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Ghostunnel is a simple 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.
Supported platforms: Ghostunnel is developed primarily for Linux and macOS,
although it should run on any UNIX system that exposes SO_REUSEPORT,
including FreeBSD, OpenBSD and NetBSD. Ghostunnel also supports running on
Windows, though without signal-based certificate reload (use --timed-reload
instead), syslog output, Landlock sandboxing, and socket activation. See the
releases directory for a full changelog.
Authentication & Authorization: Enforces mutual TLS authentication by requiring valid client certificates. Supports fine-grained access control checks on certificate fields (CN, OU, DNS/URI SAN), and declarative authorization policies via Open Policy Agent (OPA).
Certificate Hotswapping: Reload certificates without restarting via SIGHUP/SIGUSR1 or timed reload intervals, enabling use of short-lived certificates.
Flexible Certificate Sources: Load certificates and keys from PEM/PKCS#12 files, ACME (Let's Encrypt), hardware security modules (PKCS#11), macOS Keychain, Windows Certificate Store, or the SPIFFE Workload API.
Secure by Default: Listeners and targets are
restricted to localhost and UNIX sockets unless explicitly overridden with
--unsafe-listen or --unsafe-target, preventing accidental exposure. On
Linux, Landlock sandboxing is enabled by default to limit process privileges.
Metrics & Profiling: Built-in status port with JSON and Prometheus metrics endpoints, plus optional pprof profiling.
Ghostunnel also supports UNIX domain sockets, PROXY protocol v2, systemd/launchd socket activation, and more.
To get started and play around with Ghostunnel you will need X.509 client and server certificates. If you already maintain a PKI, you can use your existing certificates. Otherwise, you can use tools like mkcert or cloudflare/cfssl to build one.
For quick testing and development, you can also generate throwaway test certificates using the built-in generator:
# Generate test certificates and keys
go tool mage test:keys
This will create a test-keys directory with all the necessary certificates and keys
for testing. Note: These are test certificates only and should NOT be used in production.
Ghostunnel is available through GitHub releases and through Docker Hub.
Please note that the official release binaries are best effort, and are usually built directly via Github Actions on the latest available images. If you need compatibility for specific OS versions we recommend building yourself.
Ghostunnel uses the mage build system, a make/rake-like build tool using Go. Mage is available as a Go tool dependency (no separate install needed). You can build Ghostunnel with the commands shown below.
# Compile binary
go tool mage go:build
# Build containers
go tool mage docker:build
You can also run go tool mage -l to view all build targets and add -v to
mage commands to get more verbose output.
Ghostunnel has an extensive suite of integration tests. Our integration test suite requires Python 3.
To run tests:
# Option 1: run unit & integration tests locally
go tool mage test:all
# Option 2: run unit & integration tests in a Docker container
# This also runs PKCS#11 integration tests using SoftHSM in the container
go tool mage test:docker
# Open coverage information in browser
go tool cover -html coverage/all.profile
For more information on how to contribute, please see the CONTRIBUTING file.
To see available commands and flags, run ghostunnel --help. You can get more
information about a command by adding --help to the command, like ghostunnel server --help or ghostunnel client --help. There's also a man page.
By default, Ghostunnel runs in the foreground and logs to stdout. You can set
--syslog to log to syslog instead of stdout. If you want to run Ghostunnel
in the background, we recommend using a service manager.
Ghostunnel accepts certificates in multiple different file formats.
The --keystore flag can take a PKCS#12 keystore or a combined PEM file with the
certificate chain and private key as input (format is auto-detected). The --cert /
--key flags can be used to load a certificate chain and key from separate PEM files
(instead of a combined one).
Ghostunnel also supports loading identities from the macOS keychain or the SPIFFE Workload API and having private keys backed by PKCS#11 modules, see the "Advanced Features" section below for more information.
This is an example for how to launch Ghostunnel in server mode, listening for
incoming TLS connections on localhost:8443 and forwarding them to
localhost:8080. Note that while we use TCP sockets on localhost in this
example, both the listen and target flags can also accept paths to UNIX domain
sockets as their argument.
To set allowed clients, you must specify at least one of --allow-all,
--allow-cn, --allow-ou, --allow-dns, --allow-uri or --allow-policy. All
checks are made against the certificate of the client. Multiple flags are
treated as a logical disjunction (OR), meaning clients can connect as long as
any of the flags matches. See ACCESS-FLAGS for more
information. In this example, we assume that the CN of the client cert we want
to accept connections from is client.
Note: Before running the examples below, make sure you have generated the test
certificates by running go tool mage test:keys (see the Getting Started
section above).
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-keystore.p12 \
--cacert test-keys/cacert.pem \
--allow-cn client
Verify that clients can connect with their client certificate:
openssl s_client \
-connect localhost:8443 \
-cert test-keys/client-combined.pem \
-key test-keys/client-combined.pem \
-CAfile test-keys/cacert.pem
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 localhost:8443.
By default, Ghostunnel in client mode verifies targets based on the hostname. Various access control flags exist to perform additional verification on top of the regular hostname verification. See ACCESS-FLAGS for more information.
Start a backend TLS server:
openssl s_server \
-accept 8443 \
-cert test-keys/server-combined.pem \
-key test-keys/server-combined.pem \
-CAfile test-keys/cacert.pem
Start a Ghostunnel with a client certificate to forward connections:
ghostunnel client \
--listen localhost:8080 \
--target localhost:8443 \
--keystore test-keys/client-combined.pem \
--cacert test-keys/cacert.pem
Verify that we can connect to 8080:
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.
We can combine the above two examples to get a full tunnel. Note that you can start the tunnels in either order.
Start netcat on port 8001:
nc -l localhost 8001
Start the Ghostunnel server:
ghostunnel server \
--listen localhost:8002 \
--target localhost:8001 \
--keystore test-keys/server-combined.pem \
--cacert test-keys/cacert.pem \
--allow-cn client
Start the Ghostunnel client:
ghostunnel client \
--listen localhost:8003 \
--target localhost:8002 \
--keystore test-keys/client-keystore.p12 \
--cacert test-keys/cacert.pem
Verify that we can connect to 8003:
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.
Docker images are published to Docker Hub on each release. Three variants are available:
| Image | Tag |
|---|---|
| Alpine | ghostunnel/ghostunnel:latest, ghostunnel/ghostunnel:v1.x.x |
| Debian | ghostunnel/ghostunnel:latest-debian, ghostunnel/ghostunnel:v1.x.x-debian |
| Distroless | ghostunnel/ghostunnel:latest-distroless, ghostunnel/ghostunnel:v1.x.x-distroless |
The latest tags always point to the most recent release.
Ghostunnel supports different types of access control flags in both client and server modes to enforce authorization checks. Ghostunnel can check various attributes of peer certificates directly, including a SPIFFE ID from a peer using a SPIFFE X.509 SVIDs. In addition to this, Ghostunnel also supports implementing authorization checks via Open Policy Agent (OPA) policies for maximum flexibility. Policies can be reloaded at runtime much like certificates.
See ACCESS-FLAGS for details.
You can silence specific types of log messages using the --quiet=... flag,
such as --quiet=conns or --quiet=handshake-errs. You can pass this flag
repeatedly if you want to silence multiple different kinds of log messages.
Supported values are:
all: silences all log messagesconns: silences log messages about new and closed connections.conn-errs: silences log messages about connection errors encountered (post handshake).handshake-errs: silences log messages about failed handshakes.
In particular we recommend setting --quiet=handshake-errs if you are
running TCP health checks in Kubernetes on the listening port, and you
want to avoid seeing error messages from aborted connections on each health
check.
To trigger a reload, simply send SIGHUP (or SIGUSR1) to the process or set a time-based
reloading interval with the --timed-reload flag. This will cause Ghostunnel
to reload the certificate and private key from the files on disk. Once
successful, the reloaded certificate will be used for new connections going
forward.
Additionally, Ghostunnel uses SO_REUSEPORT to bind the listening socket on
platforms where it is supported (Linux, Apple macOS, FreeBSD, NetBSD and
OpenBSD). This means a new Ghostunnel can be started on the same host/port
before the old one is terminated, to minimize dropped connections (or avoid
them entirely depending on how the OS implements the SO_REUSEPORT feature).
Note that if you are using an HSM/PKCS#11 module, only the certificate will be reloaded. It is assumed that the private key in the HSM remains the same. This means the updated/reissued certificate must match the private key that was loaded from the HSM previously, everything else works the same.
Ghostunnel in server mode supports the ACME protocol for automatically obtaining and renewing a public certificate, assuming it's exposed publicly on tcp/443 and there are valid public DNS FQDN records that resolve to the listening interface IP.
See ACME for details.
Ghostunnel has a notion of "status port", a TCP port (or UNIX socket) that can
be used to expose status and metrics information over HTTPS. The status port
feature can be controlled via the --status flag. Profiling endpoints on the
status port can be enabled with --enable-pprof.
See METRICS for details.
Ghostunnel has support for loading private keys from PKCS#11 modules, which should work with any hardware security module that exposes a PKCS#11 interface, including YubiKeys (via the YKCS11 module).
See HSM-PKCS11 for details, including a step-by-step guide for using Ghostunnel with a YubiKey.
Ghostunnel supports loading certificates from the Windows and macOS keychains. This is useful if you have identities stored in your local keychain that you want to use with Ghostunnel, e.g. if you want your private key(s) to be backed by the Secure Enclave on newer Touch ID MacBooks.
See KEYCHAIN for details.
Ghostunnel has support for maintaining up-to-date, frequently rotated identities and trusted CA certificates from the SPIFFE Workload API.
See SPIFFE-WORKLOAD-API for details.
Ghostunnel supports socket activation via both systemd (on Linux) and launchd
(on macOS). Socket activation is supported for the --listen and --status
flags, and can be used by passing an address of the form systemd:<name> or
launchd:<name>, where <name> should be the name of the socket as defined in
your systemd/launchd configuration.
See SOCKET-ACTIVATION for examples.
Ghostunnel in server mode supports signalling of transport connection information
to the backend using the PROXY protocol
(v2), just pass the --proxy-protocol flag on startup. Use --proxy-protocol-mode
to also include TLS metadata and/or client certificate details. Note that the
backend must support the PROXY protocol and must be configured to use it when
setting this option.
See PROXY-PROTOCOL for details on modes and TLV extensions.
Ghostunnel can use Landlock to limit process privileges
on Linux. Landlock is enabled by default in best-effort mode and can be
disabled using --disable-landlock if necessary (not recommended). When
enabled, Ghostunnel will limit its access to files and sockets based on the
flags passed at startup. Note that Landlock does not work with PKCS#11 modules
and is disabled if PKCS#11 is used (as PKCS#11 modules are opaque to us we
can't craft workable Landlock rules for them).