Systemd Timers

Executive Summary

Systemd Timers (T1053.006) is a MITRE ATT&CK technique associated with Execution, Persistence, Privilege Escalation. Adversaries may abuse systemd timers to perform task scheduling for initial or recurring execution of malicious code.

Why Attackers Use It

Attackers use Systemd Timers because it provides a reliable way to advance their objective within the Execution, Persistence, Privilege Escalation tactic, often with a favorable balance of impact versus detectability on Linux environments. Defenders should assess this behavior in the context of the affected platform and adjacent activity rather than treating it as a standalone indicator.

MITRE Description

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 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.(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 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)

Attack Flow

1. Attacker gains the prerequisite access or context described below.
2. Attacker executes Systemd Timers to achieve its tactical objective (Execution, Persistence, Privilege Escalation).
3. Resulting access/data/effect is leveraged to advance the broader attack chain (see Related Techniques).

Prerequisites

• Platform(s): Linux
• ATT&CK does not define one universal permission requirement for this technique. Establish the required access from the observed implementation and affected platform.

Common Tools

• Tool attribution is implementation-specific. Use ATT&CK procedure examples and local telemetry to identify the binaries, services, scripts, accounts, or cloud resources involved.

Commands

No universal command represents Systemd Timers. Capture the exact command line, arguments, parent process, account, host, and execution time from the investigated environment; do not operationalize unverified examples.

Network Traffic

• Network observability is implementation-dependent. Review DNS, proxy, firewall, flow, authentication, and packet telemetry around the activity window, then correlate remote endpoints and protocol behavior with host evidence.

Windows Events

Sysmon Events

Detection Opportunities

No MITRE detection guidance published for this technique.

Relevant ATT&CK Data Sources: N/A

Sigma Rules

A universal Sigma rule would create unreliable results because this technique has no single guaranteed observable. Build detection logic from a documented behavior and supported data source, scope it to the affected platform, and validate it against benign administrative activity before deployment.

Splunk Queries

Start with the data sources named in the detection section. Scope searches by asset, identity, and time window; correlate the primary behavior with preceding access and subsequent actions. A portable query is intentionally not provided where the technique lacks a universal schema or observable.

Investigation Workflow

1. Confirm that the observed behavior is consistent with Systemd Timers and rule out expected administrative or application activity.
2. Establish the first-seen time, initiating identity, source system, target system, and affected resources.
3. Collect relevant host, identity, network, cloud, and application telemetry for the surrounding time window.
4. Correlate parent and child activity, remote connections, file or configuration changes, and related ATT&CK techniques.
5. Determine scope by searching for the same observable across peer assets and identities.
6. Preserve volatile evidence and record confidence, assumptions, and telemetry gaps before containment.

Containment

1. Isolate affected host(s)/account(s) identified during investigation.
2. Revoke or rotate any credentials/tokens potentially exposed.
3. Apply the mitigations listed below where not already enforced.
4. Validate no related techniques (see Related Techniques) were chained against the same asset.

Mitigation

• M1022 -- Restrict File and Directory Permissions: Restricting file and directory permissions involves setting access controls at the file system level to limit which users, groups, or processes can read, write, or execute files.
• M1018 -- User Account Management: User Account Management involves implementing and enforcing policies for the lifecycle of user accounts, including creation, modification, and deactivation.
• M1026 -- Privileged Account Management: Privileged Account Management focuses on implementing policies, controls, and tools to securely manage privileged accounts (e.g., SYSTEM, root, or administrative accounts).

Related Techniques

• T1053