GCP Access Policy Deleted

Status: test
Severity: medium
Log source: product gcp, service gcp.audit
Author: Bryan Lim
Source: github.com/SigmaHQ/sigma

Detects when an access policy that is applied to a GCP cloud resource is deleted. An adversary would be able to remove access policies to gain access to a GCP cloud resource.

Known false positives

Legitimate administrative activities

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation
Privilege Escalation	`T1098` Account Manipulation

Telemetry coverage

Platform	Record / event type
GCP	any: accesscontextmanager.googleapis.com (any method)

Rule body

title: GCP Access Policy Deleted
id: 32438676-1dba-4ac7-bf69-b86cba995e05
status: test
description: |
    Detects when an access policy that is applied to a GCP cloud resource is deleted.
    An adversary would be able to remove access policies to gain access to a GCP cloud resource.
references:
    - https://cloud.google.com/access-context-manager/docs/audit-logging
    - https://cloud.google.com/logging/docs/audit/understanding-audit-logs
    - https://cloud.google.com/logging/docs/reference/audit/auditlog/rest/Shared.Types/AuditLog
author: Bryan Lim
date: 2024-01-12
tags:
    - attack.persistence
    - attack.privilege-escalation
    - attack.t1098
logsource:
    product: gcp
    service: gcp.audit
detection:
    selection:
        data.protoPayload.authorizationInfo.permission:
            - 'accesscontextmanager.accessPolicies.delete'
            - 'accesscontextmanager.accessPolicies.accessLevels.delete'
            - 'accesscontextmanager.accessPolicies.accessZones.delete'
            - 'accesscontextmanager.accessPolicies.authorizedOrgsDescs.delete'
        data.protoPayload.authorizationInfo.granted: 'true'
        data.protoPayload.serviceName: 'accesscontextmanager.googleapis.com'
    condition: selection
falsepositives:
    - Legitimate administrative activities
level: medium

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    data.protoPayload.authorizationInfo.permission:
        - 'accesscontextmanager.accessPolicies.delete'
        - 'accesscontextmanager.accessPolicies.accessLevels.delete'
        - 'accesscontextmanager.accessPolicies.accessZones.delete'
        - 'accesscontextmanager.accessPolicies.authorizedOrgsDescs.delete'
    data.protoPayload.authorizationInfo.granted: 'true'
    data.protoPayload.serviceName: 'accesscontextmanager.googleapis.com'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`data.protoPayload.authorizationInfo.granted`	eq	`true`	`field:"gcp::authorization_granted" kind:eq value:"true"`
`data.protoPayload.authorizationInfo.permission`	eq	`accesscontextmanager.accessPolicies.accessLevels.delete` `accesscontextmanager.accessPolicies.accessZones.delete` `accesscontextmanager.accessPolicies.authorizedOrgsDescs.delete` `accesscontextmanager.accessPolicies.delete`	`field:"gcp::authorization_permission" kind:eq`
`data.protoPayload.serviceName`	eq	`accesscontextmanager.googleapis.com`	`field:"gcp::service_name" kind:eq value:"accesscontextmanager.googleapis.com"`