Exposure of Sensitive Information to an Unauthorized Actor

Summary

The package capsule-proxy is a reverse proxy for Capsule kubernetes multi-tenancy framework. A bug in the "RoleBinding" reflector used by capsule-proxy gives "ServiceAccount" tenant owners the right to list Namespaces of other tenants backed by the same owner kind and name. For example, consider two tenants "solar" and "wind". Tenant "solar", owned by a "ServiceAccount" named "tenant-owner" in the Namespace "solar". Tenant "wind", owned by a "ServiceAccount" named "tenant-owner" in the Namespace "wind". The tenant owner "solar" would be able to list the namespaces of the Tenant "wind" and vice-versa, although this is not correct. The bug introduces an exfiltration vulnerability since it allows the listing of Namespace resources of other Tenants, although just in some specific conditions: 1. "capsule-proxy" runs with the "--disable-caching=false" (default value: "false") and 2. Tenant owners are "ServiceAccount", with the same resource name, but in different Namespaces. This vulnerability doesn't allow any privilege escalation on the outer tenant Namespace-scoped resources, since the Kubernetes RBAC is enforcing this. Users are advised to upgrade. There are no known workarounds for this vulnerability. This vulnerability affects github.com/clastix/capsule-proxy package versions prior to 0.4.5.