.NET Core

WARNING! Only .NET Core is supported. The required Extism nuget package is not supported by .NET Framework.

For team servers and/or agents written in .NET Core, a simplistic example is included that can be used as a rough template.

Usage

1. Install the Extism dependencies

dotnet add package Extism.runtime.all
dotnet add package Extism.Sdk

1. To compile the C4 plugin directly into the C2 framework or agent, add the .wasm file in the Resources/ folder.

2. Compile and run!

dotnet build software.csproj
.\bin\Debug\netX.X\software.exe

More thorough documentation can be found at https://github.com/extism/dotnet-sdk

Below is an example of using a C4 plugin in .NET Core. See the full example at: https://github.com/scottctaylor12/C4/examples/net-core

Example

using System;
using System.Reflection;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Threading;

using Extism.Sdk;

class Program
{
    public class C4Output
    {
        [JsonPropertyName("success")]
        public bool Success { get; set; }
        [JsonPropertyName("status")]
        public string Status { get; set; } = string.Empty;
        [JsonPropertyName("messages")]
        public string[] Messages { get; set; } = Array.Empty<string>();
    }
    static void Main()
    {

        /*
            Example usage of the AWS S3 C4 plugin.
            Implementation details will vary based on your C2 and/or agent
        */

        // load the C4 plugin
        Plugin plugin = Initialize();

        while (true)
        {
            // The current agent ID is "12345"
            // Receive messages from AWS S3 bucket for the agent with ID "12345"
            try
            {
                string recMsg = "{\"action\":\"receive\",\"params\":{\"agent_id\":\"12345\",\"access_key\":\"AKIAXXXXXXXXXXXX\",\"secret_key\":\"SECRET\",\"region\":\"REGION\",\"bucket\":\"BUCKET-NAME\"}}";
                var result = plugin.Call("c4", Encoding.UTF8.GetBytes(recMsg));

                string output = Encoding.UTF8.GetString(result);
                var c4Output = JsonSerializer.Deserialize<C4Output>(output);

                // While debugging check the status of your request
                // Console.WriteLine($"Status: {c4Output.Status}");

                if (c4Output.Success && c4Output.Messages.Length > 0)
                {
                    foreach (var message in c4Output.Messages)
                    {
                        // Process each message as needed
                        Console.WriteLine($"Processing message: {message}");
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error: {ex.Message}");
                Console.WriteLine($"Stack trace: {ex.StackTrace}");
            }


            // Let's pretend we received a "whoami" message
            // Send a response back to the S3 bucket with the "server" as the recipient
            try
            {
                string message = "scottctaylor12"; // realistically, the message is probably a format specific to your C2
                string sendMsg = $"{{\"action\":\"send\",\"params\":{{\"agent_id\":\"server\",\"message\":\"{message}\",\"access_key\":\"AKIAXXXXXXXXXXXX\",\"secret_key\":\"SECRET\",\"region\":\"REGION\",\"bucket\":\"BUCKET-NAME\"}}}}";

                var sendResult = plugin.Call("c4", Encoding.UTF8.GetBytes(sendMsg));

                string sendOutput = Encoding.UTF8.GetString(sendResult);

                var sendC4Output = JsonSerializer.Deserialize<C4Output>(sendOutput);
                if (sendC4Output.Success)
                {
                    Console.WriteLine(sendC4Output.Status);
                }
                else
                {
                    Console.WriteLine($"Failed to send message: {sendC4Output.Status}");
                }
            }
            catch (System.Exception)
            {

                throw;
            }

            Thread.Sleep(5000);
        }
    }
    public static Plugin Initialize()
    {
        var assembly = Assembly.GetExecutingAssembly();

        var resourceName = "net_core.Resources.c4.wasm";

        using var stream = assembly.GetManifestResourceStream(resourceName);
        if (stream == null)
        {
            Console.WriteLine("Could not find embedded Wasm resource.");
            return null;
        }

        using var ms = new MemoryStream();
        stream.CopyTo(ms);
        var wasmBytes = ms.ToArray();

        var source = new ByteArrayWasmSource(wasmBytes, "c4");
        var manifest = new Manifest(new[] { source })
        {
            AllowedHosts = new[] { "*" },
        };

        var plugin = new Plugin(manifest, new HostFunction[] { }, withWasi: true);
        return plugin;
    }
}