Spawning shells

Non-interactive tty-shell

If you have a non-tty-shell there are certain commands and stuff you can't do. This can happen if you upload reverse shells on a webserver, so that the shell you get is by the user www-data, or similar. These users are not meant to have shells as they don't interact with the system has humans do.

So if you don't have a tty-shell you can't run su, sudo for example. This can be annoying if you manage to get a root password but you can't use it.

Anyways, if you get one of these shells you can upgrade it to a tty-shell using the following methods:

Using python

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

Echo

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

sh

/bin/sh -i

bash

/bin/bash -i

Perl

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

Ruby

ruby: exec "/bin/sh"

Awk

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

Find

find / -name blahblah 'exec /bin/awk 'BEGIN {system("/bin/sh")}' \;

More, less, or man

Type more, less, or man command with a file then try one of the following:

'! /bin/sh'
'!/bin/sh'
'!bash'

Lua

lua: os.execute('/bin/sh')

From within IRB

exec "/bin/sh"

From within VI

:!bash

or

:set shell=/bin/bash:shell

or execute

vi ;/bin/bash

once exit vi (:q!) we would get a shell. Helpful in scenarios where the user is asked to input which file to open

From within nmap

!sh

Interactive tty-shell

So if you manage to upgrade to a non-interactive tty-shell you will still have a limited shell. You won't be able to use the up and down arrows, you won't have tab-completion. This might be really frustrating if you stay in that shell for long. It can also be more risky, if a execution gets stuck you cant use Ctr-C or Ctr-Z without killing your session. However that can be fixed using socat. Follow these instructions.

https://github.com/cornerpirate/socat-shell

Using stty

ctrl+z (background)
stty size
(this will output rows and cols)--for example 48 and 186
stty raw -echo
fg (resume background job)
stty rows 48 cols 186

References:

http://unix.stackexchange.com/questions/122616/why-do-i-need-a-tty-to-run-sudo-if-i-can-sudo-without-a-password
http://netsec.ws/?p=337
http://pentestmonkey.net/blog/post-exploitation-without-a-tty