Detection: AWS Exfiltration via Anomalous GetObject API Activity

Updated Date: 2024-09-30 ID: e4384bbf-5835-4831-8d85-694de6ad2cc6 Author: Bhavin Patel, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies anomalous GetObject API activity in AWS, indicating potential data exfiltration attempts. It leverages AWS CloudTrail logs and uses the anomalydetection command to detect unusual patterns in the frequency of GetObject API calls by analyzing fields such as "count," "user_type," and "user_arn" within a 10-minute window. This activity is significant as it may indicate unauthorized data access or exfiltration from S3 buckets. If confirmed malicious, attackers could exfiltrate sensitive data, leading to data breaches and compliance violations.

Search

1`cloudtrail` eventName=GetObject 
2| bin _time span=10m 
3|  stats count values(requestParameters.bucketName) as bucketName by _time src_ip aws_account_id user_type user_arn userIdentity.principalId 
4| anomalydetection "count" "user_type" "user_arn" action=annotate 
5| search probable_cause=* 
6|`aws_exfiltration_via_anomalous_getobject_api_activity_filter`

Data Source

Name	Platform	Sourcetype	Source
AWS CloudTrail GetObject	AWS	`'aws:cloudtrail'`	`'aws_cloudtrail'`

Macros Used

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

aws_exfiltration_via_anomalous_getobject_api_activity_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
T1119	Automated Collection	Collection

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_10

APT1

APT28

Agrius

Chimera

Confucius

Ember Bear

FIN5

FIN6

Gamaredon Group

Ke3chang

Mustang Panda

OilRig

Patchwork

RedCurl

Sidewinder

Threat Group-3390

Tropic Trooper

Winter Vivern

menuPass

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 splunk AWS add on and Splunk App for AWS. This search works with AWS CloudTrail logs.

Known False Positives

It is possible that a user downloaded these files to use them locally and there are AWS services in configured that perform these activities for a legitimate reason. Filter is needed.

Associated Analytic Story

Data Exfiltration

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Anomalous S3 activities detected by user $user_arn$ from $src_ip$	64	80	80

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

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`
Integration	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`

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