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Features | Quick usage (.NET) | Quick usage (CLI) | Quick usage (Docker) | Documentation | Build | License | Releases

fluxzy is a fully managed and fully streamed MITM engine and a CLI app to intercept, record and alter HTTP/1.1, H2, websocket traffic over plain or secure channels.

This repository contains the source code of Fluxzy CLI which is a standalone command line application for Windows, macOS, and Linux and the .NET packages that are used by Fluxzy Desktop.

1. Features

1.1 Core features

• Intercept HTTP/1.1, H2, WebSocket traffic over plain or secure channels
• Fully streamed intermediate as proxy or transparent proxy
• Deflect operating system traffic (act as system proxy)
• Automatic root certificate installation (with elevation on Windows, macOS, and several Linux distributions)
• Certificate management: built-in feature to create CA compatible certificates
• Export as HTTP Archive
• Use a custom root certificate authority
• Choice between default .NET SSL provider and BouncyCastle
• Raw packet capture (with the extension Fluxzy.Core.Pcap)
• NSS Key log extraction (when using Bouncy Castle)
• Optional configuration-based data extraction and alteration

1.2 Alteration and traffic management features

Alteration and traffic management features are available as fluxzy actions. You can browse this dedicated search page to see built-in actions on the latest stable version. Here are a few examples:

• Add, remove, modify request and response headers
• Mock or substitute request and response body
• Forward, redirect, spoof DNS, abort connections
• Inject html snippet on intercepted request and response bodies
• Remove cache directives, add request and response cookies
• Serve static directory
• Add metadata to HTTP exchanges (tags and comments)
• Provide a specific certificate for a host

2. Quick Usage

2.1 .NET library

2.1.1 Simple usage

The main documentation is available at docs.fluxzy.io. The following shows a very basic usage of the .NET packages.

The main line to begin a capture session is to create a FluxzySetting instance and use it to create a Proxy instance.

Install NuGet package Fluxzy.Core

dotnet add package Fluxzy.Core

Create a top-level statement console app, with .NET 6.0 or above:

using System.Net;
using Fluxzy;
using Fluxzy.Core;
using Fluxzy.Rules.Actions;
using Fluxzy.Rules.Actions.HighLevelActions;
using Fluxzy.Rules.Filters;
using Fluxzy.Rules.Filters.RequestFilters;
using Fluxzy.Rules.Filters.ResponseFilters;

// Create a new setting 
var fluxzySetting = FluxzySetting.CreateDefault(IPAddress.Loopback, 8080);

fluxzySetting
    .ConfigureRule()
    // Forward request
    .WhenHostMatch("twitter.com")
    .Forward("https://www.google.com/")

    // Mock any POST request to /api/auth/token
    .WhenAll(
        new GetFilter(),
        new PathFilter("/api/auth/token", StringSelectorOperation.Contains))
    .ReplyJson("{ token: \"your fake key\" }")

    // Select wikipedia domains that produces text/html content-type
    .WhenAll(
        new HostFilter("wikipedia.[a-z]+$", StringSelectorOperation.Regex),
        new HtmlResponseFilter()
    )
    // Inject a CSS after opening head tag
    .Do(
        // Remove CSP to allow injecting CSS and scripts
        new DeleteResponseHeaderAction("Content-Security-Policy"),
        new InjectHtmlTagAction
        {
            Tag = "head",
            // Make all pages purple
            HtmlContent = "<style>* { background-color: #7155ab !important; }</style>"
        }
    );

await using var proxy = new Proxy(fluxzySetting);
var endPoints = proxy.Run();

// Register as system proxy, the proxy is restore when the IAsyncDisposable is disposed
await using var _ = await SystemProxyRegistrationHelper.Create(endPoints.First());

// Create a new HttpClient that uses the proxy 
var httpClient = HttpClientUtility.CreateHttpClient(endPoints, fluxzySetting);

var responseText = await httpClient.GetStringAsync("https://baddomain.com/api/auth/token");

Console.WriteLine($"Final answer: {responseText}");
Console.WriteLine("Press enter to halt this program and restore system proxy setting...");

Console.ReadLine();

More examples are available at docs.fluxzy.io.

2.2 Fluxzy CLI

Fluxzy CLI	Version
Windows
macOS
Linux

Sample usage

The following highlights the basic way to use fluxzy with a simple rule file.

The "rule file" is a straightforward YAML file containing a list of directives that fluxzy will evaluate during proxying.

For more detailed documentation, visit fluxzy.io or use the --help option available for each command.

Create a rule.yaml file as follows:

rules:
  - filter:
      typeKind: requestHeaderFilter
      headerName: authorization # Select only requests with authorization header
      operation: regex
      pattern: "Bearer (?<BEARER_TOKEN>.*)" # A named regex instructs fluxzy
                                             # to extract the token from the authorization
                                             # header into the variable BEARER_TOKEN
    action:
      # Write the token to a file
      typeKind: FileAppendAction # Append the token to the file
      filename: token-file.txt # Save the token to token-file.txt
      text: "${authority.host} --> ${user.BEARER_TOKEN}\r\n"  # user.BEARER_TOKEN retrieves 
                                                              # the previously captured variable 
      runScope: RequestHeaderReceivedFromClient  # Run the action when the request header 
                                                 # is received from the client
  - filter:
      typeKind: anyFilter # Apply to any exchanges
    action:
      typeKind: AddResponseHeaderAction # Append a response header
      headerName: fluxzy
      headerValue: Passed through fluxzy 

The rule file above performs two actions:

• It extract any BEARER token from the authorization header and write it to a file (`token-file.txt``)
• It appends a response header (fluxzy: Passed through fluxzy) to all exchanges

For more information about the rule syntax, visit the documentation page. Visit directive search page to see all built-in filters and actions.

Then start fluxzy with the rule file

fluxzy start -r rule.yaml --install-cert -sp -o output.fxzy -c 

• --install-cert, -sp, -o, -c, -r are optional.

• -o will save all collected data in a fluxzy file. The file will be created only at the end of the capture session.

• -sp will make fluxzy act as system proxy. The proxy settings will be reverted when fluxzy is stopped with SIGINT (Ctrl+C). The proxy settings won't be reverted if the fluxzy process is killed.

• -c will enable raw packet capture.

• --install-cert will install the default certificate on the current user. This option needs elevation and may trigger interactive dialogs on certain OS.

You can use the command dissect to read the fluxzy file or, alternatively, you can use Fluxzy Desktop to view it with a GUI.

More command and options are available, including exporting to HAR or managing certificates, you can run --help to see all available options and commands.

By default, fluxzy will bind to 127.0.0.1:44344.

Run with docker

The CLI can be run from a docker image.

docker run -it -p 43444:43444 fluxzy/fluxzy:latest start

To test:

curl -x 127.0.0.1:44344 https://www.fluxzy.io

3. Build

3.1 Requirements

• .NET 8.0 SDK
• Git bash if Windows
• libpcap or any equivalent library
• tests collecting pcap files and installing certificates requires elevation.
• An IDE is not necessary to build the app. For information, this project was developed using both Visual Studio 2022 and JetBrains Rider on Windows, macOS and Linux.

3.2 Build

• Clone the repository
• Run dotnet build src/Fluxzy.Core for Fluxzy.Core
• Run dotnet build src/Fluxzy.Core.Pcap for Fluxzy.Core.Pcap

3.3 Test

• Several tests are run against various private web servers (iis, nginx, kestrel, apache, ...) which is not currently available to the public.

4 Contact

• Use github issues for bug reports and feature requests
• Mail to [email protected] for inquiries