Linux Add Files In Known Crontab Directories

name: Linux Add Files In Known Crontab Directories
id: 023f3452-5f27-11ec-bf00-acde48001122
version: 12
creation_date: '2021-12-21'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic detects unauthorized file creation in known crontab directories on Unix-based systems. It leverages filesystem data to identify new files in directories such as /etc/cron* and /var/spool/cron/*. This activity is significant as it may indicate an attempt by threat actors or malware to establish persistence on a compromised host. If confirmed malicious, this could allow attackers to execute arbitrary code at scheduled intervals, potentially leading to further system compromise and unauthorized access to sensitive information.
data_source:
    - Sysmon for Linux EventID 11
search: |-
    | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem
      WHERE Filesystem.file_path IN ("*/etc/cron*", "*/var/spool/cron/*")
      BY Filesystem.action Filesystem.dest Filesystem.file_access_time
         Filesystem.file_create_time Filesystem.file_hash Filesystem.file_modify_time
         Filesystem.file_name Filesystem.file_path Filesystem.file_acl
         Filesystem.file_size Filesystem.process_guid Filesystem.process_id
         Filesystem.user Filesystem.vendor_product
    | `drop_dm_object_name(Filesystem)`
    | `security_content_ctime(lastTime)`
    | `security_content_ctime(firstTime)`
    | `linux_add_files_in_known_crontab_directories_filter`
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: Administrator or network operator can create file in crontab folders for automation purposes. Please update the filter macros to remove false positives.
references:
    - https://www.sandflysecurity.com/blog/detecting-cronrat-malware-on-linux-instantly/
    - https://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: a file $file_name$ is created in $file_path$ on $dest$
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