GCP Audit Logs - Storage Bucket Made Public

GCPAuditLogs
| where ServiceName == "storage.googleapis.com"
| where MethodName == "storage.setIamPermissions"
| where GCPResourceType == "gcs_bucket"
| extend 
    ServiceDataJson = parse_json(ServiceData),
    RequestMetadataJson = parse_json(RequestMetadata),
    AuthInfoJson = parse_json(AuthenticationInfo),
    AuthzInfoJson = parse_json(AuthorizationInfo)
| extend PolicyDelta = ServiceDataJson.policyDelta.bindingDeltas
| mv-expand PolicyDelta
| extend 
    Action = tostring(PolicyDelta.action),
    Member = tostring(PolicyDelta.member),
    Role = tostring(PolicyDelta.role)
| where Action == "ADD"
| where Member in~ ("allUsers", "allAuthenticatedUsers")
| extend 
    BucketName = extract(@"buckets/([^/]+)", 1, GCPResourceName),
    CallerIpAddress = tostring(RequestMetadataJson.callerIp),
    UserAgent = tostring(RequestMetadataJson.callerSuppliedUserAgent),
    AuthEmail = tostring(AuthInfoJson.principalEmail),
    Permission = tostring(AuthzInfoJson[0].permission),
    PermissionGranted = tostring(AuthzInfoJson[0].granted)
| extend 
    PublicAccessType = case(
        Member =~ "allUsers", "Public to Everyone",
        Member =~ "allAuthenticatedUsers", "Public to All Authenticated Users",
        "Unknown"),
    AccountName = tostring(split(PrincipalEmail, "@")[0]), 
    AccountUPNSuffix = tostring(split(PrincipalEmail, "@")[1])
| project TimeGenerated,
          PrincipalEmail,
          AuthEmail,
          ProjectId,
          BucketName,
          ResourceName = GCPResourceName,
          PublicAccessType,
          Member,
          Role,
          CallerIpAddress,
          UserAgent,
          MethodName,
          ServiceName,
          Severity,
          Permission,
          PermissionGranted,
          LogName,
          InsertId,
          AccountName,
          AccountUPNSuffix

name: GCP Audit Logs - Storage Bucket Made Public
relevantTechniques:
- T1530
- T1078.004
- T1567.002
id: 3a8d7f9e-4b2c-4e5d-8c6b-9f1a3d5e8c7b
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Google Cloud Platform Audit Logs/Analytic Rules/GCPStorageBucketMadePublic.yaml
requiredDataConnectors:
- dataTypes:
  - GCPAuditLogs
  connectorId: GCPAuditLogsDefinition
version: 1.0.0
severity: High
triggerThreshold: 0
tags:
- GCP
- Storage
- Data Exposure
- Cloud Security
queryPeriod: 1h
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: PrincipalEmail
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: CallerIpAddress
  entityType: IP
- fieldMappings:
  - identifier: Name
    columnName: ProjectId
  - identifier: InstanceName
    columnName: ResourceName
  entityType: CloudApplication
kind: Scheduled
alertDetailsOverride:
  alertDisplayNameFormat: GCP Storage Bucket {{BucketName}} Made Public by {{PrincipalEmail}}
  alertDescriptionFormat: |-
    User {{PrincipalEmail}} made storage bucket {{BucketName}} publicly accessible in project {{ProjectId}}.
    This may expose sensitive data to unauthorized access. Investigate immediately to determine if this action was authorized and assess potential data exposure.
    Review bucket contents and access logs for any unauthorized access attempts.    
queryFrequency: 1h
status: Available
query: |
  GCPAuditLogs
  | where ServiceName == "storage.googleapis.com"
  | where MethodName == "storage.setIamPermissions"
  | where GCPResourceType == "gcs_bucket"
  | extend 
      ServiceDataJson = parse_json(ServiceData),
      RequestMetadataJson = parse_json(RequestMetadata),
      AuthInfoJson = parse_json(AuthenticationInfo),
      AuthzInfoJson = parse_json(AuthorizationInfo)
  | extend PolicyDelta = ServiceDataJson.policyDelta.bindingDeltas
  | mv-expand PolicyDelta
  | extend 
      Action = tostring(PolicyDelta.action),
      Member = tostring(PolicyDelta.member),
      Role = tostring(PolicyDelta.role)
  | where Action == "ADD"
  | where Member in~ ("allUsers", "allAuthenticatedUsers")
  | extend 
      BucketName = extract(@"buckets/([^/]+)", 1, GCPResourceName),
      CallerIpAddress = tostring(RequestMetadataJson.callerIp),
      UserAgent = tostring(RequestMetadataJson.callerSuppliedUserAgent),
      AuthEmail = tostring(AuthInfoJson.principalEmail),
      Permission = tostring(AuthzInfoJson[0].permission),
      PermissionGranted = tostring(AuthzInfoJson[0].granted)
  | extend 
      PublicAccessType = case(
          Member =~ "allUsers", "Public to Everyone",
          Member =~ "allAuthenticatedUsers", "Public to All Authenticated Users",
          "Unknown"),
      AccountName = tostring(split(PrincipalEmail, "@")[0]), 
      AccountUPNSuffix = tostring(split(PrincipalEmail, "@")[1])
  | project TimeGenerated,
            PrincipalEmail,
            AuthEmail,
            ProjectId,
            BucketName,
            ResourceName = GCPResourceName,
            PublicAccessType,
            Member,
            Role,
            CallerIpAddress,
            UserAgent,
            MethodName,
            ServiceName,
            Severity,
            Permission,
            PermissionGranted,
            LogName,
            InsertId,
            AccountName,
            AccountUPNSuffix  
tactics:
- Collection
- InitialAccess
- Exfiltration
customDetails:
  RoleGranted: Role
  UserAgent: UserAgent
  Permission: Permission
  ProjectId: ProjectId
  ResourceName: ResourceName
  PublicAccessType: PublicAccessType
  BucketName: BucketName
description: |
  'Detects when a Google Cloud Storage bucket is made publicly accessible by granting permissions to allUsers or allAuthenticatedUsers.
  Making buckets public can expose sensitive data to unauthorized access and may indicate a misconfiguration or malicious activity.
  Adversaries may make buckets public to exfiltrate data or as part of a data exposure attack.
  This rule monitors setIamPermissions operations that add public access roles to storage buckets.'  
triggerOperator: gt