:no_entry: THIS IS A DEPRECATED DETECTION

This detection has been marked deprecated by the Splunk Threat Research team. This means that it will no longer be maintained or supported.

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Description

This search looks for EC2 instances being created with previously unseen AMIs. This search is deprecated and have been translated to use the latest Change Datamodel.

  • Type: Anomaly

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2018-03-12
  • Author: David Dorsey, Splunk
  • ID: 347ec301-601b-48b9-81aa-9ddf9c829dd3

Annotations

ATT&CK
Kill Chain Phase
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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`cloudtrail` eventName=RunInstances [search `cloudtrail` eventName=RunInstances errorCode=success 
| stats earliest(_time) as firstTime latest(_time) as lastTime by requestParameters.instancesSet.items{}.imageId 
| rename requestParameters.instancesSet.items{}.imageId as amiID 
| inputlookup append=t previously_seen_ec2_amis.csv 
| stats min(firstTime) as firstTime max(lastTime) as lastTime by amiID 
| outputlookup previously_seen_ec2_amis.csv 
| eval newAMI=if(firstTime >= relative_time(now(), "-70m@m"), 1, 0) 
| `security_content_ctime(firstTime)`
|`security_content_ctime(lastTime)` 
| where newAMI=1 
| rename amiID as requestParameters.instancesSet.items{}.imageId 
| table requestParameters.instancesSet.items{}.imageId] 
| rename requestParameters.instanceType as instanceType, responseElements.instancesSet.items{}.instanceId as dest, userIdentity.arn as arn, requestParameters.instancesSet.items{}.imageId as amiID 
| table firstTime, lastTime, arn, amiID, dest, instanceType 
| `ec2_instance_started_with_previously_unseen_ami_filter`

Macros

The SPL above uses the following Macros:

:information_source: ec2_instance_started_with_previously_unseen_ami_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • eventName
  • errorCode
  • requestParameters.instancesSet.items{}.imageId

How To Implement

You must install the AWS App for Splunk (version 5.1.0 or later) and Splunk Add-on for AWS (version 4.4.0 or later), then configure your AWS CloudTrail inputs. This search works best when you run the "Previously Seen EC2 AMIs" support search once to create a history of previously seen AMIs.

Known False Positives

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

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
25.0 50 50 tbd

: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

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