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Description

The following analytic detects the suspicious editing of cron jobs in Linux via the crontab command-line parameter. This tactic could be used by adversaries or malware to schedule execution of their malicious code, potentially leading to system compromise or unauthorized persistent access. It pinpoints this activity by monitoring command-line executions involving 'crontab' and the edit parameter (-e).
Recognizing such activity is vital for a SOC as cron job manipulations might signal unauthorized persistence attempts or scheduled malicious actions, potentially resulting in substantial harm. A true positive signifies an active threat, with implications ranging from unauthorized access to broader network compromise.
To implement this analytic, logs capturing process name, parent process, and command-line executions from your endpoints must be ingested.
Known false positives could stem from valid administrative tasks or automation processes using crontab. To reduce these, fine-tune the filter macros according to the benign activities within your environment. These adjustments ensure legitimate actions aren't mistaken for threats, allowing analysts to focus on genuine potential risks.\

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2021-12-17
  • Author: Teoderick Contreras, Splunk
  • ID: 0d370304-5f26-11ec-a4bb-acde48001122

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 = "*crontab *" Processes.process = "* -e*" by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `linux_edit_cron_table_parameter_filter`

Macros

The SPL above uses the following Macros:

:information_source: linux_edit_cron_table_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
9.0 30 30 A possible crontab edit 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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