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jxscout

jxscout is a tool designed to assist security researchers in analyzing and identifying vulnerabilities in JavaScript code. It integrates with your preferred proxy, capturing requests and storing optimized versions locally for in-depth analysis using your favorite code editor.

Work in Progress 🏗️ jxscout is currently under active development. As it continues to be improved and features expanded there may be breaking changes in future updates.

Key Features

  • Asset Organization: Automatically saves and organizes relevant static assets (HTML, JavaScript) into an intuitive folder structure.
  • Webpack Chunks Pre-Fetching: Detects and pre-fetches Webpack chunks for comprehensive analysis.
  • Code Beautification: Automatically beautifies JavaScript files, enhancing readability and facilitating easier vulnerability detection.
  • Future Enhancements (TODO) 🛠️: code optimization, source map discovery, data extraction, and more.

Requirements

Installation & Setup

To install, just run the below command or download pre-compiled binary from release page.

go install github.com/francisconeves97/jxscout/cmd/jxscout@latest

Caido Setup

In order to make jxscout work you first need to proxy requests to it. That's what the jxscout-caido plugin does. Head over to https://github.com/francisconeves97/jxscout-caido to get more details on how to install the jxscout-caido plugin.

Building locally

  1. Clone the repository
git clone https://github.com/francisconeves97/jxscout.git
cd jxscout
  1. Install dependencies and build the project
make install
make build
  1. Run the server
  • Using the binary
./dist/jxscout -working-directory /path/to/save/assets
  • Or directly with Go
go run cmd/jxscout/main.go -working-directory /path/to/save/assets
  1. Setup your proxy to ingest requests into jxscout

Usage

jxscout receives requests from Caido. To avoid doing duplicated work, jxscout doesn't try to parse HTML and find JS there. So to make sure all JS files are analyzed, you should disable your browser's cache when using jxscout.

Basic usage with scope filtering:

jxscout -working-directory /path/to/save/assets -scope "*example.com*"

All options

jxscout | static files downloader for vuln analysis

Usage:
  jxscout [flags]

Flags:
SERVER CONFIGURATION:
   -port int  port where the server will run (default 3333)

JXSCOUT CONFIGURATION:
   -working-directory string  directory where static files will be downloaded to
   -scope string[]            comma separated list of domains to consider for saving and analyzing html (e.g. "*google.com*,*facebook.com*")
   -verbose                   set to true to output logs (default true)
   -debug                     set to true to output debug logs

CONCURRENCY CONFIGURATION:
   -fetch-concurrency int             max number of simultaneous http requests (default 5)
   -save-concurrency int              max number of simultaneous saves to file system (default 5)
   -beautifier-concurrency int        max number of simultaneous beautifier processes (default 5)
   -chunk-discoverer-concurrency int  max number of simultaneous beautifier processes (default 5)

CHUNK DISCOVERY CONFIGURATION:
   -chunk-discoverer-bruteforce-limit int  max limit for the chunk discoverer to try and bruteforce chunks (default 3000)

CACHE CONFIGURATION:
   -js-requests-cache-ttl value    defines the time to wait until a js file is downloaded and processed again (default 1h0m0s)
   -html-requests-cache-ttl value  defines the time to wait until a html file is downloaded and processed again (default 1h0m0s)

Webpack Chunk Discovery Script

The chunk discovery script is written in Typescript, and can be used as a standalone script outside of jxscout. You can use your favourite JS runtime to run it. jxscout uses bun.

You can check the script here: https://github.com/francisconeves97/jxscout/blob/main/pkg/chunk-discoverer/index.ts

The script expects two args:

  • The path to the JS file to analyze for webpack chunks
  • A bruteforce limit, used when the Webpack chunk loading function can create an unlimited number of valid chunk names.

Example:

bun run pkg/chunk-discoverer/index.ts /path/to/the/js/file 10

Contributing

Feel free to leave suggestions and open pull requests, all contributions are welcome!

License

This project is licensed under the GNU General Public License. See the COPYING file for the full license text.