The Velociraptor gRPC API has a VFSGetBuffer endpoint which allows reading files from the datastore. To prevent users from reading sensitive files or accessing other orgs, the requested path is prefix checked against a list of denied prefixes. This prefix check can be bypassed allowing a user to access usually denied files. If the user has read permission in the ROOT org, this allows access to other orgs, in which the user may not have permission.
To exploit this the user must have the "reader" role on the ROOT org.
As documented https://docs.velociraptor.app/docs/deployment/security/#the-root-org , the root org is more privileged than other orgs. You should only give trusted users access to the root org.