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
Kill Chain Phase
- CIS 3
- CIS 5
- CIS 16
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`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
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
|49.0||70||70||a $process_name$ deleting cron jobs in $dest$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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