Ghostunnel

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Ghostunnel is a simple SSL/TLS proxy with mutual authentication support for securing non-TLS backend applications. Ghostunnel runs in front of a backend service and accepts TLS-secured connections, which are then proxied to the (insecure) backend. A backend can be a TCP domain/port or a UNIX socket path. In other words, ghostunnel is a very limited replacement for stunnel in server mode.

Features

Authentication/access control: Ghostunnel enforces mutual authentication by always requiring a valid client certificate. We also support access control via checks of the CN/OU fields on the subject of a client certificate. This is useful for restricting access to services that don't have native access control.

Certificate hotswapping: Ghostunnel can reload certificates at runtime without dropping existing connections. To trigger a reload, simply send SIGUSR1 to the process. This will cause ghostunnel to reload the keystore files and open a new listening socket (via SO_REUSEPORT). Once successful, the old listening socket will be closed.

Automatic reloading: Ghostunnel can be configured to automatically reload certificates. You can specify an interval with the --timed-reload flag. If the timed reload flag is enabled, ghostunnel will reload the files periodically and check for changes. If a change is detected, it will attempt to reload the listener with the new certificates/private key.

Getting started

To get started and play around with the implementation, you will need to generate some test certificates. If you want to bootstrap a full PKI, one good way to get started is to use a package like square/certstrap. If you only need some test certificates for playing around with the tunnel, you can find some pre-generated ones in the test-keys directory (alongside instructions on how to generate new ones with OpenSSL).

Build

We use glide for vendoring. Use go get github.com/Masterminds/glide or brew install glide to install it.

Then, build ghostunnel and run tests:

make build
make test

If you want to update vendored dependencies:

make update-depends

Launch

This is a short example for how to launch ghostunnel listening for incoming connections on localhost:8443 and forwarding them to localhost:8080. We assume that server.p12 is a PKCS12 keystore with the certificate and private key for the server, and that root.crt contains your trusted root certificate(s).

To set allowed clients, you must specify at least one of --allow-all, --allow-cn, --allow-ou, --allow-dns-san, or --allow-ip-san. It's possible to use these together or to specify them repeatedly to allow multiple clients. In this example, we assume that the CN of the client cert we want to accept connections from is client.

Start a ghostunnel with a server certificate:

ghostunnel \
    --listen 127.0.0.1:8443 \
    --target 127.0.0.1:8080 \
    --keystore test-keys/server.p12 \
    --cacert test-keys/root.crt \
    --allow-cn client

Verify that the client(s) can connect with their client certificate:

openssl s_client \
    -connect 127.0.0.1:8443 \
    -cert test-keys/client.crt \
    -key test-keys/client.key \
    -CAfile test-keys/root.crt

If openssl s_client can connect, then the tunnel should be working as intended! Be sure to check the logs to see incoming connections and other information. Note that by default ghostunnel logs to stderr and runs in the foreground (set --syslog to log to syslog). For deamonization, we recommend using a utility such as daemonize. For an example on how to use ghostunnel in a Docker container, see the docker subdirectory.