OverlayFS — CVE-2021–3493 || Writeup || Tryhackme

📖 Introduction

What is OverlayFS.?

OverlayFS is a Linux kernel module that allows the system to combine several mount points into one, so that you can access all the files from each within one directory structure.

It’s often used by live USBs, or some other specialist applications. One use is having a read only root file system, and another partition “overlayed” with that to allow applications to write to a temporary file system.

More resources are included in the final task (Further reading) if you’d like to learn more about OverlayFS and this exploit.

I have a very rough overview of what OverlayFS is — — →

No Answer Needed

CVE-2021–3493 — OverlayFS Exploit

Credentials for SSH

Username: overlay

Password: tryhackme123

Start the Attack box and and login into the SSH using the credentials given in the task.

Answer the questions below:

Deploy the machine with the Start Machine button in this task and wait up to 2 minutes for the VM to boot.

No Answer Required.

SSH into the machine with the credentials provided in the task text.

No Answer Rerquired

Grab the source code for the exploit from SSD-Disclosure here and save it as exploit.c on the target machine.

Go to the link provided and save the exploit as exploit.c using Vim editor or nano editor in the terminal.

Compile the exploit with gcc.

Compile the code using the command

 gcc -o exploit exploit.c

Run your compiled exploit, and get root!

./exploit

What’s the flag in /root/?

bash-4.4# id
bash-4.4# cd /root/
bash-4.4# cat flag.txt

Happy Hacking..!!