AWS Exfiltration via Anomalous GetObject API Activity

name: AWS Exfiltration via Anomalous GetObject API Activity
id: e4384bbf-5835-4831-8d85-694de6ad2cc6
version: 8
date: '2026-03-10'
author: Bhavin Patel, Splunk
status: production
type: Anomaly
data_source:
    - AWS CloudTrail GetObject
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: |-
    `cloudtrail` eventName=GetObject
      | bin _time span=10m
      | rename user_name as user
      | stats count values(requestParameters.bucketName) as bucketName
        BY signature dest user
           user_agent src vendor_account
           vendor_region vendor_product
      | anomalydetection "count" "user" action=annotate
      | search probable_cause=*
      | `aws_exfiltration_via_anomalous_getobject_api_activity_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: 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.
references:
    - https://labs.nettitude.com/blog/how-to-exfiltrate-aws-ec2-data/
    - https://help.splunk.com/en/splunk-enterprise/search/spl-search-reference/9.4/search-commands/anomalydetection
    - https://www.vectra.ai/blogpost/abusing-the-replicator-silently-exfiltrating-data-with-the-aws-s3-replication-service
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: Anomalous S3 activities detected by user $user$ from $src$
    risk_objects:
        - field: user
          type: user
          score: 20
    threat_objects:
        - field: src
          type: ip_address
tags:
    analytic_story:
        - Data Exfiltration
    asset_type: AWS Account
    mitre_attack_id:
        - T1119
    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/T1530/aws_exfil_high_no_getobject/cloudtrail.json
          sourcetype: aws:cloudtrail
          source: aws_cloudtrail