Detection: EC2 Instance Modified 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: 2024-10-17 ID: 56f91724-cf3f-4666-84e1-e3712fb41e76 Author: David Dorsey, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

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

Search

 1`cloudtrail` `ec2_modification_api_calls` [search `cloudtrail` `ec2_modification_api_calls` 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_modifications_by_user 
 5| stats min(firstTime) as firstTime, max(lastTime) as lastTime by arn 
 6| outputlookup previously_seen_ec2_modifications_by_user 
 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| spath output=dest responseElements.instancesSet.items{}.instanceId 
14| spath output=user userIdentity.arn 
15| table _time, user, dest 
16| `ec2_instance_modified_with_previously_unseen_user_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name	Value
cloudtrail	`sourcetype=aws:cloudtrail`
ec2_instance_modified_with_previously_unseen_user_filter	`search *`

ec2_instance_modified_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. To add or remove APIs that modify an EC2 instance, edit the macro ec2_modification_api_calls.

Known False Positives

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

Associated Analytic Story

Unusual AWS EC2 Modifications

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: 5