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Description

This analytic is to detect a deletion of cron job in a linux machine. This technique can be related to an attacker, threat actor or malware to disable scheduled cron jobs that might be related to security or to evade some detections. We also saw that this technique can be a good indicator for malware that is trying to wipe or delete several files on the compromised host like the acidrain malware. This anomaly detection can be a good pivot detection to look for process and user doing it why they doing. Take note that this event can be done by administrator so filtering on those possible false positive event is needed.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-04-12
  • Author: Teoderick Contreras, Splunk
  • ID: 3b132a71-9335-4f33-9932-00bb4f6ac7e8

Annotations

ATT&CK
ID Technique Tactic
T1485 Data Destruction Impact
T1070.004 File Deletion Defense Evasion
T1070 Indicator Removal on Host Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 3
  • CIS 5
  • CIS 16
CVE
1
2
3
4
5
6
7
8
9
10
11
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.action=deleted Filesystem.file_path ="/etc/cron.*" by _time span=1h Filesystem.file_name Filesystem.file_path Filesystem.dest Filesystem.process_guid Filesystem.action 
| `drop_dm_object_name(Filesystem)` 
|rename process_guid as proc_guid 
|join proc_guid, _time [ 
| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.parent_process_name != unknown by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest Processes.parent_process_name Processes.parent_process Processes.process_path Processes.process_guid 
| `drop_dm_object_name(Processes)` 
|rename process_guid as proc_guid 
| fields _time dest user parent_process_name parent_process process_name process_path process proc_guid registry_path registry_value_name registry_value_data registry_key_name action] 
| table  process_name process proc_guid file_name file_path action _time parent_process_name parent_process  process_path dest user 
| `linux_deletion_of_cron_jobs_filter`

Macros

The SPL above uses the following Macros:

Note that linux_deletion_of_cron_jobs_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

  • _time
  • Filesystem.dest
  • Filesystem.file_create_time
  • Filesystem.file_name
  • Filesystem.process_guid
  • Filesystem.file_path
  • Filesystem.action
  • Processes.dest
  • Processes.user
  • Processes.parent_process_name
  • Processes.parent_process
  • Processes.process_name
  • Processes.process_path
  • Processes.process
  • Processes.process_id
  • Processes.parent_process_id

How To Implement

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line 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 execute this command. Please update the filter macros to remove false positives.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
49.0 70 70 a $process_name$ deleting cron jobs in $dest$

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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