This one is quite easy, as it is the first Jail escape challenge. It is solved like so:
We connect to the host, and we enter the username and password. We are given the challenge’s bash code, and are asked for an input. If we enter in bash, it will spawn another shell! I used 1>&2 to ignore the jail’s restrictions, and print the output directly to the screen. If we browse the machine on the new bash terminal, we can find the flag.txt and cat it to our screen, once again using the 1>&2 redirect operator.
Flag!
FLAG-U96l4k6m72a051GgE5EN0rA85499172K