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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
  • Exploitation
NIST
  • ID.AM
CIS20
  • CIS 1
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:

Note that 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 field

  • _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

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