Detection: Abnormally High Number Of Cloud Instances Destroyed

Description

The following analytic identifies an abnormally high number of cloud instances being destroyed within a 4-hour period. It leverages cloud infrastructure logs and applies a probability density model to detect outliers. This activity is significant for a SOC because a sudden spike in destroyed instances could indicate malicious activity, such as an insider threat or a compromised account attempting to disrupt services. If confirmed malicious, this could lead to significant operational disruptions, data loss, and potential financial impact due to the destruction of critical cloud resources.

Search

 1
 2| tstats count as instances_destroyed values(All_Changes.object_id) as object_id from datamodel=Change where All_Changes.action=deleted AND All_Changes.status=success AND All_Changes.object_category=instance by All_Changes.user _time span=1h 
 3| `drop_dm_object_name("All_Changes")` 
 4| eval HourOfDay=strftime(_time, "%H") 
 5| eval HourOfDay=floor(HourOfDay/4)*4 
 6| eval DayOfWeek=strftime(_time, "%w") 
 7| eval isWeekend=if(DayOfWeek >= 1 AND DayOfWeek <= 5, 0, 1) 
 8| join HourOfDay isWeekend [summary cloud_excessive_instances_destroyed_v1] 
 9| where cardinality >=16 
10| apply cloud_excessive_instances_destroyed_v1 threshold=0.005 
11| rename "IsOutlier(instances_destroyed)" as isOutlier 
12| where isOutlier=1 
13| eval expected_upper_threshold = mvindex(split(mvindex(BoundaryRanges, -1), ":"), 0) 
14| eval distance_from_threshold = instances_destroyed - expected_upper_threshold 
15| table _time, user, instances_destroyed, expected_upper_threshold, distance_from_threshold, object_id 
16| `abnormally_high_number_of_cloud_instances_destroyed_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
AWS CloudTrail	AWS	'aws:cloudtrail'	'aws_cloudtrail'	N/A

Macros Used

| abnormally_high_number_of_cloud_instances_destroyed_filter | search * |

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

You must be ingesting your cloud infrastructure logs. You also must run the baseline search Baseline Of Cloud Instances Destroyed to create the probability density function.

Known False Positives

Many service accounts configured within a cloud infrastructure are known to exhibit this behavior. Please adjust the threshold values and filter out service accounts from the output. Always verify if this search alerted on a human user.

Associated Analytic Story

• Suspicious Cloud Instance Activities

Risk Based Analytics (RBA)

Detection Testing

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

Source: GitHub | Version: 2