Detection: Cloud Compute Instance Created With Previously Unseen Image

EXPERIMENTAL DETECTION

This detection status is set to experimental. The Splunk Threat Research team has not yet fully tested, simulated, or built comprehensive datasets for this detection. As such, this analytic is not officially supported. If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2024-10-17 ID: bc24922d-987c-4645-b288-f8c73ec194c4 Author: David Dorsey, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects the creation of cloud compute instances using previously unseen image IDs. It leverages cloud infrastructure logs to identify new image IDs that have not been observed before. This activity is significant because it may indicate unauthorized or suspicious activity, such as the deployment of malicious payloads or unauthorized access to sensitive information. If confirmed malicious, this could lead to data breaches, unauthorized access, or further compromise of the cloud environment. Immediate investigation is required to determine the legitimacy of the instance creation and to mitigate potential threats.

Search

 1
 2| tstats count earliest(_time) as firstTime, latest(_time) as lastTime values(All_Changes.object_id) as dest from datamodel=Change where All_Changes.action=created by All_Changes.Instance_Changes.image_id, All_Changes.user 
 3| `drop_dm_object_name("All_Changes")` 
 4| `drop_dm_object_name("Instance_Changes")` 
 5| where image_id != "unknown" 
 6| lookup previously_seen_cloud_compute_images image_id as image_id OUTPUT firstTimeSeen, enough_data 
 7| eventstats max(enough_data) as enough_data 
 8| where enough_data=1 
 9| eval firstTimeSeenImage=min(firstTimeSeen) 
10| where isnull(firstTimeSeenImage) OR firstTimeSeenImage > relative_time(now(), "-24h@h") 
11| table firstTime, user, image_id, count, dest 
12| `security_content_ctime(firstTime)` 
13| `cloud_compute_instance_created_with_previously_unseen_image_filter`

Data Source

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

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
cloud_compute_instance_created_with_previously_unseen_image_filter	`search *`

cloud_compute_instance_created_with_previously_unseen_image_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic

NistCategory.DE_AE

Cis18Value.CIS_10

Default Configuration

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

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

You must be ingesting your cloud infrastructure logs from your cloud provider. You should run the baseline search Previously Seen Cloud Compute Images - Initial to build the initial table of images observed and times. You must also enable the second baseline search Previously Seen Cloud Compute Images - Update to keep this table up to date and to age out old data. You can also provide additional filtering for this search by customizing the cloud_compute_instance_created_with_previously_unseen_image_filter macro.

Known False Positives

After a new image is created, the first systems created with that image will cause this alert to fire. Verify that the image being used was created by a legitimate user.

Associated Analytic Story

Cloud Cryptomining

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
User $user$ is creating an instance $dest$ with an image that has not been previously seen.	36	60	60

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	Not Applicable	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`
Integration	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`

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: 3