I use kubectl v1.3.5 and v1.2.0 in the k8s cluster. If I proxy to the cluster with

$ kubectl proxy --port=8888

I get the following error when trying to execute a command in a container:

$ kubectl --server=http://localhost:8888 exec -ti test-pod bash
error: unable to upgrade connection: <h3>Unauthorized</h3>

Other commands like get pods work fine. The server is contacted by the poxy with https://kubmaster.****.de:443 and a bearer token.