Bypassing GCP Org Policy with Custom Metadata
Channel: Kat
Date: 2021-09-11

Google makes use of custom metadata to authorize access to AI Notebooks and their web UIs.  
Individuals granted access via custom metadata need not have any IAM permissions on the compute instance, on the service account running the Notebook or even be a member of the Organization.  Authorization via custom metadata, bypasses a specific Organization Policy Constraint https://cloud.google.com/resource-manager/docs/organization-policy/restricting-domains which restricts cross-domain resource sharing.
This vulnerability was awarded $1337.00 by the Google VRP Review Panel.

See Blog Post for full details of this vulnerability: https://kattraxler.github.io/