CVE-2026-88810: Privilege escalation in downstream clusters via GlobalRole inheritedNamespacedRules

A privilege escalation issue was discovered in Rancher Manager's role-based access control. The inheritedNamespacedRules field of a GlobalRole propagates permissions into named namespaces of every downstream cluster managed by the Rancher instance, but it was not subject to the privilege-escalation validation applied to the other permission-carrying fields of a GlobalRole. As a result, a non-administrative user could be granted, through a global role  binding, permissions in downstream clusters that exceed the permissions that user already holds. This affected SUSE Rancher 2.15.2 only, and SUSE Rancher Webhook 0.11.0 up to 0.11.4, and 0.12.0 up to 0.12.1.