Linux Possible Append Cronjob Entry on Existing Cronjob File

SPLUNK detection rule by Teoderick Contreras, Splunk · Apache-2.0

The following analytic detects potential tampering with cronjob files on a Linux system by identifying 'echo' commands that append code to existing cronjob files. It leverages logs from Endpoint Detection and Response (EDR) agents, focusing on process names, parent processes, and command-line executions. This activity is significant because adversaries often use it for persistence or privilege escalation. If confirmed malicious, this could allow attackers to execute unauthorized code automatically, leading to system compromises and unauthorized data access, thereby impacting business operations and data integrity.

name: Linux Possible Append Cronjob Entry on Existing Cronjob File
id: b5b91200-5f27-11ec-bb4e-acde48001122
version: 10
creation_date: '2021-12-21'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: Hunting
description: The following analytic detects potential tampering with cronjob files on a Linux system by identifying 'echo' commands that append code to existing cronjob files. It leverages logs from Endpoint Detection and Response (EDR) agents, focusing on process names, parent processes, and command-line executions. This activity is significant because adversaries often use it for persistence or privilege escalation. If confirmed malicious, this could allow attackers to execute unauthorized code automatically, leading to system compromises and unauthorized data access, thereby impacting business operations and data integrity.
data_source:
    - Sysmon for Linux EventID 1
search: |-
    | tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes
      WHERE Processes.process = "*echo*"
        AND
        Processes.process IN("*/etc/cron*", "*/var/spool/cron/*", "*/etc/anacrontab*")
      BY Processes.action Processes.dest Processes.original_file_name
         Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid
         Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path
         Processes.process Processes.process_exec Processes.process_guid
         Processes.process_hash Processes.process_id Processes.process_integrity_level
         Processes.process_name Processes.process_path Processes.user
         Processes.user_id Processes.vendor_product
    | `drop_dm_object_name(Processes)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `linux_possible_append_cronjob_entry_on_existing_cronjob_file_filter`
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: False positives may arise from legitimate actions by administrators or network operators who may use these commands for automation purposes. Therefore, it's recommended to adjust filter macros to eliminate such false positives.
references:
    - https://attack.mitre.org/techniques/T1053/003/
    - https://blog.aquasec.com/threat-alert-kinsing-malware-container-vulnerability
    - https://www.intezer.com/blog/research/kaiji-new-chinese-linux-malware-turning-to-golang/
analytic_story:
    - XorDDos
    - Linux Living Off The Land
    - Linux Privilege Escalation
    - Scheduled Tasks
    - Linux Persistence Techniques
asset_type: Endpoint
mitre_attack_id:
    - T1053.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1053.003/cronjobs_entry/sysmon_linux.log
          source: Syslog:Linux-Sysmon/Operational
          sourcetype: sysmon:linux
      test_type: unit

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20dfbfb2-107c-4b2c-9287-fc8048617a00

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