A control plane (CP) proxy 245 can be provisioned in the cloud provider network 203 to represent particular host(s) in an edge location. CP proxies 245 are intermediaries between the control plane 218 in the cloud provider network 203 and control plane targets in the control plane 236 of provider substrate extension 224. That is, CP proxies 245 provide infrastructure for tunneling management API traffic destined for provider substrate extension servers out of the region substrate and to the provider substrate extension 224. For example, a virtualized computing service of the cloud provider network 203 can issue a command to a VMM of a server of a provider substrate extension 224 to launch a compute instance. A CP proxy 245 maintains a tunnel (e.g., a VPN) to a local network manager 242 of the provider substrate extension 224. The software implemented within the CP proxies 245 ensures that only well-formed API traffic leaves from and returns to the substrate. CP proxies 245 provide a mechanism to expose remote servers on the cloud provider substrate while still protecting substrate security materials (e.g., encryption keys, security tokens) from leaving the cloud provider network 203. The one-way control plane traffic tunnel imposed by the CP proxies 245 also prevents any (potentially compromised) devices from making calls back to the substrate. CP proxies 245 may be instantiated one-for-one with servers at a provider substrate extension 224 or may be able to manage control plane traffic for multiple servers in the same provider substrate extension.