Ghostunnel is a simple SSL/TLS proxy with mutual authentication support for securing non-TLS backend applications.
Ghostunnel supports two modes, client mode and server mode. Ghostunnel in server mode runs in front of a backend server and accepts TLS-secured connections, which are then proxied to the (insecure) backend. A backend can be a TCP domain/port or a UNIX domain socket. Ghostunnel in client mode accepts (insecure) connections through a TCP or UNIX domain socket and proxies them to a TLS-secured service. In other words, ghostunnel is a replacement for stunnel.
Supported platforms: Ghostunnel is developed primarily for Linux on x86-64 platforms, although it should run on any UNIX system that exposes SO_REUSEPORT, including Darwin (macOS), FreeBSD, OpenBSD and NetBSD. We recommend running on x86-64 only, as Go (as of Go 1.7) doesn't have constant-time elliptic curve implementations for any other architectures.
ghostunnel server --help and
ghostunnel client --help.
Authentication/access control: Ghostunnel enforces mutual authentication by always requiring a valid client certificate. We also support access control via checks on the subject (or subject alternative names) 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. Once successful, the reloaded certificate will be used for new
connections going forward.
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.
Emphasis on security: We have put some thought into making ghostunnel
secure by default. In server mode, the target backend must live on localhost
or be a UNIX socket (unless
--unsafe-target is specified). In a similar way,
in client mode the listening socket must live on localhost or be a UNIX socket
--unsafe-listen is specified). Ghostunnel negotiates TLSv1.2
and uses safe ciphers.
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).
Note that by default ghostunnel logs to stderr and runs in the foreground. You
--syslog to log to syslog. For daemonization, we recommend using
a utility such as daemonize. For an
example on how to use ghostunnel in a Docker container, see the
To install ghostunnel, simply use:
go get -u github.com/square/ghostunnel
Note that ghostunnel requires Go 1.7 or later to build.
If you want to pull a specific version, check the releases tab in Github.
To run tests:
# Run unit & integration tests make test # Open coverage information in browser go tool cover -html coverage-merged.out
For more information on how to contribute, please see the CONTRIBUTING file.
This is an example for how to launch ghostunnel in server mode, listening for
incoming TLS connections on
localhost:8443 and forwarding them to
To set allowed clients, you must specify at least one of
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
Start a backend server:
nc -l localhost 8080
Start a ghostunnel in server mode to proxy connections:
ghostunnel server \ --listen localhost:8443 \ --target localhost:8080 \ --keystore test-keys/server.p12 \ --cacert test-keys/root.crt \ --allow-cn client
Verify that clients can connect with their client certificate:
openssl s_client \ -connect localhost:8443 \ -cert test-keys/client.crt \ -key test-keys/client.key \ -CAfile test-keys/root.crt
Now we have a TLS proxy running for our backend service. We terminate TLS in ghostunnel and forward the connections to the insecure backend.
This is an example for how to launch ghostunnel in client mode, listening on
localhost:8080 and proxying requests to a TLS server on
Start a backend TLS server:
openssl s_server \ -accept 8443 \ -cert test-keys/server.crt \ -key test-keys/server.key \ -CAfile test-keys/root.crt
Start a ghostunnel with a client certificate to forward connections:
ghostunnel client \ --listen localhost:8080 \ --target localhost:8443 \ --keystore test-keys/client.p12 \ --cacert test-keys/root.crt
Verify that we can connect to
nc -v localhost 8080
Now we have a TLS proxy running for our client. We take the insecure local connection, wrap them in TLS, and forward them to the secure backend.
Full tunnel (client plus server)
We can combine the above two examples to get a full tunnel. Note that you can start the ghostunnels in either order.
Start netcat on port
nc -l localhost 8001
Start the ghostunnel server:
ghostunnel server \ --listen localhost:8002 \ --target localhost:8001 \ --keystore test-keys/server.p12 \ --cacert test-keys/root.crt \ --allow-cn client
Start the ghostunnel client:
ghostunnel client \ --listen localhost:8003 \ --target localhost:8002 \ --keystore test-keys/client.p12 \ --cacert test-keys/root.crt
Verify that we can connect to
nc -v localhost 8003
Now we have a full tunnel running. We take insecure client connections, forward them to the server side of the tunnel via TLS, and finally terminate and proxy the connection to the insecure backend.