Detection: Abnormally High Number Of Cloud Instances Launched

Description

The following analytic detects an abnormally high number of cloud instances launched within a 4-hour period. It leverages cloud infrastructure logs and applies a probability density model to identify outliers based on historical data. This activity is significant for a SOC because a sudden spike in instance creation could indicate unauthorized access or misuse of cloud resources. If confirmed malicious, this behavior could lead to resource exhaustion, increased costs, or provide attackers with additional compute resources to further their objectives.

Search

 1
 2| tstats count as instances_launched values(All_Changes.object_id) as object_id FROM datamodel=Change
 3  WHERE (
 4        All_Changes.action=created
 5    )
 6    AND All_Changes.status=success AND All_Changes.object_category=instance
 7  BY All_Changes.user _time span=1h
 8
 9| `drop_dm_object_name("All_Changes")`
10
11| eval HourOfDay=strftime(_time, "%H")
12
13| eval HourOfDay=floor(HourOfDay/4)*4
14
15| eval DayOfWeek=strftime(_time, "%w")
16
17| eval isWeekend=if(DayOfWeek >= 1 AND DayOfWeek <= 5, 0, 1)
18
19| join HourOfDay isWeekend [summary cloud_excessive_instances_created_v1]
20
21| where cardinality >=16
22
23| apply cloud_excessive_instances_created_v1 threshold=0.005
24
25| rename "IsOutlier(instances_launched)" as isOutlier
26
27| where isOutlier=1
28
29| eval expected_upper_threshold = mvindex(split(mvindex(BoundaryRanges, -1), ":"), 0)
30
31| eval distance_from_threshold = instances_launched - expected_upper_threshold
32
33| table _time, user, instances_launched, expected_upper_threshold, distance_from_threshold, object_id
34
35| `abnormally_high_number_of_cloud_instances_launched_filter`

Data Source

Name	Platform	Sourcetype	Source
AWS CloudTrail	AWS	'aws:cloudtrail'	'aws_cloudtrail'

Macros Used

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 Launched to create the probability density function.

Known False Positives

Many service accounts configured within an AWS 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

• Cloud Cryptomining

• Suspicious Cloud Instance Activities

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: 10