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

tags:
- GCP
- Storage
- Data Exposure
- Cloud Security
triggerOperator: gt
entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: PrincipalEmail
    identifier: FullName
  - columnName: AccountName
    identifier: Name
  - columnName: AccountUPNSuffix
    identifier: UPNSuffix
- entityType: IP
  fieldMappings:
  - columnName: CallerIpAddress
    identifier: Address
- entityType: CloudApplication
  fieldMappings:
  - columnName: ProjectId
    identifier: Name
  - columnName: ResourceName
    identifier: InstanceName
triggerThreshold: 0
severity: High
alertDetailsOverride:
  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.    
  alertDisplayNameFormat: GCP Storage Bucket {{BucketName}} Made Public by {{PrincipalEmail}}
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
queryPeriod: 1h
version: 1.0.0
queryFrequency: 1h
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.'  
status: Available
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Google Cloud Platform Audit Logs/Analytic Rules/GCPStorageBucketMadePublic.yaml
name: GCP Audit Logs - Storage Bucket Made Public
kind: Scheduled
id: 3a8d7f9e-4b2c-4e5d-8c6b-9f1a3d5e8c7b
relevantTechniques:
- T1530
- T1078.004
- T1567.002
customDetails:
  PublicAccessType: PublicAccessType
  BucketName: BucketName
  RoleGranted: Role
  UserAgent: UserAgent
  ProjectId: ProjectId
  Permission: Permission
  ResourceName: ResourceName
requiredDataConnectors:
- dataTypes:
  - GCPAuditLogs
  connectorId: GCPAuditLogsDefinition