Create or Modify System Process: Systemd Service

Adversaries may create or modify systemd services to repeatedly execute malicious payloads as part of persistence. Systemd is a system and service manager commonly used for managing background daemon processes (also known as services) and other system resources.[1] Systemd is the default initialization (init) system on many Linux distributions replacing legacy init systems, including SysVinit and Upstart, while remaining backwards compatible.

Systemd utilizes unit configuration files with the .service file extension to encode information about a service's process. By default, system level unit files are stored in the /systemd/system directory of the root owned directories (/). User level unit files are stored in the /systemd/user directories of the user owned directories ($HOME).[2]

Inside the .service unit files, the following directives are used to execute commands:[3]

  • ExecStart, ExecStartPre, and ExecStartPost directives execute when a service is started manually by systemctl or on system start if the service is set to automatically start.
  • ExecReload directive executes when a service restarts.
  • ExecStop, ExecStopPre, and ExecStopPost directives execute when a service is stopped.

Adversaries have created new service files, altered the commands a .service file’s directive executes, and modified the user directive a .service file executes as, which could result in privilege escalation. Adversaries may also place symbolic links in these directories, enabling systemd to find these payloads regardless of where they reside on the filesystem.[4][5][6]

ID: T1543.002
Sub-technique of:  T1543
Platforms: Linux
Permissions Required: User, root
Contributors: Emad Al-Mousa, Saudi Aramco; Tim (Wadhwa-)Brown; Tony Lambert, Red Canary
Version: 1.4
Created: 17 January 2020
Last Modified: 09 October 2023

Procedure Examples

ID Name Description
S0401 Exaramel for Linux

Exaramel for Linux has a hardcoded location under systemd that it uses to achieve persistence if it is running as root.[7][8]

S0410 Fysbis

Fysbis has established persistence using a systemd service.[9]

S0601 Hildegard

Hildegard has started a monero service.[10]

S0192 Pupy

Pupy can be used to establish persistence using a systemd service.[11]

G0106 Rocke

Rocke has installed a systemd service script to maintain persistence.[4]

S1078 RotaJakiro

Depending on the Linux distribution and when executing with root permissions, RotaJakiro may install persistence using a .service file under the /lib/systemd/system/ folder.[12]

S0663 SysUpdate

SysUpdate can copy a script to the user owned /usr/lib/systemd/system/ directory with a symlink mapped to a root owned directory, /etc/ystem/system, in the unit configuration file's ExecStart directive to establish persistence and elevate privileges.[13]

G0139 TeamTNT

TeamTNT has established persistence through the creation of a cryptocurrency mining system service using systemctl.[14][15]

Mitigations

ID Mitigation Description
M1033 Limit Software Installation

Restrict software installation to trusted repositories only and be cautious of orphaned software packages.

M1026 Privileged Account Management

The creation and modification of systemd service unit files is generally reserved for administrators such as the Linux root user and other users with superuser privileges.

M1022 Restrict File and Directory Permissions

Restrict read/write access to systemd 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 to only users who have a legitimate need.

Detection

ID Data Source Data Component Detects
DS0017 Command Command Execution

Suspicious systemd services can also be identified by comparing results against a trusted system baseline. Malicious systemd services may be detected by using the systemctl utility to examine system wide services: systemctl list-units -–type=service –all. Auditing the execution and command-line arguments of the 'systemctl' utility, as well related utilities such as /usr/sbin/service may reveal malicious systemd service execution.

DS0022 File File Creation

Systemd service unit files may be detected by auditing file creation and modification events within the /etc/systemd/system, /usr/lib/systemd/system/, and /home//.config/systemd/user/ directories, as well as associated symbolic links

File Modification

Systemd service unit files may be detected by auditing file creation and modification events within the /etc/systemd/system, /usr/lib/systemd/system/, and /home//.config/systemd/user/ directories, as well as associated symbolic links

DS0009 Process Process Creation

Suspicious processes or scripts spawned in this manner will have a parent process of ‘systemd’, a parent process ID of 1, and will usually execute as the ‘root’ user.

DS0019 Service Service Creation

Monitor for new constructed systemd services to repeatedly execute malicious payloads as part of persistence.

Service Modification

Analyze the contents of .service files present on the file system and ensure that they refer to legitimate, expected executables.

References