Cross-Cluster Impersonation Confused-Deputy Privilege Escalation

A privilege escalation vulnerability exists in Rancher's impersonation middleware (pkg/auth/requests/impersonate.go). An authenticated Rancher user with the default user
global role can gain full administrative access to the Rancher control
plane and transitively to all downstream clusters it manages.

This issue affects Rancher: from 2.11.0 before 2.11.16, from 2.12.0 before 2.12.12, from 2.13.0 before 2.13.8, and from 2.14.0 before 2.14.2.