:warning: THIS IS A EXPERIMENTAL DETECTION

This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

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Description

The following analytic identifies the creation of new open/public GCP Storage buckets. It leverages GCP PubSub events, specifically monitoring for the storage.setIamPermissions method and checks if the allUsers member is added. This activity is significant because open storage buckets can expose sensitive data to the public, posing a severe security risk. If confirmed malicious, an attacker could access, modify, or delete data within the bucket, leading to data breaches and potential compliance violations.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Email
  • Last Updated: 2024-05-17
  • Author: Shannon Davis, Splunk
  • ID: f6ea3466-d6bb-11ea-87d0-0242ac130003

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1530 Data from Cloud Storage Collection
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 13
CVE 


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`google_gcp_pubsub_message` data.resource.type=gcs_bucket data.protoPayload.methodName=storage.setIamPermissions 
| spath output=action path=data.protoPayload.serviceData.policyDelta.bindingDeltas{}.action 
| spath output=user path=data.protoPayload.authenticationInfo.principalEmail 
| spath output=location path=data.protoPayload.resourceLocation.currentLocations{} 
| spath output=src path=data.protoPayload.requestMetadata.callerIp 
| spath output=bucketName path=data.protoPayload.resourceName 
| spath output=role path=data.protoPayload.serviceData.policyDelta.bindingDeltas{}.role 
| spath output=member path=data.protoPayload.serviceData.policyDelta.bindingDeltas{}.member 
| search (member=allUsers AND action=ADD) 
| table  _time, bucketName, src, user, location, action, role, member 
| search `detect_new_open_gcp_storage_buckets_filter`

Macros

The SPL above uses the following Macros:

:information_source: detect_new_open_gcp_storage_buckets_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • data.resource.type
  • data.protoPayload.methodName
  • data.protoPayload.serviceData.policyDelta.bindingDeltas{}.action
  • data.protoPayload.authenticationInfo.principalEmail
  • data.protoPayload.resourceLocation.currentLocations{}
  • data.protoPayload.requestMetadata.callerIp
  • data.protoPayload.resourceName
  • data.protoPayload.serviceData.policyDelta.bindingDeltas{}.role
  • data.protoPayload.serviceData.policyDelta.bindingDeltas{}.member

How To Implement

This search relies on the Splunk Add-on for Google Cloud Platform, setting up a Cloud Pub/Sub input, along with the relevant GCP PubSub topics and logging sink to capture GCP Storage Bucket events (https://cloud.google.com/logging/docs/routing/overview).

Known False Positives

While this search has no known false positives, it is possible that a GCP admin has legitimately created a public bucket for a specific purpose. That said, GCP strongly advises against granting full control to the "allUsers" group.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
25.0 50 50 tbd

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

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

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