Oct. 10, 2020

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GamingServer - THM Room

Welcome back! Today I have another writeup. This time I went for a just-released room on TryHackMe called Gaming Server. I hope you enjoy it!


I started a scan with Autorecon and while that is running let’s look into what’s at port 80.

sudo autorecon

If we browse to the IP address, we can see we do have a webpage being served about some game:

And If we open the console we see right away there is a mention to a possible username of john.

Let’s see if we can find something else on that page. Autorecon is already running gobuster for us, so we should be able to look into those results in a bit.

If we look into /about.php again the console shows a commented piece of code for file uploads. Let’s see if we can upload a phpbash. You can download a copy from here.

Uploading the phpbash file did not work, there was no error either. But when looking at /uploads the file wasn’t there. It’s very possible this is just a decoy. Let’s keep looking.

There are some other interesting files: A hacker manifesto, a meme and a dictionary.

The mem is just an image of Beaker, who according to the internet is:

Beaker is the hapless assistant to Dr. Bunsen Honeydew from The Muppets.

Gobuster found another interesting directory: /secret

The secret key is an RSA Private one. Let’s see if we can ssh login as John using that key. To do that, we still need to crack the passphrase of the RSA key.

We need to use ssh2john so we can try to crack it with john:

└─$ python /usr/share/john/ secretKey > id_rsa.hash

Once that’s done let’s run john using the dictionary we found on the site as follows:

john --wordlist=dict.lst id_rsa.hash

That' works and we get the passphrase:

Now we can try to ssh login as john:

It works, we are in! yep! Let' me have this hacking cliche, just this time. 😂

Once there we just do cat user.txt and we get the first flag.

Getting root

Now let’s see how we get root. First I fire up a simple http server with python to upload to the target machine. And then run linpeas.

Remember to chmod +x before trying to run it.

Linpeas results don’t show anything that I know how to exploit, but while checking id command for the logged user something interesting comes up:

john@exploitable:/tmp$ id
uid=1000(john) gid=1000(john) groups=1000(john),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lxd)

It seems John is part of the ldx group. And if I remember correctly I read something about getting root if you are part of that group. I think it was on hacktricks. Let’s check that out.

Also check out this post about LXD which puts a nice context on this vulnerability. Follow this Link to read it.

I tried the With Internet method first, by that didn’t work. So let’s try the Method 2 and see if we get lucky this time:

We first need to create ourselves an image of Alpine, using the lxd-alpine-builder script located here.

We just need to run the builder script as sudo and it’ll start making the image for us:

Once done you’ll see a compressed file on the directory where you built the image:

now we need to upload the image to the target machine.

Now we need to let LDX know we have an image, import that image, add a device to it that mounts the file system with privileges and gives us root when we execute it:

And since we mounted our files at /mnt/root we head that way to get the root flag:

That’s it for this room, quite an interesting one. First time for me doing anything related with LXD and Alpine. It was a good lesson and I really enjoyed it.

Hope you find this useful!

Happy hacking and thanks for stopping by!

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