sslh -- A ssl/ssh multiplexer
=============================

`sslh` accepts connections on specified ports, and forwards
them further based on tests performed on the first data
packet sent by the remote client.

Probes for HTTP, TLS/SSL (including SNI and ALPN), SSH,
OpenVPN, tinc, XMPP, SOCKS5, are implemented, and any other
protocol that can be tested using a regular expression, can
be recognised. A typical use case is to allow serving
several services on port 443 (e.g. to connect to SSH from
inside a corporate firewall, which almost never block port
443) while still serving HTTPS on that port.

Hence `sslh` acts as a protocol demultiplexer, or a
switchboard. With the SNI and ALPN probe, it makes a good
front-end to a virtual host farm hosted behind a single IP
address.

`sslh` has the bells and whistles expected from a mature
daemon: privilege and capabilities dropping, inetd support,
systemd support, transparent proxying, support for HAProxy's
proxyprotocol, chroot, logging, IPv4 and IPv6, TCP and UDP,
a fork-based, a select-based model, and yet another based on
libev for larger installations.

Install
=======

Please refer to the [install guide](doc/INSTALL.md).

Security
========

Matthias Gerstner from OpenSUSE has performed a code review
of `sslh` from a security point of view, which revealed a
number of problems, including two CVE. His findings have
already been taken partly into account for the more critical
ones. The [full
review](https://security.opensuse.org/2025/06/13/sslh-denial-of-service-vulnerabilities.html)
is well worth reading if you are using `sslh` in production.

Part of the securing your installation involves configuring
connection limits. This is described in [this
guide](doc/max_connections.md).

Configuration
=============

Please refer to the [configuration guide](doc/config.md).

Transparent proxying
--------------------

Transparent proxying allows the target server to see the
original client IP address, i.e. `sslh` becomes invisible.

The same result can be achieved more easily by using
`proxyprotocol` if the backend server supports it. This is a
simple setting to add to the `sslh` protocol configuration,
usually with an equivalently simple setting to add in
the backend server configuration, so try that first. This is
explained in a [separate document](doc/proxyprotocol.md).

This means services behind `sslh` (Apache, `sshd` and so on)
will see the external IP and ports as if the external world
connected directly to them. This simplifies IP-based access
control (or makes it possible at all), and makes it possible
to use IP-based banning tools such as `fail2ban`.

There are two methods. One uses additional virtual network
interfaces. The principle and basic setup is described
[here](doc/simple_transparent_proxy.md), with further
scenarios described [there](doc/scenarios-for-simple-transparent-proxy.md).

There is also a guide to use [podman](doc/podman.md).

Another method uses iptable packet marking features, and is
highly dependent on your network environment and
infrastructure setup. There is no known generic approach,
and if you do not find directions for your exact setup, you
will probably need an extensive knowledge of network
management and iptables setup".

It is described in its own [document](doc/tproxy.md).
In most cases, you will be better off following the first
method.


Docker image
------------

How to use

---


```bash
docker run \
  --cap-add CAP_NET_RAW \
  --cap-add CAP_NET_BIND_SERVICE \
  --rm \
  -it \
  ghcr.io/yrutschle/sslh:latest \
  --foreground \
  --listen=0.0.0.0:443 \
  --ssh=hostname:22 \
  --tls=hostname:443
```

docker-compose example

```yaml
version: "3"

services:
  sslh:
    image: ghcr.io/yrutschle/sslh:latest
    hostname: sslh
    ports:
      - 443:443
    command: --foreground --listen=0.0.0.0:443 --tls=nginx:443 --openvpn=openvpn:1194
    depends_on:
      - nginx
      - openvpn

  nginx:
    image: nginx

  openvpn:
    image: openvpn
```

Transparent mode 1: using sslh container for networking

_Note: For transparent mode to work, the sslh container must be able to reach your services via **localhost**_
```yaml
version: "3"

services:
  sslh:
    build: https://github.com/yrutschle/sslh.git
    container_name: sslh
    environment:
      - TZ=${TZ}
    cap_add:
      - NET_ADMIN
      - NET_RAW
      - NET_BIND_SERVICE
    sysctls:
      - net.ipv4.conf.default.route_localnet=1
      - net.ipv4.conf.all.route_localnet=1
    command: --transparent --foreground --listen=0.0.0.0:443 --tls=localhost:8443 --openvpn=localhost:1194
    ports:
      - 443:443 #sslh

      - 80:80 #nginx
      - 8443:8443 #nginx

      - 1194:1194 #openvpn
    extra_hosts:
      - localbox:host-gateway
    restart: unless-stopped

  nginx:
    image: nginx:latest
    .....
    network_mode: service:sslh #set nginx container to use sslh networking.
    # ^^^ This is required. This makes nginx reachable by sslh via localhost
  
  openvpn:
    image: openvpn:latest
    .....
    network_mode: service:sslh #set openvpn container to use sslh networking
```

Transparent mode 2: using host networking

```yaml
version: "3"

services:
  sslh:
    build: https://github.com/yrutschle/sslh.git
    container_name: sslh
    environment:
      - TZ=${TZ}
    cap_add:
      - NET_ADMIN
      - NET_RAW
      - NET_BIND_SERVICE
    # must be set manually
    #sysctls:
    #  - net.ipv4.conf.default.route_localnet=1
    #  - net.ipv4.conf.all.route_localnet=1
    command: --transparent --foreground --listen=0.0.0.0:443 --tls=localhost:8443 --openvpn=localhost:1194
    network_mode: host
    restart: unless-stopped
  
  nginx:
    image: nginx:latest
    .....
    ports:
      - 8443:8443 # bind to docker host on port 8443

  openvpn:
    image: openvpn:latest
    .....
    ports:
      - 1194:1194 # bind to docker host on port 1194
```

Comments? Questions?
====================

You can subscribe to the `sslh` mailing list here:
<https://lists.rutschle.net/mailman/listinfo/sslh>

This mailing list should be used for discussion, feature
requests, and will be the preferred channel for announcements.

Of course, check the [FAQ](doc/FAQ.md) first!

