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, WireGuard, 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 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 services: sslh: build: https://github.com/yrutschle/sslh.git container_name: sslh environment: - TZ=${TZ} cap_add: - NET_ADMIN - NET_RAW - NET_BIND_SERVICE sysctls: - net.ipv4.conf.default.route_localnet=1 - net.ipv4.conf.all.route_localnet=1 command: --transparent --foreground --listen=0.0.0.0:443 --tls=localhost:8443 --openvpn=localhost:1194 ports: - 443:443 #sslh - 80:80 #nginx - 8443:8443 #nginx - 1194:1194 #openvpn extra_hosts: - localbox:host-gateway restart: unless-stopped nginx: image: nginx:latest ..... network_mode: service:sslh #set nginx container to use sslh networking. # ^^^ This is required. This makes nginx reachable by sslh via localhost openvpn: image: openvpn:latest ..... network_mode: service:sslh #set openvpn container to use sslh networking ``` Transparent mode 2: using host networking ```yaml services: sslh: build: https://github.com/yrutschle/sslh.git container_name: sslh environment: - TZ=${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: 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!