GCP IAM - Publicly exposed storage bucket

Status: available
Severity: medium
Time window: 1h
Source: github.com/Azure/Azure-Sentinel

Detects possible misconfiguration for bucket policy making it publicly available.

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	`T1069` Permission Groups Discovery

Telemetry coverage

Platform	Record / event type
GCP	google.iam.IAMPolicy.SetIamPolicy: Set IAM policy (IAMPolicy service)

Rule body

id: 4a433846-4b05-4a27-99d7-92093feded79
name: GCP IAM - Publicly exposed storage bucket
description: |
  'Detects possible misconfiguration for bucket policy making it publicly available.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: GCPIAMDataConnector
    dataTypes:
      - GCP_IAM
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Discovery
relevantTechniques:
  - T1069
query: |
  GCP_IAM
  | where PayloadMethodname =~ 'google.iam.v1.IAMPolicy.SetIamPolicy'
  | where ResourceType has 'bucket'
  | extend members = parse_json(todynamic(PayloadRequestPolicyBindings))[0]['members']
  | extend action = parse_json(todynamic(PayloadRequestPolicyBindings))[0]['action']
  | where members in~ ('allUsers', 'allAuthenticatedUsers')
  | where action =~ 'ADD'
  | extend AccountName = tostring(split(PayloadAuthenticationinfoPrincipalemail, "@")[0]), AccountUPNSuffix = tostring(split(PayloadAuthenticationinfoPrincipalemail, "@")[1])
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: PayloadAuthenticationinfoPrincipalemail
      - identifier: Name
        columnName: AccountName
      - identifier: UPNSuffix
        columnName: AccountUPNSuffix
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
version: 1.0.1
kind: Scheduled

Stages and Predicates

Stage 1: `source`

GCP_IAM

Stage 2: `where`

| where PayloadMethodname =~ 'google.iam.v1.IAMPolicy.SetIamPolicy'

Stage 3: `where`

| where ResourceType has 'bucket'

Stage 4: `extend`

| extend members = parse_json(todynamic(PayloadRequestPolicyBindings))[0]['members']

Stage 5: `extend`

| extend action = parse_json(todynamic(PayloadRequestPolicyBindings))[0]['action']

Stage 6: `where`

| where members in~ ('allUsers', 'allAuthenticatedUsers')

Stage 7: `where`

| where action =~ 'ADD'

Stage 8: `extend`

| extend AccountName = tostring(split(PayloadAuthenticationinfoPrincipalemail, "@")[0]), AccountUPNSuffix = tostring(split(PayloadAuthenticationinfoPrincipalemail, "@")[1])

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`PayloadMethodname`	eq	`google.iam.v1.IAMPolicy.SetIamPolicy`	`field:"gcp::method_name" kind:eq value:"google.iam.v1.IAMPolicy.SetIamPolicy"`
`ResourceType`	match	`bucket` transforms: `term`	`field:"ResourceType" kind:match value:"bucket"`
`action`	eq	`ADD`	`field:"action" kind:eq value:"ADD"`
`members`	in	`allAuthenticatedUsers` `allUsers`	`field:"members" kind:in`

Output fields

These fields are emitted when the rule matches.

Field	Source
`members`	`extend`
`action`	`extend`
`AccountName`	`extend`
`AccountUPNSuffix`	`extend`

GCP IAM - Publicly exposed storage bucket

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: extend

Stage 5: extend

Stage 6: where

Stage 7: where

Stage 8: extend

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `extend`

Stage 5: `extend`

Stage 6: `where`

Stage 7: `where`

Stage 8: `extend`