Adversaries may abuse systemd timers to perform task scheduling for initial or recurring execution of malicious code. Systemd timers are unit files with file extension <code>.timer</code> that control services. Timers can be set to run on a calendar event or after a time span relative to a starting point. They can be used as an alternative to [Cron](https://attack.mitre.org/techniques/T1053/003) in Linux environments.(Citation: archlinux Systemd Timers Aug 2020) Systemd timers may be activated remotely via the <code>systemctl</code> command line utility, which operates over [SSH](https://attack.mitre.org/techniques/T1021/004).(Citation: Systemd Remote Control)

Each <code>.timer</code> file must have a corresponding <code>.service</code> file with the same name, e.g., <code>example.timer</code> and <code>example.service</code>. <code>.service</code> files are [Systemd Service](https://attack.mitre.org/techniques/T1543/002) unit files that are managed by the systemd system and service manager.(Citation: Linux man-pages: systemd January 2014) Privileged timers are written to <code>/etc/systemd/system/</code> and <code>/usr/lib/systemd/system</code> while user level are written to <code>~/.config/systemd/user/</code>.

An adversary may use systemd timers to execute malicious code at system startup or on a scheduled basis for persistence.(Citation: Arch Linux Package Systemd Compromise BleepingComputer 10JUL2018)(Citation: gist Arch package compromise 10JUL2018)(Citation: acroread package compromised Arch Linux Mail 8JUL2018) Timers installed using privileged paths may be used to maintain root level persistence. Adversaries may also install user level timers to achieve user level persistence.(Citation: Falcon Sandbox smp: 28553b3a9d)
Systemd Timers
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1053/006  external_id: T1053.006     source_name: Systemd Remote Control  description: Aaron Kili. (2018, January 16). How to Control Systemd Services on Remote Linux Server. Retrieved July 26, 2021.  url: https://www.tecmint.com/control-systemd-services-on-remote-linux-server/     source_name: archlinux Systemd Timers Aug 2020  description: archlinux. (2020, August 11). systemd/Timers. Retrieved October 12, 2020.  url: https://wiki.archlinux.org/index.php/Systemd/Timers     source_name: gist Arch package compromise 10JUL2018  description: Catalin Cimpanu. (2018, July 10). ~x file downloaded in public Arch package compromise. Retrieved April 23, 2019.  url: https://gist.github.com/campuscodi/74d0d2e35d8fd9499c76333ce027345a     source_name: Arch Linux Package Systemd Compromise BleepingComputer 10JUL2018  description: Catalin Cimpanu. (2018, July 10). Malware Found in Arch Linux AUR Package Repository. Retrieved April 23, 2019.  url: https://www.bleepingcomputer.com/news/security/malware-found-in-arch-linux-aur-package-repository/     source_name: acroread package compromised Arch Linux Mail 8JUL2018  description: Eli Schwartz. (2018, June 8). acroread package compromised. Retrieved April 23, 2019.  url: https://lists.archlinux.org/pipermail/aur-general/2018-July/034153.html     source_name: Falcon Sandbox smp: 28553b3a9d  description: Hybrid Analysis. (2018, July 11). HybridAnalsysis of sample 28553b3a9d2ad4361d33d29ac4bf771d008e0073cec01b5561c6348a608f8dd7. Retrieved September 8, 2023.  url: https://www.hybrid-analysis.com/sample/28553b3a9d2ad4361d33d29ac4bf771d008e0073cec01b5561c6348a608f8dd7?environmentId=300     source_name: Linux man-pages: systemd January 2014  description: Linux man-pages. (2014, January). systemd(1) - Linux manual page. Retrieved April 23, 2019.  url: http://man7.org/linux/man-pages/man1/systemd.1.html     