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Description

The following analytic identifies suspicious modifications to cron jobs on Linux systems using the crontab command with list parameters. This command line parameter can be abused by malware like Industroyer2, as well as adversaries and red teamers, to add a crontab entry for executing their malicious code on a schedule of their choice. However, it's important to note that administrators or normal users may also use this command for legitimate automation purposes, so filtering is required to minimize false positives. Identifying the modification of cron jobs using list parameters is valuable for a SOC as it indicates potential malicious activity or an attempt to establish persistence on the system. If a true positive is detected, further investigation should be conducted to analyze the added cron job, its associated command, and the impact it may have on the system. This includes examining the purpose of the job, reviewing any on-disk artifacts, and identifying any related processes or activities occurring concurrently. The impact of a true positive can range from unauthorized execution of malicious code to data destruction or other damaging outcomes.

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2023-04-14
  • Author: Teoderick Contreras, Splunk
  • ID: 52f6d751-1fd4-4c74-a4c9-777ecfeb5c58

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1053.003 Cron Execution, Persistence, Privilege Escalation
T1053 Scheduled Task/Job Execution, Persistence, Privilege Escalation
Kill Chain Phase
  • Installation
  • Exploitation
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name = "crontab" Processes.process= "* -l*" by  Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.dest Processes.user 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `linux_adding_crontab_using_list_parameter_filter`

Macros

The SPL above uses the following Macros:

:information_source: linux_adding_crontab_using_list_parameter_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Processes.dest
  • Processes.user
  • Processes.parent_process_name
  • Processes.process_name
  • Processes.process
  • Processes.process_id
  • Processes.parent_process_id

How To Implement

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 application for automation purposes. Please update the filter macros to remove false positives.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
25.0 50 50 A possible crontab list command $process$ executed on $dest$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

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

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