Pcp: exposure of the redis server backend allows remote command execution via pmproxy

A flaw was found in PCP. The default pmproxy configuration exposes the Redis server backend to the local network, allowing remote command execution with the privileges of the Redis user. This issue can only be exploited when pmproxy is running. By default, pmproxy is not running and needs to be started manually. The pmproxy service is usually started from the 'Metrics settings' page of the Cockpit web interface. This flaw affects PCP versions 4.3.4 and newer.