CD = 0x102

class CommandShell(Command):
    CommandId = COMMAND_SHELL
    Name = "shell"
    Description = "Execute shell commands"
    Help = "shell <command>"
    NeedAdmin = False
    Mitr = ["T1059"]
    Params = [
        CommandParam(
            name="command",
            is_file_path=False,
            is_optional=False
        )
    ]

    def job_generate(self, arguments: dict) -> bytes:
        packer = Packer()
        packer.add_int(self.CommandId)
        packer.add_data(arguments['command'])
        return packer.buffer

class CommandPwd(Command):
    CommandId = COMMAND_PWD
    Name = "pwd"
    Description = "Print working directory"
    Help = "pwd"
    NeedAdmin = False
    Mitr = []
    Params = []

    def job_generate(self, arguments: dict) -> bytes:
        packer = Packer()
        packer.add_int(self.CommandId)
        return packer.buffer

class CommandCd(Command):
    CommandId = COMMAND_CD
    Name = "cd"
    Description = "Change directory"
    Help = "cd <path>"
    NeedAdmin = False
    Mitr = []
    Params = [
        CommandParam(
            name="path",
            is_file_path=False,
            is_optional=False
        )
    ]

    def job_generate(self, arguments: dict) -> bytes:
        packer = Packer()
        packer.add_int(self.CommandId)
        packer.add_data(arguments['path'])
        return packer.buffer

from havoc.service import HavocService
from agent import TalonAgent
import asyncio

async def main():
    # Create agent
    agent = TalonAgent()

    # Connect to Teamserver
    havoc = HavocService(
        endpoint="ws://0.0.0.0:40056/service-endpoint",
        password="service-password"
    )

    # Register agent type
    havoc.register_agent(agent)

    print(f"[+] {agent.Name} registered with Teamserver")
    print(f"[*] Available commands: {len(agent.Commands)}")
    
    # Keep service alive
    while True:
        await asyncio.sleep(1)

if __name__ == "__main__":
    asyncio.run(main())

Payload Generation

Implement the generate() method to create agent payloads:

class MyCustomAgent(AgentType):
    # ... other properties ...

    def generate(self, config: dict) -> str:
        """
        Generate agent payload based on configuration.
        
        Args:
            config: BuildingConfig values from UI
        
        Returns:
            Generated payload (string or bytes)
        """
        # Option 1: Template replacement
        with open('agent_template.py', 'r') as f:
            template = f.read()
        
        payload = template.replace('{{SLEEP}}', config['Sleep'])
        payload = payload.replace('{{JITTER}}', config['Jitter'])
        
        # Option 2: Dynamic compilation
        # payload = compile_agent(config)
        
        # Option 3: Pre-built binary with patching
        # payload = patch_binary('agent.bin', config)
        
        return payload

Testing Your Agent

Start Service

python main.py

Expected output:

[+] TalonAgent registered with Teamserver
[*] Available commands: 3

Generate Payload

In Havoc UI:

Navigate to Attack → Payload
Select your agent type
Configure options
Click Generate

Execute Agent

# Python agent example
python generated_agent.py

Interact

Agent appears in the Sessions tab. Click to interact and run commands.

Best Practices

Command Design

Use unique command IDs (avoid conflicts)
Implement comprehensive parameter validation
Provide helpful error messages
Tag with MITRE ATT&CK techniques for reporting

Error Handling

Catch and report errors gracefully
Don’t crash agent on invalid commands
Log errors for debugging
Send error output to UI console

Performance

Keep check-in intervals reasonable
Implement jitter to avoid patterns
Use async I/O where possible
Minimize payload size

Security

Encrypt agent communication
Validate all input data
Don’t hardcode credentials
Implement anti-debugging if needed

Examples

Talon - Official Python Agent

Full-featured reference implementation with HTTP/HTTPS support, command handling, and more

Get Started

Core Concepts

Demon Agent

Listeners

Extensibility

Advanced

Overview

Cross-Platform

Any Language

Custom Protocols

Unified Management

Architecture

Talon: Reference Implementation

Getting Started

Prerequisites

Creating an Agent Type

Define Agent Class

Register Agent Type

Implementing Commands

Command Structure

Command Parameters

Using Packer

Registering Commands

Session Management

Agent Check-in

Sending Command Output

Retrieving Tasks

Complete Example: Talon-Inspired Agent

Payload Generation

Testing Your Agent

Best Practices

Examples

Talon - Official Python Agent

Next Steps

Python API Reference

External C2

Build docs developers (and LLMs) love

Get Started

Core Concepts

Demon Agent

Listeners

Extensibility

Advanced

Documentation Index

​Overview

Cross-Platform

Any Language

Custom Protocols

Unified Management

​Architecture

​Talon: Reference Implementation

​Getting Started

​Prerequisites

​Creating an Agent Type

​Define Agent Class

​Register Agent Type

​Implementing Commands

​Command Structure

​Command Parameters

​Using Packer

​Registering Commands

​Session Management

​Agent Check-in

​Sending Command Output

​Retrieving Tasks

​Complete Example: Talon-Inspired Agent

​Payload Generation

​Testing Your Agent

​Best Practices

​Examples

Talon - Official Python Agent

​Next Steps

Python API Reference

External C2

Build docs developers (and LLMs) love

Overview

Architecture

Talon: Reference Implementation

Getting Started

Prerequisites

Creating an Agent Type

Define Agent Class

Register Agent Type

Implementing Commands

Command Structure

Command Parameters

Using Packer

Registering Commands

Session Management

Agent Check-in

Sending Command Output

Retrieving Tasks

Complete Example: Talon-Inspired Agent

Payload Generation

Testing Your Agent

Best Practices

Examples

Next Steps