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T1053.006 Systemd Timers

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 .timer 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 in Linux environments.1 Systemd timers may be activated remotely via the systemctl command line utility, which operates over SSH.2

Each .timer file must have a corresponding .service file with the same name, e.g., example.timer and example.service. .service files are Systemd Service unit files that are managed by the systemd system and service manager.3 Privileged timers are written to /etc/systemd/system/ and /usr/lib/systemd/system while user level are written to ~/.config/systemd/user/.

An adversary may use systemd timers to execute malicious code at system startup or on a scheduled basis for persistence.456 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.

Item Value
ID T1053.006
Sub-techniques T1053.002, T1053.003, T1053.005, T1053.006, T1053.007
Tactics TA0002, TA0003, TA0004
Platforms Linux
Permissions required User, root
Version 1.1
Created 12 October 2020
Last Modified 27 July 2021

Mitigations

ID Mitigation Description
M1026 Privileged Account Management Limit access to the root account and prevent users from creating and/or modifying systemd timer unit files.
M1022 Restrict File and Directory Permissions Restrict read/write access to systemd .timer unit files to only select privileged users who have a legitimate need to manage system services.
M1018 User Account Management Limit user access to system utilities such as ‘systemctl’ or ‘systemd-run’ to users who have a legitimate need.

Detection

ID Data Source Data Component
DS0017 Command Command Execution
DS0022 File File Modification
DS0009 Process Process Creation
DS0003 Scheduled Job Scheduled Job Creation

References

  1. archlinux. (2020, August 11). systemd/Timers. Retrieved October 12, 2020. ↩

  2. Aaron Kili. (2018, January 16). How to Control Systemd Services on Remote Linux Server. Retrieved July 26, 2021. ↩

  3. Linux man-pages. (2014, January). systemd(1) - Linux manual page. Retrieved April 23, 2019. ↩

  4. Catalin Cimpanu. (2018, July 10). Malware Found in Arch Linux AUR Package Repository. Retrieved April 23, 2019. ↩

  5. Catalin Cimpanu. (2018, July 10). ~x file downloaded in public Arch package compromise. Retrieved April 23, 2019. ↩

  6. Eli Schwartz. (2018, June 8). acroread package compromised. Retrieved April 23, 2019. ↩