Cluster identity takeover in Fleet cluster registration allows access to another cluster's Fleet namespace

A security vulnerability was discovered in SUSE Rancher Fleet's cluster registration flow, in Fleet versions before 0.12, 0.13.0 up to 0.13.17, 0.14.0 up to 0.14.12, 0.15.0 up t o 0.15.17 and 0.16.0 up to 0.16.3. The cluster identity claimed by a registration request was accepted without being bound to the registration token that the request was made with. As a result, a registration request could be associated with a managed cluster that was originally registered with a different registration token.