Bandit - overthewire.org 1-9

"Bandit" at http://overthewire.org/wargames/ is a great introductory war game if you haven't tried this kind of thing before. You use basic linux/unix skills to get the password to the next level, and every level the challenge evolves and gets a little harder or different. All of this takes place from the command line.

I won't go over the first few levels, if you are interested in this sort of thing and know what ssh and a terminal are, you can get through them with no difficulty. But don't get get put off by how simple they are because there are still some fun things ahead.

Starting at level 5, we are using find to find the password for the next level on the server. Find is a really fun command - I might use it as follows if I don't really have a clue where to start looking for something:

find / target 2> /dev/null | grep target > results.txt

which says "look everywhere for the target, be quiet about it, just give me what I am looking for without all the other things and put it in result.txt please". Of course there are less intense search methods like locate and which as well.

For the levels 5 and 6, I got to use some specific flags that I don't normally use: -readable, -group, -size, and -user. They are all fairly straightforward with -size having a few additional options, which you can of course look up. In particular, I solved them with the following commands, respectively:

find / * -readable -size 1033c 2> /dev/null

find -user bandit7 -size 33c -group bandit6 2> /devl/null

Levels 7, 8, 9 were a little different thematically in that you didn't actually need to find the file, but rather find that data within the file using strings and grep. Grep is common enough: cat foo | grep bar is a basic use where foo is the file and bar is the word you want to find. Strings is perhaps a little more on the reversing side of the house; a good preview of looking at a binary to see if anything in there looks promising - sometimes there is some low hanging fruit to be had with it. 

However I thought the most interesting challenge of the three was level 8. The idea was that they had hidden a needle in a stack of needles. The file is some 1,000 line (or more text file) where there are 100 or so different and unique strings, and the rest of the lines are duplicates of those 100 or so patterns. Except for one line which is the target - the needle hidden in the stack of needles.

To solve it I used: 

cat data.txt | sort -n | uniq -u 

I had an idea that those two would be what was required, in fact I have a one liner that I use to get the number of different logins on a computer: 

who | cut -d' ' -f1 | sort -u | wc -l

Which brings me to a point about these kind of games. Even if you aren't interested in reversing, CTF or pwning your own, you can really learn a lot from these exercises. For starters just getting more and different problems to solve using tools you are familiar with already will help you attain mastery with those tools because you will be using them in a different manner than you are accustomed to, which may perhaps lead to learning to use different flags than you normally would.

And for those of you who are beginners, you can vastly expand your knowledge of the tools. Just by playing the game you will be learning new things, thinking creatively about how to solve a problem, and gaining a better understand of the vulnerabilities you have to consider when working as a system administrator.