Detect Systemd Timers in Google Chronicle
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. Each .timer file must have a corresponding .service file with the same name. Privileged timers are written to /etc/systemd/system/ and /usr/lib/systemd/system while user level timers are written to ~/.config/systemd/user/. Adversaries may use systemd timers to execute malicious code at system startup or on a scheduled basis for persistence, and may leverage root-level timer paths to maintain privileged persistence.
MITRE ATT&CK
- Technique
- T1053 Scheduled Task/Job
- Sub-technique
- T1053.006 Systemd Timers
- Canonical reference
- https://attack.mitre.org/techniques/T1053/006/
YARA-L Detection Query
rule systemd_timer_persistence {
meta:
author = "Argus Detection Engineering"
description = "Detects abuse of systemd timers for persistence (MITRE ATT&CK T1053.006). Matches systemctl commands enabling, starting, or linking .timer units and file creation or modification events targeting privileged system-level or user-level systemd unit directories."
severity = "HIGH"
tactic = "Persistence"
technique = "T1053.006"
reference = "https://attack.mitre.org/techniques/T1053/006/"
created = "2026-04-16"
version = "1.0"
events:
(
$e.metadata.event_type = "PROCESS_LAUNCH"
and re.regex(
$e.target.process.command_line,
`systemctl.+\.timer.*(enable|start|link|daemon-reload)`
)
)
or
(
(
$e.metadata.event_type = "FILE_CREATION"
or $e.metadata.event_type = "FILE_MODIFICATION"
)
and (
re.regex(
$e.target.file.full_path,
`/(etc|usr/lib|lib)/systemd/system/[^/]+\.(timer|service)$`
)
or re.regex(
$e.target.file.full_path,
`\.config/systemd/user/[^/]+\.(timer|service)$`
)
)
)
condition:
$e
}Chronicle YARA-L 2.0 rule detecting systemd timer abuse (T1053.006) using UDM event types PROCESS_LAUNCH, FILE_CREATION, and FILE_MODIFICATION. Matches systemctl invocations that manage .timer units and filesystem writes to systemd unit directories at both privileged paths (/etc/systemd/system, /usr/lib/systemd/system, /lib/systemd/system) and user-level paths (.config/systemd/user).
Data Sources
Required Tables
False Positives & Tuning
- Package manager scriptlets executed by apt, yum, or dnf that call systemctl enable on newly installed timer units targeting /usr/lib/systemd/system/
- Configuration management platforms such as Ansible AWX or SaltStack writing timer unit files to systemd directories during scheduled fleet provisioning or configuration drift remediation
- System updates replacing existing /usr/lib/systemd/system/*.timer files for built-in services like apt-daily.timer, fwupd-refresh.timer, or motd-news.timer
Other platforms for T1053.006
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Create and Enable a Privileged Systemd Timer for Persistence
Expected signal: Auditd: SYSCALL openat/write events for /etc/systemd/system/argus-test.timer and /etc/systemd/system/argus-test.service creation. Process creation events for 'systemctl daemon-reload', 'systemctl enable argus-test.timer', 'systemctl start argus-test.timer'. Syslog: systemd entries showing 'argus-test.timer' enabled and started. After 1 minute: process creation for /bin/bash /tmp/argus_payload.sh spawned with parent=systemd.
- Test 2Create User-Level Systemd Timer for Unprivileged Persistence
Expected signal: File creation events for ~/.config/systemd/user/argus-user-test.timer and ~/.config/systemd/user/argus-user-test.service. Process creation events for 'systemctl --user daemon-reload', 'systemctl --user enable', 'systemctl --user start'. User journal entries: 'journalctl --user -u argus-user-test.timer' shows activation. On calendar trigger: process creation for /bin/bash /tmp/user_payload.sh with parent process systemd (user instance).
- Test 3Deploy Systemd Timer with Base64-Encoded Payload in ExecStart
Expected signal: File creation events for /etc/systemd/system/argus-encoded-test.service and /etc/systemd/system/argus-encoded-test.timer. The service unit file content contains 'base64 -d | bash' in ExecStart — detectable via file content inspection. Syslog: systemctl enable/start events. Process creation: /bin/bash spawned by systemd with base64 decode pipe pattern visible in command line arguments.
- Test 4Simulate Remote Systemd Timer Activation via SSH
Expected signal: File creation for unit files in /etc/systemd/system/. Process creation: systemctl enable and start commands. If run via SSH: /var/log/auth.log shows SSH session from source IP, with subsequent systemctl commands in the same session. Syslog: 'argus-remote-test.timer' enabled and started entries. Auditd: EXECVE records for systemctl with timer arguments.
References (12)
- https://attack.mitre.org/techniques/T1053/006/
- https://wiki.archlinux.org/index.php/Systemd/Timers
- https://www.tecmint.com/control-systemd-services-on-remote-linux-server/
- https://www.bleepingcomputer.com/news/security/malware-found-in-arch-linux-aur-package-repository/
- https://gist.github.com/campuscodi/74d0d2e35d8fd9499c76333ce027345a
- https://lists.archlinux.org/pipermail/aur-general/2018-July/034153.html
- https://www.hybrid-analysis.com/sample/28553b3a9d2ad4361d33d29ac4bf771d008e0073cec01b5561c6348a608f8dd7?environmentId=300
- http://man7.org/linux/man-pages/man1/systemd.1.html
- https://www.freedesktop.org/software/systemd/man/systemd.timer.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1053.006/T1053.006.md
- https://github.com/SigmaHQ/sigma/tree/master/rules/linux
- https://pberba.github.io/security/2022/01/30/linux-threat-hunting-for-persistence-systemd-timers-and-cron/
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