Detection: EC2 Instance Started With Previously Unseen User

DEPRECATED DETECTION

This detection has been marked as deprecated by the Splunk Threat Research team. This means that it will no longer be maintained or supported. If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2024-08-16 ID: 22773e84-bac0-4595-b086-20d3f735b4f1 Author: David Dorsey, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This search looks for EC2 instances being created by users who have not created them before. This search is deprecated and have been translated to use the latest Change Datamodel.

 1`cloudtrail` eventName=RunInstances [search `cloudtrail` eventName=RunInstances errorCode=success 
 2| stats earliest(_time) as firstTime latest(_time) as lastTime by userIdentity.arn 
 3| rename userIdentity.arn as arn 
 4| inputlookup append=t previously_seen_ec2_launches_by_user.csv 
 5| stats min(firstTime) as firstTime, max(lastTime) as lastTime by arn 
 6| outputlookup previously_seen_ec2_launches_by_user.csv 
 7| eval newUser=if(firstTime >= relative_time(now(), "-70m@m"), 1, 0) 
 8| where newUser=1 
 9| `security_content_ctime(firstTime)` 
10| `security_content_ctime(lastTime)` 
11| rename arn as userIdentity.arn 
12| table userIdentity.arn] 
13| rename requestParameters.instanceType as instanceType, responseElements.instancesSet.items{}.instanceId as dest, userIdentity.arn as user 
14| table _time, user, dest, instanceType 
15| `ec2_instance_started_with_previously_unseen_user_filter`

Data Source

Name Platform Sourcetype Source Supported App
N/A N/A N/A N/A N/A

Macros Used

Name Value
cloudtrail sourcetype=aws:cloudtrail
ec2_instance_started_with_previously_unseen_user_filter search *
ec2_instance_started_with_previously_unseen_user_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
T1078.004 Cloud Accounts Defense Evasion
KillChainPhase.DELIVERY
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_AE
Cis18Value.CIS_10
APT28
APT29
APT33
APT5
Ke3chang
LAPSUS$

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 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 Launches By User" support search once to create a history of previously seen ARNs.

Known False Positives

It's possible that a user will start to create EC2 instances when they haven't before for any number of reasons. Verify with the user that is launching instances that this is the intended behavior.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
tbd 25 50 50
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 ❌ Failing N/A N/A N/A
Integration ❌ Failing N/A N/A N/A

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