AWS S3 Bucket Replicated to Another Account

Identifies when the PutBucketReplication operation is used to replicate S3 objects to a bucket in another AWS account. Adversaries may use bucket replication to exfiltrate sensitive data to an environment they control.

Rule type: eql

Rule indices:

filebeat-*
logs-aws.cloudtrail-*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-6m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

Domain: Cloud
Data Source: AWS
Data Source: Amazon Web Services
Data Source: AWS S3
Resources: Investigation Guide
Use Case: Threat Detection
Tactic: Exfiltration

Version: 1

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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Triage and Analysis

Investigating AWS S3 Bucket Replicated to Another Account

This rule identifies when an S3 bucket is replicated to another AWS account. While sharing bucket replication is a common practice, adversaries may exploit this feature to exfiltrate data by replicating objects to external accounts under their control.

Possible Investigation Steps

Identify the Actor: Review the aws.cloudtrail.user_identity.arn and aws.cloudtrail.user_identity.access_key_id fields to identify who made the change. Verify if this actor typically performs such actions and if they have the necessary permissions.
Review the Sharing Event: Identify the S3 bucket involved and review the event details. Look for PutBucketReplication actions where an Account key-value pair is included signifying replication to an external account.
Request and Response Parameters: Check the aws.cloudtrail.request_parameters and aws.cloudtrail.response_elements fields in the CloudTrail event to identify the role used and account ID where the bucket was replicated.
Verify the Shared Bucket: Check the S3 bucket that was replicated and its contents to determine the sensitivity of the data stored within it.
Validate External Account: Examine the AWS account to which the bucket was replicated. Determine whether this account is known and previously authorized to access such resources.
Contextualize with Recent Changes: Compare this sharing event against recent changes in S3 configurations. Look for any other recent permissions changes or unusual administrative actions.
Correlate with Other Activities: Search for related CloudTrail events before and after this change to see if the same actor or IP address engaged in other potentially suspicious activities.
Interview Relevant Personnel: If the share was initiated by a user, verify the intent and authorization for this action with the person or team responsible for managing DB backups and snapshots.

False Positive Analysis

Legitimate Backup Actions: Confirm if the S3 bucket replication aligns with scheduled backups or legitimate automation tasks.
Consistency Check: Compare the action against historical data of similar actions performed by the user or within the organization. If the action is consistent with past legitimate activities, it might indicate a false alarm.

Response and Remediation

Immediate Review and Reversal: If the change was unauthorized, update the S3 configurations to remove any unauthorized replication rules.
Enhance Monitoring and Alerts: Adjust monitoring systems to alert on similar actions, especially those involving sensitive data or permissions.
Policy Update: Review and possibly update your organization’s policies on S3 bucket/object sharing to tighten control and prevent unauthorized access.
Incident Response: If malicious intent is confirmed, consider it a data breach incident and initiate the incident response protocol. This includes further investigation, containment, and recovery.

Additional Information:

For further guidance on managing and securing S3 buckets in AWS environments, refer to the AWS S3 documentation and AWS best practices for security.

Rule query

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any where event.dataset == "aws.cloudtrail"
   and event.action == "PutBucketReplication"
   and event.outcome == "success"
   and stringContains(aws.cloudtrail.request_parameters, "Account")

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Exfiltration
- ID: TA0010
- Reference URL: https://attack.mitre.org/tactics/TA0010/
Technique:
- Name: Transfer Data to Cloud Account
- ID: T1537
- Reference URL: https://attack.mitre.org/techniques/T1537/

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