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: 2023-04-27
- Author: Teoderick Contreras, Splunk
- ID: 3b132a71-9335-4f33-9932-00bb4f6ac7e8
Kill Chain Phase
- Actions On Objectives
- CIS 10
1 2 3 4 5 6 | 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)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `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||Linux cron jobs are deleted on host $dest$ by process GUID- $process_guid$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 2