AWS Detect Users with KMS keys performing encryption S3

name: AWS Detect Users with KMS keys performing encryption S3
id: 884a5f59-eec7-4f4a-948b-dbde18225fdc
version: 9
date: '2026-03-10'
author: Rod Soto, Patrick Bareiss Splunk
status: production
type: Anomaly
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.
data_source:
    - AWS CloudTrail
search: |-
    `cloudtrail` eventName=CopyObject requestParameters.x-amz-server-side-encryption="aws:kms"
      | rename requestParameters.bucketName AS bucketName, requestParameters.x-amz-copy-source AS src_file, requestParameters.key AS dest_file
      | rename user_name as user
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY signature dest user
           user_agent src vendor_account
           vendor_region vendor_product bucketName
           src_file dest_file
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `aws_detect_users_with_kms_keys_performing_encryption_s3_filter`
how_to_implement: 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
references:
    - https://rhinosecuritylabs.com/aws/s3-ransomware-part-1-attack-vector/
    - https://github.com/d1vious/git-wild-hunt
    - https://www.youtube.com/watch?v=PgzNib37g0M
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: User $user$ with KMS keys is performing encryption, against S3 buckets on these files $dest_file$
    risk_objects:
        - field: user
          type: user
          score: 20
    threat_objects: []
tags:
    analytic_story:
        - Ransomware Cloud
    asset_type: S3 Bucket
    mitre_attack_id:
        - T1486
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1486/s3_file_encryption/aws_cloudtrail_events.json
          sourcetype: aws:cloudtrail
          source: aws_cloudtrail