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Description

This search looks for cloud compute instances being created with previously unseen image IDs.

Annotations

ATT&CK
Kill Chain Phase
  • Actions on Objectives
NIST
  • ID.AM
CIS20
  • CIS 1
CVE
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| 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 
| `drop_dm_object_name("All_Changes")` 
| `drop_dm_object_name("Instance_Changes")` 
| where image_id != "unknown" 
| lookup previously_seen_cloud_compute_images image_id as image_id OUTPUT firstTimeSeen, enough_data 
| eventstats max(enough_data) as enough_data 
| where enough_data=1 
| eval firstTimeSeenImage=min(firstTimeSeen) 
| where isnull(firstTimeSeenImage) OR firstTimeSeenImage > relative_time(now(), "-24h@h") 
| table firstTime, user, image_id, count, dest 
| `security_content_ctime(firstTime)` 
| `cloud_compute_instance_created_with_previously_unseen_image_filter`

Macros

The SPL above uses the following Macros:

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

Lookups

The SPL above uses the following Lookups:

Required field

  • _time
  • All_Changes.object_id
  • All_Changes.action
  • All_Changes.Instance_Changes.image_id
  • All_Changes.user

How To Implement

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

RBA

Risk Score Impact Confidence Message
36.0 60 60 User $user$ is creating an instance $dest$ with an image that has not been previously seen.

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

Reference

Test Dataset

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 | version: 1