Detection: Linux Possible Cronjob Modification With Editor

Description

The following analytic detects potential unauthorized modifications to Linux cronjobs using text editors like "nano," "vi," or "vim." It identifies this activity by monitoring command-line executions that interact with cronjob configuration paths. This behavior is significant for a SOC as it may indicate attempts at privilege escalation or establishing persistent access. If confirmed malicious, the impact could be severe, allowing attackers to execute damaging actions such as data theft, system sabotage, or further network penetration.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where (Processes.process_name IN("nano","vim.basic") OR Processes.process IN ("*nano *", "*vi *", "*vim *")) AND Processes.process IN("*/etc/cron*", "*/var/spool/cron/*", "*/etc/anacrontab*") by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `linux_possible_cronjob_modification_with_editor_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 1	Linux	'sysmon:linux'	'Syslog:Linux-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Administrator or network operator can use this commandline for automation purposes. Please update the filter macros to remove false positives.

Associated Analytic Story

• Linux Living Off The Land

• Linux Persistence Techniques

• Linux Privilege Escalation

• Scheduled Tasks

Risk Based Analytics (RBA)

References

• https://attack.mitre.org/techniques/T1053/003/

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 3