OverTheWire: Bandit Level 21 → Level 22
The Bandit wargames are aimed at absolute beginners. It will teach the basics needed to be able to play other wargames.
Level Goal
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.
Commands you may need to solve this level
cron, crontab, crontab(5) (use “man 5 crontab” to access this)
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> whatis cron
cron (8) - daemon to execute scheduled commands (Vixie Cron)
> whatis crontab
crontab (1) - maintain crontab files for individual users (Vixie Cron)
crontab (5) - tables for driving cron
Helpful Reading Material
Linux/Mac Tutorial: Cron Jobs - How to Schedule Commands with crontab - YouTube
Linux crontab command help and examples
11 Cron Scheduling Task Examples in Linux
Solution
Since we know there is a task that is being executed by cron let’s have a look at all the cron jobs on the system
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bandit21@bandit:~$ ls /etc/cron.d/
cronjob_bandit15_root cronjob_bandit22 cronjob_bandit24
cronjob_bandit17_root cronjob_bandit23 cronjob_bandit25_root
Since we require the password for bandit22 the task that we are looking for should be cronjob_bandit22
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bandit21@bandit:~$ cat /etc/cron.d/cronjob_bandit22
@reboot bandit22 /usr/bin/cronjob_bandit22.sh &> /dev/null
* * * * * bandit22 /usr/bin/cronjob_bandit22.sh &> /dev/null
When we look at the cron job for bandit22 we see that there is a shell script that is being executed every second
(For detailed information on the syntax of cron jobs refer to the attached resources)
Let’s have a look at the contents of the script and try to understand what is it trying to perform
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bandit21@bandit:~$ cat /usr/bin/cronjob_bandit22.sh
#!/bin/bash
chmod 644 /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv
cat /etc/bandit_pass/bandit22 > /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv
When we look at the script we see that it is creating a file called t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv in the /tmp directory and then saving the password for the next level into that file.
Let’s view the content of the file that is created by the script
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bandit21@bandit:~$ cat /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv
Yk7owGAcWjwMVRwrTesJEwB7WVOiILLI
And there we go we have the password for the next level !!!
Logout of the current session and start the next level as bandit22
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> ssh [email protected] -p 2220
This is a OverTheWire game server. More information on http://www.overthewire.org/wargames
[email protected]'s password: Yk7owGAcWjwMVRwrTesJEwB7WVOiILLI