Detection: AWS Detect Users with KMS keys performing encryption S3

Updated Date: 2024-09-30 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.

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
AWS CloudTrail AWS icon AWS 'aws:cloudtrail' 'aws_cloudtrail'

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
INC Ransom
Indrik Spider
Magic Hound
Moonstone Sleet
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

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: 4