Local Job Scheduling

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Local Job Scheduling
Technique
ID T1168
Tactic Execution, Persistence
Platform Linux, macOS
Permissions Required User, Administrator, root
Data Sources File monitoring, Process Monitoring
Contributors Anastasios Pingios

On Linux and Apple systems, multiple methods are supported for creating pre-scheduled and periodic background jobs: cron,1 at,2 and launchd.3 Unlike Scheduled Task on Windows systems, job scheduling on Linux-based systems cannot be done remotely unless used in conjunction within an established remote session, like secure shell (SSH).

cron

System-wide cron jobs are installed by modifying /etc/crontab file, /etc/cron.d/ directory or other locations supported by the Cron daemon, while per-user cron jobs are installed using crontab with specifically formatted crontab files.3 This works on Mac and Linux systems.

Those methods allow for commands or scripts to be executed at specific, periodic intervals in the background without user interaction. An adversary may use job scheduling to execute programs at system startup or on a scheduled basis for Persistence,4567 to conduct Execution as part of Lateral Movement, to gain root privileges, or to run a process under the context of a specific account.

at

The at program is another means on Linux-based systems, including Mac, to schedule a program or script job for execution at a later date and/or time, which could also be used for the same purposes.

launchd

Each launchd job is described by a different configuration property list (plist) file similar to Launch Daemon or Launch Agent, except there is an additional key called StartCalendarInterval with a dictionary of time values.3 This only works on macOS and OS X.

Examples

  • Janicab used a cron job for persistence on Mac devices 4.

Mitigation

Limit privileges of user accounts and remediate Privilege Escalation vectors so only authorized users can create scheduled jobs. Identify and block unnecessary system utilities or potentially malicious software that may be used to schedule jobs using whitelisting tools.

Detection

Legitimate scheduled jobs may be created during installation of new software or through administration functions. Jobs scheduled with launchd and cron can be monitored from their respective utilities to list out detailed information about the jobs. Monitor process execution resulting from launchd and cron tasks to look for unusual or unknown applications and behavior.