OnionScan - Onion Services Security Scan

Wednesday, April 13, 2016

The purpose of this tool is to make you a better onion service provider. You owe it to yourself and your users to ensure that attackers cannot easily exploit and deanonymize.

Go Dependencies
  • h12.me/socks - For the Tor SOCKS Proxy connection.
  • github.com/xiam/exif - For EXIF data extraction.
  • github.com/mvdan/xurls - For some URL parsing.

OS Package Dependencies
  • libexif-dev on Debian based OS
  • libexif-devel on Fedora


Install OS dependencies
  • On Debian based operating systems:
         sudo apt-get install libexif-dev    
  • On Fedora based operating systems:
         sudo dnf install libexif-devel    

Grab with go get
    go get github.com/s-rah/onionscan   

Compile/Run from git cloned source
    go install github.com/s-rah/onionscan   
and then run the program in
Or, you can just do
    go run github.com/s-rah/onionscan.go   
to execute without compiling.

For a simple report detailing the high, medium and low risk areas found:
    ./bin/onionscan blahblahblah.onion   

The most interesting output comes from the verbose option:
    ./bin/onionscan --verbose blahblahblah.onion   

There is also a JSON output, if you want to integrate with something else:
    ./bin/onionscan --jsonReport blahblahblah.onion   

If you would like to use a proxy server listening on something other that   
, then you can use the --torProxyAddress flag:
    ./bin/onionscan --torProxyAddress= blahblahblah.onion   

Apache mod_status Protection
This should not be news , you should not have it enabled. If you do have it enabled, attacks can:
  • Build a better fingerprint of your server, including php and other software versions.
  • Determine client IP addresses if you are co-hosting a clearnet site.
  • Determine your IP address if your setup allows.
  • Determine other sites you are co-hosting.
  • Determine how active your site it.
  • Find secret or hidden areas of your site
  • and much, much more.
Seriously, don't even run the tool, go to your site and check if you have /server-status reachable. If you do, turn it off!

Open Directories
Basic web security 101, if you leave directories open then people are going to scan them, and find interesting things - old versions of images, temp files etc.
Many sites use common structures style/ , images/ etc. The tool checks for common variations, and allows the user to submit others for testing.

Whether you create them yourself or allow users to upload images, you need to ensure the metadata associated with the image is stripped.
Many, many websites still do not properly sanitise image data, leaving themselves or their users at risk of deanonymization.

Server Fingerprint
Sometimes, even without mod_status we can determine if two sites are hosted on the sam infrastructure. We can use the following attributes to make this distinction:
  • Server HTTP Header
  • Technology Stack (e.g. php, jquery version etc.)
  • Website folder layout e.g. do you use /style or /css or do you use wordpress.
  • Fingerprints of images
  • GPG Versions being used.

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