overthewire-writeups

Bandit21 -> 22: The Scheduled Task (Cron)

Challenge

Level Description

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

The Process

In Linux, cron is like an alarm clock that triggers scripts or commands at specific times. To solve this, I needed to investigate how the system was automated.

I started by looking into the cron configuration directory to find a job related to bandit22:

$ ls /etc/cron.d/
$ cat /etc/cron.d/cronjob_bandit22

The output showed a line indicating that every minute, a shell script was being executed as user bandit22: @reboot bandit22 /usr/bin/cronjob_bandit22.sh &> /dev/null * * * * * bandit22 /usr/bin/cronjob_bandit22.sh &> /dev/null

Next, I read the script to see what it actually does:

$ cat /usr/bin/cronjob_bandit22.sh

The script was very simple:

#!/bin/bash
chmod 644 /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZSc7sg2
cat /etc/bandit_pass/bandit22 > /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZSc7sg2

The script copies the password for bandit22 into a world-readable file in the /tmp directory. I just had to cat that temporary file to get the prize!

$ cat /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZSc7sg2

Password For the Next Level

[SPOILER]

What I Learned

• Cron Jobs: I learned that /etc/cron.d/ contains files that define scheduled tasks for the whole system.
• Script Analysis: I practiced reading shell scripts to understand how data is moved or transformed by automated processes.
• Permissions in /tmp: I saw how temporary directories are often used by scripts to store data, which can sometimes lead to information leakage if permissions aren’t tight.

Helpful Reading Material

• Scheduling tasks: A Guide to Cron and Crontab
• Understanding Shell Scripts: Bash Scripting for Beginners