T1543.002_systemd-service

T1543.002 Systemd Service

Sub-technique of: T1543

High-Level Description

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. 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).

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

• 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.

The .service file’s User directive can be used to run service as a specific user, which could result in privilege escalation based on specific user/group permissions.

Systemd services can be created via systemd generators, which support the dynamic generation of unit files. Systemd generators are small executables that run during boot or configuration reloads to dynamically create or modify systemd unit files by converting non-native configurations into services, symlinks, or drop-ins (i.e., Boot or Logon Initialization Scripts).

Kill Chain Phase

• Persistence (TA0003)
• Privilege Escalation (TA0004)

Platforms: Linux

What to Check

• Identify if Systemd Service technique is applicable to target environment
• Check Linux systems for indicators of Systemd Service
• Verify mitigations are bypassed or absent (4 known mitigations)
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Create Systemd Service

This test creates a Systemd service unit file and enables it as a service.

Supported Platforms: linux Elevation Required: Yes

echo "[Unit]" > #{systemd_service_path}/#{systemd_service_file}
echo "Description=Atomic Red Team Systemd Service" >> #{systemd_service_path}/#{systemd_service_file}
echo "" >> #{systemd_service_path}/#{systemd_service_file}
echo "[Service]" >> #{systemd_service_path}/#{systemd_service_file}
echo "Type=simple"
echo "ExecStart=#{execstart_action}" >> #{systemd_service_path}/#{systemd_service_file}
echo "ExecStartPre=#{execstartpre_action}" >> #{systemd_service_path}/#{systemd_service_file}
echo "ExecStartPost=#{execstartpost_action}" >> #{systemd_service_path}/#{systemd_service_file}
echo "ExecReload=#{execreload_action}" >> #{systemd_service_path}/#{systemd_service_file}
echo "ExecStop=#{execstop_action}" >> #{systemd_service_path}/#{systemd_service_file}
echo "ExecStopPost=#{execstoppost_action}" >> #{systemd_service_path}/#{systemd_service_file}
echo "" >> #{systemd_service_path}/#{systemd_service_file}
echo "[Install]" >> #{systemd_service_path}/#{systemd_service_file}
echo "WantedBy=default.target" >> #{systemd_service_path}/#{systemd_service_file}
systemctl daemon-reload
systemctl enable #{systemd_service_file}
systemctl start #{systemd_service_file}

Atomic Test 2: Create SysV Service

This test creates a SysV service unit file and enables it as a service.

Supported Platforms: linux Elevation Required: Yes

echo '#\!/bin/sh' > #{rc_service_path}/#{rc_service_file}
echo ' ' >> #{rc_service_path}/#{rc_service_file}
echo '#' >> #{rc_service_path}/#{rc_service_file}
echo '# PROVIDE: art-test' >> #{rc_service_path}/#{rc_service_file}
echo '# REQUIRE: LOGIN' >> #{rc_service_path}/#{rc_service_file}
echo '# KEYWORD: shutdown' >> #{rc_service_path}/#{rc_service_file}
echo ' ' >> #{rc_service_path}/#{rc_service_file}
echo '. /etc/rc.subr' >> #{rc_service_path}/#{rc_service_file}
echo ' ' >> #{rc_service_path}/#{rc_service_file}
echo 'name="art_test"' >> #{rc_service_path}/#{rc_service_file}
echo 'rcvar=art_test_enable' >> #{rc_service_path}/#{rc_service_file}
echo 'load_rc_config ${name}' >> #{rc_service_path}/#{rc_service_file}
echo 'command="/usr/bin/touch"' >> #{rc_service_path}/#{rc_service_file}
echo 'start_cmd="art_test_start"' >> #{rc_service_path}/#{rc_service_file}
echo '' >> #{rc_service_path}/#{rc_service_file}
echo 'art_test_start()' >> #{rc_service_path}/#{rc_service_file}
echo '{' >> #{rc_service_path}/#{rc_service_file}
echo '  ${command} /tmp/art-test.marker' >> #{rc_service_path}/#{rc_service_file}
echo '}' >> #{rc_service_path}/#{rc_service_file}
echo ' ' >> #{rc_service_path}/#{rc_service_file}
echo 'run_rc_command "$1"' >> #{rc_service_path}/#{rc_service_file}
chmod +x #{rc_service_path}/#{rc_service_file}
service art-test enable
service art-test start

Atomic Test 3: Create Systemd Service file, Enable the service , Modify and Reload the service.

This test creates a systemd service unit file and enables it to autostart on boot. Once service is created and enabled, it also modifies this same service file showcasing both Creation and Modification of system process.

Supported Platforms: linux Elevation Required: Yes

echo "#!/bin/bash" > /etc/init.d/T1543.002
echo "### BEGIN INIT INFO" >> /etc/init.d/T1543.002
echo "# Provides : Atomic Test T1543.002" >> /etc/init.d/T1543.002
echo "# Required-Start: \$all" >> /etc/init.d/T1543.002
echo "# Required-Stop : " >> /etc/init.d/T1543.002
echo "# Default-Start: 2 3 4 5" >> /etc/init.d/T1543.002
echo "# Default-Stop: " >> /etc/init.d/T1543.002
echo "# Short Description: Atomic Test for Systemd Service Creation" >> /etc/init.d/T1543.002
echo "### END INIT INFO" >> /etc/init.d/T1543.002
echo "python3 -c \"import os, base64;exec(base64.b64decode('aW1wb3J0IG9zCm9zLnBvcGVuKCdlY2hvIGF0b21pYyB0ZXN0IGZvciBDcmVhdGluZyBTeXN0ZW1kIFNlcnZpY2UgVDE1NDMuMDAyID4gL3RtcC9UMTU0My4wMDIuc3lzdGVtZC5zZXJ2aWNlLmNyZWF0aW9uJykK')) \" " >> /etc/init.d/T1543.002
chmod +x /etc/init.d/T1543.002
if [ $(cat /etc/os-release | grep -i ID=ubuntu) ] || [ $(cat /etc/os-release | grep -i ID=kali) ]; then update-rc.d T1543.002 defaults; elif [ $(cat /etc/os-release | grep -i 'ID="centos"') ]; then chkconfig T1543.002 on ; else echo "Please run this test on Ubnutu , kali OR centos" ; fi
systemctl enable T1543.002
systemctl start T1543.002
echo "python3 -c \"import os, base64;exec(base64.b64decode('aW1wb3J0IG9zCm9zLnBvcGVuKCdlY2hvIGF0b21pYyB0ZXN0IGZvciBtb2RpZnlpbmcgYSBTeXN0ZW1kIFNlcnZpY2UgVDE1NDMuMDAyID4gL3RtcC9UMTU0My4wMDIuc3lzdGVtZC5zZXJ2aWNlLm1vZGlmaWNhdGlvbicpCg=='))\"" | sudo tee -a /etc/init.d/T1543.002
systemctl daemon-reload
systemctl restart T1543.002

Dependencies:

• System must be Ubuntu ,Kali OR CentOS.

Manual Testing

If Atomic Red Team tests are not applicable, manually verify the technique by:

1. Identify Attack Surface: Determine if the target environment is susceptible to Systemd Service by examining the target platforms (Linux).

2. Assess Existing Defenses: Review whether mitigations for T1543.002 are in place. If defenses are absent or misconfigured, this technique may be exploitable.

3. Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.

Remediation Guide

M1018 User Account Management

Limit user access to system utilities such as systemctl to only users who have a legitimate need.

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.

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.

M1033 Limit Software Installation

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

Detection

Detection of Systemd Service Creation or Modification on Linux

Risk Assessment

CWE Categories

References

• airwalk backdoor unix systems
• Anomali Rocke March 2019
• freedesktop systemd.service
• Linux man-pages: systemd January 2014
• Pepe Berba Systemd 2022
• Berba hunting linux systemd
• Rapid7 Service Persistence 22JUNE2016
• Elastic Security Labs Linux Persistence 2024
• lambert systemd 2022
• Atomic Red Team - T1543.002
• MITRE ATT&CK - T1543.002