Detection: AWS Detect Users with KMS keys performing encryption S3

Updated Date: 2024-05-18 ID: 884a5f59-eec7-4f4a-948b-dbde18225fdc Author: Rod Soto, Patrick Bareiss Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies users with KMS keys performing encryption operations on S3 buckets. It leverages AWS CloudTrail logs to detect the CopyObject event where server-side encryption with AWS KMS is specified. This activity is significant as it may indicate unauthorized or suspicious encryption of data, potentially masking exfiltration or tampering efforts. If confirmed malicious, an attacker could be encrypting sensitive data to evade detection or preparing it for exfiltration, posing a significant risk to data integrity and confidentiality.

Search

1`cloudtrail` eventName=CopyObject requestParameters.x-amz-server-side-encryption="aws:kms" 
2| rename requestParameters.bucketName AS bucketName, requestParameters.x-amz-copy-source AS src_file, requestParameters.key AS dest_file 
3| stats count min(_time) as firstTime max(_time) as lastTime values(bucketName) as bucketName values(src_file) AS src_file values(dest_file) AS dest_file values(userAgent) AS userAgent values(region) AS region values(src) AS src by user 
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)` 
6|`aws_detect_users_with_kms_keys_performing_encryption_s3_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
AWS CloudTrail	AWS	`'aws:cloudtrail'`	`'aws_cloudtrail'`	N/A

Macros Used

Name	Value
cloudtrail	`sourcetype=aws:cloudtrail`
aws_detect_users_with_kms_keys_performing_encryption_s3_filter	`search *`

aws_detect_users_with_kms_keys_performing_encryption_s3_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
T1486	Data Encrypted for Impact	Impact

KillChainPhase.ACTIONS_ON_OBJECTIVES

NistCategory.DE_AE

Cis18Value.CIS_10

APT38

APT41

Akira

FIN7

FIN8

Indrik Spider

Magic Hound

Sandworm Team

Scattered Spider

TA505

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

There maybe buckets provisioned with S3 encryption

Associated Analytic Story

Ransomware Cloud

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
User $user$ with KMS keys is performing encryption, against S3 buckets on these files $dest_file$	15	30	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.

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