Reverse shell. Extrange characters when pressing ESC, arrow, etc. '^[[A'

mfvazquezr

Hi guys,

I realised that I have a problem when I am working on a reverse shell. Some keys are not working as expected and are sending extrange characters to the shell instead of their usual behaviour in a usual terminal on Linux. This is only happening on reverse shells.

https://i.ibb.co/LrksyR4/Captura.jpg

For example. When I press [UP ARROW] it writes ^[[A on the terminal.

OS: Kali Linux
Terminal: Native Linux terminal.

I googled for it but nothing.

Why is this happening?

Thank you very much!

clubby789

https://blog.ropnop.com/upgrading-simple-shells-to-fully-interactive-ttys/
The simple explanation is normally, when you press up, your shell captures that keystroke and does the appropriate action. In a reverse shell, NC is set to (for whatever reason) send that escape sequence when you press up.

acidbat

Type your comment> @clubby789 said:

https://blog.ropnop.com/upgrading-simple-shells-to-fully-interactive-ttys/
The simple explanation is normally, when you press up, your shell captures that keystroke and does the appropriate action. In a reverse shell, NC is set to (for whatever reason) send that escape sequence when you press up.

Yeah, I have always been a fan of:
python -c 'import pty; pty.spawn("/bin/bash")'
or
python3 -c 'import pty; pty.spawn("/bin/bash")'

mfvazquezr

Thank you very much! I supposed it could be something related to that.

TazWake

@mfvazquezr said:

Thank you very much! I supposed it could be something related to that.

I am 99.99999999999% confident it is this.

If it wasn't, it wouldn't only happen on reverse shells.

mRNA

rlwrap nc -lvnp 7777 (or whichever port you like)

adds a little bit comfort to your netcat reverse shell.

python ... spawn ... is great, but if there is no python on client's machine, upload a static socat binary and establishe a socat shell, google for ropnop socat upgrade if you need more details.

LMAY75

That's just how 'dumb' rev shells work. If you want a fully interactive shell you're gonna have to upgrade it with:

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

or

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

And then the standard:

Ctl+Z
stty raw -echo
fg
reset
xterm-256color
export $TERM=xterm
export $SHELL=bash

and then set the correct terminal dimensions