The following analytic is designed to detect suspicious file creation within the systemd timer directory on Linux platforms. Systemd is a system and service manager for Linux, similar to the combination of wininit.exe and services.exe on Windows. This process initializes a Linux system and starts defined services in unit files. Malicious actors, such as adversaries, malware, or red teamers, can exploit this feature by embedding a systemd service file for persistence on the targeted or compromised host.
The analytic works by monitoring logs with file name, file path, and process GUID data from your endpoints. If a .service file is created in certain systemd directories, the analytic triggers an alert. This behavior is significant for a Security Operations Center (SOC) as it may indicate a persistent threat within the network, with a potential impact of system compromise or data exfiltration.
- Type: Anomaly
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-12-20
- Author: Teoderick Contreras, Splunk
- ID: c7495048-61b6-11ec-9a37-acde48001122
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_name = *.service Filesystem.file_path IN ("*/etc/systemd/system*", "*/lib/systemd/system*", "*/usr/lib/systemd/system*", "*/run/systemd/system*", "*~/.config/systemd/*", "*~/.local/share/systemd/*","*/etc/systemd/user*", "*/lib/systemd/user*", "*/usr/lib/systemd/user*", "*/run/systemd/user*") by Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.process_guid Filesystem.file_path | `drop_dm_object_name(Filesystem)` | `security_content_ctime(lastTime)` | `security_content_ctime(firstTime)` | `linux_service_file_created_in_systemd_directory_filter`
The SPL above uses the following Macros:
linux_service_file_created_in_systemd_directory_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
To successfully implement this search, you need to be ingesting logs with the file name, file path, and process_guid executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase.
Known False Positives
False positives may arise when administrators or network operators create files in systemd directories for legitimate automation tasks. Therefore, it's important to adjust filter macros to account for valid activities. To implement this search successfully, it's crucial to ingest appropriate logs, preferably using the Linux Sysmon Add-on from Splunkbase for those using Sysmon.
Associated Analytic Story
|64.0||80||80||A service file named as $file_path$ is created in systemd folder on $dest$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 1